Pressure Instrumentation
Remade from scratch to the authoring rules: defaults asserted only where four of five projects would choose them, and scope boundaries matched to the neighboring standards
Showing changes from Rev 3
to Rev 4
in Pressure Instrumentation.
---
−title: Pressure Measurement
+title: Pressure Instrumentation
category: Instrumentation & Controls / Field Instrumentation
−toc_depth: 3
description: >
− When to use: selecting, specifying, and installing pressure measurement instruments on construction and process-facility projects — local-indicating gauges, electronic transmitters (gauge, absolute, differential, multivariable), pressure switches, diaphragm seals, snubbers, and associated isolation and test valves — across industrial process, water and wastewater, HVAC/mechanical, fire protection, and commercial work, from high vacuum through 10,000 psi gauge.
− Not intended for: differential-pressure flow elements that infer flow (use sync/flow-measurement); hydrostatic/DP level transmitters that infer tank level (use sync/level-sensors); RTDs, thermocouples, and temperature transmitters (use sync/temperature-instrumentation); pressure-regulating and pressure-relief valves with actuators (use sync/control-valves-and-actuators); fieldbus segment and network design (use sync/process-control-networks); display, alarming, and historian configuration (use sync/scada-and-hmi-systems); general loop documentation and P&ID conventions beyond the instrument itself (use sync/process-instrumentation); and BAS-native pressure points such as duct static and HVAC differential pressure (use sync/building-automation-system).
+ When to use: Instrument-tagged pressure, vacuum, and differential pressure measurement points on industrial, process, power, and water and wastewater projects: the pressure transmitter (gauge, absolute, differential, and the pressure side of a multivariable transmitter), its sensing element and isolating diaphragm, its process connection, its output signal, and its housing; diaphragm seals and capillaries; the local pressure gauge with its snubber and siphon; the pressure switch; hazardous-location protection; calibration, installation, and acceptance. Applies to every point that carries a tag in the project instrument index and is read by a process controller or designated for local indication or switching, including pressure points on central plant and plant utility piping that are not building automation points.
+
+ Not intended for: Building automation pressure points, meaning the duct static, building static, and hydronic differential pressure transmitters and switches wired to building automation field controllers, which are governed by [[sync/hvac-controls-instrumentation]] with the range and measurement error selected under [[sync/building-automation-system]]; gauges furnished as equipment trim or as a piping specialty, such as the gauges of [[sync/hydronic-specialties]], [[sync/hvac-pumps]], [[sync/boilers]], [[sync/compressed-air-systems]], [[sync/steam-and-condensate-piping]], and [[sync/fire-protection-piping]]; the RTD, thermocouple, or thermistor, its thermowell, and the verification of its temperature reading ([[sync/temperature-instrumentation]]); flow inferred from an orifice, venturi, or nozzle and the pairing of the primary element with its transmitter ([[sync/flow-measurement]]); liquid level inferred from hydrostatic head ([[sync/level-sensors]]); loop architecture, tag numbering, the instrument index, and loop diagrams ([[sync/process-instrumentation]], [[sync/control-systems-integration]]); the root valve, manifold, impulse tubing, seal pots, and heat tracing of the hook-up ([[sync/instrument-installation-and-tubing]]); pressure sensors furnished inside equipment and wired to the equipment's own controller ([[sync/compressed-air-systems]], [[sync/chillers]], [[sync/packaged-pump-stations]]); piezometers and total pressure cells in soil and groundwater ([[sync/geotechnical-instrumentation-and-monitoring]]); pressure relief, safety, and self-contained regulating valves, which are furnished under the piping or equipment standard for their service; modulating control valves with their actuators and positioners ([[sync/control-valves-and-actuators]]); and the controllers, networks, panels, raceway, and cable that receive the signal ([[sync/programmable-logic-controllers]], [[sync/process-control-networks]], [[sync/scada-and-hmi-systems]], [[sync/industrial-control-panels]], [[sync/raceways-and-conduit]], [[sync/conductors-and-cables]]).
---
# Scope {toc}
−## This standard covers pressure measurement instruments installed to indicate, transmit, or switch on process pressure in construction and process-facility projects. {note}
+## This standard covers the pressure measurement point from the instrument side of the manifold or root valve to the signal-output terminals of the transmitter or the contacts of the switch: the pressure, vacuum, and differential pressure transmitter, its sensing element and isolating diaphragm, its process connection and process flanges, its housing and output signal, the diaphragm seal and capillary where one is furnished, the local pressure gauge with its snubber and siphon, and the pressure switch. {note}
−## It governs local-indicating pressure gauges, electronic pressure transmitters (gauge, absolute, differential, and multivariable), pressure switches, diaphragm seals, gauge snubbers, and the isolation and test valves immediately associated with each instrument. The pressure range of interest runs from high vacuum through 10,000 psi gauge and from high-vacuum to high-pressure absolute service. {note}
+## A point belongs to this standard when it carries a tag in the project instrument index and its signal is read by a process controller or its reading or contact is used at the equipment, whether the pipe it sits on carries a process fluid, a plant utility, chilled water, or compressed air; a point belongs to [[sync/hvac-controls-instrumentation]] when it is wired to a building automation field controller and its range and measurement error are selected under [[sync/building-automation-system]]. The same tap on the same pipe is specified under whichever standard owns the controller that reads it, and a gauge that a piping or equipment standard furnishes as part of its own assembly stays with that standard. {note}
−## The pressure-measurement instrument family appears in nearly every facility type, and this standard applies across all of them. {note}
+## The transmitter body, its pressure sensor, its process connection, and its pressure calibration of a multivariable transmitter are specified under this standard; the RTD or thermocouple, its thermowell, and the verification of its temperature reading are specified under [[sync/temperature-instrumentation]]. {note}
−## Industrial process plants, water and wastewater treatment works, HVAC and mechanical systems, fire-protection systems, and general commercial construction all rely on pressure indication and transmission. The selection logic — range, accuracy, wetted material, connection, and signal — is common across these settings even though the service pressures and chemistries differ widely. {note}
+## The following are outside this standard and are governed elsewhere. {note}
−## Instruments shall be selected, supplied, calibrated, and installed in accordance with this standard and the project instrument index.
+- The RTD, thermocouple, or thermistor, its thermowell, and the verification of its temperature reading, governed by [[sync/temperature-instrumentation]]
+- Flow inferred from an orifice, venturi, or nozzle, including the pairing and sizing of the primary element with its transmitter, governed by [[sync/flow-measurement]]
+- Liquid level inferred from hydrostatic head, whether by a submersible sensor or by a transmitter on a tank nozzle, governed by [[sync/level-sensors]]
+- Loop architecture, tag numbering, the instrument index, and loop diagrams, governed by [[sync/process-instrumentation]] and [[sync/control-systems-integration]]
+- The root valve, the manifold, the impulse tubing, seal pots, and the heat tracing of the hook-up, governed by [[sync/instrument-installation-and-tubing]]
+- Pressure sensors furnished inside equipment and wired to the equipment's own controller, such as the discharge sensors of a packaged compressor, a chiller, or a packaged pump station, governed by the standard for that equipment, for example [[sync/compressed-air-systems]], [[sync/chillers]], and [[sync/packaged-pump-stations]]
+- Piezometers and total pressure cells in soil and groundwater, governed by [[sync/geotechnical-instrumentation-and-monitoring]]
+- Pressure relief, safety, and self-contained regulating valves, governed by the piping or equipment standard for the service they protect, and modulating control valves with their actuators and positioners, governed by [[sync/control-valves-and-actuators]]
+- Controllers and input cards, field networks and fieldbus segment design, and operator interfaces, governed by [[sync/programmable-logic-controllers]], [[sync/process-control-networks]], and [[sync/scada-and-hmi-systems]]
+- Control panels and the marshalling of field signals, governed by [[sync/industrial-control-panels]]
+- Raceway and cable for instrument wiring, governed by [[sync/raceways-and-conduit]] and [[sync/conductors-and-cables]]
+- The calibration laboratory itself; this standard references the laboratory only as the source of the traceable certificate
−## Where the project instrument index, datasheets, or P&IDs conflict with this standard, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+## Each point's tag, service, process fluid, instrument type (transmitter, local gauge, switch, or a combination), measurement reference, calibrated range, engineering units, process design pressure and temperature including startup and upset conditions, maximum static line pressure for a differential point, switch setpoint and reset direction, and safety instrumented function designation shall be as indicated on [[drawing: the instrument index and instrument data sheets]].
−## Flow inference from a differential-pressure element across an orifice plate or venturi is covered by [[sync/flow-measurement]], not this standard, even though the sensing device is a DP transmitter. {note}
+## Where a process condition needed to select or verify an instrument is not stated on the instrument data sheet, the Contractor shall request it from the Engineer in writing before procuring the instrument.
−## Hydrostatic or differential-pressure level measurement that infers liquid level in a vessel is covered by [[sync/level-sensors]]. {note}
−
−## Temperature measurement — RTDs, thermocouples, and temperature transmitters — is covered by [[sync/temperature-instrumentation]]; coordinate with that standard where a single multivariable transmitter reports both pressure and temperature. {note}
−
−## Pressure-regulating and pressure-relief valves with actuators are covered by [[sync/control-valves-and-actuators]]; this standard covers only the measuring instrument, not the final control element. {note}
−
−## Fieldbus segment design, marshalling, and network topology for transmitter communications are covered by [[sync/process-control-networks]]; display, alarming, and historian configuration are covered by [[sync/scada-and-hmi-systems]]. {note}
−
−## General instrument loop documentation, P&ID symbology beyond the pressure instrument, and control-panel wiring practice are covered by [[sync/process-instrumentation]]. {note}
−
−## Building-automation pressure points that are BAS-native sensors — duct static pressure and chilled-water differential pressure for HVAC pump control — are covered by [[sync/building-automation-system]]. {note}
−
−## Where a pressure instrument is installed on a process covered by OSHA Process Safety Management (29 CFR 1910.119) because it handles a highly hazardous chemical above its threshold quantity, the instrument's mechanical-integrity, calibration, and documentation records are PSM process-safety information; this standard sets the instrument requirements, and the project PSM program governs the records retention. {note}
−
# Referenced Standards {toc}
## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
−## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+## Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard | Title |
|----------|-------|
−| ASME B40.100-2022 | Pressure Gauges and Gauge Attachments |
−| ANSI/ISA-51.1-1979 (R1995) | Process Instrumentation Terminology |
−| ANSI/ISA-5.1-2024 | Instrumentation Symbols and Identification |
−| IEC 61511-1:2016 (ANSI/ISA-84.00.01) | Functional Safety: Safety Instrumented Systems for the Process Industry Sector |
−| IEC 61508-1:2010 | Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems |
−| ASME PTC 19.2-2010 | Pressure Measurement (Performance Test Codes) |
−| NIST SP 250-39 | NIST Calibration Services for Pressure and Vacuum |
−| ASME B16.5-2017 | Pipe Flanges and Flanged Fittings |
−| ASME B1.20.1-2013 (R2018) | Pipe Threads, General Purpose (Inch) |
−| ANSI/NEMA 250-2020 | Enclosures for Electrical Equipment (1000 Volts Maximum) |
−| NFPA 70 (NEC) Article 501 | National Electrical Code — Class I Hazardous Locations |
−| ISA TR84.00.04-2015 | Guidance for Application of IEC 61511 / ISA-84 |
−| AWWA M20 | Water Meters — Selection, Installation, Testing, and Maintenance |
−| NSF/ANSI 61 | Drinking Water System Components — Health Effects |
+| ASME B40.100 | Pressure Gauges and Gauge Attachments |
+| ASME PTC 19.2 | Pressure Measurement |
+| ASME B16.5 | Pipe Flanges and Flanged Fittings |
+| ASME B1.20.1 | Pipe Threads, General Purpose (Inch) |
+| ASME B31.3 | Process Piping |
+| ANSI/ISA-5.1 | Instrumentation Symbols and Identification |
+| ANSI/ISA-20 | Specification Forms for Process Measurement and Control Instruments, Primary Elements, and Control Valves |
+| ANSI/ISA-51.1 | Process Instrumentation Terminology |
+| ANSI/ISA-12.27.01 | Requirements for Process Sealing Between Electrical Systems and Flammable or Combustible Process Fluids |
+| ANSI/ISA-62382 | Automation Systems in the Process Industry - Electrical and Instrumentation Loop Check |
+| IEC 60770-1 | Transmitters for Use in Industrial-Process Control Systems - Methods for Performance Evaluation |
+| IEC 61518 | Mating Dimensions Between Differential Pressure (Type) Measuring Instruments and Flanged-On Shut-Off Devices up to 413 bar |
+| IEC 61511 (ANSI/ISA-61511) | Functional Safety - Safety Instrumented Systems for the Process Industry Sector |
+| API RP 551 | Process Measurement |
+| NAMUR NE 43 | Standardization of the Signal Level for the Failure Information of Digital Transmitters |
+| NSF/ANSI/CAN 61 | Drinking Water System Components - Health Effects |
+| CGA G-4.1 | Cleaning of Equipment for Oxygen Service |
+| 3-A 74- | 3-A Sanitary Standards for Sensors and Sensor Fittings and Connections |
+| NFPA 70 | National Electrical Code (Articles 500 through 505, hazardous locations) |
+| NEMA 250 | Enclosures for Electrical Equipment (1000 Volts Maximum) |
+| UL 50E | Enclosures for Electrical Equipment, Environmental Considerations |
+| UL 508 | Industrial Control Equipment |
+| UL 913 | Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous (Classified) Locations |
+| UL 1203 | Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations |
−## ANSI/ISA-51.1 remains the primary terminology authority for pressure instrument performance terms even though it predates current transmitter technology and is presently under revision; where its 1979 definitions of accuracy, span, range, hysteresis, and repeatability are cited on a datasheet, the cited terms carry the ISA-51.1 meaning. {note}
−
# Submittals {toc}
−## The Contractor shall submit the following action submittals for each pressure instrument or instrument type prior to procurement:
−- Manufacturer product data sheet showing range, accuracy class, wetted materials, and process connection
−- Completed instrument datasheet (ISA-20 style) with project tag number, calibrated range, and engineering units
−- Enclosure rating and electrical area-classification certification (NEMA / NEC) for the installed location
−- SIL certificate and safety manual where the instrument serves a safety instrumented function
−- Diaphragm-seal assembly drawing and fill-fluid data where seals are specified
−- Dimensional drawing showing mounting, process connection orientation, and conduit/cable entry
+## Action Submittals {toc}
+### The Contractor shall submit the following for the Engineer's review and return before any pressure instrument is procured:
+
+- Product data for each transmitter, gauge, switch, and diaphragm seal model, giving the sensing element, the reference accuracy and the method by which it is stated, the rangeability, the overpressure and static pressure limits, the published long-term stability and ambient temperature effect, the process temperature limits, the wetted materials, the fill fluid, the output signal, the enclosure rating, and the hazardous-location certification
+- A completed instrument data sheet in the ANSI/ISA-20 format, or a format accepted by the Engineer, for every tagged point
+- A diaphragm seal assembly drawing for each sealed point giving the seal type, process connection, diaphragm material, fill fluid, capillary length and armor, and the manufacturer's calculation of the temperature effect and the response time of the assembly at the ambient and process temperatures stated on the instrument data sheet
+- Hazardous-location certificates for each instrument in a classified location and, for intrinsically safe loops, the control drawing with the entity parameters of every device in the loop
+- A transmitter configuration sheet for each transmitter giving the calibrated range, the engineering units, the damping, the failure output direction, the transfer function, and the write-protection state
+- A mounting detail for each mounting arrangement furnished, showing the bracket, the stand, and the connection to the manifold or impulse tubing
+
```datasheet
−label: Action Submittals
+label: Required Action Submittals
type: checkbox
options:
− - Product data sheet
− - Completed instrument datasheet (ISA-20)
− - Enclosure / area-classification certification
− - SIL certificate and safety manual
− - Diaphragm-seal assembly drawing
− - Dimensional / mounting drawing
+ - "Product data for each instrument model"
+ - "Instrument data sheet for every tagged point"
+ - "Diaphragm seal assembly drawings with temperature effect calculations"
+ - "Hazardous-location certificates and intrinsically safe control drawings"
+ - "Transmitter configuration sheets"
+ - "Mounting details"
default:
− - Product data sheet
− - Completed instrument datasheet (ISA-20)
− - Enclosure / area-classification certification
− - Dimensional / mounting drawing
+ - "Product data for each instrument model"
+ - "Instrument data sheet for every tagged point"
+ - "Diaphragm seal assembly drawings with temperature effect calculations"
+ - "Transmitter configuration sheets"
+ - "Mounting details"
```
−## The Contractor shall submit the following closeout submittals before substantial completion:
−- Factory calibration certificate traceable to NIST for each instrument
−- Field loop-check records and as-left calibration data
−- Operation and maintenance manuals including recalibration procedure and interval
−- Instrument index reconciled to the as-built P&ID tag numbers
+### A sealed transmitter shall not be filled or calibrated until its seal assembly drawing has been reviewed and returned without exception.
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following for information before installation begins:
+
+- Factory calibration certificates for the transmitters, gauges, and switches covered by the certificate scope selected under Calibration
+- Manufacturer's installation instructions for each instrument model
+- The certificate of safety integrity level capability under IEC 61511 and the manufacturer's proof-test procedure for each transmitter or switch serving a safety instrumented function
+- NSF/ANSI/CAN 61 certification for each instrument whose wetted parts contact potable water
+- The cleaning certification under CGA G-4.1 for each instrument in oxygen service
+
```datasheet
−label: Closeout Submittals
+label: Required Informational Submittals
type: checkbox
options:
− - NIST-traceable calibration certificate
− - Field loop-check / as-left calibration records
− - Operation and maintenance manuals
− - Reconciled instrument index
+ - "Factory calibration certificates"
+ - "Manufacturer's installation instructions"
+ - "Safety integrity level capability certificates and proof-test procedures"
+ - "Potable water certifications"
+ - "Oxygen cleaning certifications"
default:
− - NIST-traceable calibration certificate
− - Field loop-check / as-left calibration records
− - Operation and maintenance manuals
− - Reconciled instrument index
+ - "Factory calibration certificates"
+ - "Manufacturer's installation instructions"
```
−## The Contractor shall submit the following informational submittals:
−- Manufacturer's installation, mounting, and torque instructions
−- Hazardous-location control drawing for intrinsically safe installations
−- Spare-parts and recommended-spares list
+## Closeout Submittals {toc}
+### The Contractor shall submit the following before the pressure instruments are accepted:
+
+- As-left calibration and configuration record for every transmitter, gauge, and switch, including the field verification and the installed zero trim
+- Operation and maintenance data giving the recalibration interval, the proof-test interval where applicable, and the part number of every replaceable sensor module, display, terminal block, gasket, and seal assembly
+- Warranty documentation
+
```datasheet
−label: Informational Submittals
+label: Required Closeout Submittals
type: checkbox
options:
− - Installation and torque instructions
− - IS control drawing
− - Spare-parts list
+ - "As-left calibration and configuration records"
+ - "Operation and maintenance data with recalibration intervals"
+ - "Warranty documentation"
default:
− - Installation and torque instructions
− - Spare-parts list
+ - "As-left calibration and configuration records"
+ - "Operation and maintenance data with recalibration intervals"
+ - "Warranty documentation"
```
+### Loop check records and as-built loop diagrams shall be submitted as required under [[sync/control-systems-integration]] and shall not be duplicated in this closeout package.
+
# Quality Assurance {toc}
−## Pressure gauges shall conform to ASME B40.100 for accuracy grade, dial size, scale range, and overpressure rating.
+## Conformance and Certification {toc}
−## ASME B40.100-2022 consolidates the former B40.1, B40.2, B40.5, B40.6, and B40.7 documents and is the governing standard for analog dial-type gauges. Its accuracy grades — Grade A at ± 1 % of span, Grade 2A at ± 0.5 %, and Grade B at ± 2 % — are the values cited on gauge datasheets in this standard. {note}
+### Pressure gauges, diaphragm seals, snubbers, siphons, and pressure limiter valves shall conform to ASME B40.100.
−## Each instrument shall be calibrated against a reference standard traceable to NIST per ASME PTC 19.2 before it is placed in service.
+### Transmitter performance terms shall carry the meanings of ANSI/ISA-51.1, and the reference accuracy of each transmitter shall be published as a percentage of calibrated span including the combined effects of linearity, hysteresis, and repeatability, determined under IEC 60770-1.
−## Calibration of safety-instrumented-function instruments shall be performed to a tolerance of ± 0.1 % of span.
+### A reference accuracy that leaves out hysteresis or repeatability, or that is stated at a single span rather than across the turndown, reads tighter on paper than the same transmitter reads in service, and two products stated on different bases cannot be compared; holding every submittal to the same method is what makes the accuracy field in this standard a comparison rather than a slogan. {note}
−## General process loops shall be calibrated to ± 0.5 % of span at commissioning.
+### Pressure switches shall be listed by a Nationally Recognized Testing Laboratory as industrial control equipment under UL 508 for the connected voltage and load.
−## Transmitters shall not be assumed to arrive pre-configured to the project range.
+### Instruments installed in a classified hazardous location shall be listed by a Nationally Recognized Testing Laboratory for the class, division or zone, group, and temperature code present, to UL 1203 where an explosion-proof enclosure is the means of protection and to UL 913 where intrinsic safety is the means of protection.
−## Unless the zero and span are stated on the instrument datasheet or instrument index, transmitters ship at the factory default of 0 to 100 % of catalog span. A transmitter left at catalog default reads correctly only by coincidence, and the error is silent until a loop check catches it. {note}
+### Each transmitter or switch serving a safety instrumented function designated in the instrument index shall carry a certificate of safety integrity level capability under IEC 61511 issued by an accredited assessor, with the failure rates and the proof-test coverage stated.
−## Transmitters shall be configured to the project calibrated range and engineering units before shipment or, where field configuration is specified, before loop check.
+## Source Limitation {toc}
−## Instrument tag numbers shall match the project P&ID and instrument index exactly.
+### The manufacturer source limitation applying to pressure instruments shall be as indicated in the datasheet.
−## Field-installed tags that do not match the P&ID generate commissioning RFIs and stall loop checks. Tag reconciliation is cheap during the construction-document phase and expensive at startup. {note}
+```datasheet
+label: Pressure Instrument Source Limitation
+type: radio
+options:
+ - "Single manufacturer for all transmitters and a single manufacturer for all gauges"
+ - "Single manufacturer for all transmitters, gauges, and switches"
+ - "No source limitation"
+default: "Single manufacturer for all transmitters and a single manufacturer for all gauges"
+```
−## A safety requirements specification (SRS) shall exist and be referenced before any instrument is specified as SIL-rated.
+### Transmitters from one manufacturer share a configuration tool, a spare sensor module, and a device description file in the control system, and gauges from one manufacturer share a case, a window, and a fill; requiring one manufacturer for transmitters, gauges, and switches together narrows the bid list to the few suppliers who make all three and buys nothing a two-source limit does not. {note}
−## IEC 61511 requires a documented SRS that defines the safety function, its safe state, and its target SIL before instrument selection. Calling out a "SIL 2 transmitter" with no SRS behind it is a contractual and safety risk — the rating is meaningless without the function definition that sizes it. {note}
+## Identification {toc}
+### Each instrument shall be identified by the tag number assigned under [[sync/process-instrumentation]] in accordance with ANSI/ISA-5.1.
+
+### Each transmitter, gauge, switch, and diaphragm seal assembly shall carry a stainless steel tag plate stamped or engraved with its tag number and attached with stainless steel wire or screws.
+
+### Transmitters shall additionally carry the calibrated range and engineering units on the tag plate or on a second stainless steel plate.
+
+### Two transmitters of one model ranged for different services look identical on a pipe rack, and the range on the plate is what lets a technician with a handheld communicator and a work order find the right one without reading the configuration of each. {note}
+
# Environmental and Service Conditions {toc}
−## The instrument enclosure rating shall suit the installed environment; "weatherproof" is not an enclosure classification.
+## Ambient and Process Temperature {toc}
−## A bare "weatherproof" call-out has no defined meaning under NEMA 250 or IEC 60529. Outdoor, wash-down, and wet locations require an explicit NEMA 4X (or IP66/IP67) rating, and classified areas require an explicit NEMA 7 or intrinsically safe designation. {note}
+### Instruments mounted outdoors shall operate within their published accuracy between [[parameter: site-ambient-temperature-minimum]] and [[parameter: site-ambient-temperature-maximum]], including solar gain on an unshaded housing.
−## Outdoor, wet, and wash-down locations shall use a NEMA 4X enclosure of 316 stainless steel or fiberglass, or an equivalent IP66/IP67 rating.
+### Where the process temperature at a point exceeds the published process temperature limit of the transmitter, gauge, or switch, the instrument shall be connected through impulse tubing, a siphon, or a remote diaphragm seal with capillary so that the fluid at the sensor is within the published limit.
+### An isolating diaphragm sits a fraction of an inch from the sensing element and the fill behind it, and a hot fluid against the diaphragm heats the fill and the sensor together; the length of tubing or capillary between the process and the sensor is what lets the fluid cool to the rating before it arrives. {note}
+
+### Where an absolute pressure instrument is ranged to include local atmospheric pressure, the range shall account for the atmospheric pressure at [[parameter: altitude]].
+
+## Enclosure Rating {toc}
+
+### Transmitter housings, switch enclosures, and junction boxes furnished under this standard shall carry at least the enclosure rating indicated in the datasheet, rated under NEMA 250 or UL 50E.
+
```datasheet
−label: Enclosure Rating
+label: Minimum Enclosure Rating
type: select
options:
− - NEMA 4X (316 SS) — outdoor / wash-down
− - NEMA 4X (fiberglass / polyester)
− - NEMA 7 explosion-proof — Class I Div 1
− - NEMA 4 general weatherproof — sheltered
− - NEMA 12 — indoor industrial
−default: NEMA 4X (316 SS) — outdoor / wash-down
+ - "NEMA Type 1"
+ - "NEMA Type 12"
+ - "NEMA Type 13"
+ - "NEMA Type 3R"
+ - "NEMA Type 4"
+ - "NEMA Type 4X"
+ - "NEMA Type 7"
+default: "NEMA Type 1"
```
−## Instruments in Class I Division 1 hazardous locations shall be explosion-proof (NEMA 7) or intrinsically safe with a certified barrier per NEC Article 501.
+### Type 1 is the datasheet default because it is the rating that every location satisfies; the clauses that follow raise it for the locations that need more, whatever the datasheet selects. A project whose points are mostly outdoors or in a process area raises the datasheet value instead so that the few interior points are not the exception. Type 4 excludes hose-directed water and wind-driven rain; Type 4X adds corrosion resistance for salt air, chemical fumes, and washdown chemicals; Type 12 and Type 13 exclude dust and dripping or sprayed non-corrosive liquid indoors; Type 7 is the explosion-proof construction for Class I, Division 1. {note}
−## Instruments in Class I Division 2 locations shall be intrinsically safe or nonincendive.
+### Enclosures mounted outdoors shall be rated NEMA Type 3R, Type 4, or Type 4X.
−## The choice between explosion-proof housings and an intrinsically safe loop with a barrier is a project-wide convention, not an instrument-by-instrument decision; NEC 501.15 governs conduit seals and 501.105 governs instruments in Class I locations. {note}
+### Enclosures mounted where airborne dust or non-corrosive liquid drips or sprays accumulate shall be rated NEMA Type 12, Type 13, Type 4, or Type 4X.
−## Area classification selection for the installed instrument shall be coordinated with the area classification drawings.
+### Enclosures mounted in locations subject to washdown or hose-directed water shall be rated NEMA Type 4 or Type 4X.
+### Enclosures mounted in locations exposed to corrosive fumes, salt air, or washdown chemicals shall be rated NEMA Type 4X.
+
+### Enclosures in a Class I, Division 1 location where an explosion-proof enclosure is the means of protection shall be rated NEMA Type 7 in addition to the rating required for the environment.
+
+## Hazardous Locations {toc}
+
+### The hazardous-location classification at each instrument shall be as indicated on [[drawing: the electrical area classification drawings]].
+
+### Instruments in a classified location shall be protected by the method indicated in the datasheet.
+
```datasheet
−label: Electrical Area Classification
+label: Hazardous Location Protection Method
type: radio
options:
− - General purpose (unclassified)
− - Class I Div 2 — intrinsically safe / nonincendive
− - Class I Div 1 / Zone 0 — explosion-proof
− - Class I Div 1 / Zone 0 — intrinsically safe + barrier
−default: General purpose (unclassified)
+ - "Intrinsically safe loop with a barrier or galvanic isolator in the control panel"
+ - "Explosion-proof enclosure with conduit seals"
+ - "Nonincendive equipment and wiring"
+ - "Not applicable, no classified locations"
+default: "Not applicable, no classified locations"
```
−## Transmitters shall be rated for the ambient temperature at the installed location.
+### An intrinsically safe loop keeps the field device and its wiring below ignition energy, so the housing can be opened and the transmitter configured with the area live, at the cost of a barrier per loop and an entity-parameter check on every device in it; an explosion-proof enclosure contains an ignition, so it needs conduit seals and a de-energized area before the cover comes off; nonincendive equipment is listed for Division 2 and has no standing in Division 1. The method is a plant-wide convention because it sets the panel design, the wiring practice, and the maintenance procedure for every loop. {note}
−```datasheet
−label: Ambient Temperature Rating
−type: range
−unit: °F
−min: -67
−max: 221
−step: 1
−setpoints:
− - -67
− - -40
− - 185
− - 221
−```
+### Conduit entries into enclosures in Class I locations shall be sealed in accordance with NFPA 70 Article 501 and the listing of the enclosure.
−## Standard transmitters operate from -40 °F to +185 °F (-40 °C to +85 °C); extended-range units reach -67 °F to +221 °F. Cold-climate outdoor installations and hot process-adjacent mountings both push past the standard band, and the wrong rating produces drift or a dead display in the field. {note}
+### Where a single isolating diaphragm separates a flammable or combustible process fluid from the electrical system, the instrument shall be certified under ANSI/ISA-12.27.01 for that condition.
−## Transmitters mounted on hot process lines shall be installed with capillary standoffs or impulse-line isolation so process heat does not conduct into the sensor and shift the zero.
+### The temperature code of each instrument in a classified location shall be lower than the autoignition temperature of the flammable material present, with the housing temperature at the maximum process and ambient temperature included in the determination.
−## All wetted parts of instruments in potable-water service shall be certified to NSF/ANSI 61.
+### Each intrinsically safe loop shall be documented on a control drawing that lists every device in the loop with its entity parameters and shows that the cable capacitance and inductance are within the barrier's allowed values.
−## Every material in contact with drinking water must be NSF 61 certified, including the gauge socket, the transmitter diaphragm, and any seal fill fluid. AWWA M20 carries the same requirement for water-system instruments, and the certification must be stated explicitly — it is not implied by a 316 stainless-steel call-out. {note}
+## Safety Instrumented Functions {toc}
−# Instrument Selection and Measurement Type {toc}
+### Transmitters and switches serving a safety instrumented function designated in the instrument index shall be furnished with the diagnostic coverage, the proof-test interval, and the proof-test procedure stated on the instrument data sheet.
−## The instrument type shall be selected from local gauge, electronic transmitter, pressure switch, or a combined gauge-plus-transmitter (duplex) arrangement based on the loop function.
+### Transmitters serving a safety instrumented function shall be configured with write protection enabled after commissioning and shall report the protection state to the logic solver where the protocol supports it.
+### A mechanical pressure switch shall not initiate a safety instrumented function unless the instrument index designates the switch for that function.
+
+### The determination of the safety integrity level and the design of the safety instrumented system are process safety scope outside this standard; this standard furnishes the field device with the certified capability the instrument index calls for. {note}
+
+## Process Fluid Compatibility {toc}
+
+### Every wetted part of an instrument in potable water service, including the isolating diaphragm, the seal diaphragm, the gauge tube and socket, and any fill fluid behind a single diaphragm, shall be certified under NSF/ANSI/CAN 61.
+
+### Instruments in oxygen or oxygen-enriched service shall be cleaned and packaged under CGA G-4.1 and filled with a halocarbon or other inert fill fluid, and no hydrocarbon oil or glycerin shall be present in the sensor, the seal, or the gauge case.
+
+### A hydrocarbon fill behind a diaphragm is a fuel, and a diaphragm rupture in oxygen service puts that fuel into an oxidizer at pressure; the inert fill and the clean assembly are what keep a sensor failure from becoming a fire. {note}
+
+### Instruments at points the instrument index designates for hygienic service shall have a sanitary clamp or other crevice-free connection with a flush diaphragm, a surface finish not rougher than 32 µin. Ra on product-contact surfaces, and a food-grade fill fluid, and shall be certified under 3-A 74-.
+
+### Instruments at points the instrument index designates for hydrogen service shall have a gold-plated isolating diaphragm or another diaphragm construction the manufacturer rates for hydrogen permeation at the process pressure and temperature.
+
+### Hydrogen atoms pass through a thin stainless steel diaphragm, recombine as gas in the fill behind it, and push the diaphragm outward, so the zero drifts upward over months and the sensor eventually fails; the gold layer closes the path. {note}
+
+# Measurement Points {toc}
+
+## Measurement Reference and Range {toc}
+
+### A gauge pressure instrument reads against the local atmosphere, so a gauge reading of zero is atmospheric; an absolute instrument reads against a sealed vacuum reference, so barometric change does not move it; a differential instrument reads the difference between two connections and sees the static line pressure on both; a compound instrument is a gauge instrument whose scale extends below zero into vacuum; a sealed gauge instrument reads against a sealed reference at atmospheric pressure and is the construction used where a vent to atmosphere is impractical at high ranges. Which reference a point needs is a property of the measurement and is stated in the instrument index for every point. {note}
+
+### Where the instrument data sheet states a calibrated range, that range shall govern; where it states only the operating conditions, the Contractor shall propose a range that places the normal operating pressure between 25 percent and 75 percent of span and shall submit it on the transmitter configuration sheet or the gauge product data for the Engineer's review.
+
+### An instrument ranged far above its operating pressure reads in the bottom of its scale, where a gauge pointer is hardest to read and a transmitter's accuracy as a percentage of span is spread over the least pressure; an instrument ranged too close leaves no room for a transient. Twice the operating pressure puts the normal reading near mid-scale, which is the band ASME B40.100 recommends for gauges and the band in which a transmitter's percentage-of-span error is smallest in engineering units. {note}
+
+### Instruments at points where the pressure can fall below atmospheric under any operating, startup, or upset condition stated on the instrument data sheet shall have a compound or absolute range.
+
+### Each instrument shall read in the engineering units stated on the instrument data sheet, with transmitters configured and gauge dials graduated in those units.
+
+## Local Indication Policy {toc}
+
+### Local pressure gauges shall be furnished at transmitter points as indicated in the datasheet, in addition to the gauges the instrument index designates at points with no transmitter.
+
```datasheet
−label: Instrument Type
+label: Local Gauge at Transmitter Points
type: radio
options:
− - Local-indicating gauge
− - Electronic transmitter
− - Pressure switch
− - Transmitter + local gauge (duplex)
−default: Electronic transmitter
+ - "A local gauge at every transmitter point"
+ - "A local gauge at every transmitter point whose transmitter has no local display"
+ - "A local gauge only at the transmitter points the instrument index designates"
```
−## A local gauge gives standalone visual indication with no power and no signal. A transmitter delivers a remote analog or digital signal to the control system. A pressure switch provides a discrete contact at a setpoint. The duplex arrangement pairs a transmitter for control with a local gauge for backup indication, which is the common pattern at field instruments where an operator needs to confirm the reading at the equipment. {note}
+### A gauge beside a transmitter reads with no power, no handheld, and no control system, and it gives the operator at the equipment a second opinion when the two disagree, at the cost of a second tap or a tee, a second wetted part, and a second instrument to calibrate and to leak; a transmitter display shows the same value the control system sees and nothing when the loop is down. Which of the three policies a plant holds depends on how its operators work the equipment, so the field carries no default. {note}
−## The 80 % case on US industrial and commercial projects is a two-wire 4-20 mA HART transmitter in a NEMA 4X enclosure, with a local gauge specified alongside for backup indication. {note}
+# Pressure Transmitters {toc}
−## Local gauges remain near-universal as backup even where a transmitter carries the signal, because an operator at the equipment must be able to read pressure with no power and no DCS. Treat the transmitter and the local gauge as a pair on most field instruments rather than an either/or choice. {note}
+## Sensing Element {toc}
−## The measurement reference — gauge, absolute, differential, or sealed-gauge — shall be specified explicitly for every instrument.
+### Transmitters shall have the sensing element indicated in the datasheet.
```datasheet
−label: Measurement Reference Type
+label: Transmitter Sensing Element
+type: select
+options:
+ - "Piezoresistive silicon"
+ - "Capacitance"
+ - "Resonant silicon"
+ - "Metal thin-film strain gauge"
+ - "Ceramic thick-film"
+default: manufacturer
+```
+
+### A piezoresistive silicon element is the most common and the least costly, and its output moves with temperature in a way the transmitter electronics have to correct; a capacitance element resolves very small differential pressures with low drift and tolerates high static pressure, and is the element of most differential transmitters; a resonant silicon element gives the highest stability and accuracy of the group and is offered by few manufacturers; a metal thin-film element is welded to its diaphragm with no fill fluid and serves high pressures, hydrogen, and shock and vibration where a filled sensor would not; a ceramic element has no isolating diaphragm and no fill, resists abrasion and most chemicals, and is limited in pressure range. The manufacturer's standard element for the range and service is acceptable because the performance and material fields in this standard hold the result rather than the means. {note}
+
+### Transmitters shall withstand, without damage or a shift in calibration beyond the published reference accuracy, an overpressure of not less than 1.5 times the upper range limit and not less than the maximum pressure stated on the instrument data sheet including startup and upset conditions.
+
+### Differential pressure transmitters shall have a published static line pressure rating not less than the maximum static line pressure stated on the instrument data sheet, applied to either side alone and to both sides together.
+
+### A differential sensor that is rated for a few hundred inches of water difference may sit on a line at several hundred pounds per square inch, and a manifold operated in the wrong order puts the full line pressure on one side with the other vented; the static pressure rating is what the sensor survives in that moment, and it is a separate number from the overpressure limit of the differential range. {note}
+
+### The sensor fill fluid of a transmitter shall be silicone oil unless Process Fluid Compatibility requires an inert fill or the instrument data sheet states another fluid.
+
+## Process Connection {toc}
+
+### Gauge and absolute pressure transmitters shall have the process connection indicated in the datasheet unless the instrument data sheet states another connection at a point.
+
+```datasheet
+label: Gauge and Absolute Transmitter Process Connection
+type: select
+options:
+ - "1/2 in. NPT female"
+ - "1/4 in. NPT female"
+ - "1/2 in. NPT male"
+ - "Flanged flush diaphragm, ASME B16.5"
+ - "Sanitary clamp"
+default: "1/2 in. NPT female"
+```
+
+### A 1/2 in. female thread accepts the nipple or the manifold outlet that nearly every hook-up ends in and is the connection every transmitter is offered with; a 1/4 in. thread suits small-bore tubing connected without a manifold and seals less reliably at high pressure; a male thread screws into a block manifold or a tee without a nipple; a flanged flush diaphragm puts the sensor at the pipe wall with no dead leg, for slurries and fluids that plug a tap, at the price of a seal and its temperature effect; a sanitary clamp is the crevice-free connection of hygienic piping. {note}
+
+### Differential pressure transmitters shall have the process flange form indicated in the datasheet.
+
+```datasheet
+label: Differential Transmitter Process Flange
type: radio
options:
− - Gauge (relative to atmosphere)
− - Absolute (relative to vacuum)
− - Differential (across two ports)
− - Sealed gauge / compound
−default: Gauge (relative to atmosphere)
+ - "Coplanar flange"
+ - "Traditional biplanar flange"
```
−## A gauge instrument reads relative to atmosphere; an absolute instrument reads relative to a vacuum reference; a differential instrument reads the pressure difference across two ports; a sealed-gauge instrument reads against a fixed sealed reference for cryogenic or high-vacuum service. Confusing gauge and absolute reference in vacuum or low-pressure service produces readings that are wrong by one atmosphere, so the reference is never left to be inferred. {note}
+### A coplanar flange carries both process ports on one face and mounts a compact manifold with the fewest joints; a traditional biplanar flange carries the ports on the two sides of the sensor body, mates to the manifolds and flange adapters that have been made to IEC 61518 dimensions for decades, and is the form offered by the most manufacturers. A plant that already holds spare manifolds of one form holds the field to that form. {note}
−# Range and Span {toc}
+### Differential transmitter process flanges shall have 1/4 in. NPT ports on the mating dimensions of IEC 61518 for connection to the manifold furnished under [[sync/instrument-installation-and-tubing]], with 1/2 in. NPT flange adapters furnished at the points the instrument data sheet designates for impulse tubing connected without a manifold.
−## Instrument range shall be selected so that normal operating pressure falls between 25 % and 75 % of full scale.
+### Differential transmitter process flanges shall have a drain and vent valve on each side.
−## A gauge or transmitter is least accurate at the bottom of its scale. Selecting a 0-600 psi gauge for a 100 psi system parks the pointer in the low end where readability and accuracy are worst, while a range that sits the normal reading near mid-scale uses the instrument's best band. This 25-75 % rule from ASME B40.100 is the single most common range error and the easiest to avoid. {note}
+### Threaded process connections shall conform to ASME B1.20.1 and flanged connections to ASME B16.5.
−## Maximum operating pressure shall not exceed 75 % of full-scale range for steady service, or 50 % of range for pulsating service.
+### Process flanges, flange adapters, and drain and vent valves shall be of Type 316 stainless steel or of the isolating diaphragm material where that material is a higher alloy.
−## The instrument range, in engineering units, shall be selected for the service.
+## Wetted Materials {toc}
+### The isolating diaphragm of each transmitter, or the process diaphragm of its seal where one is furnished, shall be of the material indicated in the datasheet at points for which the instrument data sheet does not designate a material.
+
```datasheet
−label: Calibrated Range
−type: range
−unit: psi
−min: 0
−max: 10000
−step: 1
+label: Wetted Diaphragm Material for Points Not Otherwise Designated
+type: select
+options:
+ - "Type 316L stainless steel"
+ - "UNS N10276 nickel-molybdenum-chromium alloy"
+ - "UNS N04400 nickel-copper alloy"
+ - "Tantalum"
+ - "Titanium"
+ - "Gold-plated Type 316L stainless steel"
+ - "Alumina ceramic"
+default: "Type 316L stainless steel"
```
−## Typical service ranges are well established and should be used as the starting point for range selection.
+### Type 316L serves water, steam, air, and most process fluids and is the diaphragm every manufacturer stocks; the nickel-molybdenum-chromium alloy serves oxidizing and reducing acids, wet chlorine, and high chlorides; the nickel-copper alloy serves hydrofluoric acid, seawater, and caustic; tantalum serves the strongest acids, including hot hydrochloric and sulfuric, at the highest price of the group; titanium serves seawater, wet chlorine, and oxidizing acids; a gold layer on Type 316L closes the hydrogen path; alumina ceramic resists abrasion and nearly every chemical except hydrofluoric acid and strong caustic, with no fill behind it. The data sheet designates another material where the fluid at a point rules the default out. {note}
−## HVAC and domestic water run 0-160 psi; chilled and hot water 0-100 psi; low-pressure steam 0-30 psi; high-pressure steam 0-300 psi; compressed air 0-200 psi; and natural-gas utility service 0-15 psi or 0-60 psi. These are starting points to be checked against the 25-75 % rule for the actual normal operating pressure, not substitutes for it. Coordinate gas-service ranges with [[sync/natural-gas-piping]] and hydronic ranges with [[sync/hydronic-piping]]. {note}
+### A wetted material shall be not less resistant to the process fluid than the piping material at the connection.
−## Overpressure capability shall meet or exceed the service.
+### Gaskets and O-rings in contact with the process fluid shall be of an elastomer or fluoropolymer the manufacturer rates for the fluid, pressure, and temperature stated on the instrument data sheet.
+## Output Signal {toc}
+
+### Transmitters shall deliver the output signal indicated in the datasheet.
+
```datasheet
−label: Overpressure Rating
+label: Transmitter Output Signal
type: select
options:
− - 130 % of full scale (gauge, ASME B40.100 Grade A)
− - 2x range (transmitter, standard)
− - 3x range (transmitter, high-overpressure)
− - Specify static line-pressure limit (DP cell)
−default: 130 % of full scale (gauge, ASME B40.100 Grade A)
+ - "4-20 mA with HART"
+ - "4-20 mA without digital communication"
+ - "FOUNDATION Fieldbus H1"
+ - "PROFIBUS PA"
+ - "WirelessHART"
+ - "Modbus RTU over RS-485"
+default: "4-20 mA with HART"
```
−## ASME B40.100 Grade A gauges are rated to withstand 130 % of full-scale without permanent error. Transmitters typically tolerate 2x to 3x their range without damage. For differential-pressure cells the static line pressure that the cell sees is a separate and often larger limit than the DP overpressure, and it must be specified alongside the DP range. {note}
+### A 4-20 mA loop with HART runs on two wires, reads on any analog input, and carries configuration and diagnostics over the same pair; without HART the transmitter is configured at its terminals and reports nothing but the value; a fieldbus transmitter puts the value and diagnostics on a segment shared with other devices and needs the segment design, power conditioner, and host integration that go with it; a wireless transmitter needs no field wiring and reports at an interval set by its battery life, which is what decides where it can be used; a Modbus transmitter suits a remote terminal unit or a packaged system with a serial port and has no live zero to show a broken wire. {note}
−## Differential-pressure transmitters shall have a static line-pressure rating equal to or greater than the maximum line pressure the high side will see.
+### Transmitters with a 4-20 mA output shall be two-wire loop-powered devices that deliver their full output into the loop resistance of the installed loop at the minimum supply voltage of the control panel power supply.
−## A DP cell can be destroyed by static pressure on the high-side connection that exceeds the cell's static rating even when the differential is small. Ignoring static line pressure is a classic DP-cell failure, so the static rating is specified together with the DP range, never separately. {note}
+### HART transmitters shall support HART revision 7 or later.
−# Accuracy Class {toc}
+### Transmitters shall drive their output to the failure level under NAMUR NE 43 on a sensor fault or an internal fault, in the direction stated on the instrument data sheet for each point.
−## Gauge accuracy grade shall be specified per ASME B40.100.
+### A WirelessHART transmitter shall not serve a point used for closed-loop control or a safety instrumented function unless the instrument index designates the point for wireless service.
+### Fieldbus and wireless transmitters shall join segments and networks designed under [[sync/process-control-networks]].
+
+### A level transmitter on a fuel storage tank furnished under [[sync/fuel-dispensing-and-storage-tanks]] that provides an analog output to the plant monitoring system shall deliver the output signal selected above and shall meet the hazardous-location requirements of this standard.
+
+## Transmitter Performance {toc}
+
+### Transmitters shall have a published reference accuracy, stated under Quality Assurance, not exceeding the value indicated in the datasheet at the calibrated span of each point, at points for which the instrument data sheet does not state an accuracy.
+
```datasheet
−label: Gauge Accuracy Grade
+label: Maximum Reference Accuracy for Points Not Otherwise Designated
+type: range
+unit: '% of calibrated span'
+min: 0.025
+max: 0.5
+setpoints: [0.025, 0.04, 0.05, 0.065, 0.075, 0.1, 0.15, 0.2, 0.25, 0.5]
+```
+
+### The transmitter's error is one term in the loop's error budget beside the installation effects and the input card, so a transmitter tighter than the control system can use buys nothing, and the price step between a utility-grade and a premium transmitter is large; the budget for the loop is set by what the control system does with the value, which is why the field carries no default and the data sheet states a tighter value at the points that need one. {note}
+
+### Transmitters shall have a published rangeability from the upper range limit to the minimum calibrated span of not less than the ratio indicated in the datasheet, with the reference accuracy held over the published turndown at which it applies.
+
+```datasheet
+label: Minimum Rangeability, Upper Range Limit to Minimum Span
+type: range
+unit: to 1
+min: 5
+max: 200
+setpoints: [5, 10, 15, 20, 30, 50, 100, 150, 200]
+```
+
+### Rangeability is what lets one sensor module serve many points and one spare serve them all, and it is also where the accuracy claim gives way: a transmitter turned down past the ratio at which its reference accuracy is stated carries a larger error that the product data states as a separate formula. A plant that standardizes on a few modules wants a high ratio; a plant that buys each point at its own range needs little. {note}
+
+### Transmitters shall have a published long-term stability and a published ambient temperature effect at the calibrated span, each stated in the product data, and the sum of the reference accuracy, the ambient temperature effect over the installed ambient range, and the stability over the recalibration interval selected under Calibration shall not exceed the total error stated on the instrument data sheet at points where one is stated.
+
+### Transmitters shall have adjustable output damping, configurable from the terminals or over the digital protocol, and shall be furnished with the damping stated on the transmitter configuration sheet.
+
+### Transmitters shall be configurable for range, engineering units, damping, transfer function, and failure direction without a pressure source connected.
+
+## Housing and Electrical Connection {toc}
+
+### Transmitter housings shall be of the material indicated in the datasheet.
+
+```datasheet
+label: Transmitter Housing Material
type: radio
options:
− - Grade A (± 1 % of span)
− - Grade 2A (± 0.5 % of span)
− - Grade B (± 2 % of span)
−default: Grade A (± 1 % of span)
+ - "Coated die-cast aluminum"
+ - "Stainless steel"
+default: "Coated die-cast aluminum"
```
−## Grade A delivers ± 1 % of span and is the field default; Grade 2A delivers ± 0.5 % for readings used in adjustment or acceptance; Grade B at ± 2 % is acceptable only for coarse utility indication. The grade is matched to how the reading is used, not chosen for its own sake. {note}
+### A coated aluminum housing is light, inexpensive, and offered in every configuration, and its coating is what stands between it and a salt or chemical atmosphere; a stainless housing resists that atmosphere without a coating at several times the price and weight, and is the housing hygienic plants hold to so that nothing on the line is painted. {note}
−## Transmitter reference accuracy shall be specified as a percentage of calibrated span.
+### Transmitter housings shall have the conduit entry indicated in the datasheet.
```datasheet
−label: Transmitter Reference Accuracy
−type: select
+label: Transmitter Conduit Entry
+type: radio
options:
− - ± 0.065 % of span (high accuracy)
− - ± 0.1 % of span
− - ± 0.25 % of span (standard)
− - ± 0.5 % of span (utility)
−default: ± 0.1 % of span
+ - "1/2 in. NPT"
+ - "3/4 in. NPT"
+ - "M20 x 1.5"
+default: "1/2 in. NPT"
```
−## Mid-tier process transmitters specify a reference accuracy from ± 0.065 % to ± 0.25 % of calibrated span. Tighter accuracy carries cost and is justified by custody-transfer, performance-test, or safety-loop service rather than applied universally. {note}
+### A 1/2 in. entry fits the conduit size that serves a single loop and is the entry every housing is offered with; a 3/4 in. entry fits a larger conduit or a cable gland for armored cable and takes a reducer when the conduit is smaller; a metric entry suits equipment imported with metric glands and takes a listed adapter to join a conduit system under NFPA 70. {note}
−# Process Connection {toc}
+### Transmitter housings shall have a separate terminal compartment isolated from the electronics, threaded covers with a gasket that holds the enclosure rating required under Environmental and Service Conditions, and a housing that rotates on the sensor module for display and conduit orientation.
−## The default process connection for gauges and most transmitters shall be 1/2 in NPT conforming to ASME B1.20.1.
+### Transmitters shall be furnished with a local display as indicated in the datasheet.
```datasheet
−label: Process Connection
−type: select
+label: Transmitter Local Display
+type: radio
options:
− - 1/2 in NPT (male)
− - 1/4 in NPT (male)
− - ASME B16.5 Class 150 RF flange
− - ASME B16.5 Class 300 RF flange
− - Coplanar flange (DP transmitter)
− - Tri-clamp (sanitary)
−default: 1/2 in NPT (male)
+ - "Display on every transmitter"
+ - "Display on transmitters at points with no local gauge"
+ - "No local display"
```
−## The 1/2 in NPT connection is the workhorse for both gauges and transmitters; 1/4 in NPT appears on small or high-pressure instruments. NPT threads are the most common pressure-instrument connection and are governed by ASME B1.20.1. Flanged connections per ASME B16.5 are reserved for elevated temperature or high pressure. {note}
+### A display shows the reading and the diagnostic state at the instrument, which lets a technician check a loop without a handheld communicator, and on a transmitter mounted at eye level it does what a gauge does with the loop live; it adds a windowed cover, a module to stock, and a cost per point, and it shows nothing when the loop is down. The choice pairs with the local gauge policy under Measurement Points. {note}
−## Steam service above 400 °F or pressure above 600 psi shall use an ASME B16.5 flanged connection of Class 300 or higher, rated for the service temperature and pressure.
+### Transmitters shall be furnished with integral transient protection as indicated in the datasheet.
−## Gauge process-connection orientation shall be specified as lower-mount, lower-back, or back-mount to suit the panel or piping arrangement.
−
```datasheet
−label: Gauge Connection Orientation
+label: Integral Transient Protection
type: radio
options:
− - Lower mount
− - Lower-back mount
− - Back mount (panel)
−default: Lower mount
+ - "Integral transient protection on every transmitter"
+ - "Integral transient protection on outdoor and remotely located transmitters"
+ - "No integral transient protection"
```
−# Wetted Materials {toc}
+### A transient protector in the terminal compartment clamps the surge that lightning or a switching event induces on the loop before it reaches the electronics, and it is the cheapest point at which to protect a transmitter at the end of a long outdoor run; a transmitter inside a building on a short loop from a protected panel sees little, and the protector adds a terminal block to each point and a leakage path to ground that an insulation test has to allow for. {note}
−## Wetted materials shall be selected for compatibility with the process chemistry; 316 stainless steel is the default but is not universally suitable.
+## Multivariable Transmitters {toc}
+### Where the instrument index designates a multivariable transmitter, the transmitter shall be furnished with the pressure sensor, process connection, output signal, and performance required by this standard, shall accept the temperature element furnished under [[sync/temperature-instrumentation]], and shall report the differential pressure, the static pressure, and the process temperature as separate variables over the digital protocol.
+
+### Where a multivariable transmitter computes a flow, the computation and the primary element are furnished under [[sync/flow-measurement]] and the transmitter under this standard.
+
+# Diaphragm Seals and Capillaries {toc}
+
+## Seal Provision and Assembly {toc}
+
+### Diaphragm seals shall be furnished at the points the instrument index designates, of the seal type, process connection, and extension stated on the instrument data sheet.
+
+### A seal puts a flexible diaphragm and a captive fill between the process and the sensor, so a fluid that would plug, corrode, freeze, or overheat the sensor never reaches it, and the transmitter then reads the fill pressure as the process pressure; the fill expands with temperature and sags with its own head in a capillary, so every seal adds a temperature error and a response delay that the assembly drawing has to quantify. {note}
+
+### Each seal, its capillary, and its transmitter shall be furnished as one assembly, filled, evacuated, and calibrated together by the transmitter manufacturer, and shall not be disconnected after filling.
+
+### A seal shall be of the flush type where the data sheet states a fluid that is viscous, crystallizing, or solids-bearing, and of the extended type where the process nozzle at the point is longer than the diaphragm's reach.
+
+### A flushing ring shall be furnished between the process flange and the seal at the points the instrument data sheet designates for flushing or calibration access.
+
+## Seal Fill Fluid {toc}
+
+### Seal assemblies shall be filled with the fluid indicated in the datasheet at points for which the instrument data sheet does not designate a fluid.
+
```datasheet
−label: Wetted Material
+label: Seal Fill Fluid for Points Not Otherwise Designated
type: select
options:
− - 316 stainless steel
− - 17-4 PH stainless steel (high pressure)
− - Hastelloy C-276
− - Monel
− - PTFE-wetted / PTFE-lined
− - Carbon steel (dry-gas utility only)
−default: 316 stainless steel
+ - "Silicone oil"
+ - "High-temperature silicone oil"
+ - "Halocarbon oil"
+ - "Glycerin and water"
+ - "Food-grade white mineral oil"
+ - "Propylene glycol and water"
+default: "Silicone oil"
```
−## 316 SS covers most water, air, steam, and benign-process service. It is not suitable for high-chloride, strong-acid, or strong-caustic chemistry, where chloride stress-corrosion cracking and pitting attack the wetted parts. Hastelloy C-276, Monel, or PTFE-lined wetted parts must be specified explicitly for aggressive chemistry such as chlorine, acids, and caustics — they are never assumed from a generic stainless call-out. {note}
+### Silicone oil holds its viscosity over the widest temperature band and is the fill every manufacturer offers first; a high-temperature silicone extends the band toward 600°F at the cost of a larger temperature effect; halocarbon is inert and is the fill for oxygen and chlorine; glycerin and water and propylene glycol and water are the fills accepted for food contact behind a single diaphragm, with freezing points that rule them out of cold service; food-grade white mineral oil is the hygienic fill with the lowest freezing point. The fluid is a process-contact material the moment the diaphragm fails, so its rating for the fluid matters as much as the diaphragm metal. {note}
−## Carbon-steel wetted parts shall be used only for dry, non-corrosive gas-utility indication and shall not be used in any wet or corrosive service.
+### Seal fill fluids shall be rated by the manufacturer for the vapor pressure at the maximum process temperature and for the lowest ambient and process temperature stated on the instrument data sheet, including vacuum service where the data sheet states it.
−# Diaphragm Seals {toc}
+## Capillaries {toc}
−## A flush-diaphragm remote or direct seal shall be specified for viscous, slurry, crystallizing, or sanitary service.
+### Capillaries shall be of Type 316 stainless steel with stainless steel flexible armor over their full length, of the length stated on the instrument data sheet and not longer than the manufacturer's published maximum for the fill and the range.
+### The two capillaries of a differential pressure seal assembly shall be of equal length and of the same fill, and shall be routed together so that both see the same ambient temperature.
+
+### Two capillaries of different lengths or on different sides of a pipe hold different volumes of fill at different temperatures, and the difference between the two expansions is read as a differential pressure that moves with the sun. {note}
+
+### Capillaries shall not be bent to a radius smaller than the manufacturer's published minimum, and no section of a capillary shall bear the weight of the transmitter or the seal.
+
+# Local Pressure Gauges {toc}
+
+## Gauge Element and Accuracy {toc}
+
+### Local gauges shall have the pressure element indicated in the datasheet at points for which the instrument data sheet does not designate an element.
+
```datasheet
−label: Diaphragm Seal
+label: Gauge Element for Points Not Otherwise Designated
type: radio
options:
− - None (direct connection)
− - Flush-diaphragm seal (process)
− - Flush-diaphragm seal, sanitary / 3-A
− - Remote seal with capillary
−default: None (direct connection)
+ - "Bourdon tube"
+ - "Diaphragm or capsule"
+ - "Bellows"
+ - "Electronic digital gauge"
+default: "Bourdon tube"
```
−## A direct-connected gauge or transmitter on a viscous, slurry, or crystallizing process plugs at the connection and stops reading. A flush-diaphragm seal isolates the instrument behind a process-wetted diaphragm and a captive fill fluid, keeping the process out of the sensing element. Sanitary and hygienic processes require a flush seal with a tri-clamp connection and a 3-A certified or NSF-listed assembly. {note}
+### A Bourdon tube is a flattened tube that straightens with pressure, has no fill and no power, and reads from about 15 psi to the highest ranges made; a diaphragm or capsule element flexes under pressure and resolves ranges in inches of water and ounces per square inch that a Bourdon tube cannot; a bellows element serves low ranges and compound ranges with a larger movement; an electronic digital gauge reads a sensor to a display, resolves to a fraction of a percent with no parallax, and needs a battery or a loop to power it. {note}
−## The seal fill fluid shall be selected for the service temperature and any food or potable-water contact requirement.
+### Gauges with a full-scale range in inches of water column or ounces per square inch shall have a diaphragm, capsule, or bellows element regardless of the selection above.
+### Gauges shall meet the ASME B40.100 accuracy grade indicated in the datasheet at points for which the instrument data sheet does not state a grade.
+
```datasheet
−label: Fill Fluid
+label: Gauge Accuracy Grade for Points Not Otherwise Designated
type: select
options:
− - Glycerin (standard / vibration)
− - Silicone oil (high temperature)
− - Food-grade mineral oil (sanitary)
− - Food-grade silicone (sanitary)
− - Halocarbon (oxygen service)
−default: Glycerin (standard / vibration)
+ - "Grade 4A"
+ - "Grade 3A"
+ - "Grade 2A"
+ - "Grade 1A"
+ - "Grade A"
+ - "Grade B"
+ - "Grade C"
+ - "Grade D"
+default: "Grade 2A"
```
−## Glycerin is the standard fill for general and vibrating service; silicone oil suits high-temperature ambients above 140 °F; food-grade white mineral oil or food-grade silicone is required for sanitary and NSF service. The fill fluid is a process-contact material through the diaphragm, so its food or potable rating matters as much as the diaphragm metal. {note}
+### Grade 2A, accurate to one half of one percent of span across the scale, is the grade of the stainless process gauge that industrial suppliers stock in every range and is the default for that reason; Grade 1A and Grade A cost less and are the commercial gauges of building services, with Grade A accurate to one percent through the middle half of the scale and two percent at the ends; Grade 3A and Grade 4A are test gauges accurate to a quarter and a tenth of one percent, used as references rather than as indicators; Grade B and Grade C are utility gauges whose error grows toward the ends of the scale, and Grade D is a utility gauge accurate to five percent across the scale; their readings serve to show that pressure is present rather than how much. {note}
−# Local Gauges {toc}
+## Gauge Case and Dial {toc}
−## Local-indicating gauges shall be Bourdon-tube dial gauges with a stainless-steel case unless the datasheet specifies a digital or differential type.
+### Gauges shall have the nominal dial size indicated in the datasheet at points for which the instrument data sheet does not state a size.
```datasheet
−label: Local Gauge Type
−type: radio
−options:
− - Bourdon-tube dial gauge
− - Digital gauge (LCD, battery)
− - Differential-pressure dial gauge (low DP)
−default: Bourdon-tube dial gauge
+label: Gauge Dial Size for Points Not Otherwise Designated
+type: range
+unit: in.
+min: 1.5
+max: 12
+setpoints: [1.5, 2, 2.5, 3.5, 4, 4.5, 6, 8.5, 12]
+default: 4.5
```
−## The Bourdon-tube dial gauge is the standard local indicator for most pressure service. A digital gauge with an LCD display suits readings taken close-up where resolution matters, and a differential-pressure dial gauge (diaphragm or piston type) suits filter-monitoring and other low-DP applications where a Bourdon tube cannot resolve the small difference. {note}
+### A 4-1/2 in. dial is readable from the floor at a pipe rack and is the size in which every process gauge range and grade is stocked; the 2-1/2 in. and 3-1/2 in. dials fit a manifold or a panel and are read close up; the 6 in. and larger dials are read across a room or from grade at an elevated line. {note}
−## Gauge dial size shall be 4 in for standard field mounting, 6 in for eye-level panel boards, and 2.5 in for manifold-mounted or space-constrained locations.
+### Gauge cases shall be of the material indicated in the datasheet.
```datasheet
−label: Gauge Dial Size
+label: Gauge Case Material
type: radio
options:
− - 2.5 in (manifold / tight space)
− - 4 in (standard field)
− - 6 in (panel / control room)
−default: 4 in (standard field)
+ - "Type 304 stainless steel"
+ - "Phenolic, solid-front with blowout back"
+ - "Glass-fiber-reinforced thermoplastic"
+ - "Painted steel"
+default: "Type 304 stainless steel"
```
−## Dial size is driven by viewing distance and available space. A 4 in dial reads cleanly at the equipment, a 6 in dial reads across a control room or panel front, and a 2.5 in dial fits a crowded manifold. Oversizing wastes space and undersizing hurts readability. {note}
+### A stainless case resists the weather and the washdown of a process area and is the case on the stocked process gauge; a solid-front phenolic case puts a wall between the element and the dial and vents a tube rupture out the back, away from the reader; a reinforced thermoplastic case is light and resists corrosion at low cost and softens at high ambient temperature; a painted steel case is the lowest-cost commercial case and rusts where its coating is scratched. {note}
−## Gauges in vibrating service shall be liquid-filled with glycerin (or silicone for high-temperature ambients) to damp pointer flutter and protect the movement.
+### Gauges at points where the fluid is flammable, toxic, or a compressed gas above 1000 psi shall have a solid-front case with a blowout back regardless of the selection above.
+### Gauge windows shall be laminated safety glass, tempered glass, or a plastic the manufacturer rates for the case fill and the ambient temperature, and plain annealed glass shall not be used.
+
+### Gauge dials shall be white with black graduations and numerals, graduated in the engineering units stated on the instrument data sheet, with a pointer that reads to the graduation without parallax.
+
+## Gauge Connection {toc}
+
+### Gauges shall have the connection size indicated in the datasheet at points for which the instrument data sheet does not state a size, threaded to ASME B1.20.1.
+
```datasheet
−label: Gauge Case Fill
+label: Gauge Connection Size for Points Not Otherwise Designated
type: radio
options:
− - Dry (non-vibrating service)
− - Glycerin-filled (vibration)
− - Silicone-filled (high temperature)
−default: Dry (non-vibrating service)
+ - "1/4 in. NPT"
+ - "1/2 in. NPT"
+default: "1/2 in. NPT"
```
−## Low differential-pressure indication for filter and strainer monitoring shall use a diaphragm or piston differential gauge with a range suited to the clean-to-dirty pressure drop, typically 0-10 in w.c. through 0-25 psi.
+### Gauges with a 4-1/2 in. or larger dial are made with a 1/2 in. connection and gauges with a 2-1/2 in. or smaller dial with a 1/4 in. connection, so the connection follows the dial at the ends of the size range and is a choice only in between; a 1/2 in. socket is stiffer against vibration and matches the manifold and valve ports of a process hook-up. {note}
−# Electronic Transmitters {toc}
+### Gauges shall have the connection location indicated in the datasheet.
−## Transmitters shall provide a 4-20 mA two-wire output with HART revision 7 unless a digital fieldbus is specified.
−
```datasheet
−label: Signal Output
+label: Gauge Connection Location
type: radio
options:
− - 4-20 mA, two-wire, HART rev 7
− - 4-20 mA, two-wire (no HART)
− - Foundation Fieldbus H1
− - PROFIBUS PA
− - WirelessHART (IEC 62591)
−default: 4-20 mA, two-wire, HART rev 7
+ - "Lower"
+ - "Center back"
+ - "Lower back"
+default: "Lower"
```
−## The two-wire 4-20 mA loop with HART revision 7 is the 80 % default for US industrial projects: it powers and signals on one pair, and HART carries digital configuration and diagnostics over the analog loop. Foundation Fieldbus H1, PROFIBUS PA, and WirelessHART (ISA100/IEC 62591) are specified where the project network architecture in [[sync/process-control-networks]] calls for them. {note}
+### A lower connection stands the gauge upright on a nipple or a gauge valve at the pipe and is the location of the stocked process gauge; a center back connection mounts the gauge through a panel or a flush bracket with the dial facing the reader; a lower back connection suits a panel with the piping dropping behind it and a surface-mounted bracket. {note}
−## HART revision shall be specified as revision 7 minimum.
+### Gauge tubes and sockets shall be of the material indicated in the datasheet at points for which the instrument data sheet does not designate a material.
−## HART 5 and HART 7 are not fully interoperable, and a transmitter that defaults to HART 5 may not present its full diagnostics to a current HART multiplexer or DCS. Specifying HART revision 7 minimum avoids a commissioning surprise where the device communicates but the host cannot read everything it expects. {note}
+```datasheet
+label: Gauge Tube and Socket Material for Points Not Otherwise Designated
+type: select
+options:
+ - "Type 316 stainless steel"
+ - "Phosphor bronze tube with brass socket"
+ - "UNS N04400 nickel-copper alloy"
+ - "UNS N06600 nickel-chromium-iron alloy"
+default: "Type 316 stainless steel"
+```
−## Loop-powered transmitters shall accept a supply of 10.5 to 42.4 VDC, with 24 VDC nominal supplied from the control panel.
+### A stainless tube and socket serve water, steam, air, oils, and most process fluids and are the wetted parts of the stocked process gauge; a bronze tube with a brass socket is the commercial gauge for water, air, and oil at lower cost and is attacked by ammonia, acids, and sulfur compounds; the nickel-copper alloy serves hydrofluoric acid, seawater, and caustic; the nickel-chromium-iron alloy serves high-temperature and high-pressure service and chlorides where a stainless tube would crack. {note}
+## Gauge Case Fill {toc}
+
+### Gauge cases shall be liquid-filled as indicated in the datasheet.
+
```datasheet
−label: Power Supply
+label: Gauge Case Fill Policy
type: radio
options:
− - Loop-powered (two-wire, 24 VDC nominal)
− - Four-wire line-powered
−default: Loop-powered (two-wire, 24 VDC nominal)
+ - "Liquid-filled at every gauge"
+ - "Liquid-filled at the points the instrument index designates for pulsation or vibration"
+ - "Dry at every gauge"
```
−## A local LCD indicator shall be provided on transmitters where an operator reads the value at the instrument and no separate local gauge is installed.
+### A liquid fill damps pointer flutter, lubricates the movement, and keeps condensation off the inside of the window, so a filled gauge on a pump discharge or a compressor outlives a dry one many times over; a fill adds cost to every gauge, hides a small leak in the case, is read with a vented plug that an installer has to open, and is a contaminant in a few services. Filling every gauge saves the step of deciding per point and is the policy of plants with reciprocating equipment throughout; filling only where designated is the policy of plants with mostly steady service. {note}
+### Liquid-filled gauges shall be filled with the fluid indicated in the datasheet.
+
```datasheet
−label: Local Display
+label: Gauge Case Fill Fluid
type: radio
options:
− - None
− - LCD indicator
−default: LCD indicator
+ - "Glycerin"
+ - "Silicone oil"
+ - "Halocarbon oil"
+default: "Glycerin"
```
−## Differential-pressure transmitters shall be furnished with a coplanar or biplanar flange and an integral or close-coupled valve manifold.
+### Glycerin is the fill on nearly every liquid-filled gauge sold, is inexpensive, and thickens until the pointer stalls at about -4°F; silicone oil keeps its viscosity to about -40°F and in high ambient heat; halocarbon oil is inert and is the fill for oxygen and chlorine service, where glycerin is a fuel. {note}
−## A DP transmitter cannot be zeroed, calibrated, or removed in service without an isolation manifold. The two-valve manifold isolates a single-port instrument; the three-valve manifold equalizes a DP cell for zero check; the five-valve manifold adds bleed/vent ports for full block-and-bleed on a DP transmitter. The manifold is part of the DP installation, not an accessory. {note}
+### Where [[parameter: site-ambient-temperature-minimum]] is below 0°F, liquid-filled gauges mounted outdoors shall be filled with silicone or halocarbon oil regardless of the selection above.
−## Multivariable transmitters that report both pressure and process temperature shall be coordinated with [[sync/temperature-instrumentation]] for the temperature element specification and calibration.
+### Liquid-filled gauges shall have a vent plug or a fill plug with a vent position, and the vent shall be opened after installation.
−# Pressure Switches {toc}
+### A filled case that is sealed reads the pressure of the fill's own expansion against the element as a few percent of zero error on a hot afternoon; the vent lets the case breathe. {note}
−## Pressure switches shall be snap-action with an adjustable setpoint and a deadband suited to the control function.
+## Snubbers, Siphons, and Pressure Limiters {toc}
+### Gauges and switches at the points the instrument index designates for pulsating service shall be furnished with a snubber of the type indicated in the datasheet.
+
```datasheet
−label: Pressure Switch Configuration
−type: select
+label: Snubber Type
+type: radio
options:
− - SPDT snap-action, adjustable setpoint
− - DPDT snap-action, adjustable setpoint
− - SPDT, fixed deadband
−default: SPDT snap-action, adjustable setpoint
+ - "Porous sintered-metal"
+ - "Piston"
+ - "Adjustable needle"
```
−## A pressure switch closes or opens a discrete contact at a setpoint to start a pump, trip an alarm, or interlock equipment. The single-pole double-throw snap-action switch is the common form. Where the switch performs a safety function, a transmitter with a programmable trip in the logic solver is generally preferred over a mechanical switch because it is testable and diagnosable per [[sync/process-instrumentation]]. {note}
+### A porous snubber damps through a sintered disc, has no moving part, and plugs in dirty or viscous fluid; a piston snubber damps through the clearance around a loose piston that rises and falls with the pulse, clears itself, and is offered in several piston sizes for different fluids; an adjustable needle snubber is throttled in the field to the damping the gauge needs and can be throttled shut by mistake. Which one a plant stocks depends on the fluids its pulsating lines carry, so the field carries no default. {note}
−## The pressure-switch setpoint shall be specified in service engineering units.
+### Gauges and switches in steam service shall be connected through a siphon of the pigtail or coil type conforming to ASME B40.100, filled with water before the instrument is pressurized.
+### A siphon traps a column of condensate between the steam and the element, so the element reads the pressure through a cool liquid rather than through live steam; a dry siphon on first pressurization passes steam straight to the element until condensate forms, which is why it is filled first. {note}
+
+### Gauges at points where the instrument data sheet states pressure excursions above the full-scale range shall be furnished with a pressure limiter valve conforming to ASME B40.100, set to close below the full-scale range of the gauge.
+
+## Differential Pressure Gauges {toc}
+
+### Differential pressure gauges at the points the instrument index designates for filter, strainer, or pump differential indication shall have the element indicated in the datasheet.
+
```datasheet
−label: Switch Setpoint
−type: range
−unit: psi
−min: 0
−max: 600
−step: 1
−setpoints:
− - 60
+label: Differential Pressure Gauge Element
+type: radio
+options:
+ - "Piston"
+ - "Diaphragm"
+ - "Bellows"
+ - "Dual Bourdon tube"
```
−# Overpressure and Pulsation Protection {toc}
+### A piston element is a magnet-coupled piston against a spring, tolerates the full static pressure on either side and a reversal, and is the low-cost gauge for a filter whose differential matters only as it approaches the changeout point; a diaphragm element resolves a few inches of water with the static pressure on both sides and is the gauge for low differentials in liquid service; a bellows element serves low differentials in gas and compound ranges; a dual Bourdon gauge reads two separate elements against one dial and shows both pressures and their difference, at the cost of the accuracy of two elements combined. {note}
−## A snubber shall be specified for gauges and transmitters in pulsating service from reciprocating pumps, compressors, or pulsating flow.
+### Differential pressure gauges shall have a published static pressure rating not less than the maximum static line pressure stated on the instrument data sheet, and shall withstand that pressure applied to either side alone without damage or a shift in calibration.
+# Pressure Switches {toc}
+
+## Switch Construction {toc}
+
+### Pressure switches shall be of the type indicated in the datasheet.
+
```datasheet
−label: Snubber
+label: Pressure Switch Type
type: radio
options:
− - None (steady service)
− - Sintered-metal snubber
− - Adjustable piston snubber
−default: None (steady service)
+ - "Electromechanical snap-action switch"
+ - "Electronic pressure switch with programmable setpoint"
+default: "Electromechanical snap-action switch"
```
−## Pressure pulses from reciprocating equipment fatigue a Bourdon tube or sensor in weeks. A snubber — sintered-metal or adjustable piston type — damps the pulses before they reach the sensing element. On a pulsating-service gauge the snubber and a glycerin case fill are specified together, because each addresses a different part of the same problem. {note}
+### An electromechanical switch moves a snap-action contact with a diaphragm, piston, or Bourdon element against a spring, needs no power, and holds its setpoint for years with a deadband fixed by the mechanism; an electronic switch reads a sensor, sets its setpoint and deadband from a keypad or over a protocol, shows the pressure on a display, and reports its own faults, and it needs a supply and costs several times as much. {note}
−## An isolation valve shall be provided at every gauge and transmitter so the instrument can be isolated for calibration or removal without shutting down the process.
+### Pressure switches shall have the contact arrangement indicated in the datasheet at points for which the instrument data sheet does not state an arrangement.
```datasheet
−label: Isolation Valve / Manifold
−type: select
+label: Pressure Switch Contact Arrangement
+type: radio
options:
− - 1/2 in NPT needle valve (gauge saver)
− - Two-valve block-and-bleed manifold
− - Three-valve manifold (DP)
− - Five-valve manifold (DP, block-and-bleed)
−default: 1/2 in NPT needle valve (gauge saver)
+ - "Single-pole double-throw"
+ - "Double-pole double-throw"
+ - "Two independent single-pole double-throw contacts"
+default: "Single-pole double-throw"
```
−## A 1/2 in NPT needle valve (gauge saver) isolates a single-port instrument. A two-valve block-and-bleed manifold serves a single-port transmitter, and a five-valve manifold serves a differential-pressure transmitter. Without isolation, calibration and replacement require a line shutdown, which is rarely acceptable in service. {note}
+### A single-pole double-throw contact gives one circuit a closing and an opening path and is what a controller input or an alarm needs; a double-pole arrangement switches two circuits together, for a control circuit and a status indication from one setpoint; two independent contacts can be set at two pressures within one switch, for an alarm and a trip, with the deadband of each set separately. {note}
−# Functional Safety {toc}
+### Switch setpoints shall be adjustable over the published adjustable range without disassembly, and the switch shall be furnished set to the setpoint and the reset direction stated on the instrument data sheet with the setpoint falling within the middle half of the adjustable range.
−## Instruments serving a safety instrumented function shall be SIL-rated and certified per IEC 61508, and applied within a safety instrumented system per IEC 61511.
+### Switch deadband shall be adjustable where the instrument data sheet states a reset pressure, and shall not exceed the deadband stated there.
+### Switch contacts shall be rated for the voltage and the connected load stated on the loop diagram, and contacts switching a controller input at less than 100 mA shall be gold-flashed or hermetically sealed.
+
+### A silver contact relies on the arc of a few hundred milliamperes to burn off the film that forms on it, and switched into a dry circuit it builds that film until the input stops reading the contact; a gold flash or a sealed contact has no film to burn. {note}
+
+### Switch sensing elements shall withstand the overpressure and static pressure required of transmitters under Pressure Transmitters, with wetted parts of the material selected under Wetted Materials at points for which the instrument data sheet does not designate a material.
+
+### Switches shall have a published repeatability of the setpoint not worse than 1 percent of the adjustable range.
+
+# Calibration {toc}
+
+## Factory Calibration {toc}
+
+### Individual calibration certificates traceable to a national metrology institute shall be furnished for the scope indicated in the datasheet.
+
```datasheet
−label: Safety Rating
+label: Individual Calibration Certificate Scope
type: radio
options:
− - Standard (non-SIL)
− - SIL 2 certified (IEC 61508)
− - SIL 3 certified (IEC 61508)
−default: Standard (non-SIL)
+ - "Every transmitter, every gauge, and every switch"
+ - "Every transmitter, with a lot conformance certificate for gauges and switches"
+ - "Transmitters, gauges, and switches at the points designated in the instrument index, with lot conformance certificates elsewhere"
```
−## Overpressure-protection and loss-of-containment safety loops require a SIL 2 or SIL 3 transmitter certified per IEC 61508 for hardware fault tolerance and average probability of failure on demand. The instrument's certified SIL is a property of the device; the SIL of the safety function is established by the SRS and verified for the whole loop, including the logic solver and final element in [[sync/control-valves-and-actuators]]. {note}
+### An individual certificate records the instrument's measured error at stated pressures and is what a loop error budget and a recalibration trend are built on; a lot certificate states that the lot met its grade or its reference accuracy, which is all a Grade A gauge or a general-purpose transmitter on an indication-only loop needs. The cost is a bench test per device, so the scope follows how many points carry an error budget the published accuracy alone does not satisfy. {note}
−## Human-factors requirements for safety-loop pressure displays and alarms shall be evaluated per ISA TR84.00.04 guidance where the loop relies on operator response.
+### Every transmitter and switch serving a safety instrumented function, and every gauge of Grade 3A or Grade 4A, shall carry an individual calibration certificate regardless of the scope selected above.
−# Testing {toc}
+### Transmitter certificates shall report the as-shipped error at 0, 25, 50, 75, and 100 percent of the calibrated span, rising and falling, against a reference standard whose uncertainty is not more than one quarter of the transmitter's reference accuracy at that span.
−## Each instrument shall pass a factory acceptance calibration to ASME PTC 19.2 against a dead-weight tester or equivalent reference before shipment.
+### Gauge certificates shall report the error at not fewer than five points across the scale, rising and falling, in accordance with ASME B40.100.
−## Each loop shall be field loop-checked at commissioning end-to-end, from the instrument through the control system, using a HART communicator or fieldbus configurator as applicable.
+### Switch certificates shall report the actuation and reset pressures at the set point, rising and falling, over not fewer than three cycles.
−## Installed impulse lines and instrument connections shall be hydrostatically leak-tested at 1.5x design pressure after installation, before the instrument is returned to service.
+### Sealed transmitter assemblies shall be calibrated with the seal and capillary attached and mounted in the orientation of the installation stated on the assembly drawing.
−## As-left calibration data shall be recorded for every instrument at commissioning and retained in the closeout package.
+## Field Verification {toc}
+### Before installation, each transmitter shall be verified at zero and at not fewer than one point above 50 percent of span with a portable reference whose uncertainty is not more than one quarter of the transmitter's reference accuracy, and the reading recorded on the as-left calibration record.
+
+### A device whose field verification disagrees with its factory certificate by more than its combined published error shall be returned and replaced rather than adjusted.
+
+### After installation and before loop check, each transmitter shall be zero-trimmed in its installed orientation with the process isolated and the sensor vented, and a differential transmitter equalized, and the trim recorded on the as-left calibration record.
+
+### The fill behind the diaphragm has weight, and a transmitter mounted with its diaphragm vertical reads that head as a zero offset of a fraction of an inch of water that a bench calibration with the diaphragm horizontal never saw; a sealed assembly with a capillary carries a larger head, and a wet leg on a differential point a larger one still. The trim at the installed orientation is what removes them, and it cannot be done on the bench. {note}
+
+### Each transmitter's as-left configuration, including the range, engineering units, damping, transfer function, failure direction, and write-protection state, shall be recorded on the as-left calibration record.
+
+### Each switch shall be verified at its setpoint and reset pressure with a portable reference after installation, and the actuation and reset pressures recorded on the as-left calibration record.
+
+### Loop checks from the instrument to the controller shall be performed and recorded under [[sync/control-systems-integration]] in accordance with ANSI/ISA-62382.
+
+### The recalibration interval stated in the operation and maintenance data shall be not longer than the interval indicated in the datasheet.
+
```datasheet
−label: Field Test Protocol
−type: checkbox
+label: Maximum Recalibration Interval
+type: range
+unit: months
+min: 6
+max: 60
+setpoints: [6, 12, 24, 36, 60]
+default: 12
+```
+
+### A transmitter drifts with thermal cycling, overpressure events, and the hydrogen or chemical attack its diaphragm sees, and a gauge movement wears with every pulse, so the interval is a judgment about the service rather than the device; the published stability over the interval is one term in the total error under Transmitter Performance, so a longer interval and a tight total error cannot both be held on a utility-grade transmitter; a point feeding a safety instrumented function follows its proof-test interval where that is shorter. {note}
+
+## Repeat Testing {toc}
+
+### The cost of repeating a factory calibration or a field verification after a failure shall be borne by the Contractor.
+
+# Installation {toc}
+
+## Transmitter and Switch Mounting {toc}
+
+### Transmitters shall be mounted as indicated in the datasheet at points for which the instrument index does not designate a mounting.
+
+```datasheet
+label: Transmitter Mounting for Points Not Otherwise Designated
+type: radio
options:
− - Factory acceptance calibration (ASME PTC 19.2)
− - Field loop check at commissioning
− - Hydrostatic leak test at 1.5x design pressure
− - As-left calibration record
−default:
− - Factory acceptance calibration (ASME PTC 19.2)
− - Field loop check at commissioning
− - As-left calibration record
+ - "Direct-mounted on the manifold at the process tap"
+ - "Bracket-mounted on a 2 in. pipe stand or wall near the tap"
+ - "Rack-mounted with other transmitters at a common location"
```
−## The recalibration interval shall be set by service criticality.
+### A direct-mounted transmitter has no impulse tubing to slope, freeze, or leak and the fewest joints, and it sits at the height and in the heat and vibration of the tap; a transmitter on a stand near the tap is read and serviced at eye level away from the line, at the cost of a short tubing run and a stand; a rack gathers many transmitters where a technician can reach them all and runs long tubing from each tap, with the lag, the freeze protection, and the leak points that length brings. The process fluid and the layout of the lines decide which a plant holds as its norm, so the field carries no default. {note}
+### Mounting brackets shall be of the material indicated in the datasheet.
+
```datasheet
−label: Recalibration Interval
+label: Mounting Bracket Material
type: radio
options:
− - Annual (SIL / critical)
− - 2 years
− - 5 years (general process)
−default: 5 years (general process)
+ - "Type 304 stainless steel"
+ - "Carbon steel, zinc-plated or painted"
```
−## Safety-instrumented-function and critical instruments are recalibrated annually; general process transmitters carry a maximum interval of five years under typical plant standards. The interval belongs in the operation and maintenance manual and feeds the facility's mechanical-integrity program. {note}
+### A stainless bracket with stainless bolting outlasts the transmitter in a wet or corrosive area; a plated or painted carbon steel bracket costs less and serves indoors, and streaks rust down the stand where its coating is cut by the U-bolt. {note}
−# Installation {toc}
+### Bracket-mounted transmitters shall be mounted on a pipe stand or wall bracket at a height between 4 ft and 5 ft above grade or platform, within the tubing length the instrument data sheet states for the point.
−## Instruments shall be installed at a height and orientation that allow an operator to read the indication and reach the isolation valve from grade or a permanent platform.
+### Transmitters and switches shall not be supported by their impulse tubing or capillary, and a transmitter connected directly to a manifold shall be supported by the manifold's own mounting bracket or by the process connection where the manufacturer rates the connection to carry it.
−## Impulse lines shall be sloped to drain condensate in gas service and to vent gas in liquid service, with the slope and direction suited to the process phase.
+### Transmitters shall be mounted with the housing oriented so that the display faces the operator position and the conduit entry faces down or to the side, with a drip loop in any cable entering the housing and an unused entry closed with a listed plug.
−## In gas service the impulse line slopes back toward the process so condensate drains away from the instrument; in liquid service it slopes so gas vents back to the line. A line sloped the wrong way traps liquid or gas in the impulse leg and produces a standing offset in the reading that no calibration can remove. {note}
+### Differential transmitters in liquid service shall be mounted below the taps, and in gas service above the taps, unless the hook-up drawing under [[sync/instrument-installation-and-tubing]] shows another arrangement with the seal pots or vents that make it read correctly.
−## Conduit and cable entries on transmitters in classified areas shall be sealed per NEC 501.15 where required, and intrinsically safe wiring shall be installed per the manufacturer's control drawing.
+### Transmitters and switches shall be accessible for configuration, zero trim, and removal from grade or a permanent platform without removing insulation, scaffolding, or another device.
−## Instruments shall be tagged with a permanent stainless-steel or engraved tag bearing the P&ID tag number, fastened so it cannot be lost during operation or maintenance.
+## Gauge Installation {toc}
−## Transmitters shall not be supported by their process connection alone where vibration or piping movement is present; a bracket or stanchion mount shall be provided.
+### Gauges shall be installed upright on a gauge valve or on the manifold outlet furnished under [[sync/instrument-installation-and-tubing]], with the dial facing the operator position and readable from grade or a permanent platform.
−```datasheet
−label: Mounting Method
−type: radio
−options:
− - Direct process-connection mount
− - 2 in pipe-stand / stanchion bracket
− - Panel / wall bracket
− - Remote mount with capillary or impulse line
−default: 2 in pipe-stand / stanchion bracket
−```
+### Gauges on vibrating equipment, where the instrument index does not designate a liquid fill, shall be remote-mounted on a bracket connected by flexible tubing or hose rather than mounted on the equipment.
+### Gauge threads shall be made up with a sealant rated for the fluid and temperature, applied to the male thread only, and tightened with a wrench on the socket and never on the case.
+
+### Snubbers, siphons, and pressure limiter valves shall be installed between the gauge valve and the gauge, in the orientation the manufacturer publishes, with a siphon filled with water before the valve is opened.
+
+## Sealed Assembly and Capillary Installation {toc}
+
+### Seal assemblies shall be installed in the orientation shown on the reviewed assembly drawing, with the transmitter at the elevation relative to the seal that the drawing states.
+
+### Capillaries shall be routed along the pipe or structure, supported at intervals not exceeding 3 ft, protected from traffic and from contact with hot surfaces, and coiled without kinks where excess length is stored.
+
+### Insulation shall be finished around the seal and the capillary at the pipe and the transmitter left clear, coordinated with [[sync/mechanical-insulation]].
+
+## Grounding and Electrical {toc}
+
+### Metal housings, brackets, and the raceway serving transmitters and switches shall be bonded to the equipment grounding system under [[sync/grounding-and-bonding]].
+
+### Signal pair shields shall be continuous through junction boxes and grounded at the control panel end only, with the shield at the instrument insulated from the housing.
+
+### Signal pairs shall be installed in raceway under [[sync/raceways-and-conduit]], separated from power conductors in accordance with the manufacturer's instructions and [[sync/industrial-control-panels]].
+
# Delivery, Storage, and Handling {toc}
−## Instruments shall be delivered in the manufacturer's original protective packaging with process-connection thread protectors and electrical-entry plugs in place.
+## Instruments shall be delivered in the manufacturer's original packaging with tag numbers, calibration certificates, and installation instructions enclosed, and with process connections capped and conduit entries plugged.
−## Instruments shall be stored indoors in a clean, dry, vibration-free location within the manufacturer's storage temperature range until installation.
+## Transmitters, gauges, and switches shall be stored indoors in a clean, dry location within the storage temperature range published by the manufacturer until installation.
−## Calibrated transmitters shall be protected from impact and electrostatic discharge during storage and handling, and the calibration tag or certificate shall remain with each unit.
+## Sealed assemblies shall be shipped and stored with the seal and transmitter connected, the diaphragm covered by its protective plate, and the capillary coiled to not less than the manufacturer's published minimum radius.
−# Warranty {toc}
+## A seal diaphragm is a few thousandths of an inch thick and set flush to its flange, and a fingernail or a dropped tool dents it into a permanent zero shift; the protective plate stays on until the flange is bolted up. {note}
−## The manufacturer shall warrant each instrument against defects in materials and workmanship for a minimum of 24 months from startup or 30 months from shipment, whichever expires first.
+## Liquid-filled gauges shall be stored and shipped upright with the vent closed.
−## Diaphragm seals and fill-fluid assemblies shall carry the same warranty term as the instrument they serve.
+# Warranty {toc}
+## Pressure instruments and seal assemblies shall be warranted against defects in materials and workmanship for the period indicated in the datasheet, measured from the date of substantial completion.
+
```datasheet
−label: Warranty Term
−type: radio
−options:
− - 12 months from startup
− - 24 months from startup / 30 months from shipment
− - 36 months from startup
−default: 24 months from startup / 30 months from shipment
+label: Pressure Instrument Warranty Period
+type: range
+unit: years
+min: 1
+max: 5
+setpoints: [1, 2, 3, 5]
+default: 1
```
+## The warranty shall cover repair or replacement of the failed transmitter, gauge, switch, or seal assembly and the calibration, field verification, and zero trim of the replacement.
+
+## Where a device is repaired or replaced under warranty, the repaired or replaced device shall carry a new warranty of the same term from the date of the repair, or the remainder of the original term, whichever ends later.
+
# Spare Parts {toc}
−## The Contractor shall furnish recommended spare parts for the installed pressure instruments.
+## The Contractor shall deliver the spare parts indicated in the datasheet at substantial completion.
```datasheet
−label: Recommended Spares
+label: Spare Parts Delivered at Substantial Completion
type: checkbox
options:
− - Spare gauge isolation / needle valves
− - Spare snubbers
− - Transmitter LCD / display modules
− - Manifold seal kits
− - One spare transmitter per critical range
+ - "Transmitters of each model and sensor range installed"
+ - "Gauges of each range, grade, and connection installed"
+ - "Pressure switches of each model installed"
+ - "Seal assemblies of each type and material installed"
+ - "Transmitter display modules and terminal blocks of each model installed"
+ - "Snubbers and siphons of each type installed"
default:
− - Spare gauge isolation / needle valves
− - One spare transmitter per critical range
+ - "Transmitters of each model and sensor range installed"
+ - "Gauges of each range, grade, and connection installed"
```
−## A practical spares package covers the wear and consumable items: gauge isolation/needle valves, snubbers, transmitter LCD modules, manifold seal kits, and at least one complete spare of each critical transmitter range used in the project. Stocking a spare of each critical range avoids a long lead time when a safety or production loop loses its instrument. {note}
+## Spare parts of each selected class shall be furnished in the quantity indicated in the datasheet for every ten installed, with not fewer than one of each.
+
+```datasheet
+label: Spare Part Quantity per Ten Installed
+type: range
+unit: units
+min: 1
+max: 5
+setpoints: [1, 2, 3, 5]
+default: 1
+```
+
+## Spare parts shall match the installed devices in model, range, wetted material, output signal, and firmware, and shall be turned over against a written inventory signed by the Owner's representative.