+---
+title: Pressure Measurement
+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).
+---
+
+# Scope {toc}
+
+## This standard covers pressure measurement instruments installed to indicate, transmit, or switch on process pressure in construction and process-facility projects. {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}
+
+## The pressure-measurement instrument family appears in nearly every facility type, and this standard applies across all of them. {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}
+
+## Instruments shall be selected, supplied, calibrated, and installed in accordance with this standard and the project instrument index.
+
+## 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.
+
+## 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}
+
+## 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.
+
+| 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 |
+
+## 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
+
+```datasheet
+label: 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
+default:
+ - Product data sheet
+ - Completed instrument datasheet (ISA-20)
+ - Enclosure / area-classification certification
+ - Dimensional / mounting drawing
+```
+
+## 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
+
+```datasheet
+label: Closeout Submittals
+type: checkbox
+options:
+ - NIST-traceable calibration certificate
+ - Field loop-check / as-left calibration records
+ - Operation and maintenance manuals
+ - Reconciled instrument index
+default:
+ - NIST-traceable calibration certificate
+ - Field loop-check / as-left calibration records
+ - Operation and maintenance manuals
+ - Reconciled instrument index
+```
+
+## 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
+
+```datasheet
+label: Informational Submittals
+type: checkbox
+options:
+ - Installation and torque instructions
+ - IS control drawing
+ - Spare-parts list
+default:
+ - Installation and torque instructions
+ - Spare-parts list
+```
+
+# Quality Assurance {toc}
+
+## Pressure gauges shall conform to ASME B40.100 for accuracy grade, dial size, scale range, and overpressure rating.
+
+## 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}
+
+## Each instrument shall be calibrated against a reference standard traceable to NIST per ASME PTC 19.2 before it is placed in service.
+
+## Calibration of safety-instrumented-function instruments shall be performed to a tolerance of ± 0.1 % of span.
+
+## General process loops shall be calibrated to ± 0.5 % of span at commissioning.
+
+## Transmitters shall not be assumed to arrive pre-configured to the project range.
+
+## 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}
+
+## Transmitters shall be configured to the project calibrated range and engineering units before shipment or, where field configuration is specified, before loop check.
+
+## Instrument tag numbers shall match the project P&ID and instrument index exactly.
+
+## 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}
+
+## A safety requirements specification (SRS) shall exist and be referenced before any instrument is specified as SIL-rated.
+
+## 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}
+
+# Environmental and Service Conditions {toc}
+
+## The instrument enclosure rating shall suit the installed environment; "weatherproof" is not an enclosure classification.
+
+## 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}
+
+## Outdoor, wet, and wash-down locations shall use a NEMA 4X enclosure of 316 stainless steel or fiberglass, or an equivalent IP66/IP67 rating.
+
+```datasheet
+label: 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
+```
+
+## 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.
+
+## Instruments in Class I Division 2 locations shall be intrinsically safe or nonincendive.
+
+## 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}
+
+## Area classification selection for the installed instrument shall be coordinated with the area classification drawings.
+
+```datasheet
+label: Electrical Area Classification
+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)
+```
+
+## Transmitters shall be rated for the ambient temperature at the installed location.
+
+## 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}
+
+```datasheet
+label: Ambient Temperature Rating
+type: range
+unit: °F
+min: -67
+max: 221
+step: 1
+setpoints:
+ - -40
+ - 185
+```
+
+## 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.
+
+## All wetted parts of instruments in potable-water service shall be certified to NSF/ANSI 61.
+
+## 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}
+
+# Instrument Selection and Measurement Type {toc}
+
+## 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.
+
+## 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}
+
+```datasheet
+label: Instrument Type
+type: radio
+options:
+ - Local-indicating gauge
+ - Electronic transmitter
+ - Pressure switch
+ - Transmitter + local gauge (duplex)
+default: Electronic transmitter
+```
+
+## 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}
+
+## 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}
+
+## The measurement reference -- gauge, absolute, differential, or sealed-gauge -- shall be specified explicitly for every instrument.
+
+## 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}
+
+```datasheet
+label: Measurement Reference Type
+type: radio
+options:
+ - Gauge (relative to atmosphere)
+ - Absolute (relative to vacuum)
+ - Differential (across two ports)
+ - Sealed gauge / compound
+default: Gauge (relative to atmosphere)
+```
+
+# Range and Span {toc}
+
+## Instrument range shall be selected so that normal operating pressure falls between 25 % and 75 % of full scale.
+
+## 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}
+
+## Maximum operating pressure shall not exceed 75 % of full-scale range for steady service, or 50 % of range for pulsating service.
+
+## The instrument range, in engineering units, shall be selected for the service.
+
+```datasheet
+label: Calibrated Range
+type: range
+unit: psi
+min: 0
+max: 10000
+step: 1
+setpoints:
+ - 0
+ - 150
+```
+
+## Typical service ranges are well established and should be used as the starting point for range selection.
+
+## 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}
+
+## Overpressure capability shall meet or exceed the service.
+
+## 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}
+
+```datasheet
+label: Overpressure Rating
+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)
+```
+
+## Differential-pressure transmitters shall have a static line-pressure rating equal to or greater than the maximum line pressure the high side will see.
+
+## 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}
+
+# Accuracy Class {toc}
+
+## Gauge accuracy grade shall be specified per ASME B40.100.
+
+## 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}
+
+```datasheet
+label: Gauge Accuracy Grade
+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)
+```
+
+## Transmitter reference accuracy shall be specified as a percentage of calibrated span.
+
+## 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}
+
+```datasheet
+label: Transmitter Reference Accuracy
+type: select
+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
+```
+
+# Process Connection {toc}
+
+## The default process connection for gauges and most transmitters shall be 1/2 in NPT conforming to ASME B1.20.1.
+
+## 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}
+
+```datasheet
+label: Process Connection
+type: select
+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)
+```
+
+## 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.
+
+## 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
+type: radio
+options:
+ - Lower mount
+ - Lower-back mount
+ - Back mount (panel)
+default: Lower mount
+```
+
+# Wetted Materials {toc}
+
+## Wetted materials shall be selected for compatibility with the process chemistry; 316 stainless steel is the default but is not universally suitable.
+
+## 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}
+
+```datasheet
+label: Wetted Material
+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
+```
+
+## 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.
+
+# Diaphragm Seals {toc}
+
+## A flush-diaphragm remote or direct seal shall be specified for viscous, slurry, crystallizing, or sanitary service.
+
+## 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}
+
+```datasheet
+label: Diaphragm Seal
+type: radio
+options:
+ - None (direct connection)
+ - Flush-diaphragm seal (process)
+ - Flush-diaphragm seal, sanitary / 3-A
+ - Remote seal with capillary
+default: None (direct connection)
+```
+
+## The seal fill fluid shall be selected for the service temperature and any food or potable-water contact requirement.
+
+## 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}
+
+```datasheet
+label: Fill Fluid
+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)
+```
+
+# Local Gauges {toc}
+
+## Local-indicating gauges shall be Bourdon-tube dial gauges with a stainless-steel case unless the datasheet specifies a digital or differential type.
+
+## 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}
+
+```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
+```
+
+## 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.
+
+## 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}
+
+```datasheet
+label: Gauge Dial Size
+type: radio
+options:
+ - 2.5 in (manifold / tight space)
+ - 4 in (standard field)
+ - 6 in (panel / control room)
+default: 4 in (standard field)
+```
+
+## Gauges in vibrating service shall be liquid-filled with glycerin (or silicone for high-temperature ambients) to damp pointer flutter and protect the movement.
+
+```datasheet
+label: Gauge Case Fill
+type: radio
+options:
+ - Dry (non-vibrating service)
+ - Glycerin-filled (vibration)
+ - Silicone-filled (high temperature)
+default: Dry (non-vibrating service)
+```
+
+## 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.
+
+# Electronic Transmitters {toc}
+
+## Transmitters shall provide a 4-20 mA two-wire output with HART revision 7 unless a digital fieldbus is specified.
+
+## 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}
+
+```datasheet
+label: Signal Output
+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
+```
+
+## HART revision shall be specified as revision 7 minimum.
+
+## 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}
+
+## Loop-powered transmitters shall accept a supply of 10.5 to 42.4 VDC, with 24 VDC nominal supplied from the control panel.
+
+```datasheet
+label: Power Supply
+type: radio
+options:
+ - Loop-powered (two-wire, 24 VDC nominal)
+ - Four-wire line-powered
+default: Loop-powered (two-wire, 24 VDC nominal)
+```
+
+## 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.
+
+```datasheet
+label: Local Display
+type: radio
+options:
+ - None
+ - LCD indicator
+default: LCD indicator
+```
+
+## Differential-pressure transmitters shall be furnished with a coplanar or biplanar flange and an integral or close-coupled valve manifold.
+
+## 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}
+
+## Multivariable transmitters that report both pressure and process temperature shall be coordinated with [[sync/temperature-instrumentation]] for the temperature element specification and calibration.
+
+# Pressure Switches {toc}
+
+## Pressure switches shall be snap-action with an adjustable setpoint and a deadband suited to the control function.
+
+## 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}
+
+```datasheet
+label: Pressure Switch Configuration
+type: select
+options:
+ - SPDT snap-action, adjustable setpoint
+ - DPDT snap-action, adjustable setpoint
+ - SPDT, fixed deadband
+default: SPDT snap-action, adjustable setpoint
+```
+
+## The pressure-switch setpoint shall be specified in service engineering units.
+
+```datasheet
+label: Switch Setpoint
+type: range
+unit: psi
+min: 0
+max: 600
+step: 1
+setpoints:
+ - 60
+```
+
+# Overpressure and Pulsation Protection {toc}
+
+## A snubber shall be specified for gauges and transmitters in pulsating service from reciprocating pumps, compressors, or pulsating flow.
+
+## 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}
+
+```datasheet
+label: Snubber
+type: radio
+options:
+ - None (steady service)
+ - Sintered-metal snubber
+ - Adjustable piston snubber
+default: None (steady service)
+```
+
+## 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.
+
+## 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}
+
+```datasheet
+label: Isolation Valve / Manifold
+type: select
+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)
+```
+
+# Functional Safety {toc}
+
+## 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.
+
+## 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}
+
+```datasheet
+label: Safety Rating
+type: radio
+options:
+ - Standard (non-SIL)
+ - SIL 2 certified (IEC 61508)
+ - SIL 3 certified (IEC 61508)
+default: Standard (non-SIL)
+```
+
+## 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.
+
+# Testing {toc}
+
+## Each instrument shall pass a factory acceptance calibration to ASME PTC 19.2 against a dead-weight tester or equivalent reference before shipment.
+
+## 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.
+
+## 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.
+
+## As-left calibration data shall be recorded for every instrument at commissioning and retained in the closeout package.
+
+```datasheet
+label: Field Test Protocol
+type: checkbox
+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
+```
+
+## The recalibration interval shall be set by service criticality.
+
+## 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}
+
+```datasheet
+label: Recalibration Interval
+type: radio
+options:
+ - Annual (SIL / critical)
+ - 2 years
+ - 5 years (general process)
+default: 5 years (general process)
+```
+
+# Installation {toc}
+
+## 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.
+
+## 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.
+
+## 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}
+
+## 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.
+
+## 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.
+
+## 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.
+
+```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
+```
+
+# 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 stored indoors in a clean, dry, vibration-free location within the manufacturer's storage temperature range 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.
+
+# Warranty {toc}
+
+## 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.
+
+## Diaphragm seals and fill-fluid assemblies shall carry the same warranty term as the instrument they serve.
+
+```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
+```
+
+# Spare Parts {toc}
+
+## The Contractor shall furnish recommended spare parts for the installed pressure instruments.
+
+## 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}
+
+```datasheet
+label: Recommended Spares
+type: checkbox
+options:
+ - Spare gauge isolation / needle valves
+ - Spare snubbers
+ - Transmitter LCD / display modules
+ - Manifold seal kits
+ - One spare transmitter per critical range
+default:
+ - Spare gauge isolation / needle valves
+ - One spare transmitter per critical range
+```