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SynC · Historical revision

Temperature Instrumentation

Revision3
EditedOct 2, 2026
StatusSuperseded
Contents

View changes in this revision   Revision history

Historical revision. This is editorial revision 3, kept so citations to it stay resolvable. It is not the current text of this standard — see the current revision.

SynC Standards Team — Specifier (Platform Standards) ✓ OfficialDiscloses employment SynC (SynC Platform Team)
Remade for neutrality: every choice explained, project facts as parameters, scope boundaries linked both ways

1 Scope

NOTE This standard covers the temperature measurement point from the thermowell at the pipe or vessel to the signal-output terminals of the transmitter or, where no transmitter is furnished, to the terminals of the connection head: the sensing element, its insert and sheath, the thermowell, the connection head, the transmitter, the thermocouple extension wire, and the local dial thermometer. (1.1)
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, whether the pipe it sits in carries a process fluid, a plant utility, or chilled water; a point belongs to HVAC Controls InstrumentationHVAC Instrumentation and Control DevicesResolves to the current adopted revision.sync/hvac-controls-instrumentation when it is wired to a building automation field controller and its element and measurement error are selected under Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system. The same thermowell in the same pipe is specified under whichever standard owns the controller that reads it. (1.2)
NOTE The temperature element, its thermowell, and the temperature calibration of a multivariable transmitter are specified under this standard; the transmitter body, its pressure sensor, its process connection, and its pressure calibration are specified under Pressure InstrumentationPressure InstrumentationResolves to the current adopted revision.sync/pressure-instrumentation. (1.3)
NOTE The following are outside this standard and are governed elsewhere. (1.4)
  • Pressure, differential pressure, flow, and level instruments, governed by Pressure InstrumentationPressure InstrumentationResolves to the current adopted revision.sync/pressure-instrumentation, Flow MeasurementFlow MeasurementResolves to the current adopted revision.sync/flow-measurement, and Level SensorsLevel MeasurementResolves to the current adopted revision.sync/level-sensors
  • Loop architecture, instrument tag numbering, the instrument index, and loop diagrams, governed by Process InstrumentationProcess InstrumentationResolves to the current adopted revision.sync/process-instrumentation and Control Systems IntegrationControl Systems Integration and TestingResolves to the current adopted revision.sync/control-systems-integration
  • Temperature sensors furnished inside equipment and wired to the equipment's own controller, such as transformer winding sensors, chiller motor sensors, and the sensors shipped in packaged air handling units, governed by the standard for that equipment, for example Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers, ChillersChillersResolves to the current adopted revision.sync/chillers, and Air Handling UnitsAir Handling UnitsResolves to the current adopted revision.sync/air-handling-units
  • Heat-tracing control sensors and thermostats furnished with the heat-tracing controls, governed by Electric Heat TracingElectric Heat TracingResolves to the current adopted revision.sync/electric-heat-tracing
  • Ground temperature arrays and thermal conductivity testing, governed by Geotechnical Instrumentation And MonitoringGeotechnical Instrumentation and MonitoringResolves to the current adopted revision.sync/geotechnical-instrumentation-and-monitoring
  • Controllers and input cards, field networks and fieldbus segment design, and operator interfaces, governed by Programmable Logic ControllersProgrammable Logic ControllersResolves to the current adopted revision.sync/programmable-logic-controllers, Process Control NetworksProcess Control NetworksResolves to the current adopted revision.sync/process-control-networks, and SCADA And HMI SystemsSCADA and HMI SystemsResolves to the current adopted revision.sync/scada-and-hmi-systems
  • Control panels and the marshalling of field signals, governed by Industrial Control PanelsIndustrial Control PanelsResolves to the current adopted revision.sync/industrial-control-panels
  • Raceway for instrument wiring, governed by Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit
  • Laboratory thermometry and the calibration laboratory itself; this standard references the laboratory only as the source of the traceable certificate
1.5 Each point's tag, service, process fluid, calibrated range, process design pressure and temperature, maximum fluid velocity including startup and upset conditions, line size, and insertion length shall be as indicated on the instrument index and instrument data sheets.
1.6 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.

2 Referenced Standards

2.1 Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 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
IEC 60751 Industrial Platinum Resistance Thermometers and Platinum Temperature Sensors
ASTM E1137/E1137M Standard Specification for Industrial Platinum Resistance Thermometers
ASTM E230/E230M Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
ASTM E585/E585M Standard Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
ASTM E608/E608M Standard Specification for Mineral-Insulated, Metal-Sheathed Base Metal Thermocouples
ASTM E220 Standard Test Method for Calibration of Thermocouples by Comparison Techniques
ASTM E644 Standard Test Methods for Testing Industrial Resistance Thermometers
ASME PTC 19.3 TW Thermowells
ASME B40.200 Thermometers, Direct Reading and Remote Reading
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-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 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
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 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

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for the Engineer's review and return before any temperature instrument or thermowell is procured:
  • Product data for each element, insert, connection head, transmitter, and dial thermometer model, giving the sensing element, tolerance class or limits of error, the transmitter reference accuracy and ambient rating, 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 dimensional drawing for each thermowell giving the process connection, stem profile, root and tip diameters, bore, insertion length, lagging extension, and material
  • A wake-frequency calculation under ASME PTC 19.3 TW for each thermowell in flowing service, at the maximum velocity stated on the instrument data sheet
  • Material certificates and mill test reports for thermowell stock
  • 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 sensor type and connection, the failure output direction, the damping, and the sensor matching coefficients where sensor matching is furnished
Required Action Submittalscheckbox
☑ Product data for each instrument model
☑ Instrument data sheet for every tagged point
☑ Thermowell dimensional drawings
☑ Thermowell wake-frequency calculations
☑ Thermowell material certificates and mill test reports
☐ Hazardous-location certificates and intrinsically safe control drawings
☑ Transmitter configuration sheets
3.1.2 The thermowell drawings and the wake-frequency calculations shall be submitted together, and a thermowell shall not be fabricated until its calculation has been reviewed and returned without exception.

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following for information before installation begins:
  • Factory calibration certificates for the elements and transmitters 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 element and transmitter serving a safety instrumented function
  • Positive material identification reports for alloy thermowells where required under Testing
Required Informational Submittalscheckbox
☑ Factory calibration certificates
☑ Manufacturer's installation instructions
☐ Safety integrity level capability certificates and proof-test procedures
☐ Positive material identification reports

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following before the temperature instruments are accepted:
  • As-left calibration and configuration record for every element and transmitter, including the field verification results
  • Thermowell test records
  • Operation and maintenance data giving the recalibration interval, the proof-test interval where applicable, and the part number of every replaceable insert, transmitter, and gasket
  • Warranty documentation
Required Closeout Submittalscheckbox
☑ As-left calibration and configuration records
☑ Thermowell test records
☑ Operation and maintenance data with recalibration intervals
☑ Warranty documentation
3.3.2 Loop check records and as-built loop diagrams shall be submitted as required under Control Systems IntegrationControl Systems Integration and TestingResolves to the current adopted revision.sync/control-systems-integration and shall not be duplicated in this closeout package.

4 Quality Assurance

4.1 Conformance and Certification

4.1.1 Platinum RTD elements shall conform to IEC 60751 or ASTM E1137/E1137M for resistance-versus-temperature relationship and tolerance.
4.1.2 Thermocouple elements and extension wire shall conform to ASTM E230/E230M for electromotive force tables, limits of error, and color code, and mineral-insulated thermocouples to ASTM E608/E608M.
4.1.3 Thermowells shall be designed and evaluated under ASME PTC 19.3 TW.
4.1.4 Dial thermometers shall conform to ASME B40.200.
4.1.5 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.
4.1.6 Each element and transmitter 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.

4.2 Source Limitation

4.2.1 The manufacturer source limitation applying to temperature instruments shall be as indicated in the datasheet.
Temperature Instrument Source Limitationradio
● Single manufacturer for all transmitters and a single manufacturer for all elements and thermowells
○ Single manufacturer for all temperature instruments
○ No source limitation
NOTE Transmitters from one manufacturer share a configuration tool, a spare, and a device description file in the control system, and elements and thermowells from one manufacturer share an insert length convention and a spare insert. Requiring one manufacturer for both narrows the bid list to the suppliers who make both, which few do, and buys nothing a two-source limit does not. (4.2.2)

4.3 Data Sheets and Identification

4.3.1 Each instrument shall be identified by the tag number assigned under Process InstrumentationProcess InstrumentationResolves to the current adopted revision.sync/process-instrumentation in accordance with ANSI/ISA-5.1.
4.3.2 Each element, transmitter, thermowell, and dial thermometer shall carry a stainless steel tag plate stamped or engraved with its tag number and attached with stainless steel wire or screws.
NOTE A thermowell installed before its element arrives is identified only by its tag plate, and a plate that reads the same as the one on the element is what lets the element reach the right well on a pipe rack of identical connections. (4.3.3)

5 Environmental and Service Conditions

5.1 Ambient Conditions

5.1.1 Instruments mounted outdoors shall operate within their published accuracy between Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum and Site Ambient Temperature MaximumSite Ambient Temperature MaximumParameterEach project supplies its own value.site-ambient-temperature-maximum, including solar gain on an unshaded housing.
5.1.2 A head-mounted transmitter shall be rated for the temperature reached inside the connection head at the maximum process temperature, with the head conducting heat from the thermowell through the extension.
5.1.3 Where the temperature inside the connection head at the maximum process temperature would exceed the transmitter's rated ambient, the transmitter shall be field-mounted away from the head regardless of the mounting selected under Transmitters.
NOTE Heat travels up the thermowell and the extension into the head at a rate set by the extension length and the ambient air around it, and a transmitter that drifts on hot afternoons and reads correctly at night is one that sits in a head hotter than its rating. (5.1.4)

5.2 Enclosure Rating

5.2.1 Connection heads, transmitter housings, 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.
Minimum Enclosure Ratingselect
NEMA Type 1
NEMA Type 12
NEMA Type 13
NEMA Type 3R
NEMA Type 4
NEMA Type 4X
NEMA Type 7
NOTE 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. (5.2.2)
5.2.3 Enclosures mounted outdoors shall be rated NEMA Type 3R, Type 4, or Type 4X.
5.2.4 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.
5.2.5 Enclosures mounted in locations subject to washdown or hose-directed water shall be rated NEMA Type 4 or Type 4X.
5.2.6 Enclosures mounted in locations exposed to corrosive fumes, salt air, or washdown chemicals shall be rated NEMA Type 4X.
5.2.7 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.

5.3 Hazardous Locations

5.3.1 The hazardous-location classification at each instrument shall be as indicated on the electrical area classification drawings.
5.3.2 Instruments in a classified location shall be protected by the method indicated in the datasheet.
Hazardous Location Protection Methodradio
○ 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
NOTE An intrinsically safe loop keeps the field device and its wiring below ignition energy, so the head 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. (5.3.3)
5.3.4 Conduit entries into enclosures in Class I locations shall be sealed in accordance with NFPA 70 Article 501 and the listing of the enclosure.
5.3.5 Where a single process seal separates the process fluid from the electrical system, the instrument shall be certified under ANSI/ISA-12.27.01 for that condition.
5.3.6 The temperature code of each instrument in a classified location shall be lower than the autoignition temperature of the flammable material present, with the connection head temperature at the maximum process temperature included in the determination.
5.3.7 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.

5.4 Safety Instrumented Functions

5.4.1 Elements and transmitters 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.
5.4.2 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.
NOTE 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. (5.4.3)

6 Sensing Elements

6.1 Element Technology

6.1.1 The sensing element at each point shall be the technology designated in the instrument index or, where the index does not designate one, the technology indicated in the datasheet.
Element Technology for Points Not Otherwise Designatedradio
● Platinum RTD
○ Thermocouple
○ Thermistor
NOTE A platinum RTD holds its calibration for years and resolves tenths of a degree, within a range that ends near 600°C and with a response slowed by its mass; a thermocouple reaches furnace and exhaust temperatures, responds faster in a thin sheath, and drifts with exposure, so it needs a periodic check against a reference; a thermistor resolves hundredths of a degree over a narrow range below about 150°C with no lead-resistance error and a nonlinear curve the transmitter or input card has to hold. The index designates another technology where the process temperature or response time at a point rules the default out. (6.1.2)
6.1.3 An element shall not be applied outside the temperature range the manufacturer publishes for its tolerance class or limits of error.

6.2 Platinum RTD Elements

6.2.1 Platinum RTD elements shall have the nominal resistance at 0°C indicated in the datasheet.
RTD Nominal Resistance at 0°Cradio
● Pt100
○ Pt1000
NOTE A Pt1000 element produces ten times the resistance change of a Pt100 for the same temperature change, so the same lead resistance is a tenth of the error, which matters on a two-wire connection; nearly every process transmitter and input card accepts Pt100 and a smaller number accept Pt1000. (6.2.2)
6.2.3 RTD elements shall be furnished with the lead configuration indicated in the datasheet.
RTD Lead Configurationradio
○ Two-wire
● Three-wire
○ Four-wire
NOTE Two leads add their own resistance to the element's and read it as temperature; three leads let the transmitter subtract the resistance of one lead on the assumption that the other matches it; four leads let the transmitter measure the element with no lead error at all, at the cost of a fourth conductor and an input that supports it. The length of the lead between the element and the transmitter is what decides how much the configuration is worth. (6.2.4)
6.2.5 Where two-wire leads are selected, the leads shall terminate at a head-mounted transmitter in the same connection head as the element.
6.2.6 RTD elements shall meet the tolerance class indicated in the datasheet over the calibrated range of the point.
RTD Tolerance Classradio
○ Class AA
● Class A
○ Class B
○ Class C
NOTE Each IEC 60751 class halves the allowed error of the one below it, and each tighter class is available over a narrower temperature range, so a Class AA element is offered to roughly 250°C and a Class A element to roughly 500°C, with Class B covering the full range of the technology. A tighter class costs more per element and buys nothing where the transmitter and the control system are not held to a matching error. (6.2.7)
6.2.8 Elements procured to ASTM E1137/E1137M shall meet a grade whose tolerance is equal to or tighter than the selected class over the calibrated range of the point.
6.2.9 RTD sensing elements shall be of the construction indicated in the datasheet.
RTD Sensing Element Constructionradio
○ Thin-film
○ Wire-wound
NOTE A thin-film element is a platinum layer on a ceramic substrate, small enough to respond quickly and robust against vibration, with a usable range that ends near 500°C; a wire-wound element is a platinum coil that reaches 600°C and holds the tightest tolerance over a wide range, and whose coil can shift under sustained vibration. (6.2.10)

6.3 Thermocouple Elements

6.3.1 Thermocouples shall be of the type designated in the instrument index or, where the index does not designate one, the type indicated in the datasheet.
Thermocouple Type for Points Not Otherwise Designatedselect
Type J
Type K
Type E
Type T
Type N
Type R
Type S
Type B
NOTE Type K covers the widest range of the base-metal types in oxidizing and inert atmospheres and drifts at a known rate above 800°C; Type N holds its calibration better than Type K at the same temperatures and costs more; Type J suits reducing atmospheres and rusts in moist ones; Type T is the most accurate base-metal type below 350°C and the one used at cryogenic temperatures; Type E produces the largest signal per degree. Types R, S, and B are platinum alloys for furnace service above the base-metal range, with Type B usable to the highest temperatures and insensitive below about 50°C. (6.3.2)
6.3.3 Thermocouples shall meet the limits of error indicated in the datasheet under ASTM E230/E230M.
Thermocouple Limits of Errorradio
● Standard limits of error
○ Special limits of error
NOTE Special limits of error are met by selecting wire from tighter lots, which roughly halves the allowed error at a modest premium on the element and leaves the drift rate of the type unchanged. (6.3.4)
6.3.5 Thermocouple measuring junctions shall be of the type indicated in the datasheet.
Thermocouple Junction Typeradio
● Ungrounded
○ Grounded
○ Exposed
NOTE An ungrounded junction is isolated from the sheath, so a transmitter wired to it sees no ground loop through the thermowell and the control system; a grounded junction is welded to the sheath and responds faster at the cost of that isolation, so it suits an isolated transmitter input and a loop with no other ground; an exposed junction responds fastest and has no protection from the medium, so it suits dry gas and short-term measurement. (6.3.6)
6.3.7 Noble-metal thermocouples shall be furnished with high-purity alumina insulators and a protection tube rated for the process atmosphere and temperature.

6.4 Thermistor Elements

6.4.1 Requirements in this article apply where a thermistor is selected under Element Technology or designated in the instrument index.
6.4.2 Thermistor elements shall be negative-temperature-coefficient devices furnished with the manufacturer's published resistance-temperature curve, and the transmitter or input card reading them shall hold that curve.
6.4.3 Thermistor elements shall be interchangeable to within ±0.2°C over the calibrated range of the point without individual calibration of the transmitter to the element.
6.4.4 Thermistors shall not be applied at points where the process temperature can exceed the manufacturer's published upper limit for the element under any operating or upset condition stated on the instrument data sheet.

6.5 Insert and Sheath Construction

6.5.1 Elements shall be furnished as inserts of the construction indicated in the datasheet.
Element Insert Constructionradio
● Mineral-insulated metal-sheathed insert
○ Sheathed insert with ceramic-insulated conductors
○ Ceramic protection tube with insulated conductors
NOTE A mineral-insulated insert packs the conductors in compacted magnesium oxide inside a drawn metal sheath, so it bends, resists vibration, and keeps moisture out of the insulation; a sheathed insert with ceramic insulators is rigid and serves where the element must be rebuilt in the field or the mineral insulation would be exceeded by the temperature; a ceramic protection tube is the construction for noble-metal thermocouples in furnace gas, where a metal sheath would contaminate the wire. (6.5.2)
6.5.3 Sheaths shall be of the material indicated in the datasheet.
Element Sheath Materialselect
Type 304 stainless steel
Type 316 stainless steel
Type 310 stainless steel
UNS N06600 nickel-chromium-iron alloy
UNS N06625 nickel-chromium-molybdenum alloy
NOTE Inside a thermowell the sheath sees the air in the bore and not the process, so a stainless sheath serves to about 870°C and the choice above that is driven by temperature: Type 310 and UNS N06600 hold up in oxidizing gas to about 1150°C, and UNS N06625 adds resistance to chlorides and sulfur compounds where the sheath is directly immersed. (6.5.4)
6.5.5 Inserts shall have the sheath outside diameter indicated in the datasheet.
Insert Sheath Outside Diameterrange
in.
0.1250.1880.250.375
NOTE A thinner sheath responds faster and bends more easily; a thicker sheath holds a larger wire-wound element and survives rougher handling. The thermowell bore follows the sheath diameter, so a project that holds one diameter can carry one spare insert for every well. (6.5.6)
6.5.7 Each insert shall be spring-loaded so that the tip is held against the bottom of the thermowell bore, and shall be replaceable from the connection head without removing the thermowell from the process.
6.5.8 Each point shall be furnished with the number of sensing elements indicated in the datasheet.
Sensing Elements per Pointradio
● Single element
○ Dual element
NOTE A dual-element insert carries two independent elements in one sheath, so a control loop and a monitoring loop can share one thermowell, a transmitter can switch to the second element when the first fails, and the two readings can be compared for drift; both elements share the sheath, so a sheath failure takes both. (6.5.9)

7 Thermowells

7.1 Thermowell Provision

7.1.1 Every element in a pipe or a closed vessel shall be installed in a thermowell unless the instrument index designates the point for direct immersion.
7.1.2 Direct immersion shall be limited to open tanks, channels, ducts, and ambient air, and to closed systems that operate at atmospheric pressure with a fluid that is neither flammable, toxic, nor hot enough to injure on contact.
NOTE The thermowell separates the element from the process, so the element is replaced without draining, depressurizing, or opening the line, and a sheath failure does not become a leak. (7.1.3)
7.1.4 The thermowell connection on the pipe or vessel, whether a threaded coupling, a weld boss, a nozzle, or a flanged branch, shall be furnished and installed under the piping or vessel specification at the locations indicated on the piping drawings.
7.1.5 Thermowells shall be delivered to the piping installer before the section of pipe or the vessel they serve is closed and pressure tested.

7.2 Thermowell Construction

7.2.1 Thermowells shall be of the construction indicated in the datasheet.
Thermowell Constructionradio
● Machined from solid bar stock
○ Fabricated from tube and bar
NOTE A thermowell machined from bar has no weld in the pressure boundary and is the construction ASME PTC 19.3 TW evaluates; a fabricated well is a tube welded to a connection and a tip, which is cheaper in long lengths and large diameters and carries welds that have to be examined and a geometry the performance test code does not cover. (7.2.2)
7.2.3 Thermowell stems shall have the profile indicated in the datasheet.
Thermowell Stem Profileradio
● Tapered
○ Stepped
○ Straight
NOTE A tapered stem has the highest natural frequency for a given length and the largest root, so it passes the wake-frequency calculation at higher velocities and longer insertions than the other profiles; a stepped stem keeps a thin tip for fast response on a stiff root and is the usual answer where a tapered stem is too slow; a straight stem is the cheapest to machine and the first to fail the calculation at any velocity. (7.2.4)
7.2.5 Thermowells shall have the process connection indicated in the datasheet.
Thermowell Process Connectionselect
Threaded NPT
Flanged
Socket weld
Weld-in
Lap-joint Van Stone
Sanitary clamp
NOTE A threaded well installs in a coupling and is removed with a wrench, and its thread is the one path through which a leak can develop; a flanged well matches the piping class, removes without disturbing the pipe, and is the connection a wake-frequency calculation favors for its stiff root; a socket-weld or weld-in well is a permanent part of the pressure boundary with no joint to leak and no way out except cutting; a lap-joint well is a flanged well whose flange rotates for bolt alignment; a sanitary clamp well suits hygienic piping with no thread or crevice at the product. The piping class at each point decides which of these the piping specification provides. (7.2.6)
7.2.7 The connection size, thread form, flange class, and facing of each thermowell shall match the connection furnished under the piping or vessel specification at that point, with flanges to ASME B16.5 and threads to ASME B1.20.1.
7.2.8 The thermowell bore shall be sized to the selected insert sheath diameter with the diametral clearance the thermowell manufacturer publishes for a spring-loaded insert.
7.2.9 Thermowells in insulated lines shall have a lagging extension of a length not less than the insulation thickness specified under Mechanical InsulationMechanical InsulationResolves to the current adopted revision.sync/mechanical-insulation at that line.

7.3 Thermowell Material

7.3.1 Thermowells shall be of the material indicated in the datasheet.
Thermowell Materialselect
Type 316/316L stainless steel
Type 304/304L stainless steel
Carbon steel
Duplex stainless steel UNS S31803
UNS N04400 nickel-copper alloy
UNS N06600 nickel-chromium-iron alloy
UNS N06625 nickel-chromium-molybdenum alloy
UNS N10276 nickel-molybdenum-chromium alloy
Titanium Grade 2
Brass
NOTE Type 316/316L serves water, steam, and most process fluids and is the material every supplier stocks; Type 304/304L is cheaper and gives up chloride resistance; carbon steel matches carbon steel piping in non-corrosive utility service and rusts in the bore; duplex stainless resists chloride pitting and stress cracking in brine and seawater; nickel-copper alloy serves seawater and hydrofluoric acid; the nickel-chromium alloys serve high-temperature and high-chloride service and the nickel-molybdenum-chromium alloy serves oxidizing and reducing acids; titanium serves seawater and chlorine solutions; brass serves low-pressure water at low cost. Which one a project holds as its default depends on the fluid in most of its lines, so the field carries no default. (7.3.2)
7.3.3 Thermowell material shall be not less resistant to the process fluid than the piping material at the connection, and shall be the piping material where the piping specification requires alloy or lined pipe at that point.
7.3.4 Thermowell stock shall be furnished with a mill test report traceable to the heat.

7.4 Wake Frequency and Immersion

7.4.1 Each thermowell in flowing service shall be evaluated under ASME PTC 19.3 TW for the stem profile, insertion length, bore, material, and process connection furnished, at the maximum fluid velocity, density, and temperature stated on the instrument data sheet, including startup and upset conditions.
7.4.2 A thermowell that does not pass the evaluation shall be redesigned by shortening the insertion, changing the profile, adding a velocity collar or support, or changing the process connection, and resubmitted at no additional cost to the Owner.
NOTE Vortices shed from a stem in flowing fluid push it at a frequency that rises with velocity, and when that frequency approaches the stem's natural frequency the stem resonates and fatigues at the root until the tip breaks off into the line; the calculation finds the margin between the two frequencies and the stress at the root, and both have to clear before the well is cut. (7.4.3)
7.4.4 Where a thermowell falls outside the geometry the performance test code covers, the Contractor shall submit an alternative analysis, prepared by the thermowell manufacturer and accepted by the Engineer, before the thermowell is fabricated.
7.4.5 The insertion length of each thermowell shall be the length stated on the instrument data sheet.
7.4.6 The thermowell tip shall lie within the central one-third of the pipe inside diameter or, where the wake-frequency evaluation does not permit that length, not less than 2.5 in. beyond the inside wall of the pipe.
7.4.7 Where the pipe is too small for the required immersion, the thermowell shall be installed in an elbow with the tip pointing upstream, in a tee, or in an enlarged section of pipe furnished under the piping specification.
NOTE A tip that stops short of the flowing core reads the wall, and the wall is cooled by the ambient and the insulation around it, so the error grows with the difference between process and ambient and is largest on the hot and cold lines where the measurement matters most. (7.4.8)

8 Connection Heads

8.1 Connection Head Construction

8.1.1 Connection heads shall be of the material indicated in the datasheet.
Connection Head Materialradio
● Coated die-cast aluminum
○ Stainless steel
○ Glass-fiber-reinforced polymer
NOTE A coated aluminum head is light, inexpensive, and offered in every configuration, and its coating is what stands between it and a salt or chemical atmosphere; a stainless head resists that atmosphere without a coating at several times the price and weight; a polymer head is immune to corrosion and to galvanic contact with the thermowell, is not offered in explosion-proof form, and loses strength at the temperatures a hot process can conduct into the head. (8.1.2)
8.1.3 Connection heads shall have the conduit entry indicated in the datasheet.
Connection Head Conduit Entryradio
● 1/2 in. NPT
○ 3/4 in. NPT
○ M20 x 1.5
NOTE A 1/2 in. entry fits the conduit size that serves a single loop and is the entry every head 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. (8.1.4)
8.1.5 Connection heads shall have a threaded screw cover with a captive chain or a hinged cover, with a gasket that holds the enclosure rating required under Environmental and Service Conditions.
8.1.6 Connection heads for head-mounted transmitters with a local display shall have a cover with a window.
8.1.7 Terminal blocks in connection heads shall be ceramic or glass-filled thermoplastic rated for the head temperature at the maximum process temperature, with the terminals of a thermocouple head made of the thermocouple alloy or the matching extension alloy.
8.1.8 Each connection head shall be mounted to its thermowell through an extension of nipple, union, and nipple of the length needed to clear the pipe insulation and to hold the temperature inside the head within the rating of the transmitter and terminal block.

9 Transmitters

9.1 Transmitter Provision

9.1.1 Temperature transmitters shall be furnished as indicated in the datasheet.
Transmitter Provisionradio
● Transmitter at every point
○ Transmitter where designated in the instrument index, element wired to the controller input elsewhere
○ Element wired to the controller input at every point, no transmitters
NOTE A transmitter converts the element's resistance or millivolt signal to a standard signal at the point of measurement, so lead resistance, noise pickup, and thermocouple extension wire end at the head and the control system needs one kind of input card; wiring the element directly removes a powered device from every point and puts the conversion in the input card, which then needs the lead compensation, the cold-junction reference, and the linearization for each element type it reads, and holds every lead run to the error its length produces. (9.1.2)

9.2 Transmitter Mounting

9.2.1 Transmitters shall be mounted as indicated in the datasheet.
Transmitter Mountingradio
● Head-mounted in the connection head
○ Field-mounted in a housing on a pipe stand or wall near the element
○ DIN-rail-mounted in a junction box or control panel
NOTE A head-mounted transmitter has the shortest element leads and no separate housing, and lives in the temperature the head reaches; a field-mounted transmitter sits in its own housing with a display at eye level, away from the heat and vibration of the line, at the cost of a stand and a short element lead run; a DIN-rail transmitter collects many points into one panel and runs raw element signals back to it, which saves field housings and puts the conversion where the leads are longest. (9.2.2)
9.2.3 Where the element is not accessible from grade or a platform for configuration and maintenance, the transmitter shall be field-mounted at an accessible location regardless of the mounting selected above.

9.3 Output Signal

9.3.1 Transmitters shall deliver the output signal indicated in the datasheet.
Transmitter Output Signalselect
4-20 mA with HART
4-20 mA without digital communication
FOUNDATION Fieldbus H1
PROFIBUS PA
WirelessHART
Modbus RTU over RS-485
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. (9.3.2)
9.3.3 Transmitters with a 4-20 mA output shall be two-wire loop-powered devices.
9.3.4 Transmitters shall drive their output to the failure level under NAMUR NE 43 on a sensor open circuit, a sensor short circuit, or an internal fault, in the direction stated on the instrument data sheet for each point.
9.3.5 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.
9.3.6 Fieldbus and wireless transmitters shall join segments and networks designed under Process Control NetworksProcess Control NetworksResolves to the current adopted revision.sync/process-control-networks.
9.3.7 Temperature elements on fuel storage tanks furnished under Fuel Dispensing And Storage TanksFuel Storage TanksResolves to the current adopted revision.sync/fuel-dispensing-and-storage-tanks shall deliver the output signal selected above and shall meet the hazardous-location requirements of this standard.

9.4 Transmitter Performance

9.4.1 Transmitters shall have a published reference accuracy for a Pt100 input not exceeding the value indicated in the datasheet.
Maximum Transmitter Reference Accuracy, Pt100 Inputrange
°C
0.050.10.150.20.30.5
NOTE The transmitter's error adds to the element's, so a transmitter tighter than the element's tolerance class buys little, and one looser than it wastes the class; the budget for the loop is set by what the control system does with the value, which is why the field carries no default. (9.4.2)
9.4.3 Transmitters shall provide galvanic isolation between the sensor input and the output.
9.4.4 Transmitters shall accept the element types and lead configurations selected under Sensing Elements and shall be configurable for range, sensor type, damping, and failure direction without a reference source connected.
9.4.5 Transmitters shall be matched to their RTD elements as indicated in the datasheet.
Transmitter-to-Element Sensor Matchingradio
○ Sensor matching for every RTD transmitter and element pair
○ Sensor matching for the points designated in the instrument index
○ No sensor matching
NOTE Sensor matching loads the element's individually measured resistance-temperature coefficients into the transmitter, so the pair reads to the element's calibration rather than to the class tolerance; it needs an individually calibrated element, a transmitter that accepts the coefficients, and a re-entry of the coefficients whenever either is replaced, which is a maintenance step a plant either builds into its procedures or does not. (9.4.6)
9.4.7 Transmitters shall be furnished with a local display as indicated in the datasheet.
Transmitter Local Displayradio
○ Display on every transmitter
○ Display on field-mounted transmitters, none on head-mounted transmitters
○ No local display
NOTE A display shows the reading and the diagnostic state at the instrument, which lets a technician check a loop without a handheld communicator; on a head-mounted transmitter it needs a windowed cover and is read at the head's elevation, which on a pipe rack is from a ladder. (9.4.8)

10 Thermocouple Extension Wire and Element Leads

10.1 Thermocouple Extension Wire

10.1.1 Thermocouple signals between the measuring junction and the cold-junction reference shall be carried on extension or compensating wire of the grade matched to the thermocouple type under ASTM E230/E230M, color-coded to that standard.
10.1.2 Extension wire shall run unbroken from the connection head to the transmitter or input card that provides the cold-junction reference, with every intermediate terminal made of the matching alloy.
NOTE A copper splice in a thermocouple circuit forms a second pair of junctions whose voltage follows the temperature of the splice, and the measurement then wanders with the weather in the junction box. (10.1.3)
10.1.4 Where a head-mounted transmitter is furnished at a thermocouple point, the cold-junction reference shall be in the transmitter and no extension wire shall be run beyond the connection head.
10.1.5 Thermocouple extension wire shall be twisted and shielded, with the shield grounded at the control panel end only.

10.2 Element Leads

10.2.1 RTD and thermistor leads between the element and a transmitter or input card outside the connection head shall be copper, twisted, shielded, and furnished with the conductor count of the lead configuration selected under Sensing Elements.
10.2.2 Element leads and transmitter signal pairs shall be installed in raceway under Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit, separated from power conductors in accordance with the manufacturer's instructions and Industrial Control PanelsIndustrial Control PanelsResolves to the current adopted revision.sync/industrial-control-panels.
10.2.3 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.

11 Local Dial Thermometers

11.1 Dial Thermometer Construction

11.1.1 Local dial thermometers at the points designated in the instrument index shall be of the type indicated in the datasheet.
Dial Thermometer Typeradio
● Bimetal dial thermometer
○ Gas-actuated dial thermometer
○ Loop-powered digital indicator
NOTE A bimetal thermometer has no fill and no electronics, reads at the well, and is the lowest-cost local indication; a gas-actuated thermometer reads through a capillary at a distance from the well and holds its accuracy at low temperatures where a bimetal coil loses sensitivity; a loop-powered indicator reads the transmitter output, so it shows the same value the control system sees and nothing when the loop is down. (11.1.2)
11.1.3 Dial thermometers shall have the dial size indicated in the datasheet.
Dial Thermometer Dial Sizerange
in.
35
11.1.4 Dial thermometers shall meet ASME B40.200 Grade A accuracy.
11.1.5 Bimetal thermometers shall have an every-angle adjustable stem and a hermetically sealed case.
11.1.6 Dial thermometers shall be ranged so that the normal operating temperature of the point falls within the middle half of the scale.
11.1.7 Dial thermometers in pipes and closed vessels shall be installed in thermowells meeting the requirements of this standard.
11.1.8 Gas-actuated thermometers shall have a capillary of the length stated on the instrument data sheet, armored over its full length.

12 Calibration

12.1 Factory Calibration

12.1.1 Individual calibration certificates traceable to a national metrology institute shall be furnished for the scope indicated in the datasheet.
Individual Calibration Certificate Scoperadio
○ Every element and every transmitter
○ Every transmitter, with a lot conformance certificate for elements
○ Elements and transmitters at the points designated in the instrument index, with lot conformance certificates elsewhere
NOTE An individual certificate records the element's measured error at stated temperatures and is what sensor matching and a tight loop budget are built on; a lot certificate states that the lot met its class, which is all a Class B element wired to a general-purpose input needs. The cost is a bench test per device, so the scope follows how many points carry an error budget the class tolerance alone does not satisfy. (12.1.2)
12.1.3 Elements of Class AA tolerance and every element and transmitter serving a safety instrumented function shall carry an individual calibration certificate regardless of the scope selected above.
12.1.4 Individual element certificates shall report the measured error at not fewer than three temperatures spanning the calibrated range of the point, with RTD elements tested under ASTM E644 and thermocouples under ASTM E220.
12.1.5 Transmitter certificates shall report the as-shipped error at 0%, 50%, and 100% of the calibrated range with a precision resistance or voltage source at the input.

12.2 Field Verification

12.2.1 Before installation, each element and transmitter pair shall be verified together at one temperature within the calibrated range using a dry-block calibrator or an ice bath, and the reading recorded on the as-left calibration record.
12.2.2 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.
12.2.3 Each transmitter's as-left configuration, including the range, sensor type, lead configuration, damping, failure direction, and matching coefficients, shall be recorded on the as-left calibration record.
12.2.4 Each thermocouple loop shall be verified for correct cold-junction compensation by comparing the reading at the control system with a reference at the measuring junction.
12.2.5 The insulation resistance between the element circuit and the sheath of each RTD insert shall be verified at not less than 100 MΩ at 100 V DC before installation.
12.2.6 Loop checks from the instrument to the controller shall be performed and recorded under Control Systems IntegrationControl Systems Integration and TestingResolves to the current adopted revision.sync/control-systems-integration in accordance with ANSI/ISA-62382.
12.2.7 The recalibration interval stated in the operation and maintenance data shall be not longer than the interval indicated in the datasheet.
Maximum Recalibration Intervalrange
months
6122436
NOTE A thermocouple drifts with exposure and an RTD drifts with thermal cycling and vibration, so the interval is a judgment about the service rather than the device; a point feeding a safety instrumented function follows its proof-test interval where that is shorter. (12.2.8)

13 Testing

13.1 Thermowell Testing

13.1.1 Each thermowell shall be tested and examined by the manufacturer as indicated in the datasheet before shipment.
Thermowell Testing and Examinationcheckbox
☑ Hydrostatic test of the bore and stem
☐ Liquid penetrant examination of welds
☐ Positive material identification of alloy stock
☑ Dimensional inspection against the reviewed drawing
13.1.2 Where a hydrostatic test is selected, the thermowell shall be tested externally at not less than 1.5 times the design pressure of the piping class at the connection with no leakage into the bore.
13.1.3 Positive material identification shall be performed on every thermowell of a material other than carbon steel or Type 304 or Type 316 stainless steel, regardless of the selection above.
13.1.4 Welds in fabricated thermowells shall be examined by liquid penetrant regardless of the selection above.
13.1.5 Thermowell test and examination records shall identify the thermowell by tag number and shall be included in the closeout submittal.

13.2 Repeat Testing

13.2.1 The cost of repeating a factory calibration, a field verification, or a thermowell test after a failure shall be borne by the Contractor.

14 Installation

14.1 Thermowell and Element Installation

14.1.1 Thermowells shall be installed perpendicular to the pipe axis, or in an elbow with the tip pointing upstream.
14.1.2 Thermowells shall be installed at a distance downstream of a mixing point, an injection point, or a heat exchanger sufficient for the stream to be mixed, as stated on the instrument data sheet.
14.1.3 Thermowells on vertical lines and vessels shall be installed with the connection head above the thermowell unless the thermowell is in a bottom or side nozzle.
14.1.4 Inserts shall be installed with the spring compressed so that the tip bears on the bottom of the bore.
14.1.5 Where the process temperature does not exceed 200°C, the thermowell bore shall be filled with a thermally conductive compound before the insert is installed; above that temperature the bore shall be left dry.
NOTE A conductive compound fills the air gap between the sheath and the bore and cuts the response time by a large fraction; the compounds dry out and bake hard above a few hundred degrees and then bind the insert in the well. (14.1.6)
14.1.7 Thermowell threads shall be made up with a sealant rated for the process temperature, and flanged thermowells shall be installed with the gasket and bolting of the piping class.

14.2 Connection Head and Transmitter Installation

14.2.1 Connection heads shall be oriented so that the conduit entry faces down or to the side, with a drip loop in any cable entering the head.
14.2.2 Field-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 10 ft of the element unless the instrument data sheet states a longer lead run.
14.2.3 Transmitters and connection heads shall be accessible for configuration and insert replacement without removing insulation, scaffolding, or another device.
14.2.4 Metal thermowells, connection heads, transmitter housings, and the raceway serving them shall be bonded to the equipment grounding system under Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding.
14.2.5 Pipe insulation shall be finished around the lagging extension and the connection head left clear, coordinated with Mechanical InsulationMechanical InsulationResolves to the current adopted revision.sync/mechanical-insulation.

15 Delivery, Storage, and Handling

15.1 Instruments shall be delivered in the manufacturer's original packaging with tag numbers, calibration certificates, and installation instructions enclosed.
15.2 Thermowell bores and process threads shall be capped until the element is installed.
15.3 Elements and transmitters shall be stored indoors in a clean, dry location within the storage temperature range published by the manufacturer until installation.
15.4 Mineral-insulated inserts and thermocouple cable shall be stored with their ends sealed.
NOTE Compacted mineral insulation absorbs moisture through an open end, and the insulation resistance falls until the end is dried and resealed. (15.5)

16 Warranty

16.1 Temperature instruments and thermowells shall be warranted against defects in materials and workmanship for the period indicated in the datasheet, measured from the date of substantial completion.
Temperature Instrument Warranty Periodrange
years
1235
16.2 The warranty shall cover repair or replacement of the failed element, transmitter, or thermowell and the calibration and field verification of the replacement.
16.3 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.

17 Spare Parts

17.1 The Contractor shall deliver the spare parts indicated in the datasheet at substantial completion.
Spare Parts Delivered at Substantial Completioncheckbox
☑ Inserts of each type, length, and tolerance class installed
☑ Transmitters of each model installed
☐ Thermowells of each material and connection not stocked by the manufacturer
☐ Dial thermometers of each range installed
☐ Connection head gaskets and covers of each model installed
17.2 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.
Spare Part Quantity per Ten Installedrange
units
1235
17.3 Spare parts shall match the installed devices in model, range, tolerance class, and firmware, and shall be turned over against a written inventory signed by the Owner's representative.

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