1 Scope
1.1This standard governs field-mounted temperature sensing and transmitting assemblies used to measure, indicate, and transmit process and ambient temperature in process control and HVAC/mechanical systems.
NOTE The standard covers resistance temperature detectors, thermocouples, bimetallic and filled-system thermometers, integral- and remote-mount transmitters, thermowell assemblies, connection heads, and associated extension and compensating cable. (1.2)
NOTE It applies to temperature elements in pipe, vessel, duct, and ambient air service from cryogenic (-200°C) through high-temperature process service (approximately 1260°C thermocouple range), with 4-20 mA analog, HART, WirelessHART, FOUNDATION Fieldbus, and Modbus RTU output configurations. (1.3)
NOTE The standard addresses both process/industrial use cases (IEC/ISA-centric, thermowell-focused) and HVAC/building-automation use cases (duct sensors, room sensors, pipe-immersion sensors), because both fall within the Instrumentation and Controls discipline. (1.4)
NOTE The following are outside the scope of this standard and are governed elsewhere. (1.5)
- Pressure and differential-pressure transmitters and gauges — see Pressure Instrumentation.
- Flow measurement devices (orifice plates, vortex meters, magnetic flowmeters), even when temperature-compensated — see Flow Measurement.
- Level sensors and level transmitters — see Level Sensors.
- Loop architecture, P&ID conventions, and the instrument index — see Process Instrumentation.
- Temperature sensors integrated within and shipped as part of packaged HVAC equipment (VAV box controllers, AHU discharge sensors) — see the relevant equipment standard such as Variable Air Volume Terminals or Makeup Air Units.
- Geotechnical temperature monitoring (ground temperature arrays, thermal conductivity testing) — see Geotechnical Instrumentation And Monitoring.
- Electrical heat-tracing temperature sensors wired as part of the heat-trace control system.
- Laboratory-grade precision thermometry and NIST-traceable calibration facilities.
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
NOTE ISA-MC96.1 has been withdrawn as a standalone standard and its technical content folded into ASTM E230 and IEC 60584; this standard references ASTM E230 as the primary US thermocouple authority and retains ISA-MC96.1 only for extension-wire color coding. (2.3)
| Standard |
Title |
| IEC 60751:2022 |
Industrial Platinum Resistance Thermometers and Platinum Temperature Sensors |
| ASTM E230/E230M-17 |
Specification and Temperature-EMF Tables for Standardized Thermocouples |
| IEC 60584-1:2013 |
Thermocouples — Part 1: EMF Specifications and Tolerances |
| ASME PTC 19.3 TW-2016 |
Thermowells — Performance Test Codes |
| ASME B40.200-2008 (R2013) |
Thermometers, Direct Reading and Remote Reading |
| ISA-MC96.1-1982 (R2018) |
Temperature Measurement Thermocouples |
| ISA-51.1-1979 (R1993) |
Process Instrumentation Terminology |
| NFPA 70 (NEC) |
National Electrical Code (Article 250 Grounding, Article 500 Hazardous Locations) |
| ANSI/ISA-12.27.01-2003 (R2019) |
Requirements for Process Sealing Between Electrical Systems and Flammable or Combustible Process Fluids |
| IEC 61511 / ISA-84.00.01-2004 |
Functional Safety — Safety Instrumented Systems for the Process Industry Sector |
3 Submittals
3.1The Contractor shall submit the following action submittals for each temperature instrument or assembly type prior to fabrication or procurement:
- Product data sheets identifying sensor technology, range, accuracy class, output, and enclosure rating.
- Completed instrument data sheets (ISA-20 format or Engineer-approved equivalent) for every tag.
- Thermowell dimensional drawings with insertion length, bore, root and tip diameters, and process connection.
- ASME PTC 19.3 TW-2016 wake-frequency calculations for every thermowell in flowing process service.
- Hazardous-area certification (intrinsic safety, explosion-proof, or non-incendive) for instruments in classified areas.
- Material certifications and, where wetted, mill test reports for thermowell stock.
☑ Product data sheets
☑ Instrument data sheets (ISA-20)
☑ Thermowell dimensional drawings
☑ ASME PTC 19.3 TW wake-frequency calculations
☐ Hazardous-area certification
☐ Material certifications / mill test reports
3.2The Contractor shall submit the following informational submittals:
- Factory calibration certificates, NIST-traceable where required by this standard.
- Manufacturer installation, operation, and maintenance instructions.
- Loop diagrams showing element, transmitter, cable type, and DCS/PLC termination.
- For safety-instrumented applications, the IEC 61511 SIL capability statement and proof-test procedure.
☑ Factory calibration certificates
☑ Installation/operation/maintenance instructions
☑ Loop diagrams
☐ SIL capability statement and proof-test procedure
3.3The Contractor shall submit the following closeout submittals at project completion:
- As-installed loop diagrams and instrument index.
- Field calibration and loop-check records.
- Warranty documentation.
☑ As-installed loop diagrams and instrument index
☑ Field calibration and loop-check records
☑ Warranty documentation
4 Quality Assurance
4.1Temperature instruments and assemblies shall be the product of a manufacturer regularly engaged in the production of industrial temperature instrumentation.
4.2All instruments of a given type and service shall be the product of a single manufacturer to maintain interchangeability of spare elements and transmitters.
4.3Factory calibration shall be NIST-traceable for all RTD Class A and Class AA elements and for all instruments used in safety-instrumented functions.
4.4Calibration shall be performed at the ice point (0°C) plus two span points bracketing the operating range.
4.5Instruments installed in classified hazardous locations shall carry third-party certification (UL, FM, CSA, or ATEX/IECEx) appropriate to the area classification.
4.6For safety-instrumented functions, the element and transmitter shall be certified to the required Safety Integrity Level per IEC 61511, with the proof-test interval and proof-test procedure stated on the instrument data sheet.
5 Environmental and Service Conditions
5.1The Contractor shall verify that each instrument's published ambient and process temperature ratings envelope the site service conditions before procurement.
5.2Head-mount transmitter electronics shall be rated for the connection-head ambient temperature, which for high-process-temperature service is elevated by conduction from the thermowell.
NOTE For high-process-temperature service, the connection-head ambient is elevated by conduction from the thermowell and may exceed the transmitter electronics rating; verify the ambient derating before specifying a head-mount transmitter. (5.3)
5.4Where the process temperature would drive the connection-head ambient above 70°C, a remote-mount transmitter shall be used in lieu of a head-mount transmitter.
5.5Enclosures and connection heads installed outdoors or in wash-down areas shall be rated NEMA 4X (IP66) minimum.
5.6Instruments in Class I Division 1 locations shall be explosion-proof (NEMA 7) or protected by an approved intrinsically safe barrier.
5.7Instruments in Class I Division 2 locations shall be intrinsically safe, non-incendive, or otherwise approved for the classification.
5.8Process seals shall be provided at conduit entries on instruments in hazardous locations in accordance with ANSI/ISA-12.27.01 where a single seal is relied upon.
● Non-hazardous (general purpose)
○ Class I Division 2 (intrinsically safe / non-incendive)
○ Class I Division 1 (explosion-proof or intrinsically safe)
○ Zone 1 (Ex d or Ex ia)
○ Zone 2 (Ex nA or Ex ic)
● NEMA 4X (IP66)
○ NEMA 4 (IP65)
○ NEMA 7 (explosion-proof)
○ NEMA 4X stainless steel
6 Sensor Technology Selection
NOTE Sensor technology shall be selected on the basis of required accuracy, temperature range, and output type. (6.1)
NOTE An RTD shall be specified where the service requires high accuracy and long-term stability within the -200°C to +850°C range; a thermocouple shall be specified where the service exceeds the RTD range, requires fast response, or requires a rugged sheathed element in severe environments. (6.2)
NOTE A bimetallic dial thermometer or filled-system remote thermometer shall be specified only for local indication where no electrical output to the control system is required. (6.3)
● RTD (Pt100, platinum)
○ RTD (Pt1000, platinum)
○ Thermocouple
○ Bimetallic dial thermometer
○ Filled-system remote thermometer
6.4 Resistance Temperature Detectors
6.4.1RTD elements shall be platinum, conforming to IEC 60751:2022 resistance-versus-temperature tables and tolerance classes.
6.4.2RTD elements in field installations shall be three-wire minimum to compensate for lead resistance; two-wire RTDs shall not be used for lead runs exceeding 3 m.
6.4.3RTD elements in precision and safety-instrumented service shall be four-wire to eliminate lead-resistance error entirely.
NOTE Two-wire RTD connection on field runs is a common source of uncompensated lead-resistance error and is prohibited here for that reason except for short factory-internal leads. (6.4.4)
NOTE RTD accuracy class shall be IEC 60751 Class A for industrial process control and Class B for general HVAC and building automation; Class AA shall be reserved for precision and safety-instrumented service. (6.4.5)
NOTE Class B tolerance is ±(0.30 + 0.005|t|)°C, Class A is ±(0.15 + 0.002|t|)°C, and Class AA is ±(0.10 + 0.0017|t|)°C, each evaluated at the measured temperature t in °C. (6.4.6)
6.4.7RTDs used in IEC 61511 SIL 2 loops shall be Class A or better with an individual calibration certificate; Class B shall not be used for SIL-rated temperature measurement.
● Pt100, 3-wire
○ Pt100, 4-wire
○ Pt100, 2-wire (factory-internal leads only)
○ Pt1000, 3-wire
○ Class B (±0.30°C at 0°C) — HVAC/building automation
● Class A (±0.15°C at 0°C) — industrial process
○ Class AA (±0.10°C at 0°C) — precision/SIL
6.5 Thermocouples
6.5.1Thermocouple elements shall conform to ASTM E230/E230M for EMF tables and limits of error; IEC 60584-1 shall apply for export or global projects.
NOTE Thermocouple type shall be selected for the process temperature range and atmosphere. (6.5.2)
NOTE Type K (-200°C to 1260°C) shall be the default for general oxidizing process service; Type J (-40°C to 750°C) for reducing atmospheres; Type E (-200°C to 900°C) where the highest sensitivity is required; Type T (-200°C to 350°C) for cryogenic and food service; Type N for high-temperature oxidizing service; and noble-metal Types R and S for furnace service. (6.5.3)
NOTE Type K standard limits of error are ±2.2°C or ±0.75% of reading, whichever is greater; special limits are ±1.1°C or ±0.4%. (6.5.4)
6.5.5Thermocouple extension or compensating cable shall be type-matched to the thermocouple per ISA-MC96.1; copper extension wire shall not be used with a thermocouple element.
NOTE Using copper extension wire with a thermocouple introduces a parasitic EMF error that varies with ambient temperature and corrupts the measurement; type-matched cable carries the thermoelectric reference unbroken to the cold junction. (6.5.6)
6.5.7Cold-junction compensation shall be provided at a single defined location; thermocouple extension cable shall not be spliced to copper at intermediate terminal blocks ahead of the transmitter or DCS cold junction.
6.5.8Where a thermocouple home run from a junction box to the marshalling cabinet would otherwise use copper, a head-mount transmitter shall be specified to convert to a 4-20 mA copper loop at the instrument.
● Type K (-200 to 1260°C, general oxidizing)
○ Type J (-40 to 750°C, reducing)
○ Type E (-200 to 900°C, high sensitivity)
○ Type T (-200 to 350°C, cryogenic/food)
○ Type N (high-temperature oxidizing)
○ Type R/S (noble metal, furnace)
● Standard (±2.2°C or ±0.75%)
○ Special (±1.1°C or ±0.4%)
Type KX (for Type K)
Type JX (for Type J)
Type EX (for Type E)
Type TX (for Type T)
Type NX (for Type N)
Copper (RTD / transmitter output only)
6.6 Number of Sensing Elements
6.6.1Single-element assemblies shall be used for general indication and control service.
6.6.2Dual-element assemblies shall be specified where redundancy is required for safety-instrumented functions, or where independent control and monitoring measurements are taken from one penetration.
NOTE Dual-element construction lets a control loop and a safety loop share one thermowell penetration without sharing a common element failure, and supports averaging or hot-standby schemes. (6.6.3)
● Single element
○ Dual element (redundant)
7 Output and Transmitter
NOTE Output and protocol shall be selected to match the control system interface and the accuracy budget. (7.1)
7.2New field temperature transmitters shall provide a 4-20 mA analog output with superimposed HART revision 7 digital signal as the minimum, unless a fieldbus or wireless architecture is specified for the project.
7.3WirelessHART output shall be limited to monitoring-only or retrofit service where wiring a new loop is impractical and the measurement is not used for closed-loop control or safety.
7.4Local-indication-only service (bimetallic or filled-system) shall be specified where no electrical signal to the control system is required.
7.5Transmitter total loop accuracy shall be within ±1.0°C for process control and within ±0.5°C for precision applications, including element, transmitter, and reference uncertainty.
NOTE Transmitter accuracy is typically ±0.1°C to ±0.5°C and is span-dependent; the loop accuracy budget shall account for the element tolerance class in addition to the transmitter. (7.6)
● 4-20 mA + HART rev 7
○ 4-20 mA analog only
○ WirelessHART (monitoring/retrofit)
○ FOUNDATION Fieldbus
○ Modbus RTU
○ Local indication only (no electrical output)
● Integral / head-mount (on element connection head)
○ Remote-mount (DIN-rail or panel)
● ±1.0°C (process control)
○ ±0.5°C (precision)
7.7 Transmitter Mounting
7.7.1Integral head-mount transmitters shall be used where the connection-head ambient remains within the transmitter electronics rating, typically -40°C to +85°C.
7.7.2Remote-mount transmitters shall be used where the process temperature would raise the connection-head ambient above the electronics rating, or where the element location is inaccessible for configuration and maintenance.
NOTE Ordering a head-mount transmitter for high-process-temperature service without checking the ambient derating is a recurring field failure: a 300°C process can heat the connection head above the 85°C electronics limit and cause drift or failure. (7.7.3)
8 Thermowells
8.1A thermowell shall be provided for every temperature element installed in pressurized piping, process vessels, or any service where element removal under pressure or process leakage is a safety concern.
NOTE Specifying a bare RTD or thermocouple element in pressurized piping creates a personnel-safety and process-leak hazard and is prohibited; the thermowell isolates the element from the process and permits removal without breaching containment. (8.2)
8.3Bare elements (no thermowell) shall be limited to duct service and other non-pressurized service such as HVAC air measurement.
8.4Thermowell material shall be compatible with the process fluid.
NOTE 316 stainless steel shall be the default thermowell material; nickel-chromium-molybdenum alloy (UNS N10276), nickel-copper alloy (UNS N04400), nickel-chromium alloy (UNS N06600/N06625), or alumina ceramic shall be specified for corrosive or high-temperature service. (8.5)
8.6Thermowell process connection rating shall match the pipe specification.
NOTE Specifying a thermowell with a lower pressure rating than the piping class (e.g., 150# flange on a 600# line) is a common RFI generator; cross-check the piping class before procurement to avoid this error. (8.7)
● Thermowell required (pressurized piping/vessel)
○ Bare element (duct / non-pressurized)
316 stainless steel
304 stainless steel
Nickel-chromium-molybdenum alloy (UNS N10276)
Nickel-copper alloy (UNS N04400)
Nickel-chromium alloy (UNS N06600)
Alumina ceramic
● Tapered (stepped)
○ Straight
○ Flanged
○ Threaded (NPT)
○ Socket-weld
1/2" NPT male
3/4" NPT male
1" NPT male
ANSI 150# flange
ANSI 300# flange
ANSI 600# flange
Socket-weld
● 1/2" NPT (pipe ≤4", ≤600 psig)
○ 3/4" NPT (larger pipe)
○ Flanged ANSI 150#
○ Flanged ANSI 300#
8.8 Wake-Frequency and Insertion Length
8.8.1An ASME PTC 19.3 TW-2016 wake-frequency (Strouhal) calculation shall be submitted for every thermowell in flowing process service to confirm structural adequacy against vortex-induced resonance.
8.8.2A wake-frequency calculation shall be required for all thermowells where fluid velocity exceeds 1 m/s for liquids or 10 m/s for gases.
NOTE Thermowell resonance failure in high-velocity service is a documented field failure mode in which vortex shedding excites the thermowell at its natural frequency and fatigues the root; the PTC 19.3 TW calculation governs L/D limits and the fatigue assessment. (8.8.3)
8.8.4The frequency ratio of natural to shedding frequency shall be at least 1.3 for an unsupported thermowell per ASME PTC 19.3 TW; stepped or tapered thermowells shall be preferred for high-velocity service.
8.8.5Thermowell insertion length shall place the tip at a minimum of 60% of the pipe inside diameter into the flow stream to limit conduction error.
8.8.6The insertion-length-to-bore ratio shall satisfy L/D greater than 5 to limit conduction error along the well.
NOTE Insertion length shall be verified against the pipe inside diameter on the instrument data sheet so the well neither bottoms out nor falls short of the 60%-immersion target. (8.8.7)
NOTE A standard 6-inch-insertion thermowell bottoms out in a 2-inch pipe; insertion length versus pipe size is the single most common RFI generator in this category and shall always be checked against the pipe ID. (8.8.8)
NOTE Use the following guidance for nominal insertion length versus pipe size, subject to the wake-frequency calculation. (8.8.9)
| Pipe size (NPS) |
Nominal pipe ID |
Target tip immersion (60% ID) |
Typical insertion length (U) |
| 2" |
~52 mm |
~31 mm |
2.5" (63 mm) |
| 3" |
~78 mm |
~47 mm |
4.5" (114 mm) |
| 4" |
~102 mm |
~61 mm |
6.0" (150 mm) |
| 6" |
~154 mm |
~92 mm |
7.5" (190 mm) |
| 8" |
~203 mm |
~122 mm |
10.5" (267 mm) |
| ≥10" |
per drawing |
60% of ID |
per wake-frequency calculation |
NOTE For pipe smaller than 3 inches, a tapered thermowell in an elbow or a pipe expansion (tee with a larger-bore run) shall be used where straight-run immersion cannot meet the 60% target. (8.8.10)
● Required (flowing process service)
○ Not required (static / non-pressurized)
Per drawings — thermowell schedule
9 Element Construction and Connection Head
NOTE Element construction shall be selected for the protection-tube environment and required response time. (9.1)
NOTE Bare elements shall be used inside thermowells in clean, non-severe service; mineral-insulated metal-sheathed (MIMS) elements shall be used where vibration, moisture ingress, or bending is a concern; ceramic protection tubes shall be used for high-temperature furnace service. (9.2)
NOTE Sheath or protection-tube material shall be 316 stainless steel for general service, nickel-chromium alloy (UNS N06600 or UNS N06625) for high-temperature oxidizing service, and alumina ceramic for furnace service. (9.3)
9.4The connection head shall be cast aluminum for general service and stainless steel for corrosive or wash-down service.
9.5The conduit entry shall be sized 1/2" or 3/4" NPT to match the project wiring method.
9.6The connection head enclosure rating shall be NEMA 4X (IP67) minimum for general process service.
9.7The connection head enclosure rating shall be NEMA 7 for Class I Division 1 hazardous locations.
● Bare element (in thermowell)
○ Mineral-insulated metal-sheathed (MIMS)
○ Ceramic protection tube
316 stainless steel
Nickel-chromium alloy (UNS N06600)
Nickel-chromium alloy (UNS N06625)
Alumina ceramic
● Cast aluminum (epoxy-coated)
○ Stainless steel
● 1/2" NPT
○ 3/4" NPT
○ M20
10 Local Indicating Thermometers
10.1Bimetallic dial thermometers shall conform to ASME B40.200 and shall be provided with an every-angle adjustable stem and a thermowell where installed in pressurized service.
10.2Filled-system remote thermometers (capillary bulb and dial) shall be used where a local reading is required at a distance from the process connection that a rigid-stem dial cannot reach.
NOTE Dial size shall be selected for the required reading distance; a 3-inch dial is typical at arm's length and a 5-inch dial where the gauge must be read from a walkway or grade. (10.3)
NOTE Bimetallic and filled-system thermometers provide local indication only and shall not be relied upon for control or alarm functions, which require an electrical-output element and transmitter. (10.4)
○ Bimetallic dial (every-angle adjustable)
○ Filled-system remote (capillary)
● None (no local indication)
11 HVAC and Building Automation Sensors
11.1Duct-mounted air-temperature elements shall be bare Pt100 RTDs without thermowells, with a remote-mount or transmitter output suitable for the building automation system.
11.2Averaging elements shall be specified for supply, return, and mixed-air measurement in ducts where a single-point sensor would not represent the bulk air temperature across the duct cross-section.
NOTE A single-point sensor in a large or stratified duct cross-section can misrepresent mixed-air temperature; averaging-element length or multiple point locations shall follow ASHRAE duct-measurement guidance. (11.3)
11.4Pipe-immersion RTDs for hydronic heating and chilled-water service shall be installed in thermowells in accordance with the pressurized-service requirements of this standard.
11.5Room and space temperature sensors shall be Pt100 or Pt1000 RTDs with an enclosure and aesthetic suited to the occupied space and the building automation system interface.
○ Duct air (single-point)
● Duct air (averaging)
○ Pipe immersion (thermowell)
○ Room / space
Per drawings — duct sensor schedule
12 Extension and Field Cable
12.1RTD field wiring shall be copper, with a dedicated three-conductor (three-wire RTD) or four-conductor (four-wire RTD) twisted, shielded cable per loop.
12.2Thermocouple field wiring ahead of any transmitter shall be type-matched compensating or extension cable per ISA-MC96.1, color-coded to the thermocouple type, twisted, shielded, and 20 AWG minimum for runs exceeding 15 m.
NOTE Cable shields shall be continuous and grounded at one end only, at the control-system end, to avoid ground loops. (12.3)
12.4Armored or jacketed cable shall be provided where the field route requires mechanical protection; armor and conduit shall be bonded and grounded per NEC Article 250.
● Copper, 3-conductor twisted shielded (3-wire RTD)
○ Copper, 4-conductor twisted shielded (4-wire RTD)
○ Thermocouple extension/compensating, twisted shielded
○ Copper, 2-conductor twisted shielded (transmitter output)
● Unarmored (in conduit)
○ Interlocked armor
○ Continuously welded armor
13 Testing
13.1Every instrument shall be bench-calibrated and tagged before installation, with the calibration record retained for the closeout submittal.
13.2Each loop shall be field loop-checked end to end, verifying 4 mA at the lower range value (LRV) and 20 mA at the upper range value (URV).
13.3Thermocouple loops shall be verified for correct cold-junction compensation at ambient conditions during the loop check.
13.4Insulation resistance of RTD elements and field cable shall be tested and recorded prior to energization.
13.5Safety-instrumented loops shall be proof-tested per the IEC 61511 procedure stated on the instrument data sheet before the safety function is placed in service.
NOTE A loop is not accepted until the measured value at the control system agrees with a traceable reference at two points spanning the operating range within the loop accuracy budget. (13.6)
☑ Bench calibration and tagging
☑ End-to-end loop check (LRV/URV)
☐ Cold-junction compensation verification (TC)
☑ Insulation resistance test
☐ SIL proof test (safety loops)
14 Installation
14.1Thermowells shall be installed so that the tip reaches the required immersion depth into the flow stream and, where practical, points slightly into the flow in elbows for fastest response.
14.2Elements shall be spring-loaded against the bottom of the thermowell to ensure thermal contact, and the annular gap shall be filled with thermal compound where the manufacturer requires it.
14.3Connection heads shall be installed so the cover and conduit entry permit drainage and prevent moisture accumulation in the head.
14.4Transmitters shall be installed accessible for configuration and calibration without removing the element from the thermowell.
14.5Instruments shall be installed to permit removal of the element from the thermowell without breaking into the pressurized process.
14.6Conduit and cable entries into connection heads in classified areas shall be sealed in accordance with NEC Article 500 and the certification of the instrument.
14.7Metal thermowells, connection heads, and conduit systems shall be grounded and bonded in accordance with NEC Article 250.
15 Delivery, Storage, and Handling
15.1Instruments shall be delivered in the manufacturer's original packaging with tags, calibration certificates, and protective thread or flange covers intact.
15.2Instruments shall be stored indoors in a clean, dry, temperature-controlled environment until installation.
15.3Thermowell bores and process threads shall be kept capped until the element is installed to prevent contamination and thread damage.
15.4Electronic transmitters shall be protected from moisture, impact, and electrostatic discharge during storage and handling.
16 Warranty
16.1The 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 occurs first.
16.2The warranty shall cover repair or replacement of failed elements, transmitters, and thermowells, including the cost of recalibration of replacement units.
○ 12 months
● 24 months
○ 36 months
17 Spare Parts
NOTE The Contractor shall furnish spare sensing elements and transmitters sufficient to maintain the installed instruments without procurement delay. (17.1)
17.2Spare parts shall be furnished as follows:
- One spare element of each type, range, and accuracy class for every ten installed, minimum one of each.
- One spare transmitter of each model and configuration for every ten installed, minimum one of each.
- Spare thermowells for any non-standard material or process connection that is not stock.