Thermocouple
Choose the alloy, process atmosphere, protection and readout together. The same operating temperature can call for different complete constructions.
Review the specification →GUILCOR · Thermocouples
Thermocouple
temperature sensors
Choose the alloy, the circuit and the complete probe.
From refrigeration to high-temperature furnaces, thermocouples cover very different tasks. Compare the sensing types, understand the millivolt signal and specify the construction that your process needs.
SELECTION / YOUR APPLICATION
Find your starting point in Thermocouple.
Type K
The equipment is configured for Type K. Select the sheath, junction and process connection around the actual operating conditions.
Explore Type K →Type N
The application is being reviewed for Type N. Compare the documented characteristic and stability requirements with the protection system and readout.
Explore Type N →These links support a specification review. They do not establish interchangeable parts or availability of a complete assembly.
Interactive reference explorer
Compare voltage characteristics before choosing an input.
Enter a temperature within the selected reference-function range.
Compare the NIST reference characteristics for B, E, J, K, N, R, S and T. The graph shows voltage relative to a 0 °C reference junction. Changing the type changes the curve, available interval and output; it does not select a product.
Reference voltage
Reference-function interval
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Reference curves are not complete-probe temperature ratings. Type C, D and G use separate supplier reference data and are covered in their own guides.
Operating principle
How the voltage becomes a temperature.
A thermocouple produces a thermoelectric voltage from two different conductors in a temperature gradient. The measured voltage depends on both the measuring junction and the reference junction. It is not a resistance sensor and does not need a measuring current to generate its signal; the readout electronics still require power.
Use the reference function for the exact type. With a reference junction at 0 °C, its tabulated voltage is E(T). With terminals at another temperature, the measured signal is E(Thot) − E(Tref). A single constant sensitivity is only a local approximation; it is not a substitute for the nonlinear reference curve.
Emeasured = E(Thot) − E(Tref)
Family guide
Compare all eleven thermocouple types.
| Type | Conductor pair (+ / −) | Selection focus |
|---|---|---|
| Type B | Pt–30%Rh (+) / Pt–6%Rh (−) | Resolve small signals in high-temperature processes. |
| Type E | Nickel–chromium (+) / copper–nickel (−) | Compare sensitivity where you actually measure. |
| Type J | Iron (+) / copper–nickel (−) | Check the iron leg and the complete installation. |
| Type K | Nickel–chromium (+) / nickel–aluminium (−) | Make cold-junction compensation visible. |
| Type N | Nickel–chromium–silicon (+) / nickel–silicon–magnesium (−) | Check the input curve when changing from Type K. |
| Type R | Pt–13%Rh (+) / platinum (−) | Match a noble-metal signal to the input range. |
| Type S | Pt–10%Rh (+) / platinum (−) | Turn calibration results into an actionable check. |
| Type T | Copper (+) / copper–nickel (−) | Match response time to the process change. |
| Type C | W–5%Re (+) / W–26%Re (−) | Specify the atmosphere before the temperature. |
| Type D | W–3%Re (+) / W–25%Re (−) | Keep the matched wire pair and curve together. |
| Type G | Tungsten (+) / W–26%Re (−) | Protect the unalloyed tungsten leg during handling. |
Selection checklist
Specify the complete sensing assembly.
Electrical and thermal requirements
- Exact thermocouple type, reference curve and polarity.
- Minimum, normal and maximum temperature, including excursions and dwell time.
- Required wire tolerance or calibration uncertainty, with the applicable interval and certificate.
- Cold-junction, instrument, drift and installation contributions to the total error.
- Response-time requirement with the medium, flow and test conditions stated.
Mechanical and environmental requirements
- Atmosphere, chemical exposure, pressure and protection materials.
- Wire diameter, sheath diameter, insertion length and measuring-junction construction.
- Cable insulation, connector, sealing and mounting arrangement.
- Vibration, bending, handling and maintenance constraints.
- Calibration points, traceability and the inspection or replacement plan.
A reference-function range describes the mathematical characteristic. It is not the permitted continuous operating range of every wire, sheath, cable, connector or finished probe. Obtain the rating of the exact assembly; the most restrictive component and service condition govern selection.
Wiring and compatibility
Connect, compensate and configure the input.
Preserve the thermoelectric circuit
Keep the positive and negative conductors correctly identified through the probe, cable and connector. Use extension or compensating cable specified for the thermocouple type and its own permitted temperature interval. Verify the applicable colour-code convention; colour alone is not a universal identifier.
At the transition to the instrument, keep the two terminals as close as practical to the same known temperature. Place the compensation sensor where it represents that transition, away from local heat sources and gradients.
Configure the measuring input
Measuring junction → matching cable → reference terminals → differential input → compensation → type-specific conversion
Verify type selection, polarity, input range, common-mode limits, isolation, open-sensor detection and filtering. A grounded junction may create a ground path through the sheath; an ungrounded construction can provide isolation. Match the junction style to response, electrical and environmental requirements.
Mechanical integration
Choose the probe construction for the process.
A sensing element is only one part of the assembly. Select the mechanical format, materials, cable and connection around the real installation. GUILCOR can review these requirements for a prototype or production series.
Practical answers
Frequently asked questions.
Does a thermocouple need cold-junction compensation?
A thermocouple measurement needs a known reference junction. Modern instruments commonly measure the terminal temperature and compensate electronically. A controlled 0 °C reference is another method; a plain voltage measurement with an unknown terminal temperature is insufficient.
What determines accuracy and response time?
The complete assembly and measuring chain matter. Include calibration or tolerance, drift, reference-junction error, electronics and thermal installation. Response time depends on junction construction, sheath size, medium, flow and contact; there is no single value for a letter type.
Can thermocouples connect directly to an RTD or thermistor input?
Normally not. Those inputs measure resistance, whereas a thermocouple supplies a small voltage. Use an input or transmitter explicitly designed and configured for the selected thermocouple type.
Further reading
Explore related thermocouple types.
NIST reference functions · Cold-junction compensation guidance · Tungsten–rhenium reference
GUILCOR / YOUR ENQUIRY
Define your Thermocouple enquiry.
Describe the thermocouple, its protection system and the process together. The alloy name alone does not establish the rating of the complete probe.
Missing a reference or datasheet?
Send the component marking, equipment reference and any photographs or documents you have. These provide a starting point for identifying what must be confirmed.
The outline helps prepare your enquiry. Copying it does not send a request.
FOUR DETAILS THAT MOVE THE DISCUSSION FORWARD
01
Thermocouple and readout
Thermocouple type and reference characteristic, tolerance or calibration requirements, instrument model, cold-junction compensation, cable type and polarity.
02
Measurement conditions
Normal and peak temperatures, process atmosphere, pressure or flow where applicable, cycling, required response and contamination exposure.
03
Assembly and connection
Sheath or protection tube material and dimensions, junction construction, insertion, mounting, cable length and connection details.
04
Project and validation
Sample and production quantities, target delivery, calibration or documentation needs, and the checks required before approval.