Thermocouples and RTDs produce different signals and respond differently to wiring, vibration, temperature range and installation. Controller input and probe design are as important as sensor type.
Use this guide to prepare a design review or RFQ. Final ratings depend on the complete product, installation, controls and operating environment.
Selection inputs that change the design
| Decision | Information to provide | Why it matters |
|---|---|---|
| Signal | Thermocouple millivoltage | RTD resistance |
| Strength | Wide range and robust high-temperature options | Stable measurement in its intended range |
| Wiring | Correct alloy, polarity and compensation | Lead resistance and wire count |
| Typical choice | High temperature or fast response | Accuracy and stability at moderate temperature |
Start with the measurement requirement
Define continuous and peak temperature, accuracy, response and atmosphere. A broad catalog range does not mean every cable and sheath shares the same limit.
Confirm controller input. A Type K input cannot directly read a Pt100, and RTD curve and wiring must match the instrument.
Design the mechanical probe
Diameter, insertion, sheath and junction affect response and life. A small probe responds quickly but may need protection.
Use a thermowell when containment or replacement requires it, while accounting for response delay.
Control wiring errors
Thermocouple extension cable must match type and polarity. Unintended junctions create errors.
For RTDs, select wire count for lead length and accuracy, and route signals away from power wiring.
Common specification mistakes
- Choosing only by maximum temperature
- Mixing thermocouple alloys
- Ignoring RTD lead resistance
- Installing outside the process zone
RFQ checklist
- Sensor type and input
- Temperature and atmosphere
- Accuracy and calibration
- Probe and mounting
- Cable, shielding and connector
Review the matching Temperature Sensors product range, then send this checklist with your drawing for an engineer-reviewed quotation.
Engineering review and validation
Before approving Thermocouple vs RTD: Selecting an Industrial Temperature Sensor, document the measured installation dimensions, normal and peak operating temperatures, available electrical supply, controller input, surrounding atmosphere and expected duty cycle. Compare these values with the supplier drawing rather than relying only on a catalog family name. During commissioning, record resistance, current, warm-up time, sensor response and temperature distribution. Retain this baseline with the machine records so maintenance teams can distinguish normal aging from poor contact, contamination, wiring damage or a control-system fault.
Frequently asked questions
Is RTD always more accurate?
System error also includes construction, wiring, calibration, mounting and readout.
What is a grounded junction?
It is electrically connected to the sheath, often faster but more exposed to ground-loop noise.
Why use 3-wire Pt100?
Compatible instruments can compensate for matched lead resistance.