RTD vs Thermocouple
Side by side comparison: how they work, where each fits, and which to choose.
Quick answer: Choose an RTD for accuracy and stability up to about 600 °C. Choose a thermocouple for higher temperatures, fast response, vibration or low cost.
RTD vs Thermocouple: Comparison Table
| Aspect | RTD | Thermocouple |
|---|---|---|
| Principle | Resistance of platinum rises with temperature | Voltage from two dissimilar metals (Seebeck effect) |
| Typical range | about −200 to 600 °C | about −200 to 1700 °C depending on type |
| Accuracy (new sensor) | Class A: ± 0.35 °C at 100 °C | Type K class 1: ± 1.5 °C |
| Stability | Very good | Drifts with time at high temperature |
| Response | Slower, larger element | Faster, small junction |
| Wiring | 3 or 4 wire copper | Matching extension cable, needs cold junction compensation |
| Cost | Higher | Lower |
Choose RTD when
- Control and custody measurements below about 600 °C
- Where long term stability matters
- Where you want copper cable to a head transmitter
Choose Thermocouple when
- Furnaces, flue gas and anything above about 600 °C
- Fast changing temperatures
- High vibration or very small sensors
Key Differences Explained
Both sensors usually feed a temperature transmitter that converts the signal to 4 to 20 mA. The RTD needs a small excitation current and lead resistance compensation; the thermocouple needs cold junction compensation and the right extension cable.
In the overlap range, from about 0 to 400 °C, most plants prefer Pt100 RTDs for their better accuracy and stability, and keep thermocouples for high temperature service.
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Frequently Asked Questions
What is the difference between RTD and Thermocouple?
Choose an RTD for accuracy and stability up to about 600 °C. Choose a thermocouple for higher temperatures, fast response, vibration or low cost.
Which is more accurate, RTD or thermocouple?
An RTD. A class A Pt100 is about four times tighter than a class 1 type K thermocouple at 100 °C.
Can a transmitter accept both?
Most universal temperature transmitters can be configured for RTD or thermocouple input.
Why do thermocouples drift?
The wire composition changes slowly at high temperature, changing its output.
Learn more on the blog
Thermocouple and RTD installation precautions
A practical guide on instrumentationblog.in that goes deeper into this topic with field examples.
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