RTD vs Thermocouple: Which Temperature Sensor to Choose?

The short answer

Choose an RTD when you need high accuracy and stability at low and medium temperatures, especially below 400–600 °C. Choose a thermocouple when you need a higher temperature range, fast response, rugged construction or a lower-cost sensor for high-volume equipment.

Both sensors are widely used in industrial temperature measurement, but they behave differently and suit different applications.

How an RTD works

An RTD (resistance temperature detector) uses a metal resistance element, usually platinum. The resistance rises in a predictable way as temperature increases. A Pt100 element is 100 Ω at 0 °C and is the most common industrial RTD.

RTDs are known for:

High accuracy and repeatability
Good long-term stability
Linear output over a wide range
Compatibility with 2-, 3- and 4-wire measurement

Their main limitations are a lower maximum temperature and slower response than a exposed thermocouple.

How a thermocouple works

A thermocouple uses two dissimilar metals joined at a measuring junction. The junction produces a small voltage that changes with temperature. Common types are K, J, T and E.

Thermocouples are known for:

Very high temperature capability
Fast response
Rugged, small and low-cost construction
Wide availability of probes, wire and connectors

Their main limitations are lower accuracy, drift over time and the need for cold-junction compensation.

Comparison at a glance

Accuracy: RTD is usually better, especially with Class A or tighter elements.
Temperature range: Thermocouple wins at high temperature; Type K can be used up to around 1200 °C depending on sheath and atmosphere.
Response time: A fine-wire or exposed-junction thermocouple is faster.
Stability: RTD is more stable over time.
Cost: Thermocouple probes and wire are often lower cost for high-volume OEM applications.
Cable length: A 4-wire RTD handles long cables well; thermocouple extension wire must match the thermocouple type and polarity.

When to choose an RTD

HVAC, chillers, boilers and water systems
Food, dairy and pharmaceutical processes
Laboratory and metrology measurements
Applications requiring ±0.1 °C or better
Long cable runs where a 3- or 4-wire connection is practical

See our RTD and thermistor sensors for Pt100 probes, surface sensors, elements and transmitters.

When to choose a thermocouple

Kilns, furnaces and heat-treatment equipment
Plastics extrusion and injection moulding
Engine, exhaust and combustion testing
High-temperature ovens and kilns above 600 °C
Fast-response measurements or rugged OEM equipment

See our thermocouple range for Type K probes, surface sensors, armored probes and thermocouple wire.

Common mistakes

Using a thermocouple for a ±0.1 °C laboratory measurement without calibration
Using an RTD above its maximum temperature or in a vibrating application without protection
Forgetting cold-junction compensation on a thermocouple input
Using 2-wire RTDs on long cables and losing accuracy
Choosing a probe by price without checking sheath material, diameter and response time

Need help choosing?

Send us the temperature range, accuracy target, environment and cable length. Our engineers can recommend an RTD or thermocouple, suggest the probe construction and quote a standard or custom build. Contact our team.