PT100 or Thermocouple - which sensor measures better?
PT100 resistance thermometers and thermocouples cover different temperature measurement tasks. This guide compares temperature range, accuracy per IEC 60751 and IEC 60584, and response time to show which sensor suits which process measurement.
View temperature sensorsHow do PT100 and thermocouple work?
A PT100 is a platinum resistance thermometer whose electrical resistance rises with temperature: exactly 100 Ω at 0 °C and around 138.5 Ω at 100 °C. A thermocouple instead uses the Seebeck effect: two dissimilar metals generate a temperature-dependent thermal voltage in the millivolt range at the junction.
The PT100 measures absolutely and needs a supply current, but delivers a very linear, stable signal. The thermocouple measures the difference between the hot junction and a reference (cold) junction and therefore requires cold-junction compensation in the transmitter.
- PT100: 100 Ω at 0 °C, temperature coefficient α = 0.00385 Ω/Ω/°C.
- PT1000: same curve but 1000 Ω - less influence from lead resistance.
- Thermocouple: the signal is a voltage, no supply needed, but compensating cable is required.
Temperature range, accuracy and response time compared
The three decisive criteria are range, accuracy and response time. The PT100 wins on precision in the mid range, thermocouples on high temperatures and fast reaction.
Thermocouple types cover different ranges depending on the metal pairing: type K (NiCr-Ni) up to around 1200 °C is the universal type, type J up to 750 °C, type T for low temperatures, and the noble-metal types R, S and B reach 1700 °C. Within its range the PT100 stays clearly more accurate and repeatable.
Which sensor suits which process measurement?
Selection depends on temperature level, required accuracy, response speed and environment. Connection type and transmitter also play a role.
- Laboratory, heating, refrigeration and HVAC: PT100 for high accuracy and stability.
- Furnaces, melts, exhaust and burners: thermocouple type K, S or B for high temperatures.
- Fast control loops and small parts: thin sheathed thermocouple with short response time.
- Long cable runs: PT100 in 4-wire connection or PT1000 to eliminate lead resistance.
- Heavy vibration and shock: the thermocouple is mechanically more robust than the delicate Pt element.
How to convert sensor signals to 4-20 mA or digital bus signals correctly.
Read the guideFrequently asked questions
Is a PT100 more accurate than a thermocouple?
Up to about 600 °C, yes. A class A PT100 reaches ±0.15 °C at 0 °C, while a class 1 thermocouple is typically ±1.5 °C. At high temperatures the thermocouple plays to its strength.
Why does a thermocouple respond faster?
The junction is a small welded point with very little mass. It therefore takes up temperature changes faster than the slower Pt resistance element of the PT100, often in under one second.
Why the 3- or 4-wire connection on a PT100?
The resistance of the lead wires falsifies the reading. The 3-wire circuit largely compensates this error, the 4-wire circuit eliminates it completely and gives the most accurate result.
Which thermocouple type should I choose?
Type K is the universal type up to around 1200 °C. For low temperatures use type T, for very high temperatures the noble-metal types R, S and B up to 1700 °C. The type depends on temperature and medium.
Looking for the right temperature sensor?
We supply PT100 resistance thermometers and thermocouples of all types, including transmitters - tested to IEC 60751 and IEC 60584.
Standard-tested
Sensors to IEC 60751 and IEC 60584.
Defined classes
Tolerance classes A/B and 1/2 documented.
Calibratable
Factory or accredited calibration on request.
Expert advice
Specialists help with type and connection.