When do you need a thermocouple and what kind of thermocouple do you need?

Table of contents

What is a thermocouple sensor? 

A thermocouple consists of two (or more) dissimilar metals joined on one side. These 2 wires produce a voltage relative to the temperature of the application the thermocouple is used in. When temperature increases, the voltage becomes stronger. This voltage can thereafter be interpreted as temperature.

What is thermocouple wire?

The original method to measure temperature is to combine two dissimilar alloys (thermocouple wire) together at the sensing end by welding. When properly joined, a thermo-electric current is produced that can be read to determine temperature (Seebeck effect). Sometimes this method of temperature measurement is still the most cost-effective method. Typically, the thermocouple wire will be insulated with ceramic beads and placed in a seamless or welded stainless steel or Inconel tubes.

When do I need a thermocouple sensor?

Thermocouples are needed when high temperatures need to be measured or temperatures in hazardous environments, such as environments with high vibration or with toxic gasses. They are less common when high precision measurement is required for temperature ranges varying from 0 to 300°C.  For this temperature range RTDs are more accurate. 

What kind of thermocouple sensor do I need?

This depends on the temperature you need to measure. The thermocouple alloys are described as types. For example, a type K thermocouple alloy contains a NiCr-Ni junction, providing the widest operating range of all thermocouples. Below you can find a list of temperature ranges for each thermocouple type. When choosing a thermocouple for your application, keep in mind that the diameter of the sensor can have an impact on the application range and the lifetime of the sensor.

Thermocouple Useful application range
Type K -270°C .. +1260°C
Type N -270°C .. +1260°C
Type J -210°C .. +760°C
Type E -270 .. +900°C
Type T -270°C .. +370°C
Type R -50°C .. +1480°C
Type S -50°C .. +1480°C
Type B 0°C .. +1700°C

What are the most common thermocouple junctions?

The most common thermocouple junction is a type K (NiCr-Ni) junction. This type of thermocouple junction has the widest temperature range of all thermocouple types. Furthermore, type K thermocouples tend to be cost-efficient, accurate and reliable.

In the 1960’s, the type N (NiCroSil-NiSil) thermocouple was developed. This thermocouple type had a positive effect on short range ordering. The type N and type K thermocouples share the same accuracy and temperature range, but type N thermocouples tend to be more stable.

Is there a difference between a thermocouple probe, sensor and insert?

No there is not. These three words are commonly used to describe the same themperature sensor using thermocouple wires.

See our brochure for more information about MI thermocouple cable