- What is a type J thermocouple?
- What is the measuring range and characteristic curve of a type J thermocouple?
What is a type J thermocouple?
Thermocouples are thermoelectric sensors with two wires made of different materials. These are connected together at one point (measuring point) and a thermoelectric voltage can be measured at their ends (reference junction), which also changes when the temperature changes. This thermoelectric effect is also called Seebeck effect.
Thermocouples measure the temperature difference between the measuring point and the reference junction, i.e. the temperature at the reference junction must be known.
Thermocouples differ in the different alloys from which the thermocouple wires are made. Based on these materials, different characteristic curves and measuring ranges can be mapped.
Like platinum sensors, thermocouples are also standardized and can be immersed regardless of the manufacturer. They also have a very fast response time and can be used at very high or very low temperatures. They are inexpensive and come in many different types. Thermocouples also have disadvantages: they are more sensitive than resistance-based temperature probes. Their characteristic curve is not linear. The measuring principle should be known to the user in order to avoid measuring errors.
What is the measuring range and characteristic curve of a type J thermocouple?
The standard specifies measuring ranges for thermocouples in which the respective measuring accuracy of the tolerance class applies. If the thermocouple is used outside this specified measuring range, it is not possible to specify the measuring accuracy. If the thermocouple is operated outside the specified measuring range of its respective tolerance class, irreversible changes may also occur in the thermocouple, which subsequently leads to a measurement deviation (even within the specified range). Use beyond the measuring range of the tolerance class constitutes improper use and will result in a loss of warranty.
Measuring ranges according to standard:
- Class 1: -40 °C to 750 °C
- Class 2: -40 °C to 750 °C
Accuracy classes thermocouple Type K acc. to DIN IEC 60584
|Class ||Formula |
|Class 1 ||-40 °C to +375 °C: ±1,5 °C | +375 °C to +750 °C: ±0,004 |t| |
|Class 2 ||-40 °C to +333 °C: ±2,5 °C | +333 °C to +750 °C: ±0,0075 |t| |
Example values Accuracy
|Class ||Values at 100 °C ||Values at 500 °C ||Values at 1000 °C |
|Class 1 ||±1,5 °C ||±2,0 °C ||±2,8 °C |
|Class 2 ||±2,5 °C ||±3,75 °C ||±5,25 °C |