What is the limit of a Type B thermocouple?
Thermoelectric potential (EMF) is extremely small in the medium and low temperature ranges, making Type B thermocouples inaccurate for temperature measurements below 600°C. The low EMF value results in poor linearity. Because thermocouples are made of precious metals, they are expensive.
How accurate is a Type B thermocouple?
Type B thermocouples typically achieve Class 1 or Class 2 accuracy. The allowable absolute error ranges from ±0.5°C to ±1.5°C across different temperature ranges.
How do I calibrate a thermocouple?
A thermocouple is an instrument that measures temperature using the thermoelectric effect. They are made of two different metals or alloys. When the two ends of a thermocouple have different temperatures, a thermoelectric potential difference is generated, which is converted into a temperature signal. This principle is based on the fact that the electrical properties of a material change with temperature. Therefore, the demand for thermocouple calibration is increasing. The following are some steps for thermocouple calibration:
Zero-point calibration verifies that the thermocouple outputs zero electromotive force at zero temperature. To do this, place the measuring end of the thermocouple in ice-point water and record the output electromotive force after the temperature stabilizes. If the electromotive force is zero or close to zero, the thermocouple has passed the zero-point calibration.
Temperature calibration verifies that the thermocouple output is accurate at different temperatures. A standard thermometer can be used to calibrate the thermocouple. First, use a standard thermometer to measure the temperature to be calibrated. Then, place the thermocouple at that temperature and record the output electromotive force. Compare the thermocouple output with the standard thermometer’s measurement result. If the two are close, the thermocouple has passed the temperature calibration.
Linearity calibration verifies that the thermocouple output conforms to a linear relationship. This method involves placing the thermocouple at various temperatures, recording the output electromotive force (EMF). This data is then processed using methods such as regression analysis to determine the relationship between the thermocouple output and temperature. If the resulting relationship is close to linear, the thermocouple linearity verification has been passed.
Environmental influence verification verifies that the thermocouple output is stable under different environmental conditions. Common environmental factors include humidity, vibration, and electromagnetic fields. The thermocouple can be placed in different environmental conditions, the output electromotive force (EMF) recorded, and its stability observed. If the output is stable, the thermocouple is unaffected by environmental factors. The thermocouple has passed environmental influence verification.
Interchangeability verification verifies that the outputs of two thermocouples are consistent. Two thermocouples are placed at the same temperature, the output electromotive force (EMF) is recorded, and the difference is compared. If there is no difference or the difference is small, the two thermocouples are interchangeable.
