Temperature sensor
As the name indicates, a temperature sensor is an instrument that can be used to measure temperature. It has an output signal proportional to the applied temperature. When the temperature of the sensor changes, the output will also change accordingly. There are various kinds of temperature sensors that have different output signals. Some have a resistance output, some have a voltage signal, some have a digital signal and many more.
Calibration a temperature sensor
You can either generate an accurate temperature, or you can use a calibrated reference temperature sensor to measure the generated temperature. For example, you may insert the reference sensor and the sensor to be calibrated into a liquid bath (preferably a stirred one) and you can perform calibration at that temperature point. Alternatively, a so called dry-block temperature source can be used. For industrial and professional calibration, typically temperature baths or dry-blocks are used. These can be programmed to heat or cool the temperature into a certain set point.
Calibration a temperature sensor– things to consider
Temperature source
As mentioned, It is necessary to have a temperature source to calibrate a temperature sensor. It is just not possible to simulate temperature. For industrial purposes, a temperature dry-block is most commonly used. It is handy and portable and typically accurate enough. A liquid bath can be used for higher accuracy needs. That is anyhow not typically easily portable but can be used in laboratory conditions. For zero Centigrade point, a stirred ice-bath is often used. It is pretty simple and affordable yet provides a good accuracy for the zero point.
Reference temperature sensor
It is necessary to know with a very high degree of accuracy the temperature of the heat source. Dry-blocks and liquid baths offer an internal reference sensor that measures the temperature. But for more accurate results, you should be using a separate accurate reference temperature sensor that is inserted in the same temperature as the sensor(s) to be calibrated. That kind of reference sensor will more accurately measure the temperature that the sensor to be calibrated is measuring.
As for thermodynamic characteristics, the reference sensor should be as similar as possible compared to the sensor to be calibrated, to ensure they behave the same way during temperature changes. The reference sensor and sensor to be calibrated should be immersed in the same depth in the temperature source. Typically, all sensors are immersed to the bottom of a dry-block.
Calibration points
In industrial calibration, you need to pick enough calibration points to see that the sensor is linear. Often it is enough to calibrate 3 to 5 points throughout the range. Depending on the sensor type, you may need to take more points, if you know that the sensor may not be linear.
Adjusting / trimming a temperature sensor
Unfortunately, most temperature sensors cannot be adjusted or trimmed. If there is an error in the calibration, you cannot adjust that. Instead you will need to use coefficients to correct the sensor’s reading.
Documentation
As with any calibration, the temperature sensor calibration needs to be documented in a calibration certificate.
Traceability
In calibration, the reference standard used, must have a valid traceability to National Standards, or equivalent.
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