Changes in environmental conditions also affect sensors. Temperature usually has the greatest influence on the accuracy of pressure measurements. To minimise the influence of temperature on the measurement result, so-called temperature compensation is often used. To do this, the measurement deviation caused by temperature fluctuations is determined and the sensor is adjusted accordingly.
Temperature compensation is the counteracting or correcting of unwanted temperature effects. This concept is very important in the manufacture of precision components and many electronic components and assemblies.
There are two forms of temperature compensation:
Active temperature compensation provides the most accurate results and is the method used most frequently.
Digital pressure sensors use electronic circuits that provide an analogue output signal proportional to the input pressure. There are three factors in the sensor circuitry that are affected by changes in ambient temperature: the zero pressure output voltage, the pressure sensitivity range and the bridge resistance. Temperature-compensated sensors are equipped with certain correction techniques and minimise the influence of temperature changes on these factors.
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You can use a small junction box with a temperature controller that keeps it always at a certain temperature. By knowing the temperature at which the cold junction is located, as well as the type of thermocouple, the temperature can be calculated and compensated.
A measuring device (in the form of a transmitter, DCS input card or temperature calibrator) can measure the temperature of the cold junction all the time and automatically perform on-line compensation for this error. Since the measuring device also knows the thermocouple type, it can perform the compensation automatically and continuously. This is the easiest way to do it.
A 3-wire connection is used to compensate for the temperature and resistance of the leads. As a precaution when using a 3-wire system, the lead wires should be of the same type, length and cross-section to compensate for the temperature effects of each lead wire.
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A strain gauge is used to measure strain. Compensation of the effect of temperature on a strain gauge is necessary in order to reduce the effect of temperature on measurement results. The main reasons for introducing thermal compensation in strain gauges are:
