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Is the temperature compensation of the pressure gauge the same as that of the cold end of the process calibrator?


Due to the influence of environment, sensor material, time and other factors, under different ambient temperatures, the indicators of the standard and the measured instrument will change, so that the actual measurement results will be different; Even in the same temperature, different measurement cycle, the index will be different, but as long as its value in the tolerance range, we can be identified as its tolerance is in line with the grade requirements.


Due to the use of different sensors, their various parameters are different, so the temperature compensation algorithm will be different, because the use of temperature compensation, linear correction, stress aging and other techniques, high accuracy pressure meter, its comprehensive repeatability and linear indicators are better, the range of fluctuations is also smaller. It doesn't make sense to simply say which one is more finely compensated.


Cold end temperature compensation, which belongs to the temperature category, is related to the thermocouple, and it is not the same concept as the temperature compensation of the pressure sensor.


We first need to know how the thermocouple works and how the standard values in the dividing meter are obtained.


How the thermocouple works: two conductors of different materials form a closed loop. When there is a temperature gradient at both ends, a current will flow through the loop. We calculate the corresponding temperature by measuring this electromotive force.


Temperature measurement: since there is a temperature gradient, there must be a high temperature end and a low temperature end, the high temperature we generally called the hot end, also known as the working end, the low temperature we generally called the cold end, also known as the free end. The standard value on the dividing table is the cold end at zero as the standard, however, when measuring the instrument is usually at room temperature, because the cold end is not zero, resulting in the reduction of thermoelectric potential difference, so that the measurement is not accurate, there are errors. If the temperature of the cold end (environment) changes during the measurement, the accuracy of the measurement will be seriously affected. In the cold end to take certain measures to compensate so as to eliminate this effect is called the thermocouple of the cold end compensation. The cold end compensation resistance of PT100 can measure the ambient temperature in real time. So as to eliminate the influence of ambient temperature on the measurement results.


Cold end compensation wire: in practice, there is a certain resistance in the ordinary wire, which is equivalent to adding a resistance to the closed circuit, which has a great impact on the measurement results. In order to eliminate this effect, we need to use cold end compensation wire. As the cold end of precious metal materials are relatively expensive, the work is generally selected and the material properties are very close to the relatively cheap material to replace, so it is equivalent to the cold end directly connected with the measuring circuit of the instrument, thus eliminating the impact of ordinary wire resistance.


For thermocouple temperature measurement or analog output, we recommend the use of a matching compensation wire, and according to the characteristics of the thermocouple or secondary meter under test (whether with built-in temperature compensation) to choose whether to enable the built-in temperature compensation function.



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