The temperature of the cold end of the thermocouple is also called the cold end reference temperature, cold end temperature, and reference temperature. As a thermocouple itself, it is an element that responds to temperature differences. The millivolt value it generates is only related to the temperature difference between the hot and cold ends. If one end is
℃
and
the other end is
℃, then the millivolt value generated by the thermocouple itself only corresponds to
℃. When used for temperature measurement, for example, when measuring an object with
℃ and the environment is
℃, then the millivolt value corresponding to
℃ is obtained
,
Just add the ambient
℃ to get the temperature of the object being measured. This
℃ (ambient temperature) is the cold end reference temperature. Most temperature measuring instruments can automatically detect the cold junction temperature and automatically add it, which is called automatic cold junction compensation. But it becomes redundant when calibrating the meter, so the automatic cold junction compensation must be turned off or manually corrected when calibrating the meter.
The thermoelectric potential of a thermocouple is related to the hot electrode material and the temperature of the two contacts. The thermocouple index meter and the thermometer based on the index meter scale are all based on the condition that the temperature of the thermocouple reference end is equal to
>℃. Therefore, we must follow this condition when using it. If the reference terminal temperature
> does not vary
>℃, although the measured temperature
>is constant, the thermoelectric potential
>(
>,
>) will also change as the reference terminal temperature
> changes.
For example, we insert a nickel-chromium
>nickel-silicon thermocouple into a tubular electric furnace at
>℃. When the temperature of the reference end of the thermocouple is
>℃, its output The thermoelectric potential is
> millivolts. If the temperature at the reference terminal is
>℃, the thermoelectric potential output by the thermocouple drops to
> millivolts. This means that the temperature at the reference terminal is not equal to
>Measurement error introduced at ℃. If the reference junction temperature changes, the measurement error introduced will be variable. It can be seen that when the reference terminal temperature is not equal to
>℃, it has a very important impact on the accuracy of the measured temperature.
When using a thermocouple to measure temperature, it is troublesome to keep the reference end temperature at
>°C. This is generally only necessary when making precise measurements in the laboratory. In common engineering measurements, the reference end temperature is mostly at room temperature or in a fluctuating temperature zone. At this time, to measure the actual temperature, correction or compensation measures must be taken.
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