When measuring thermocouple potential, why is the accuracy level of potential difference meter higher than that of moving coil instrument?
The greater the internal resistance of the measuring instrument, the closer the measured voltage to the voltage source, so the internal resistance of the measuring instrument in the industry must be greater than 1 to 10K Omega, and the error of the measurement can be accepted;
The thermoelectric potential of a thermocouple can be considered as a voltage source with a certain internal resistance;When measuring, the current produced by the voltage source forms partial pressure on the internal resistance of the power supply and the internal resistance of the measuring instrument, and the measuring instrument measures the voltage formed by the current on the internal resistance of the measuring instrument;
A potential difference meter generates a voltage equal to the potential being measured, and then reads the voltage to be measured according to the magnitude of the voltage generated. The principle of its work (measurement) determines that its internal resistance is theoretically infinite. Therefore, when the potential difference meter and the moving coil instrument are used to measure the thermal potential, the loop measurement accuracy of the potential difference meter is theoretically higher than that of the moving coil instrument.
