Working principle of electronic potentiometer

　　The principle block diagram of the electronic potentiometer is shown in Figure 1. The DC potential input by the thermocouple is compared with the potential in the measuring bridge circuit. The difference voltage after comparison is amplified by the electronic amplifier and output. The value is large enough to drive the reversible motor, so that the reversible motor drives the sliding arm in contact with the sliding wire resistor to move, thereby changing the resistance value of the sliding wire resistor, so that the potential of the measuring bridge circuit is balanced with the thermoelectric potential generated by the thermocouple. When the measured temperature changes and the thermocouple generates a new thermoelectric potential, the bridge circuit has a new unbalanced voltage output, which is amplified by the amplifier and drives the reversible motor to rotate, changing the position of the sliding arm again until a new balance is reached. While the sliding arm moves, the pointer and recording pen connected to it move along the scale with temperature graduations and the recording paper. Each equilibrium position of the sliding arm corresponds to a certain coordinate value on the scale with temperature graduations and the recording paper, so the corresponding temperature can be automatically indicated and recorded. When the temperature reaches a given value, the temperature can also be automatically controlled by an additional adjustment mechanism.

　　Although the electronic potentiometer has different models and varieties, its measurement principle and basic structure are basically similar, as shown in Figure 1. It consists of a thermocouple, a measuring bridge, an amplifier, a reversible motor, an indicating and recording mechanism, an adjusting mechanism, a power supply and other parts.

　　(1) Measuring bridge The measuring bridge in the electronic potentiometer is used to generate a DC voltage to balance the thermoelectric potential generated by the thermocouple, so it plays a major role in the instrument. It consists of the bridge arm resistors and a regulated power supply, as shown in Figure 2.

　　(2) Amplifier The amplifier in the electronic potentiometer is actually equivalent to a zeroing instrument. Its function is to amplify the difference signal after comparing the thermoelectric potential generated by the thermocouple with the potential output by the measuring bridge circuit, and drive the actuator (reversible motor) to move according to a certain ratio, as shown in Figure 3.

　　Figure 1 Schematic diagram of electronic potentiometer

　　Figure 2 Measurement bridge

　　Figure 3 Amplifier electrical principle

　　(3) Reversible motor: It acts as an actuator in the electronic potentiometer, driving the sliding contacts to achieve automatic balancing of the measuring bridge and driving the pointer and recording pen to move.

　　(4) Indicating and recording mechanism The indicating and recording mechanism in the electronic potentiometer can automatically record the temperature measured by the instrument.

　　(5) Adjustment mechanism The adjustment mechanism in the electronic potentiometer can automatically adjust the temperature to a given value and implement automatic temperature control. The old electronic potentiometer also has a working current adjustment mechanism to standardize the bridge working current.