Introduction to Multimeter Calibration Methods
Basic principle: When the detected potential forms a closed circuit with a known potential of equal magnitude and opposite direction, no current flows in the circuit due to potential balance. At this time, the measured potential can be determined based on the known potential.
Method:
1. By passing a standard current through a precision resistor box, you can obtain many accurate voltage values corresponding to it.
2. Connect a precision resistor and a potentiometer for current regulation in series to the circuit composed of a resistance box and a power supply. The precision resistor → resistance box → potentiometer → power supply → returns to the precision resistor, ,
3. Now measure the potential on the precision resistor without affecting the current. The method is to align the standard potential to the top (your 200mv), adjust the potentiometer (the voltage drop on the precision resistor will change accordingly), until there is no current generated in the circuit composed of the standard battery and precision resistor (measured with a ammeter). At this point, the potential (voltage drop) on the precision resistor is equal to the standard potential, and the standard current value is obtained. Assuming your precision resistor is 2 ohms, the output is a standard current of 100 milliamps.
At this point, if your standard resistance box is 1 ohm, the voltage drop across the two ends of the resistance box is 1X100=100 millivolts. Similarly, if the resistance box is 100 ohms, the voltage drop is 10 volts. You can now directly determine the voltage drop on the resistor box from its reading.
4. One end of the multimeter to be calibrated is connected to the resistance box and potentiometer, and the other end is connected to the resistance box connected to the precision resistor through the same ammeter. The multimeter → resistance box → ammeter → return to the multimeter to form the third circuit.
Pay attention to adjusting the potentiometer at any time to make the ammeter point to zero. At this point, the standard current will not change due to your multimeter being connected to the measurement circuit, so the measured value is accurate. If the potentiometer is not adjusted, once the multimeter is connected, it will cause a shunt, and the standard current will change, resulting in inaccurate measurement values
