Principles of Multimeter Calibration
Basic principle: When the potential to be detected forms a closed loop with a known potential of equal magnitude and opposite direction, no current flows in the circuit due to potential balance, and the potential to be measured can be known based on the known potential.
practice:
1. The standard current flows through a precision resistance box, and you can get many accurate voltage values corresponding to the precision resistance box.
2. Connect a precision resistor and a potentiometer for current adjustment in series to the circuit formed by the resistance box and the power supply, precision resistor→resistance box→potentiometer→power supply→back to precision resistor,
3. Now measure the potential across the precision resistor without affecting the current. The method is to connect 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 in the second loop composed of the standard battery and the precision resistor (use the tester Current measurement), at this time, the potential (voltage drop) on the precision resistor is equal to the standard potential, so the standard current value is obtained. Assuming your precision resistor is 2 ohms, the standard current is 100 mA. At this time, if your standard resistance box is 1 ohm, then the voltage drop across the resistance box is 1X100=100 millivolts. Similarly, if the resistance box is 100 ohms, the voltage drop is 10 volts. You can now tell the voltage drop across the resistor box directly from the reading.
4. One end of the multimeter to be calibrated is connected to the end connected to the resistance box and the potentiometer, and the other end is connected to the other end of the resistance box connected to the precision resistor through the same galvanometer. Multimeter → resistance box → galvanometer → return to the multimeter to form the third loop.
Pay attention to adjust the potentiometer at any time to let the galvanometer point to zero. At this time, the standard current will not change because your multimeter is connected to the measurement circuit, so the measured value is accurate. (If the potentiometer is not adjusted, a shunt will be caused as soon as the multimeter is connected, the standard current will change, and the measured value will be inaccurate)
