Basic Principles and Usage Methods of Multimeters
The basic principle of a multimeter is to use a sensitive magneto electric DC ammeter (microampere meter) as the meter head. When a small current passes through the meter, there will be a current indication. But the meter head cannot pass high currents, so it is necessary to shunt or reduce the voltage by connecting some resistors in parallel or series on the meter head, in order to measure the current, voltage, and resistance in the circuit. Below are separate introductions.
The dial of the multimeter (taking MF50 model as an example) is shown in the above figure. Change the measurement item and measurement range by turning the knob of the switch. The mechanical zero adjustment knob is used to keep the pointer in the left zero position at rest. The "Ω" zero knob is used to align the pointer with the right zero position when measuring resistance to ensure accurate measurement values.
Measure resistance: First, short-circuit the meter bars together to deflect the pointer to the right, then adjust the "Ω" zero knob to make the pointer point exactly to 0. Then, touch the two meter bars separately at both ends of the measured resistor (or circuit), read the reading of the pointer on the Ohm scale line (the first line), and multiply it by the number on that scale to obtain the resistance value of the measured resistor. For example, when measuring resistance in R * 100 range and the pointer points to 80, the measured resistance value is 80 * 100=8K. Due to the dense readings on the left side of the "Ω" scale line, it is difficult to see accurately, so the appropriate ohm range should be selected for measurement. Place the pointer in the middle or right of the scale line so that the reading is clear and accurate. Every time you shift gears, you should short-circuit the two gauge rods again and readjust the pointer to zero position in order to measure accurately.
Measure DC voltage: First estimate the magnitude of the measured voltage, then turn the conversion switch to the appropriate V range, connect the positive meter rod to the "+" end of the measured voltage, and connect the negative meter rod to the "-" end of the measured voltage. Then, based on the range number of the gear and the pointer on the DC symbol "DC -" scale line, read out the magnitude of the measured voltage. If measured in the V250 voltage range, the indicated values from 0 to 250 can be directly read.
Measure DC current: First estimate the magnitude of the measured current, then turn the conversion switch to the appropriate mA range, and connect the multimeter in series in the circuit. Simultaneously observe the scale line marked with the DC symbol "DC" and read out the measured current value.
Measuring AC voltage: The method of measuring AC voltage is similar to measuring DC voltage, but the difference is that AC voltage does not have a positive or negative distinction, so when measuring AC, the meter rod does not need to be divided into positive and negative. The reading should be based on the pointer position on the scale line marked with the AC symbol.
