How to Use a Multimeter

A multimeter is divided into analog and digital types.

Analog multimeters use a magnetic electromechanical measuring mechanism at their core, displaying measured values with a pointer;

Digital multimeters use a digital voltmeter as their core, equipped with different converters, displaying measured values on a liquid crystal display.

The basic principle of a multimeter is to use a sensitive magnetic electromechanical DC ammeter (microamp meter) as the meter head. When a small current passes through the meter head, it will indicate current. However, the meter head cannot handle large currents, so some resistors must be connected in parallel and series with the meter head to shunt or reduce voltage, allowing for the measurement of current, voltage, and resistance in the circuit.

Using a multimeter (taking the MF35 model as an example). The measurement item and range can be changed by turning the selector switch. The mechanical zero adjustment knob is used to keep the pointer at rest at the left zero position. The “Ω” zero adjustment knob is used to align the pointer to the right zero position when measuring resistance to ensure measurement accuracy.

The measurement ranges of the multimeter are as follows:

(1) DC Voltage: 6 ranges—0-6V; 0-30V; 0-150V; 0-300V; 0-600V; 0-30KV (2) AC Voltage: 6 ranges—0-6V; 0-30V; 0-150V; 0-300V; 0-600V; 0-30KV

(3) DC Current: 6 ranges—0-2.5mA; 0-25mA; 0-250mA; 0-1A; 0-5A; 0-30A

(4) AC Current: 6 ranges—0-2.5mA; 0-25mA; 0-250mA; 0-1A; 0-5A; 0-30A

(5) Resistance: 5 ranges—R*1; R*10; R*100; R*1K; R*10K

Measuring resistance: –First, short-circuit the test leads together to deflect the pointer to the right, then adjust the “Ω” zero adjustment knob to make the pointer point exactly to 0. Then, touch the two test leads to both ends of the resistor (or circuit) to read the pointer’s position on the ohm scale (the first line), and multiply by the marked number of that range to get the resistance value. For example, when measuring resistance in the R*100 range, if the pointer reads 80, the measured resistance value is 80*100=8K. Since the left part of the “Ω” scale has dense readings, it is difficult to read accurately, so choose an appropriate ohm range to keep the pointer in the middle or right part of the scale for clearer and more accurate readings. Each time you change the range, you should short-circuit the two test leads again and readjust the pointer to zero to ensure accurate measurements.

Measuring DC Voltage: –First, estimate the size of the voltage to be measured, then turn the selector switch to the appropriate V range, connect the positive lead to the “+” terminal of the measured voltage, and the negative lead to the “-” terminal. Then, based on the range number and the standard DC symbol “DC-” on the second-line scale, read the size of the measured voltage. For example, if measuring in the V300 range, you can directly read the indicated value of 0-300. If measuring in the V30 range, simply remove one “0” from the number on the scale to read 30, and similarly read 200, 100 as 20, 10. For instance, if measuring DC voltage in the V6 range, if the pointer reads 15, the measured voltage is 1.5 volts.

Measuring DC Current: –First, estimate the size of the current to be measured, then turn the selector switch to the appropriate mA range, and connect the multimeter in series with the circuit as shown. Observe the scale marked with the DC symbol “DC”, and if the current range is set to 3mA, you should remove two “0”s from the number 300 on the scale, reading it as 3, and similarly read 200, 100 as 2, 1, allowing you to read the measured current value. For instance, if measuring DC current in the 3mA range, if the pointer is at 100, then the current is 1mA.

Measuring AC Voltage: –The method for measuring AC voltage is similar to that for measuring DC voltage, except that since AC voltage has no positive or negative distinction, the test leads do not need to be differentiated. The reading method is the same as that for measuring DC voltage, but the numbers should be read on the scale marked with the AC symbol “AC”.

A multimeter is a relatively precise instrument, and improper use can lead to inaccurate measurements and can easily cause damage. However, as long as we master the usage methods and precautions of the multimeter and proceed with caution, the multimeter can last a long time. When using a multimeter, attention should be paid to the following:

1. Do not rotate the switch to the wrong position when measuring current and voltage. If you mistakenly set it to resistance or current range while measuring voltage, it can easily damage the meter. When not in use, it’s best to set the range to the highest AC voltage to avoid damage from improper use.

2. When measuring DC voltage and current, pay attention to the “+” and “-” polarity and do not connect them incorrectly. If the pointer reverses, immediately switch the leads to avoid damaging the pointer and meter head.

3. If you do not know the size of the voltage or current being measured, start with the highest range, then select the appropriate range for testing to avoid excessive deflection of the pointer, which could damage the meter head. The closer the selected range is to the measured value, the more accurate the measurement will be.

4. When measuring resistance, do not touch the bare ends of the components (or the metal parts of the test leads) with your hands, as the resistance of the human body in parallel with the measured resistance can lead to inaccurate results.

5. When measuring resistance, if you short-circuit the two test leads and adjust the “zero ohm” knob to the maximum, and the pointer still does not reach the 0 point, this phenomenon is usually due to insufficient battery voltage inside the meter, and a new battery should be replaced for accurate measurements.

6. When not in use, do not leave the multimeter set to the resistance range, as there is a battery inside, and if the two leads accidentally touch, it can short-circuit, wasting the battery and potentially damaging the meter head.

Note:

There are many models of multimeters: MF47 series (A, B, C, D, E, F, T), MF500, MF5-1, MF50, MF18, MF10, MF14, MF35, MF79,

The MF35 model has the best accuracy, followed by the MF14, and the MF47 is the least accurate.