1、 Preparation before use

Confirm type and range

Check if the AC voltmeter is a dedicated AC meter (with a dial marked with the symbol "~" or "AC"), and avoid using a DC meter to measure AC voltage (which may damage the instrument).

According to the voltage range of the tested circuit, select a range greater than the estimated voltage (such as 250V or 300V range if the tested voltage is about 220V). If it is impossible to estimate, prioritize the maximum range and gradually lower it.

Check the status of the instrument

Observe whether the pointer returns to zero: When not powered on, if the pointer deviates from zero, use a screwdriver to adjust the "mechanical zero adjustment" knob below the dial for calibration.

Test the insulation of the probe: Check if the probe wire is damaged, if the plug is loose, and ensure that the insulation layer is intact.

2、 Measurement operation steps

Select gear

Turn the dial knob to the AC voltage (ACV) position and select the corresponding range based on the estimated voltage (such as "AC250V" and "AC500V").

Parallel connection circuit

The AC voltmeter should be connected in parallel with the tested circuit: the red probe should be connected to the live wire (or high potential end) of the circuit, and the black probe should be connected to the neutral wire (or low potential end).

Example: When measuring household 220V voltage, connect the red probe to the live wire hole of the socket and the black probe to the neutral wire hole. Do not connect the circuit in series (which may cause a short circuit).

Power on to read values

After connecting the circuit, observe the stable position of the pointer and read the value according to the range.

Reading example: If the range is 250V, the dial scale consists of 50 grids, each grid represents 5V, and the pointer points to 40 grids, then the voltage is 40 × 5=200V.

3、 Precautions

safe operation

Maintain one handed operation during measurement to avoid touching the metal part of the probe and prevent electric shock.

High voltage scenarios (such as industrial circuits) require wearing insulated gloves and using high-voltage specialized probes.

Range adjustment rules

If the pointer deflection angle is too small (such as less than 1/3 of the range), the power should be turned off and replaced with a smaller range to avoid excessive error.

It is strictly prohibited to switch the range while powered on to prevent instantaneous current damage to the instrument.

Reading and recording

When reading, the line of sight should be perpendicular to the dial to avoid reading errors caused by viewing angle deviation.

When recording values, indicate the unit (V) and verify if the range is correct (misreading 220V as 22V can cause serious deviations).

4、 Abnormal situation handling

Pointer reverse deviation: it indicates that the polarity of the stylus is reversed. After the power is cut off, replace the red and black stylus.

Pointer over range: Immediately power off, replace with a larger range and re measure to avoid instrument overload damage.

Pointer jitter: It may be due to unstable circuit voltage or poor contact of the probe. Check the circuit connection and retry.

By following the above steps, the measurement can be safely and accurately completed using an AC voltmeter. If it is a digital AC voltmeter, the operating logic is similar, but there is no need for mechanical zeroing. The reading is directly displayed as a number, and attention should be paid to selecting the "ACV" gear and confirming the range.