How to use a digital multimeter to measure AC and DC high voltage?

The maximum range of a digital multimeter for measuring AC and DC voltage is generally around 700V and 1000V, which cannot meet the requirements in some occasions. In this case, a voltage divider resistor can be connected in series to the input end of the red test lead to expand the range, thereby measuring high voltage.

(1) Detection method. If the magnification is n, and the internal resistance of the digital multimeter is Ro (usually 10MΩ), then the series voltage divider resistor is

Rf=(n-1RO

At this time, because the voltage applied across the meter is only 1/n of the voltage being measured, the reading displayed on the meter must be multiplied several times to be equal to the voltage being measured.

For example, for a digital multimeter with a maximum range of DC1000V and an internal resistance of 10MΩ, to expand the range by 10 times, a 90Mfl (≥1W) voltage divider resistor needs to be connected in series. If the meter reads 335V, the measured voltage is 3350V.

(2) Issues that must be noted: When using a digital multimeter to measure AC or DC high voltage, special attention must be paid to personal safety because the voltage being tested is relatively high.