Measuring High Voltage Skillfully with Digital Multimeter
Usually the maximum range of the DC range of the digital multimeter is 700V, and the maximum range of the AC is 1000V, which cannot meet the requirements in some occasions. At this time, the method of connecting resistors in series can be used to expand the range, so as to achieve the purpose of measuring high voltage.
The method is: connect a voltage divider resistor in series with the six terminals of the red meter stick. If the multiple of the expanded range is n, and the internal resistance of the digital multimeter is R0 (generally 10MΩ), then the series-connected voltage divider resistor Rf=(n-1)R0. At this time, because the voltage applied to both ends of the meter is only 1/n of the measured voltage, the reading displayed on the meter must be multiplied by n times to be equal to the measured voltage. For example, for a digital multimeter with a maximum range of 1000V, its internal resistance is 10MΩ. To increase the capacity by 10 times, a voltage divider resistor of 90MΩ (≥1W) needs to be connected in series. If the reading of the meter is 400V, the measured voltage is 4000V.
It is worth mentioning that special attention should be paid to personal safety when measuring high voltage to prevent contact accidents.
