How to use the low voltage range of a pointer multimeter to connect an external resistor to detect high voltage?

The pointer multimeter used by electricians can usually only detect AC and DC voltages below 500V. When you need to detect high voltage, you can use the following method to connect an external resistor for detection. The pointer multimeter used by electricians can usually only detect AC and DC voltages below 500V. When you need to detect high voltage, you can use the following method to connect an external resistor for detection.

(1) Detection connection circuit. The connection circuit when using the low voltage range of the pointer multimeter to detect high voltage is shown in Figure 5-2. R in the figure is the internal resistance of the pointer multimeter, and R is the external voltage-dropping resistor.

(2) Determination of the voltage-dropping resistor value. In the detection circuit of Figure 5-2, the resistance value of the series voltage-dropping resistor R can be calculated using the following formula:

    R = [(UM1/UM2) -I]Rv

    Or R-(UM2-UM1)UL, where UM1 is the original voltage range of the pointer multimeter;

    UM. - The range of the voltage range of the pointer multimeter after expansion;

    Rv-internal resistance of pointer multimeter;

    U． ——Voltage sensitivity of pointer type multimeter.

(3) Determination of the power of the voltage-dropping resistor. In the detection circuit of Figure 5-2, the power value of the series voltage-dropping resistor R can be calculated using the following formula:

    p=12R, where P is the power value of the series-connected voltage-dropping resistor R;

    The current flowing through the series resistor R when the pointer multimeter is extended to full scale.

(4) Calculation examples.

    [Example 5-1] The sensitivity of a pointer multimeter in the 500V DC voltage range is 10kl/V. The calculation method when it is expanded to 2500V is as follows.

    1) The resistance value of the series voltage-dropping resistor R is

    R-(UM2-UM1)UI.

    一(2500V-500V)×10kQ／V=20 000kQ—20Mfl