How to measure dc voltage with a digital multimeter

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Steps for measuring dc voltage with a digital multimeter.
 

How to measure dc voltage with a digital multimeter

1. Turn dial to DC V Symbol. Some digital multimeters (DMMs) also include mV. If uncertain of which to choose, start with DC V Symbol, which handles higher voltage.

2. First insert the black probe into the COM jack.

3. Then insert the red probes into the V Ω jack. When finished, remove the probes in reverse order: red first, then black.

4. Connect the test probes to the circuit: black to the negative polarity test point (circuit ground), red to positive test point.

Note: Most modern DMMs automatically detect polarity. When measuring dc voltage, it is not critical for the red lead to contact a positive terminal or black to touch negative. Just recognize if the probes touch opposite terminals, a negative symbol will appear in the display. With an analog multimeter, red leads should always touch a positive terminal and black a negative terminal. Otherwise, damage to the meter will occur.

5. Read the measurement in the display.

Other useful functions when measuring dc voltage

6. Modern DMMs default to Autorange based on the function selected on the dial. To select a specific fixed measurement range, press the RANGE button multiple times until the desired range is selected. If the voltage measurement falls within the range of a lower mV setting, follow these steps:

  1. Disconnect the test probes.
  2. Change the dial setting to [mV dc symbol].
  3. Reconnect the test probes and read the measurement.

7. Press the HOLD button to capture a stable measurement. It can be viewed after the measurement is complete.

8. Press the MIN/MAX button to capture the lowest and highest measurement. The DMM beeps each time a new reading is recorded.

9. Press the relative (REL) or delta (Δ) button to set the DMM to a specific reference value. Measurements above and below the reference value are displayed.

Note: Avoid this common technician mistake: inserting test probes into incorrect input jacks. If measuring dc voltage, be certain to insert the red probe into the input jack marked V, not A. The display should show the dcV symbol. Placing test probes in A or mA inputs and then measuring voltage will create a short in the measurement circuit.

Voltage Measurement Analysis

Automotive 12 V battery charge table

As shown in the chart above, a fully charged auto battery rated for 12 volts may have an open-circuit voltage ranging from 11.9 V to 12.6 V (typically 2.2 V per cell).

AC and DC Voltage Measurements

Reference: Digital Multimeter Principles by Glen A. Mazur, American Technical Publishers.

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Digital Multimeter Fundamentals

An in-depth look at an indispensable tool

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