1. Transfer the dial to v. Some digital megohm meters (DMM) also include mv. If you are not sure which to choose, start with v for the higher voltage.

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

3. Then insert the red probe into the V socket. When done, remove the probes in reverse order: first red, then black.

4. Connect the test probe to the circuit: connect black to the negative test point (circuit grounding) and red to the positive test point.

Note: most modern DMMS automatically detect polarity. When measuring dc voltage, the red lead touching the positive terminal or the black touching the negative terminal is not critical. Once the probe is identified as touching the opposite terminal, a negative sign appears on the display. When using a simulated megometer, the red wire should always be in contact with the positive terminal and the black wire should always be in contact with the negative terminal. Otherwise the instrument will be damaged.

5. Read the measured value on the display screen.

Other useful functions for measuring dc voltage

6. Modern digital megohm meters default to automatic range according to the functions selected on the turntable. To select a specific fixed measurement RANGE, press the RANGE button several times until the desired RANGE is selected. If the voltage measurement falls within a lower mv setting, follow these steps:

Disconnect the test probe.

Change dial Settings to [mV dc symbol].

Reconnect the test probe and read the measured value.

7. Press the hold button to capture stable measurements. The measurement can be viewed after completion.

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

9. Press the relative (REL) or increment button to set DMM to a specific reference value. Displays measurements above and below the reference value.

Note: avoid the common technician error of inserting the test probe into the wrong input jack. If you want to measure dc voltage, be sure to insert the red probe into the input jack marked V instead of A. The display screen should display the dcV symbol. Placing the test probe in the A or mA input and then measuring the voltage will cause A short circuit in the measuring circuit.

Voltage measurement analysis

Voltage measurements are usually used: a) to determine the presence of a voltage at a given point; B) ensure that the voltage is at an appropriate level.

Ac voltages vary widely (between -10% and + 5% of the power rating) and do not cause any problems in the circuit. However, for dc voltages, even small changes can indicate a fault.

The exact amount of acceptable dc voltage variation depends on the application.

In some dc applications, large dc variations are not only acceptable but intentional.