How to Use a Digital

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Mar 27, 2012 | 09:09 AM

workaholic

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How to Use a Digital

Voltmeter (DVM)

One of the most important tools for charging and starting systems diagnostics is the digital voltmeter (DVM). Some people refer to them as digital multi-meters or DMM’s since most of them are capable of testing ohms and continuity.
For our purposes we are mostly interested in DC voltage. This is symbolized on most meters as “DCV” or a straight line. You will notice all digital voltmeters have three holes for the wires to plug in. The black wire or “common” goes in the middle. The red wire plugs into the + sign which would be labeled DC Voltage.

Turn the power switch to
“on” and we’re ready to go. Some test leads (or the red and black
wires) have optional alligator clips that screw on. We suggest using the
alligator on the black or negative terminal (-) and leaving the red or positive
(+) terminal as a pin.

The more expensive meters are self scaling, which means they will automatically adjust the read out display to the setting it needs to be. Some digital volt meters require the proper scale you need, to be set manually. For example: a Radio Shack 22-183A digital volt meter has a selector switch 300mV which is for measuring extremely small voltages. The “mV” means millavolt scale.

The next scale is a 3, then 30, 300, and 3000. Since automotive voltages are under 15VDC we could read them on any scale above 3, but we can read most accurately on the 30. Now, lets measure the voltage in a car battery. Turn the selector to DC volts, then select the proper scale.

The digital volt meter should have the black wire in common, and the red wire in DC Volts. Place the black test wire on the negative terminal of the battery, place the red test wire on the positive terminal of the battery. The display should be showing you the condition of the battery being tested