Digital Multimeters

All digital multimeters combine the features of an ammeter, a voltmeter, and an ohmmeter. Figure 1 shows a typical DMM, although different makes and models may have a different number of digits in the display unit and the input/output jacks may be in slightly different positions. Since a DMM is an important tool, you will want to learn how to use one correctly.

Figure 2 – Typical Digital Multimeter

Multimeter with the digital display, function dial, input jacks and probe leads labelled

The upper portion of the DMM houses the display unit. The middle portion of the DMM houses the function switch, and the bottom portion contains the jacks for test leads.

The function switch normally has positions that will allow a technician to measure:

  • AC/DC Volts (V)
  • AC/DC Amps (A)
  • Resistance Ohms (Ω)

In addition, some DMMs have function switch positions that will allow a technician to measure and to test diodes and capacitors. Some DMMs require manual setting of ranges; others have an auto ranging feature.

All DMMs may be used to measure voltage, current, and resistance. More advanced DMMs may measure frequency, relative power differences, or other important circuit parameters. Each measurement function has similarities and differences that you need to learn about.

Many meters will use symbols on the display, switch, and connections. Figure 2 lists some of the common symbols you may see.

Figure 2 – Common Symbols

 wave shaped symbol that means AC  AC
 Symbol of a line with 3 dots below meaning DC  DC
 Ω  Ohms
 A symbol of a horizontal line with a wave underneath meaning AC or DC  AC or DC
 Hz  Hertz
+  Positive
 µF  MicroFarad
 m  Milli
M  mega
Symbol of a battery with plus and minus signs meaning low battery Low battery
Symbol of a circle with a square in the middle meaning manual range or automatic touch hold Manual range or automatic touch hold
A symbol of multiple semi-circles meaning continuity beeper Continuity beeper
A symbol of a horizontal line intersecting a vertical line and triangle meaning diode Diode
A symbole of multiple horizontal lines with one vertical line on top meaning ground Ground
A horizontal line intersecting a rectangle meaning fuse Fuse
A symbol of two nested squares meaning double insulation Double insulation
A symbol of two vertical lines nested between two horizontal lines meaning capacitor Capacitor
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