How to Read a Digital Voltmeter
A digital voltmeter is an instrument used to measure the voltage of electrical devices and circuits. They come with two openings for probes, where the black one is negative and the red one is positive. Their digital display shows the amount of the voltage being read. They can measure either AC or DC, with ranges such as micro or milli to thousands of volts. These ranges are selected by use of a knob or switch. Common sizes are tabletop or handheld. Multimeters on the proper setting can operate as voltmeters. This is useful for testing electrical components.
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Things You'll Need
- Digital multimeter or voltmeter
- Probes
- Dry cell battery, such as AA or C
- LED
- Alligator clips (Optional)
Instructions
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1
Turn the multimeter or voltmeter on. Make sure that it is on a DC voltage setting, which may be indicated by a short line placed above three smaller lines that are side by side.
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2
Place the instrument on a setting of at least 1.5 volts. On a multimeter, the side of the dial used to do voltage measurements is usually indicated by a V.
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3
Hold the red probe of the multimeter or voltmeter against the positive terminal or side of the battery and the black probe on the negative terminal. These terminals are labeled with plus or minus signs. You may need to use alligator clips to keep the probes from slipping.
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4
Find the voltage by looking at the display. New batteries will have a value near 1.5 volts, but batteries that have been used may be much lower.
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5
Repeat Steps 3 and 4, but with the red probe against the negative side of the battery and the black probe on the positive side. Notice that the value is now negative; for example, it may be --1.5 volts. This means that the polarity is reversed, so that the meter is reading the voltage in the wrong direction.
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6
Place a probe on each of the leads of an LED. Record the voltage. If the polarity is negative, reverse the probes. For LEDs, the negative lead may be indicated by the shorter leg.
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7
Hold the LED near a light source by placing it in sunlight or near a lamp. Repeat Step 6. The voltage will be slightly higher, because all diodes are sensitive to light, though LEDs are built to exploit this property.
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8
Turn the multimeter or voltmeter off.
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Tips & Warnings
The reaction of an ordinary diode to light may also be tested, though some may require a millivolt setting.
If you get a reading indicating overload or zero while performing a measurement, try adjusting the voltage up or down until you see a number.
Handheld multimeters and voltmeters run on batteries. Always make sure to turn them off when not in use.
