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# How to Measure Voltage in a Circuit

The last video demonstrated the basics of how to use manual and auto-ranging multimeters. The video below will demonstrate how to test voltage, current, and resistance in a circuit. For the purpose of covering one topic at a time, I will cover measuring voltage in this blog, with separate blogs for current and resistance to follow.

Figure 1

Alright, this topic seems pretty straightforward. Place the probes in the circuit, and you have your measurement. Right? Not really. First, you need to know what exactly you are wanting to measure. The total circuit voltage? An individual component voltage drop? The voltage readout on the multimeter will depend upon where you place the probes.

First, grab the multimeter and plug the black probe into the “COM” port. Plug the red probe into the “V” port. Note that the “V” or voltage port will likely be used for other measurements as well, and may not just say “V” above it. If you are measuring DC voltage, turn the dial to VDC or the V with one continuous line above it and one dotted line (see figure 1). If you are measuring AC voltage, turn the dial to VAC or the V with a sin wave over it (see figure 1). If the meter is manual ranging, the options will look more like the photo below, and you’ll have to select the range you want to measure. Always start higher and work your way down through the ranges as needed.

*Note: Each meter will look different and have their own max values, this image is just an example and not a direct representation of every meter.

Once the probes are plugged in and the dial is turned to the proper setting, place the probes on either side of the supply voltage. If a negative reading is given, just switch the probes around so the ‘COM’ (black) probe is on the negative lead. To measure the voltage of an individual component, place the probes on each side of the component, making sure the ‘COM’ or black probe is on the negative lead and red probe is on the positive lead.

Voltage measurements provide critical information when it comes to troubleshooting. Not only can it tell you if the circuit is being provided too much or too little voltage, but then you can identify which individual component is the cause based on the voltage drop. Components such as wires, circuit board traces, and fuses with a larger than expected voltage drop across them can indicate a problem. Ready to start measuring? View our wide selection of multimeters at: digikey.com/multimeters.