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When choosing the best digital voltmeter, you may want to consider the price, accuracy, precision, ruggedness, input impedance, and where you want to use it. If you want a digital voltmeter for simple troubleshooting, the one you need is very different from a calibration laboratory-type voltmeter. Digital voltmeters that can be bought from hardware and online stores have various features.
Low-priced digital voltmeters may be good enough for most of your needs because of the improved digital technology and quality of test equipment. Higher-priced digital voltmeters usually have special features that are needed for a specific use. Some digital voltmeters have special functions, such as measuring temperature or current by using a specially customized digital accessory probe.
Accuracy may not be a big concern if the digital voltmeter is used as a troubleshooting tool, and a slightly high percentage of error is fine when checking the presence or absence of power line voltage. For calibration laboratories, however, very accurate digital voltmeters are needed as a voltage reference. Precision usually goes together with accuracy. A very precise digital voltmeter may not be accurate, but an accurate voltmeter may need to be quite precise. If the real voltage reading is 12.05 volts direct current (VDC), then a reading of 12.0 VDC is less precise than 11.900 VDC, but 12.0 VDC is more accurate with an error of only 0.05 VDC.
Various digital voltmeters are packaged in protective casings to survive falls or shock. Laboratory voltmeters are usually designed to rest on top of a bench. The importance of ruggedness is a matter of where the voltmeter will be used.
Input impedance suggests the amount of electrical loading that a digital voltmeter will cause on a circuit under test. When measuring the voltage of a 12 VDC source with a 100-kilo-ohm (k-ohm) internal resistance, for instance, the open circuit voltage is actually 12 VDC. If a digital voltmeter has an internal resistance of 1,000 k-ohm, the actual reading on the digital voltmeter becomes 10.909 VDC.
A very good digital voltmeter drains very little power and has both a sophisticated power control circuitry and long battery life. Ideally, the test probes are easy to source and buy. The test probe usually has a connector, such as a partially insulated banana plug, on the voltmeter side. There are also digital voltmeters with alligator clip attachments to the test probe tip that can be used in many environments.
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