Digital voltmeters are instruments that measure voltage or voltage drop in a circuit. They use
solid-state components and display values digitally. Typically, digital voltmeters are used to
locate excessive resistance that may indicate an open circuit or ground. They are also used to
identify low voltage or voltage drops that may indicate a poor connection.
Digital voltmeters are connected in parallel with the circuit being tested so that the meter can tap
a small amount of current. The positive lead is connected to the circuits positive side and the
negative lead is connected to the circuits ground. The digital voltmeters internal resistance is the
input impedance, which is usually expressed in ohms per volt. This amount is relatively high in
order to prevent the device from drawing significant current and disturbing the operation of the
circuit being tested. The sensitivity of the current meter and the value of the series resistance
determine the range of voltages that digital voltmeters can measure.
Digital voltmeters are usually designed around a special type of analog-to-digital converter
called an integrating converter. Voltmeter accuracy is affected by many factors, including
temperature and supply voltage variations. They can measure a range of alternating current (AC)
voltages, direct current (DC) voltages, or both AC and DC voltages. Devices typically display
between three and seven digits. Some digital voltmeters can also capture minimum and
maximum voltages called spike readings.