Tool shops often carry low-cost voltmeters that do a good-enough job for most applications. If you need accuracy and a robust meter, you are going to have to pay for a higher-quality device.
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A digital voltmeter, or DVM, is used to take highly accurate voltage measurements. These instruments measure the electrical potential difference between two conductors in a circuit. They are electric voltmeters and the preferred standard, as they offer several benefits over their analog counterparts.
Voltmeters are used to measure the gain or loss of voltage between two points in a circuit. The leads are connected in parallel on each side of the circuit being tested. The positive terminal of the meter should be connected closest to the power supply, and the negative terminal should be connected after the circuit being tested. The analog dial or digital display will exhibit the voltage measurement.
A digital voltmeter typically consists of an analog to digital converter (A/D) with a digital display. The analog signal is converted into a digital code proportionate to the magnitude of the signal. Voltages from picovolts to megavolts are measurable, though the scale usually graduates in millivolts, volts, or kilovolts. Frequencies between zero and several megahertz may also be measured.
These tools measure both alternating current (AC) and direct current (DC) in electronics. Common laboratory and commercial applications involve electromechanical machinery with a current flowing through wires and circuits. Often, a voltmeter is used to monitor a unit, such as a generator. Portable or handheld devices, such as the digital multimeter (DMM), for example, may combine several functions into one instrument measuring voltage, current, and resistance. This is the preferred tool of an electrician.
Many DVMs integrate outputs for monitoring, controlling, transmitting, and printing of data. Advanced systems are often connected to computers, allowing for automation, optimization of processes, and prevention of malfunctions and critical failure safeties. Chemical plants can convert measurements to voltage, and control and monitor temperature, pressure, level, or flow. Medical equipment, such as x-ray machines, may use this tool to make sure the voltage of the equipment is in the proper range.
Digital voltmeters have a number of advantages when compared to their analog counterparts. The most obvious benefit is the ease of use when reading the digital display. Electric amplifiers and attenuators extend measurable ranges. A digital model has superior resolution and a higher order of accuracy within plus or minus 0.5%. It also indicates a negative quantity when polarity is reversed. Analog meters are more fragile and susceptible to damage.