DMMs

Digital multimeters (DMMs) are portable instruments used to measure electrical quantities. They combine the functions of a voltmeter, ammeter, and ohmmeter in a single device, often with additional testing capabilities for more advanced measurements.

DMMs can measure DC and AC voltage, DC and AC current, resistance, and continuity or diode status. Many models also measure capacitance, frequency, temperature, and sometimes transistor characteristics or insulation resistance. Measurements are displayed on a digital readout, and many units offer auto-ranging to automatically select the appropriate scale, while others require manual range selection.

A DMM typically consists of a display, input jacks for test leads, a protective case, and internal circuitry controlled by a microprocessor. Input jacks usually include a common ground and separate ports for current measurement; some designs use a separate clamp-on sensor for current. Features on modern DMMs can include data logging, USB or Bluetooth connectivity, and companion software. Voltage measurements generally present high input impedance to minimize circuit loading, while current measurements rely on shunt resistors or, in the case of clamp meters, a magnetic core sensor.

DMMs are widely used in electronics repair, electrical installation, automotive diagnostics, and educational settings. They range from compact handheld models for field work to benchtop units for laboratory use. Safety considerations include selecting models with appropriate CAT safety ratings, using proper insulated probes, and observing fuse protection and electrical isolation standards.

Historically, digital multimeters became prevalent in the 1970s, replacing analog meters with digital displays and advancing features such as auto-ranging and data storage.