The digital multimeter (DMM) has evolved from the classic multimeter with pointer instrument and differs from this by the digital display. From the basic functions, a multimeter is a measuring device with which you can measure various electrical quantities. Usually DC and AC voltage, DC and AC current and resistance.
A battery operated digital multimeter is a digital display meter for measuring electrical quantities: DC voltage, AC voltage, DC current, AC current and resistance. Some can also measure temperature, capacitance, and inductance. According to the procedure, a digital multimeter converts the analog input values to be measured into digital measured values in an A/D converter and displays them on a multi- digit LCD display. Depending on the measuring function, the measuring ranges are adapted to the measured value by resistors connected in series or in parallel.
Essential characteristic values of digital multimeters concern the measuring ranges, measuring accuracy and linearity, which depends on the used A/D converter principle, whereby mostly the slope method or the dual slope method is used. Standard digital multimeters have a 3- or 4-digit display and a measuring accuracy of less than 1 %, top devices achieve accuracies of 0.01 %.
In addition to measurement accuracy and resolution, other distinguishing features include special functions for measuring RMS values or voltage ratios, automatic range switching, measured value storage and output via various interfaces, for diode and transistor tests, for AC voltage measurements in larger frequency ranges, or special functions for measurements on cables.
Multimeters and digital multimeters are protected by protective circuits such as reverse polarity protection, against overvoltages and overloads, even when high voltages are accidentally applied to the most sensitive measuring ranges.