The basic analog multimeter is commonly referred to as a VOM (volt-ohmmilliammeter). The VOM shown measures ac and dc volts from 250 mV full scale to 1000 V, dc from 50 μA full scale to 10 A, ohms up to 20 M, and decibels (dB) with a total of 29 ranges. The accuracy on dc is 62 percent of full scale and 63 percent of full scale on ac. The lower-priced and most popular type of VOM has input sensitivities of 20,000 /V on dc and 5000 /V on ac. Note that the ac circuits are rectifier-type (average sensing). Maximum frequency coverage is about 100 kHz. VOMs of this type are also available with mirror scales providing dc accuracies of 61 percent of full scale and ac accuracy at 62 percent of full scale.
For those applications requiring higher input impedance, such as 10 M, an field-effect transistor (FET) VOM is available. In addition to the high input impedance, the FET VOM offers other advantages significant for troubleshooting electronic circuits. It typically has a 100-mV full-scale ac and dc range, a 1-μA dc fullscale current range, and “low-power” ohms selection.
