Solution: The digital multimeter (DMM):

• It is a versatile instrument found on virtually all workbenches. All DMMs can make basic ac and dc voltage, current, and resistance measurements.

• Voltage and resistance measurements are the principal quantities measured with DMMs. For current measurements, the leads are switched to a separate set of jacks and placed in series with the current path.

• In this mode, the meter acts like a short circuit, so serious problems can occur if the meter is incorrectly placed in parallel.

• In addition to the basic measurements, most DMMs can also test diodes and capacitors and frequently will have other capabilities such as frequency measurements.

• Most new DMMs have an auto-ranging feature, meaning that the user is not required to select a range for making a measurement.

• If the range is not set automatically, the user needs to set the range switch for voltage measurements higher than the expected reading to avoid damage to the meter.

• In digital circuits, DMMs are the preferred instrument for setting dc power supply voltages or checking the supply voltage on various points in the circuit.

• Because digital signals are non-sinusoidal, the DMM is generally not used for measurements of digital signals (although the average or rms value can be determined in some cases).

• For signal measurements, the oscilloscope is the preferred instrument.

• In addition, DMMs are used in digital circuits for testing continuity between points in a circuit and checking resistors with the ohmmeter function.

Typical test bench and handheld DMMs are shown in Figure.:

• For checking a circuit path or looking for a short, DMMs are the instrument of choice.

• Many DMMs sound a beep or tone when there is continuity between the leads, making it handy to trace paths without having to look at the display.

• If the DMM is not equipped with a continuity test, the ohmmeter function can be used instead.

• Measurements of continuity or resistance are never done in “live” circuits, as any circuit voltage will disrupt the readings and can be dangerous.