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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.