Digital Multimeter

A digital multimeter (DMM) is a device that can measure voltage, current, and resistance. Unlike an oscilloscope, which can measure and display a varying voltage vs. time, a multimeter can only display one value at a time. Therefore, multimeters can only be used to measure constant values. The following quantities can be measured.

• DC Voltage
• AC Voltage (RMS)
• DC Current
• AC Current (RMS)
• Resistance
• Capacitance

In addition, a multimeter can be used for continuity and diode testing.

The front panel of a multimeter is shown. The screen displays the value of the measurement, and options associated with the measurement can be adjusted with the buttons below the screen. The buttons to the right of the screen are used to adjust the measurement type. The functions in blue above these buttons can be accessed by clicking the [Shift] button. On the right side of the DMM is where you connect probes.

There are two types of probes at the IDC that can be used to take measurements. Test probes (left) need to be held on the circuit being measured, so they are best for quick measurements. Banana plugs (right) can be connected to alligator clips, which can be secured to a wire in a circuit. Both types of probes are connected to the multimeter in the same way.

The probes must be connected to the correct inputs on the multimeter. For voltage, resistance, and capacitance, connect the probes as shown below. The other ends of the probes should be connected in parallel (across a component). For resistance and capacitance measurements, it is important to remove the resistor or capacitor from the circuit. If left in a circuit, voltages and parallel resistances/capacitances can significantly affect the measurement.

For current, the probes must be connected differently, as shown below. The 3A next to the lower input signifies that the multimeter can handle up to 3A of current. If you are trying to measure a current above or close to 3A, another device must be used to obtain an accurate measurement and avoid damaging the multimeter. Current measurements must be taken in series, meaning the path of current must flow through the multimeter. You need to break open a part of the circuit and insert the multimeter in the path.

Once the probes are properly connected, you need to select a measurement type by clicking one of the buttons shown below. DCV means DC volts, ACV means AC volts (this is an RMS voltage), and Ω2W signifies resistance. You can select capacitance by clicking [Shift] [Freq], which corresponds to the capacitor symbol above the [Freq] button. For current measurements, first confirm that the probes are connected to the current inputs and that the probes are connect to your circuit in series. Then, click [Shift] [DCV] for DC Current and [Shift] [ACV] for AC Current. If the multimeter is set to auto trigger and auto range, the measured value will be displayed on the screen.