- Digital Multimeter Definition: A digital multimeter is defined as a device that measures electrical parameters like voltage, current, and resistance, displaying the results digitally.
- Main Parts: The main parts of a digital multimeter include the display, selection switch, ports, and probes, each crucial for accurate measurements.
- Measuring Current: To measure current, connect the multimeter in series with the circuit and set the switch to the appropriate current range.
- Measuring Voltage: To measure voltage, connect the probes in parallel with the circuit component and set the switch to the voltage range.
- Checking Continuity: To perform a continuity check, set the multimeter to continuity mode and ensure the device beeps when the probes touch two points, indicating a low resistance path.
A digital multimeter is defined as a device used to measure electrical parameters such as voltage, current and resistance. The term “digital” refers to its digital display, while “multimeter” reflects its ability to measure several parameters. A typical digital multimeter includes a selection switch, display, ports and probes.
Insert the probes into the appropriate ports and connect them across the parameter to be measured. Set the selection switch to the correct position for that measurement, and the multimeter will display the value.
Digital multimeters are generally used to measure three main parameters: current, voltage and resistance. They can also perform special functions such as diode checks, capacitance measurement, Transistor hFE (DC current gain), frequency measurement and continuity checks. This article covers the most common uses of a multimeter: measuring current, voltage and resistance, plus performing diode and continuity checks.
Current Measurement by Using a Digital Multimeter
To measure current, the digital multimeter mimics an ammeter. Insert the red probe into the mA socket for low current or the 20A socket for high current, then set the switch to the expected current range. Break the circuit and connect the meter in series so the load current passes through it; when power is on, the meter displays the current flowing through the circuit. Never place the probes in parallel across a powered source while the leads sit in the current sockets: the meter’s very low resistance would act almost like a short circuit and blow its internal fuse.
Voltage Measurement by Using a Digital Multimeter
To measure voltage, the digital multimeter acts like a voltmeter. Insert the red probe into the ‘V’ socket and the black probe into the ‘COM’ socket. Select the expected voltage range and choose either AC or DC, then connect the leads in parallel with the component or point where the voltage is measured. The meter will display the voltage value.
Resistance Measurement by Using a Digital Multimeter
In this case we configure the multimeter to act like an ohmmeter. The red and black probes go into the sockets marked ‘V’ and ‘COM’ respectively, and the selection switch is set to an expected range in the ohmmeter region (Figure 1). On a de-energised circuit, connect the leads across the component whose resistance is to be known; the display then shows its resistance value.
Diode Check by Using a Digital Multimeter
For this case, insert the probes into the same sockets as for voltage measurement and turn the selection switch to the diode-check position shown in Figure 1. When the red lead connects to the positive terminal of the diode and the black lead to its negative terminal, the meter should show a low reading. With the red lead on the negative terminal and the black lead on the positive terminal, the meter should show a high value. Readings matching this pattern indicate a working diode; readings that differ suggest a fault. More information is available in the article “Diode testing”.
Continuity Check by Using a Digital Multimeter
A continuity check reveals whether a low-resistance path exists between two points, that is whether the points are shorted. To perform one, insert the probes into the same sockets as for voltage measurement and point the selector switch at the continuity-check position (Figure 1). Then touch the points under test with the probe leads. If the multimeter beeps, the points are shorted through a low-resistance path; otherwise the resistance between them can be read from the display.
