‘–’ (negative) of the circuit. The COM lead is usually black, but there is no difference between the red and the black leads other than the colour. The red lead is connected to the VΩmA port for measuring V (voltage), Ω (resistance), diodes or continuity. This is the most common use of a DMM. To measure a.c. or d.c. current, the red lead is connected to the 300mA port or if more than 300mA is expected, then connect to the 10A port. If unsure of the expected current reading, always connect to the 10A port first. NOTE THAT NOT ALL DMM’S SUPPORT THESE MEASUREMENTS.
There are several symbols on the DMM, these are shown as follows:
Measuring Leads The leads have a banana type connector, usually ‘sleeved’ for protection on the end that connects to the DMM. Any lead with banana plugs will work but take care if they are uninsulated. Probes are usually RED and BLACK (COM) and have a probe on the other end, usually insulated for protection. Some probes can be removed and replaced with ‘crocodile’ clip ends.
Usual ports of a DMM
WARNING: The 10A port will usually be marked whether there is an internal fuse or not. Be very careful when using this port, and do not use this port for long continuous durations (not more than 10s). Testing Continuity Probably the most frequently used and one of the easiest functions of a DMM is the continuity test. It is used to test continuity from point A to B in a circuit, whether a cable/ wire is conducting or not or whether a switch is properly functioning or not.
Multimeter Leads
The leads are plugged into two ports of the DMM.
COM stands for common, and is always connected to the Ground (GND) or earth or
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