The continuity test function is usually represented by a “sounder” symbol
Select the continuity function and connect the probes across a wire or circuit. It’s useful to have crocodile clips for this application. If the connection is good, a continuous buzzer sound will be heard. If there is a problem in the wire, there will be no sound or a distorted sound. It is important when testing for continuity that there are NO voltages present in the circuit. Measuring Resistance One of the easiest measurements to make using a DMM is resistance. The Ohmmeter section of the DMM is represented by Ω (omega) symbol. DMM’s can usually measure resistance up to 2MΩ.
Measuring 75Ω Resistor
The probes can be connected either way around, as the result will not be affected by the orientation of the probes. If a negative (-) result is shown, this could indicate that there is a voltage present. An example of this maybe when measuring earth continuity where there are voltage differences between the two points being measured. In this case the earthing must be investigated further. If measuring the resistance of a coax terminator (non d.c. blocking type), the expected result should also be 75 Ω.
Diode Test Some DMMs have dedicated diode testing functionality, which can be useful for checking diodes and some special types of transistors (as a transistor is essentially two diodes connected back-to-back). D.C. pass one- way splitters, can be tested with the diode function test in order to confirm direction of current flow.
Set the knob to the desired range in the resistance measurement and connect the probes to the leads of the resistor. The measured resistance will be displayed on the display. If using an auto range DMM, it is only necessary to select the Ω range.
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CAI Feedback Spring 2024
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