Electrical Industry Canada: Tools, Equipment & Technology - 8

Step-by-Step Guide to Measuring Resistance
with a Digital Multimeter
* You may see the MΩ symbol because the resistance of
Measuring resistance determines the condition of a circuit or
component. High resistance means lower current flow, lower resistance
means higher current flow.
The resistance of control circuit components (switches or relay
contacts for example) will begin at a low level and increase over time due
to wear or dirt build up. Motor and solenoid loads decrease in resistance
over time because of moisture or insulation breakdown.
unattached test leads is high.
* When the leads are connected to a component a digital
multimeter will use the Autorange mode to find the best range.
* You can manually set the range with the Range button.
* Removing the component being tested from the circuit for best
results. When connected to the circuit you may pick up parallel
components.
Measuring resistance:
1. First have power to circuit OFF.
If a circuit includes a capacitor, discharge the capacitor before taking
any resistance reading.
2. Next make sure the digital multimeter dial is set to resistance, or
ohms. Oſten, there will be multiple modes (continuity, capacitance or
diode) for one setting as shown in the image below.
* The display should show OLΩ. With Resistance mode, a digital
multimeter automatically begins measuring resistance before the leads
are connected.
ELECTRICAL INDUS TRY CANADA
3. The next step is to insert the black test lead into the COM jack.
4. Then insert the red lead into the VΩ jack. When finished, remove
the leads in reverse order: red first, then black.
5. Connect the test leads across the component being tested.
Make sure that contact between the test leads and circuit is good.
For very low-resistance measurements, use the relative mode (REL: see
below). It may also be referred to as zero or Delta (Δ) mode. This
automatically subtracts test lead resistance-typically 0.2 Ω to 0.5 Ω. If
test leads touch (are shorted together), the display should show 0 Ω.
VOLUME 2, ISSUE 1
8
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