7.3 Test lead null
When checking continuity or measuring low values of resistance it is useful to make allowance for the resistance of
the test-leads. This is known as nulling. If you null your test-leads, their resistance is no longer included in the value
shown on the display when you make a measurement.
The null value is displayed in the lower centre of the main display area:
7.3.1 To null a test lead:
1. Plug the test leads into the green and red sockets at the rear
of the instrument.
2. Turn the left-hand rotary knob to the Continuity / Resistance
(Ω) position.
3. Short the leads together.
NOTE : This must be a good connection. A poor null will
introduce a high null value and potentially artificially low
resistances in the main measurement.
Ideally use crocodile type clips or press the probe tips into
a good conductor such as a copper coin.
4. Press and release the test button.
Check that the null icon appears at the bottom centre
of the display. The resistance of the null value is shown
below the null icon.
Fig 15: Continuity null
NOTE : It is a good idea to occasionally check the null value is correct, as test leads may not always give a
consistent lead resistance if they are wearing out and need replacement.
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Continuity testing and resistance measurement
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