The Virtual Repairman's Technical Reference
How to check
resistance (continuity) in a component-
A Digital Multi-meter
(Ohmmeter) is needed for testing components:
An ohmmeter can be used to directly
measure an unknown resistance R.
This is the simplest way to measure resistance. It is
important to realize
that an ohmmeter can not
when the resistance is connected in a circuit and a
current is flowing through it!
two million ohms
||two hundred kilohm
two hundred thousand ohms
twenty thousand ohms
two thousand ohms
||two hundred ohm
Setting up the meter
To use the multi-meter as an
ohmmeter turn the selector dial to point to the ohms range. On
some models (usually not on the cheaper ones) the meter will
have a single ohms setting and will auto select the best range
resistance you must connect the test leads to the sockets
labeled 'COM' and 'Ω'. These may be in different
positions on your meter but the labeling should be the same.
anything connected between the test leads the display will give
an out of range indication (-1 in this case) to show that the
resistance is too large to measure. In effect, you are trying to
measure the resistance of the air between the two inputs, which
is very large.
the meter is working touch the leads together and the display
should read 0.0 Ω. It may read
slightly higher, e.g. 0.3 Ω. This
is the resistance of the test leads themselves.
Turn the selector dial to the lowest
resistance range that gives a valid reading.
In this case the resistance wire has a
resistance of 4.2 Ω.
overall accuracy of the reading will depend upon the
multi-meter model. The more expensive the meter the better
the accuracy will be. For a cheap meter the accuracy is
typically in the region of +/- 1% of the displayed value.
Check in the manual for the accuracy of your model.
important to select the correct measurement range. In the
above example if the 2 kΩ range
is selected the display will read
.004 kΩ and the decimal place will be lost. If the
dial is set to 20 kΩ the
display may read 0.00 kΩ!
Always turn the dial down to the lowest range to get the
calculate resistance and voltage using meter readings: