Actron AutoTroubleShooter CP7677 - Manual (Page 6)

6
Setting the Range
Two of the most commonly asked ques-
tions about digital multimeters are What
does Range mean? and How do I know
what Range the multimeter should be
set to?
What Does Range mean?
Range refers to the largest value the
multimeter can measure with the rotary
switch in that position. If the multimeter
is set to the 20V DC range, then the
highest voltage the multimeter can mea-
sure is 20V in that range.
EXAMPLE: Measuring Vehicle Battery
Voltage (See Fig. 1)
Now assume we set the multimeter to
the 2V range. (See Fig. 2)
The multimeter display now shows a “1”
and nothing else. This means the multi-
meter is being overranged or in other
words the value being measured is larger
than the current range. The range should
be increased until a value is shown on
the display. If you are in the highest
range and the multimeter is still showing
that it is overranging, then the value
being measured is too large for the mul-
timeter to measure.
How do I know what Range the multi-
meter should be set to?
The multimeter should be set in the
l o w e s t p o s s i b l e r a n g e w i t h o u t
overranging.
EXAMPLE: Measuring an unknown re-
sistance
Let’s assume the multimeter is con-
nected to an engine coolant sensor with
unknown resistance. (See Fig. 3)
Fig. 2
Fig. 1
Let’s assume the multimeter is con-
nected to the battery and set to the 20V
range.
The display reads 12.56. This means
there is 12.56V across the battery termi-
nals.
Fig. 3
Start by setting the multimeter to the
largest OHM range. The display reads
0.0
Ω
or a short circuit.
This sensor can’t be shorted so reduce
the range setting until you get a value of
resistance.
At the 200K
Ω
range the multimeter mea-
sured a value of 4.0. This means there is
4K
Ω
of resistance across the engine
coolant sensor terminals. (See Fig. 4)
If we change the multimeter to the 20K
Ω
range (See Fig. 5) the display shows a
Red
Black
Red
Black
Black Red