Reading a Digital Multimeter (DMM)

1. DMM Reading
Northampton Community College
Jack Schreiber

2. 1 – 3 ½ Digit display
2 – Back light
3 – Rotary switch
4 – Hold button
5 – 10A jack
6 – Common jack
“black probe”
(negative)
7 – VΩmA jack “red”
probe (positive)

3. Symbols used on digital meters

4. Meter Safety
Never change the range
setting with the meter
connected to a live
circuit.
Always select a higher
range than you expect to
measure, if you are
unsure select the highest
range.
The most accurate
readings are taken with
the range set to the
lowest possible setting for
the value under test.

5. Meter Safety
Never hold the meter in
your hand when taking a
reading under power.
For current readings
above 200mA its best to
use a clamp-on meter.
Always wear you personal
safety protective
equipment.
For low voltage that
means safety glass are
the minimum

6. When the “H” is lit on the
display the hold function
is selected
The “–” in the display
shows a negative voltage
or current is applied the
red probe – switch
polarity to take the
reading
The battery symbol
denotes the battery needs
to be replaced

7. Never measure more
than 240V on the 600V
range due to the fuse
protection of the meter
It’s best to connect the
black probe to the
neutral side when
measuring AC but it’s
not required
The 200V range will
display up to 199.9V
max
Reading shown is 238 V
AC on the 600V AC
range

8. Measure current up to 0.2A
starting with the 200mA
range
Above 0.2A a clamp-on
ammeter is recommended
as the 10A range is not
fused
Always remove the probe
from the mA jack
immediately after taking the
reading
Always switch the meter off
after taking a current
reading on any range
The reading shown is
199.9mA DC on the 200mA
range

9. Ohm’s range - always make
sure the power is off to the
circuit under test
Always make sure the item
is isolated when measuring
ohm’s
For accurate resistance
readings short the probes
first then subtract this
amount from you final
reading
Always use the lowest
possible range for the most
accurate reading
Reading shown is 96.5
ohms on the 200 ohm scale.

10. DC voltage – use
proper polarity if the “-”
sign shows switch the
probes
Again the lower the
range the more
accurate the reading
Example use the 20 V
range to read a 9 V
battery not the 200 V
range
Reading shown is
8.73V on the 20V DC
range

11. Example of a typical
camp-on ammeter
Proper use requires
clamping around only
one current carrying
conductor at a time
Not designed for high
voltage (over 600V)
applications

12. Looping the conductor will
increase the reading by
100% for each loop.
Looping allows for reading
low values. Just remember
to divide the reading by the
number of loops.
Example: 10 loops with a
reading of 12 A is actually
1.2 A