The zero ohms control is a potentiometer for
adjusting the 0 reading on ohmmeter functions.
The reset is a circuit breaker and is used to
protect the meter movement. Not all multimeters
have this protection, but most have some sort of
protection, such as a fuse.
When the multimeter is not in use, it should
have the leads disconnected and be switched to
the highest voltage scale and ac. These switch
positions are most likely to prevent damage if the
next person using the meter plugs in the meter
leads and connects them to a circuit without
checking the function switch and the dc/ac
selector.
SCALES.— The numbers on the uppermost
scale in figure 3-24 are used for resistance
measurement. If the multimeter was set to the
R x 1 function, the meter reading would be
approximately 12.7 ohms.
The numbers below the uppermost scales are
used for de voltage and current. These numbers
are also used with the scale just below them for
ac voltage and current. The fourth scale from the
top and the numbers just below the scale are used
for the 2.5-volt ac function only. The lowest scale
(labeled dB) is not discussed. Figure 3-24 shows
how the given needle position should be
interpreted with various functions selected.
Multimeter Safety Precautions
As with other meters, the incorrect use of a
multimeter could cause injury or damage. The
following safety precautions are the minimum for
1.
2.
3.
4.
5.
6.
7.
using a multimeter:
De-energize and discharge the circuit
completely before connecting or discon-
necting a multimeter.
Never apply power to the circuit while
measuring resistance with a multimeter.
Connect the multimeter in series with the
circuit for current measurements, and in
parallel for voltage measurements.
Be certain the multimeter is switched to ac
before attempting to measure ac circuits.
Observe proper dc polarity when measuring
dc
When you are finished with a multimeter,
switch it to the OFF position, if available.
If there is no off position, switch the
multimeter to the highest ac voltage
position.
Always start with the highest voltage or
current range.
Figure 3-24.—A multimeter scale and readings.
8.
9.
10.
11.
Select a final range that allows a reading
near the middle of the scale.
Adjust the 0 ohms reading after changing
resistance ranges and before making a
resistance measurement.
Be certain to read ac measurements on the
ac scale of a multimeter.
Observe the general safety precautions for
electrical and electronic devices.
All valves are not constructed in the same
manner. Therefore, the electrical tests performed
on a valve should be accomplished as directed by
the appropriate MIM. The voltage and resistance
3-38
