1-41
The multimeter shown in figure 1-37 may look complicated, but it is very easy to use. You have
already learned about ammeters, voltmeters, and ohmmeters; the multimeter is simply a combination of
these meters.
Most multimeters use a d’Arsonval meter movement and have a built-in rectifier for ac measurement.
The lower portion of the meter shown in figure 1-37 contains the function switches and jacks (for the
meter leads).
The use of the jacks will be discussed first. The COMMON or -jack is used in all functions is
plugged into the COMMON jack. The +jack is used for the second meter lead for any of the functions
printed in large letters beside the FUNCTION SWITCH (the large switch in the center). The other jacks
have specific functions printed above or below them and are self-explanatory (the output jack is used with
the dB scale, which will not be explained in this chapter). To use one of the special function jacks, except
+10 amps, one lead is plugged into the COMMON jack, and the FUNCTION SWITCH is positioned to
point to the special function (small letters). For example, to measure a very small current (20
microamperes), one meter lead would be plugged into the COMMON jack, the other meter lead would be
plugged into the 50A AMPS jack, and the FUNCTION SWITCH would be placed in the 50V/IA AMPS
position. To measure currents above 500 milliamperes, the +10A and -10A jacks would be used on the
meter with one exception. One meter lead and the FUNCTION SWITCH would be placed in the
10MA/AMPS position.
MULTIMETER CONTROLS
As described above, the FUNCTION SWITCH is used to select the function desired; the -DC,
+DC, AC switch selects dc or ac (the rectifier), and changes the polarity of the dc functions. To measure
resistance, this switch should be in the +DC position.
The ZERO OHMS control is a potentiometer for adjusting the 0 reading on ohmmeter functions.
Notice that this is a series ohmmeter. The RESET is a circuit breaker used to protect the meter movement
(circuit breakers will be discussed in chapter 2 of this module). 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
the ones most likely to prevent damage if the next person using the meter plugs in the meter leads and
connects the meter leads to a circuit without checking the function switch and the dc/ac selector.
MULTIMETER SCALES
The numbers above the uppermost scale in figure 1-38 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.
