the fleet. It is a small, compact unit that weighs
different average and effective values. Since this
10 pounds, including the optional battery pack.
meter mechanism responds only to the average
It is capable of measuring ac and dc voltages to
value, you must take into consideration the
a maximum of 1,000 volts and resistance to 10
waveform shape when calibrating the meter for
megohms. Standard features of the Model 8100A
effective value. Thus, the meter reading is correct
include protection against overvoltages, a select-
only on waveforms for which the meter is
able input filter, autopolarity. push-button
calibrated. In this respect, the instrument has a
function, and range selection. Also, it has a full
definite limitation because waveforms may vary
four-digit readout plus a 1 in a fifth digit to show
considerably in conventional circuits. For
overranging. The unit operates from voltages of
example, the sine-wave voltage response of a
half-wave rectifier is 32 percent of maximum for
either 115 or 230 volts at frequencies from 50 to
the average value, and 50 percent for the effective
500 Hz. An optional rechargeable nickel-cadmium
battery pack can power the unit for 8 continuous
value. The full-wave rectifier response is 64 and
hours. Accessories and options besides the
71 percent, respectively. In the design of the
rechargeable battery pack are a high-frequency
meter, these values are taken into consideration,
probe, a high-voltage probe, and switched ac/dc
and the scales are plotted to read in effective units
when calibrated against an accurate standard.
current shunts.
DIGITAL MULTIMETER
The digital multimeter is an accurate, reliable
Ordinary ohmmeters cannot be used to
measuring instrument used at the organizational,
measure multimillion ohm values of resistances,
intermediate, and depot levels of maintenance.
such as those in conductor insulation. To test for
insulation breakdown, you use a much higher
The instrument is easy to use and read. Also, some
potential than that supplied by the battery of an
digital multimeters have a battery pack for the
portable operation.
ohmmeter. This potential is placed between the
The Fluke Model 8100A (fig. 2-5) is repre-
conductor and the outside of the insulation. You
will use a megger (megohmmeter) for these tests.
sentative of digital multimeters presently used in
Figure 2-5.-Digital multimeter.
