values (megohmmeter), and for dBm measure-
Q6. List the two disadvantages of the volt-ohm-
milliammeter.
ments. This meter is a solid-state differential
voltmeter providing the capability of making dc
voltage measurements from 10 microvolt to
1,100 volts. It also measures ac voltages from
Q7. What type meter should you use to test for
0.001 to 1,100 volts over a frequency range from
insulation breakdown?
5 hertz to 100 kilohertz. You can make both of
these measurements without concern of loading
the circuit. It has four voltage readout dials that
vary the resistance of the divider assembly as
described above.
Q8. What test equipment shows you the wave
shape of current or voltages?
The differential voltmeter uses a built-in null
detector to measure an unknown voltage. The
meter circuitry compares the unknown voltage to
a known, adjustable reference voltage supplied
Q9. What is a discontinuity?
by the meter. The reference voltage is from a
high-voltage dc power supply and decade resistor
divider assembly strings. You use voltage readout
dials to adjust the decade resistor assembly. In
Q10. What meter compares an unknown voltage
this way, you can divide the output from the
with a known internal reference voltage and
high-voltage power supply precisely into incre-
shows the difference in their values?
ments as small as 10 microvolt. The readout dials
adjust the meter pointer to 0, and the unknown
voltage is on the voltage dials.
A primary feature of a differential voltmeter
is that it does not draw current from the unknown
AIRCRAFT WIRE AND CABLES
source for dc measurements when you make the
measurement. Therefore, the determination of the
Learning Objective: Recognize aircraft
unknown dc potential is independent of its source.
wire and cable characteristics and various
means of identifying and splicing wires and
cables.
REVIEW SUBSET NUMBER 3
An important part of aircraft electrical
maintenance is determining the correct wire or
Q1. Describe how you would connect a
voltmeter to the circuit under test?
cable (fig. 2-10) for a given job. For electrical
installations, a wire is a stranded conductor,
covered with an insulating material. The term
cable, as used in aircraft electrical installation,
Q2. When using a meter, you should start at
includes the following:
what range?
Two or more insulated conductors con-
tained in the same jacket (multiconductor
cable)
Q3. A circuit in which current no longer flows
is known as an
.
Two or more insulated conductors twisted
together
One or more insulated conductors covered
Q4. What test do you perform to find an open
with a metallic braided shield (shielded
circuit?
cable)
A single insulated center conductor with
a metallic braided outer conductor (RF
Q5. Blown fuses and open circuit breakers are
cable)
usually an indication of what type of fault?
