2548H INSTRUCTION MANUAL
56-101-00420 Rev. C
Ch. 3
Nov
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07
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14
Page 17 of 33
D. Insulation Test Procedure
Note: When using the manufacturer's adapter cables, ensure that the adapter's
connectors and box are not exposed to the airframe ground. (The connectors,
box and shielding “float” from ground for tests. Touching or grounding could
cause incorrect readings.)
Do not touch the connectors or box while performing
the test.
Note: In order to do the desired test, it may be necessary to set an aircraft tank selector
switch to a required position. Refer to the appropriate Maintenance Manual for
the proper procedure.
(1) Set the T/S’s ON/OFF switch to ON.
(2) Read the resistance measurement on the MEGOHMS scale of the test meter.
Verify that the resistance is no less than the resistance for the shield to aircraft
ground for the applicable aircraft.
Note: The meter pointer may drift slowly after initial movement due to capacitance
charging time or the presence of moisture. Allow the pointer to stabilize or
to reach the minimum acceptable scale value.
(3) Rotate the INS TEST POINTS selector to each of the remaining positions.
(4) If there are other HI-Z or LO-Z leads in the system, connect the panel receptacle to
the corresponding pair and repeat test.
Note: References to compensator leads are to be considered LO-Z leads.
(5) Reconfigure and repeat procedure for each corresponding pair.
(6) Access the other amplifiers.
(7) Reconfigure the aircraft and T/S.
(8) Repeat the System Insulation Test for each tank system until all tanks are tested.
(9) Set the T/S switch to OFF.
(10) Disconnect all test equipment
(11) Continue to section 6. SYSTEM CAPACITANCE TEST . However, if the system
insulation test does not produce the required results, perform steps listed in section
5. INDIVIDUAL TANK UNIT INSULATION TEST.
