2548H INSTRUCTION MANUAL
56-101-00420 Rev. C
Ch. 3
Nov
/
07
/
14
Page 20 of 33
Caution: Do not connect the connectors from the opposite end of the adapter
cable.
(2) Connect the HI-Z COAX lead to the Test Set’s CAP BRIDGE HI-Z COAX
receptacle and the LO-Z TANK lead to the Test Set’s CAP BRIDGE LO-Z TANK
receptacle from the adapter cable.
Caution: Short unshielded LO-Z leads and the Test Set’s LO-Z COMP receptacle
to ground with shorting caps or ground leads.
Note: References to compensator leads mean LO-Z leads.
C. Capacitance Test Procedure
(1) Set the Test Set’s ON/OFF switch to ON.
(2) Push and hold the PRESS TO MEASURE pushbutton while setting the TANK CAP
pF thumbwheels for a meter null.
Note: If the nominal capacitance value is known, begin with the thumbwheels set
to this value. If the nominal value is not known, set all thumbwheels to zero
(0); then increase the left hand thumbwheel one digit at a time while the
meter decreases. When the meter increases, reduce the setting by one
digit. Repeat procedure for each thumbwheel, (moving to the right) until the
best null is achieved. If the last or more digits indicate zero (0), reduce the
previous digit by one (1) and search for a lower null.
(3) Verify a null of 100 µA or less.
Note: Failure of the Tank unit to adjust to null may be due to poor HI-Z shielding in
the aircraft. To troubleshoot, remove all 400 Hz power from the aircraft. If a
high null continues, there may be high resistance connections, poor
insulation, or a defective tank unit.
A failure to null means a short circuit. A
very low capacitance reading at null means an open circuit
.
(4) Release the PRESS TO MEASURE pushbutton.
(5) If there are additional HI-Z and/or LO-Z leads in the system configuration, repeat
the procedure for each corresponding pair.
(6) Reconfigure the aircraft and the Test Set. Repeat the SYSTEM CAPACITANCE
TEST for each tank system until all tanks are tested.
(7) Set the Test Set’s ON/OFF switch to OFF.
(8) Disconnect all test equipment.
(9) If necessary, perform the INDIVIDUAL TANK UNIT CAPACITANCE TEST.
Otherwise, continue to section 8. AMPLIFIER TEST/CALIBRATION.
