W DOC AIRBUS | AMM A320F

Loop Impedance Test

TASK 20-28-00-720-014-A
Loop Impedance Test

1. Reason for the Job
This test is to measure the electrical resistance. It uses induction of an AC (Alternate Current) into a closed loop.
This procedure is not applicable to the closed loops installed in fuel tanks or surge tanks (explosive atmosphere), or at the boundary of an explosive atmosphere.
2. Job Set-up Information
 A. Fixtures, Tools, Test and Support Equipment
REFERENCE
QTY
DESIGNATION
ALT20200001
1
TESTKIT-LOOP RESISTANCE
 B. Referenced Information
REFERENCE
DESIGNATION
TASK 20-28-00-869-002-A
Table of the Maximum Permitted Resistance-Values
TASK 20-28-00-912-802-A
Electrical Bonding - General Maintenance Procedure
F Loop Resistance Test with an Injection Unit and a Measuring Unit
F Loop Resistance Test with One Injection/Measuring Unit and Two Clip-on Transformers (Typical)
3. Job Set-up
Subtask 20-28-00-869-081-A
A. Equipment
   (1) Get a ALT20200001 TESTKIT-LOOP RESISTANCE, (induced current of 1A at 1KHZ)
The loop resistance tester contains:
  • A current injection source
  • A battery charging unit
  • A clip-on transformer (current monitoring)
  • A clip-on transformer (current induction)
  • A multimeter (with test leads).
NOTE: The loop test set models can have:
  • One injection/measuring unit
  • One injection/measuring unit and two clip-on transformer
  • An injection unit and a measuring unit.
Subtask 20-28-00-420-096-A
B. Installation of the Test Equipment
WARNING: DO NOT TOUCH THE SOCKETS 1 AND 2 OF THE CURRENT INJECTION SOURCE WHEN IT IS CONNECTED. THE OUTPUT VOLTAGE CAN BE MORE THAN 200 VOLTS AC. THERE IS A RISK OF ELECTRICAL SHOCK.
CAUTION: MAKE SURE THAT THE TEST EQUIPMENT IS CORRECTLY INSTALLED BEFORE YOU MEASURE THE BONDING VALUES.
   (1) Connect the test equipment at the applicable locations.
F Loop Resistance Test with an Injection Unit and a Measuring Unit
F Loop Resistance Test with One Injection/Measuring Unit and Two Clip-on Transformers (Typical)
NOTE: The current injection source injects the "I loop" AC current into the loop tested through a clip-on transformer (current induction).
This current then flows through:
  • The applicable braided conduit
  • Its bonding connections to the structure
  • The structure.
    A second clip-on transformer (current monitoring) senses the AC "I loop" induced current and the multimeter (used as an AC amperemeter) then measures this current.
    For the loop tester that has only one clip-on transformer, the same clip-on transformer injects and measures the current.
     (a) Make sure that there is no unwanted material between the jaws of the clip-on transformers.
     (b) Put the clip-on transformer in a location that is easy to see. Make sure that the clip-on transformer is not closed on a bolt or on other parts of the hardware.
NOTE: The clip-on transformer jaws must touch each other.
4. Procedure
Subtask 20-28-00-869-082-A
A. Measurement (applicable for tools with an injection unit and a measuring unit)
   (1) Set the current injection to its minimum value.
   (2) Set the multimeter to the AC amperemeter.
   (3) Energize the current injection source. Make sure that the charge is correct.
   (4) Set the current injected into the loop to 1A with a precision of +/- 10%.
   (5) Read the resistance value R.
Subtask 20-28-00-869-101-A
B. Measurement (applicable for tools with one injection/measuring unit)
F Loop Resistance Test with One Injection/Measuring Unit and Two Clip-on Transformers (Typical)
   (1) If adjustable, set the injection current to a maximum limit of 1A.
   (2) If adjustable, set the measurement frequency to 1KHZ.
   (3) If adjustable, set the measurement range to a value higher than the maximum permitted value of the measured assembly.
   (4) Energize the injection source. Read the resistance value R on the injection/measuring unit.
Subtask 20-28-00-869-102-A
C. Maximum Resistance Values
   (1) Make sure that the measured values are not higher than the maximum permitted resistance-values (Ref. AMM TASK 20-28-00-869-002).
   (2) If the measured values are more than the maximum permitted resistance-values (Ref. AMM TASK 20-28-00-912-802).
5. Close-up
Subtask 20-28-00-020-064-A
A. Removal of the Test Equipment
   (1) For the injection unit and the measuring unit:
     (a) Set the multimeter to OFF position
     (b) De-energize the current injection source.
   (2) For the injection unit/measuring unit:
  • Set the injection/measuring unit to off.
   (3) Disconnect the test equipment.
Subtask 20-28-00-942-111-A
B. Close Access
   (1) Make sure that the work area is clean and clear of tools and other items.
[Rev.10 from 2021] 2026.03.31 23:00:20 UTC
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