RTCA/DO-160F SECTION 22 CABLE BUNDLE TESTS

RTCA/DO-160F SECTION 22 CABLE BUNDLE TESTS

There seems to be a debate regarding the required test levels that must be reached when testing an EUT (equipment under test) using the cable induction or ground injection methods. I have been told that this debate goes all the way to SC135. However, the purpose of this discussion is to find out how the requirement is being interpreted and justification for those interpretations.

It is my opinion that the test level or limit level must be reached during testing. During generator performance verification only the test level must be reached (see par 22.5.2.1.1 b), but this does not assure that the test generator will be capable of achieving the required level when testing the EUT. This capability depends on the test generator design and the impedance of the cable being tested. Worst case from the test generator point of view would be a cable under test that resulted in reaching both the test level and limit level simultaneously.

Pin injection testing is referenced because the procedure for generator calibration establishes a generator setting that is to be repeated during testing. No such procedure exists in the cable induction or ground injection procedures.

22.5 Test Procedures

22.5.1 Pin Injection Tests

22.5.1.1 Procedures – Generator Calibration

22.5.1.1e

The procedure put forth here demonstrates how DO-160F SECTION 22 identifies a preset generator level that is established during calibration. Recording the generator setting and verifying the impedance of the generator is how the severity of this test is controlled. The voltage and current that the EUT will be subjected to depends on the impedance of the pin under test. Paragraph 22.5.1.2 Procedures – Test Sequence c. requires that the generator be set as previously established in Paragraph 22.5.1.1 Procedures – Generator Calibration. This is different than the approach taken for cable induction and ground injection.

22.5.2 Cable Bundle Tests

22.5.2g Cable Bundle Tests

The test is always acceptable if the test level is reached before the limit level. However, if the limit level is reached before the test level then an evaluation of the waveshape is required to determine if the test is acceptable or if another test is necessary. The criteria are different for each waveform. Paragraph 22.5.2h(1) through (4) and 22.5.2i(1) and (2) provide guidance for making this determination.

22.5.2.1.1b Procedures – Generator Performance Verification (cable induction)

22.5.2.2.1a Procedures – Generator Performance Verification (ground injection)

The test waveform is verified to have the correct shape at the required test level into either an open circuit for voltage tests or into a short circuit for current tests. It is not required that the generator produce the limit level and waveshape associated with the limit level during generator performance verification.

22.5.2.1.2d Procedures – Test Sequence (cable induction)

22.5.2.2.2e Procedures – Test Sequence (ground injection)

Here you are instructed to increase the generator setting until the test level or limit level is reached into the tested cable.

Conclusion:

When testing is performed on an EUT the generator level is to be increased until either the test level or limit level is attained. I do not see any justification for considering the settings on the generator as they were during generator performance verification a “pre-calibrated test level” that is not to be exceeded. I will keep an open mind, so if anyone can justify a different interpretation or identify a flaw in mine, your input will be greatly appreciated.