Is it allowed to place a capacitor between the LISN and the DUT using CISPR25 spec?

Question

I am very new to the EMC world (co worker quit Friday and now its my problem) I was asked by my supervisor to check the CISPR25 spec to see if it is allowed to put a 1000 uf cap between HV+ and HV- between the LISN and the DUT. I have the CISPR25 (2016 version) spec and I have spent the last hour searching through it for the answer but so far I have found nothing that says if it is allowed or not.

We are concerned with CE420 and RE310 testing specifically.

I am hoping someone with a lot more experience then me can point me in the right direction.

I really appreciate any help you can provide.

Show a schematic of what you propose. Include the device you want testing. The devil will be in the detail. — Andy aka, Jul 15 '21 at 17:40
I have no idea, but if it's just for the test, I would say 'no'. If it's going to be built into your product, then I would say 'probably yes' — Voltage Spike, Jul 15 '21 at 17:42

score 1 · Answer 1 · answered Jul 15 '21 at 18:32

The test using a LISN uses high inductance coils on the AC input in order to simulate long transmission lines with a more balanced impedance for Line and Neutral at the RF range of interest.

The purpose is to measure the conducted emissions to the grid without load effects. Adding a cap would cheat this measurement for testing the DUT.

This is the job for the DUT using one or two CM chokes with a Pi filter cap to earth to suppress common and differential mode conducted noise in both directions.

Is it allowed to place a capacitor between the LISN and the DUT using CISPR25 spec?

1 Answers1