Common Mode choke for 4-20mA input

[yashrk]

Hey guys,

We are going through IEC 61000-4-3 IEC 61000-4-6 test for one of our products.
The input power source for the device is the same line which will be used for 4-20mA. Mostly it will be connected to 24V DC input (max 35V)

For passing the test we are putting in a common mode choke on the line. We have low update rate in the range of tens of hertz. Now for AC (Mains) line it is recommended to use X & Y capacitor. But for our application as we don't have such a high voltage do we need the Mains AC rated capacitor or we can get away by using normal ceramic 100V caps? As you can imagine we do have space constrain.

Thanx!
Yash

[bjbb]

Do not understand discussion of x/y caps for radiated immunity tests.

'X' and 'Y' are cap safety ratings for stuff that are intended to be used for various configuration where Class I or II construction is used for protection from shock (actually x-caps are not intended to provide protection from shock), and are typically associated with design requirements for passing conducted emissions tests for connection to AC mains. DC mains have different requirements and test conditions (see -4-6).

[yashrk]

Sorry my bad I meant IEC 61000-4-6

Ok, some more context here.

So I know that common mode choke is used primarily for passing conducted emissions. We only have linear regulators so it's not a issue for us.

The problem which we are facing is with conducted susceptibility were we are having drifting in our sensor reading and also random keypresses on our membrane keypad if the de-bounce delay is low.

Do not understand discussion of x/y caps for radiated immunity tests.

Thing I know is that we need to add common mode and differential mode filter to remove all the the noise. For differential mode noise we are adding two ferrite beads on 24+ anf GND with capacitor in between hence forming a LC filter.

Now for common mode noise we know that we need a common mode choke. But all the examples and the literature I have about the common mode choke is with respect to AC mains supply and not much information for DC supply. The main issue we are having is with the safety capacitor.
As we are not working with mains voltages do we need safety capacitors or we can work with generic appropriately voltage rated capacitors?

[yashrk]

Anyone??