Hi there!

I'm facing some issues in meeting EMC requirements as per IEC standard.

My input analog signal is ranging from -10 V to +10 V; input current is <1mA.
I have used MOVs, TVS diode to protect the circuit from high frequency noise.
I have conducted following tests on the system signal lines.
1. high energy surge: IEC-61000-4-5
2. common mode voltage: IEC-61000-4-16

The system passed above tests with criteria 'B'

How can i make it pass with criteria 'A'?

what additional filters i need to add?

Description of unit/system: the system generates alarm whenever signal crosses predefined threshold. the threshold can be set locally. for the test i've set threshold=1.5V & i've fed input signal=1V thru voltage source. During the EMC tests when noise is imposed on the signal lines,alarm occurs. i want alarm to be OFF throughout the test.

Any help/suggestions will be highly appreciated.

 

MOVs and TVS diodes can clip noise across their terminals but often the noise finds ways around the clipper through grounds or signal and power conductors. A well-placed ferrite bead can help, also passing passing all I/O through a ferrite core to create a high frequency common mode choke for all I/O including (especially including) power might help. Adding, improving, or moving bypass capacitors might help. There are lots of methods and tricks, but which ones might be effective in your product?

From what you have told us about what you want to do the only possible advice is to hire a consultant who has done this before.

If you post more information about the equipment that fails the test -what is it? What is happening internally to trigger the alarm?

Can you provide schematics and pictures of the internal wiring of the unit? The more detailed, the better quality feedback you will get.