Yesterday an engineer showed me a strange thing. It is an isolated
DC input I/O with relay output. The isolation specification is low.
So every input is going through an opto-coupler and the circuits
are quite simple. Strange thing is that there is a long trace
underneath all the optos and it is connecting to the common
shield connection. Apparently this is not for safety reasons as
it actually reduce clearance/creepage distance (still enough).
So I can only guess it is for EMI reasons.

Any clue?

Regards,
Xiaofan
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist