Group,
I have an application which is causing me some grief because it is a
departure from a setup I am used to. I hope you can help. The application
is automotive.
I have a cab mounted microprocessor based automotive product which runs
off a dedicated PSU. The product case is all plastics and the PSU case is
all metal. To picture the product, imagine if you will, an intelligent gear
lever
(stick shift) with buttons on the top for changing gears (this is only an
analogy)!
The cable between this product and its PSU is multi-way screened (shielded)
and has a proprietary connector on one end for my product and a standard
multi-way connector on the other end for a PSU. The cable is about 30cm long.
On my product, the cable shield terminates on the PCB (separate plane)
to which all my small RF filters are connected. This plane is not quite the
same as battery -ve on the PCB. I have filters between battery -ve and this
plane.
At the PSU end, the general regime has been to terminate the cable shield
onto the chassis of the PSU.
A new application has arisen which does not require this PSU, and must use
non-shielded cable. I have the option to cut off the PSU-end connector and
supply my product with a flying lead.
My concerns are as follows:
1 - Opting for non-shielded cable could reduce the effectiveness of my EMC
measures
2 - Opting for shielded cable that is not terminated could upset my filter
circuits on the
PCB. I fear that leaving the cable shield unterminated at the PSU end
might be
worse than having no cable shield at all
Unfortunately, I am at design stage so have no product to test. I need to make
a
quick call so as not to hold up the cable manufacturers. Is there some
judgement
one can make based on experience with shielded and unshielded cables (I have
little)?
I have the option to terminate the shield on a metallic bracket near the PSU,
but for
technical reasons, this bracket is not connected to chassis. Would this help,
make no difference or actually make things worse?
As usual, apologies that the description is probably not very clear, but I
would
gladly supply further info if anyone feels it may be a scenario they have
encountered before. BTW, the RI test level is 100V/m.
Thanx in advance.
Rgds
- Chris
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