how many "Resister/ cap network" between PE to Ground are necessary?

[vijayendra]

Hello All,

In our set-up, there are 2 backplanes and both are interfaced with each other using cables.
Each backplane has multiple RJ45 connectors and SubD connectors, which are used for data transfer between them other PCBs mounted on the backplane.

The backplane has
- input supply of 24V, 5V to supply power for other PCBs,
- one common PCB ground,
- PE, mounting holes,
- many press fit connectots for mounting other PCBs

The plated mounting holes and shield (case) of all the connectors are connected to PE and PE is connected to PCB ground using resistor (100k) and capacitive (100n) network.
The intention of this circuit between PE and GND is prevents static buildup and dampen electrical noise on the chassis.
- High frequency current collected by the chassis will flow to ground via capacitor.
- DC current will flow also but be attenuated by the resistor.

Please suggest me whether this is a good way of designing?

Query:

Do I need to provide one set (res/cap network) for each connector or couple of them or only one set is sufficient?
Also is there a specific area on the PCB where this network needs to be placed.

Please sugest me.
Thanks.

VJ

 

[zeyad.kassaby]

this a good design may by more than it needs.
I had many problems before with high freq modulation over power especially with combined analog and digital circuits design .
more safe is the better then having funny behaviour .
after finishing use a scope (earthed) and measure the 24vdc and 5vdc and return of them or use a voltmeter on AC and measure the dc volts the readings should be less then 0.4 volts but i think with that design your's will be around 50 mvolts ac.
hope it helps
Zeyad

 

[vijayendra]

Query:
Do I need to provide one set (res/cap network) for each connector or couple of them or only one set is sufficient?
Also is there a specific area on the PCB where this network needs to be placed.

Please sugest me.
Thanks.

 

[zeyad.kassaby]

Query:
Do I need to provide one set (res/cap network) for each connector or couple of them or only one set is sufficient?
Also is there a specific area on the PCB where this network needs to be placed.

Please sugest me.
Thanks.

this depends on how is the shield cover of the cable itself .simple check measure with ohm meter the resistance between both connector if it's zero ohm ,it means that there is shield then connect it directly to PE if not use your set for each connector
hope it helps
Zeyad

 

[vijayendra]

hello All,
There are some other responses like
- Connect signal reference (GND) to PE (or chassis or chassis GND)
- Do not connect, keep them isolated
- Place sunbber circuit (res/cap) network between GND and chassis (chassis GND)

I am confused, any suggestions please to this query and the query before?
Thanks.