Circuit Ground and Chassis Ground

[vikaskumar1983]

In most of the PCB boards which are the part of a chassis box where backplane exists, we creates two grounds. One is your circuit ground and another is chassis ground. These two grounds are separated by a parallel combination of a resistor [ 1Mohms] and a capacitor [1000PF,100V]. I want to know why to separate these two grounds in this way. And if we short these two grounds then what will happen ?

Please see the attached document also.


Thanks

 

[dick_freebird]

A metal chassis is a huge antenna and you may pick up an
extra amount of electrical noise in your signal ground
if you tie them hard. The chassis only needs to be at a man-
safe potential and the rest of it you'd rather not "see".

 

[snafflekid]

There does not need to be any resistor and capacitor joining the grounds, I think this prevents static buildup and dampen electrical noise on the chassis. High frequency current collected by the chassis will flow to ground. DC current will flow also but be attenuated by the resistor.