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Subject: Signal ground v.s. chasis earth

Date: 05/30/00 at 8:06 PM
Posted by: toysl
E-mail: to_ysl@hotmail.com
Message Posted:

Hi,

I often see circuit (both digital and analog) being protected by a Transzorb or MOV connected between input/output and the chasis earth. i.e.

polyswitch
Input(+) >-----/\/\/\/\----+-----> signal processor
|
---
\ / Transzorb or MOV
---
|
|
---
///

The similar circuit arrangement is also seen on the negative input (i.e. input(-)).

Could you please let me know what is the significant of chasis earth? Why input surge is clamped to chasis earth instead of circuit ground? What's the different between chasis earth and circuit ground (they are not connected)? When to use chasis earth, and when to use circuit ground?

Thanks for your help.

cheers,
Lee.


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