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Subject: Re: Earth v.s. circuit ground

Date: 08/15/00 at 10:50 PM
Posted by: toysl
E-mail: to_ysl@hotmail.com
Message Posted:

In Reply to: Re: Earth v.s. circuit ground posted by Brian Richardson on 08/15/00 at 6:06 PM:

Hi Brian,

Thanks for your elaboration!

However, I am still puzzled with some points in your post.

1. Is signal ground (our circuit reference) and chasis earth (the earth of our 3-pin plug to which the chasis is earthed) equal potential? Probably what you mean is: they are not electrically connected, but sitting at the same potential. But how?

2. What is common mode capacitor? Is that the capacitor for filtering purpose, normally located at the output of the rectifier-bridge?

3. How does the "high frequency signals on earth line can see high impedance to ground (circuit ground?) due to inductance of wire", if they are not connected (i.e. circuit ground and earth of 3-pin plug are not connected)?

4. I don't quite get your explanation in the third paragraph. You mean if the spike is on the data line, then we can protect the device by connecting over-voltage protection device between data line and circuit ground. However, quite oftenly, I see OV protection devices being connected between the data line and the earth of chasis (i.e. earth of 3-pin plug). Just wondering what is the different between them?

Please help to clarify my doubt.

Thanks in advance.

Lee.


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