FreeLists / si-list / [SI-LIST] Re: How to Measure Ground Noise

[Zhangkun <zhang_kun@xxxxxxxxxx>]

Doug

Do you have any paper on this topic?

Best Regards

Zhangkun
2005.4.8
----- Original Message ----- 
From: "Doug Smith" <doug@xxxxxxxxxx>
To: <Istvan.Novak@xxxxxxx>
Cc: <zhang_kun@xxxxxxxxxx>; <istvan.novak@xxxxxxx>; <ospyng@xxxxxxxxx>; 
<si-list@xxxxxxxxxxxxx>
Sent: Friday, April 08, 2005 12:27 PM
Subject: Re: [SI-LIST] Re: How to Measure Ground Noise


> Hi Zhangkun, Istvan, and the group,
> 
> I would like to modify Istvan's response somewhat.
> 
> Ground currents flowing from the circuit, through the probe ground 
> lead, and down the shield into the scope chassis typically (although 
> not always) dominates everything else. It is just L(of the ground 
> lead)di/di that creates a voltage across the probe from tip to ground 
> lead attachment point to the probe. The probe reads this voltage like 
> any other. This voltage is typically about 50 to 100 times larger than 
> what leaks through the probe cable shield.
> 
> Doug
> 
> Istvan Novak wrote:
> 
> > Dear Zhangkun,
> > 
> > If you connect the signal and ground pins of a probe together and
> > connect both to a ground point on your system, the signal you see on the
> > oscilloscope could be a combination of several things: close-field
> > radiated noise picked up by the active probe head, radiated noise picked
> > up by the cable connecting the probe head to the scope, large
> > common-mode noise converted somewhere along the path due to saturation
> > of circuitry, etc., etc. The purpose of such baseline measurement is not
> > necessarily to identify the sources or these noise contributors one by
> > one, rather to establish their cumulative effect as a lower limit of the
> > measured values, below which you need to throw out the data.
> > 
> > Best regards,
> > Istvan
> 
> .......lots of lines deleted
> 
> 
> -- 
> -------------------------------------------------------
>      ___          _       Doug Smith
>       \          / )      P.O. Box 1457
>        =========          Los Gatos, CA 95031-1457
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