[SI-LIST] Re: TDR's and ESD Protection
- From: Martyn Gaudion <martyn.gaudion@xxxxxxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx, JSAWDY@xxxxxxxxxxx
- Date: Wed, 27 Mar 2002 01:42:23 +0000
Hello John,
Yes, TDR heads are prone to ESD damage, and testing coaxial
cables can be demanding on the heads. As you say they are
very expensive to replace. If I remember correctly Tek used to
offer a static isolation unit to reduce the incidence of damage,
though any solution like this, as Jeff Loyer correctly notes, will
sacrifice rise time.
But as you can see there is a perfomance / operating cost trade off.
Just a note that the more recent Polar CITS series of TDRs do support
differential
test. However they are optimised for test on bare boards..
Kind regards
Martyn Gaudion
www.polarinstruments.com
At 16:32 26/03/2002 -0500, you wrote:
>We are experiencing a high failure rate on our Tektronix SD-24 TDR heads
>when we test cable assemblies. Our cables assemblies sometimes are 40 to 80
>feet in length and consist of multiple coax and twinax cables within each
>assembly. We typically use the TDR to measure differential electrical
>length and skew of the finished assembly.
>
>We use wrist straps and conductive mats on the benches. We short all pins
>to ground before we connect to the TDR to try to remove any residual
>charges.
>
>I am wondering if anyone else has some experience with this and if they
>might have a solution.
>
>I have also heard that "mechanical noise" generated by movement of the cable
>may be a culprit but I am not sure of the magnitude of such noise. Can
>anyone confirm that this is a possibility?
>
>Does anyone have any experience to suggest that one brand may be more robust
>then another or that one model of head may be more robust.
>
>Looking forward to your responses,
>John
>
>John F. Sawdy, Senior Applications Engineer
>Meritec, a division of Associated Enterprises
>voice mail: 440-354-3148 x 267
>fax: 440 -354-0687
>mailto:jsawdy@xxxxxxxxxxx
>
>
>
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