[SI-LIST] FET probe caution
- From: "Douglas C. Smith" <doug@xxxxxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Tue, 04 Sep 2001 20:14:12 -0700
Hi All,
A common accessory for FET probes can, in some cases, cause a
significant error in the measurement and cause a great deal of time lost
when debugging a circuit. My September Technical Tidbit at:
http://www.dsmith.org
describes the problem.
The accessory in question is a probe tip with a small ground "spring" or
"pin" on a hinge and uses a small ferrite core to improve probe
response. Its use can make the FET probe ten times more sensitive to
logic noise on the board and other EMI that you are not trying to
measure. Such a sensitivity can cause one to "see" a glitch that is not
there on a logic signal, a real time burner in the development lab or
troubleshooting environment. The article presents scope data to show the
magnitude of the problem which affects several brands of FET probes.
The Technical Tidbit area is at the bottom of the index page.
----------
In addition, I have posted pictures to the website from Montreal and the
IEEE EMC
Symposium that was held there a few weeks ago. The link to the pictures
is just above the Technical Tidbit area at the bottom of the index page.
Doug
--
-------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
========= Los Gatos, CA 95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
/ /\ \ ] / /\ \ Mobile: 408-858-4528
| q-----( ) | o | Email: doug@xxxxxxxxxx
\ _ / ] \ _ / Website: http://www.dsmith.org
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