If you don't feel like constructing the probe that Ted describes, a similar one can be purchased that pushes on to the ground reference shaft. It has two tiny metal probes spaced a few millimeters apart and a few millimeters long. One of the probes is of course ground, and the other signal. These probes are used for high frequency RF measurements. I do not have access to catalogs just now, but Hewlett Packard and Tektronix would be possible sources.
George Waters ICP [email protected] wrote: > The first thing to do is to make sure that the oscilloscope is on a clean > power source. Make sure that it is plugged into a branch circuit different > from the ESD test equipment. > > Next, reduce the length of the ground lead. Even if you are using the > shortest ground clip available with the scope, the lead will be too long. > The loop area formed by the ground lead will act as an antenna. (As a > test, you could place the scope probe by the test unit with the ground lead > clipped to the probe tip. You will still see a significant signal on the > "grounded" probe.) > > Remove the cap from the probe to expose the ground reference shaft. Take > some hook-up wire and wrap a few tight turns around the ground barrel of > the probe. Cut it off with enough length from the coil to solder to the > board. Remove the coil and solder it to a good ground reference on the > circuit board near the point that you want to measure. Take another short > piece of hook-up wire and solder it to the signal that you do want to > measure. Place the probe through the coil for the ground and wrap the > signal wire around the probe tip. This should let you do some hands free > measurement. > > This will keep the ground return loop as small as possible. The coaxial > scope probe cable should block enough noise to prevent coupling along that > path. You will still see some radiated noise getting into the probe, but > you will get much more accurate measurements than you can with the standard > scope probe ground leads. > > Ted Eckert > Regulatory Compliance Engineer > American Power Conversion > > Please respond to "Bailey, Jeff" <[email protected]> > > To: "'emc-pstc'" <[email protected]> > cc: (bcc: Ted Eckert/SDD/NAM/APCC) > From: "Bailey, Jeff" <[email protected]> on 12/22/99 12:56 PM > Subject: ESD troubleshooting > > Hello all, first off I would like to thank all who responded to my inquiry > about the EMC program offered by UMR, I am looking into enrolling further > now. > > I am now looking for any pointers from those more experienced than I. I > have a product that is giving me some grief when indirect ESD events > applied > to the HCP are applied at 4kV and above. I would like to be able to view > the disturbances that are present on the PCB during the event so I can try > to trace down where they are coming from and judge what attempts at fixing > the problem actually provide any difference. Can any of you give me some > pointers or rules of thumb on how to keep the interference from the event > form coupling onto a set of scope leads? I can see lots of noise but > cannot > definitely say that it is present on the PCB or if it is just coupling into > the leads. There is noise present visible when the scope probes are left > unconnected but the trace is quite different from that seen with them > connected to the PCB. (but of course there is no solid reference with the > probes unconnected) > > I need to isolate the scope leads from the test so I can actually see what > is getting on to the PCB, is this actually possible??? > > Thanks for any comments or help. > > Best Regards and best wishes for the holiday season to everyone!! > :-) > > Jeff Bailey > EMC Technologist > SST - A Division of Woodhead Canada Ltd. > Phone: (519) 725 5136 ext. 363 > Fax: (519) 725 1515 > Email: [email protected] > Web: www.sstech.on.ca > > All comments contained in the message are my own and do not necessarily > express the views of SST/Woodhead Canada Limited. > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
