When/Why do you use the ground cable on the Tek A6302 current probe? - Page 1
Forum section: electronics / testgear

author: IDEngineer
author_rank: Super Contributor
timestamp: November 05, 2020, 11:44:12 pm
content: Two of these just arrived and I'm running them through their paces.I last used one of these many years ago and don't remember if I used its ground cable or not. Neither the probe manual nor the amplifier manual discuss when to use the probe's ground cable.Detection of current in a lead through the probe should not strictly require a ground reference, and I don't see any noise improvement with or without the cable connected.What's the tribal lore on this? Thanks!

author: tautech
author_rank: Super Contributor
timestamp: November 05, 2020, 11:47:24 pm
content: High RF environments and/or bare wires with elevated voltages.....all just common sense stuff.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 05, 2020, 11:55:23 pm
content: OK, so no "magic". The manuals specifically state that the probes are "indirectly grounded" through the amplifier so presumably the shield is referenced to amplifier ground and thus not dependent upon the probe's own remote ground.Thanks!

author: garrettm
author_rank: Frequent Contributor
timestamp: November 06, 2020, 12:09:32 am
content: Quote from: tautech on November 05, 2020, 11:47:24 pmMaybe. But from what I understand, it's for lowering errors due to shunt capacitance. See the attached snippet from my HP 1110A AC current probe's user manual. Yeah, yeah, it's not a Tek probe, but the physical principle still holds.

author: tautech
author_rank: Super Contributor
timestamp: November 06, 2020, 01:11:22 am
content: Quote from: garrettm on November 06, 2020, 12:09:32 amSpecifically from a P6021 current probe manual:An alligator-style ground clip is supplied to improve EMI rejection at high frequencies (2 MHz and above). Snap the ground lead to the probe transformer post and attach the alligator clip directly to RF ground. This will reduce ringing and help bypass capacitively-coupled RF currents that can flow into the probe cable.

author: garrettm
author_rank: Frequent Contributor
timestamp: November 06, 2020, 02:00:20 am
content: @tautechThanks.That's a little more clear than the HP text. But the idea is the same: keep capacitive currents away from the electrostatic shield of the probe head.Problem is, I doubt anyone actually uses the ground clips as they are kind of annoying. Most probes I see on the secondhand market are missing the clips altogether.

author: tautech
author_rank: Super Contributor
timestamp: November 06, 2020, 02:54:08 am
content: Quote from: garrettm on November 06, 2020, 02:00:20 amYes I've never used them however never found the need to......yet.I've bought a few secondhand P6021's over the years and none were with ground leads however a nice tidy P6022 I got last year did have one.Certainly the exception to the rule however I believe an ordinary probe reference lead will fit.

author: alm
author_rank: Super Contributor
timestamp: November 06, 2020, 10:53:26 am
content: It's a standard ground lead, the same type was (and probably is) also by the Tektronix 5mm passive voltage probes, and many other probes of similar size. Probably the shortest length will not be very useful given the location of the ground post.

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 06, 2020, 11:37:44 am
content: Quote from: garrettm on November 06, 2020, 02:00:20 amNot exactly. The idea is to have capacitive currents go to the probe shield and find a low impedance path to ground from there. Otherwise, these same currents will mix with the signal ground going to the amplifier through the long cable. As the manual says, "This will reduce ringing and helpbypasscapacitively-coupled RF currents that can flow into the probe cable."

author: IDEngineer
author_rank: Super Contributor
timestamp: November 06, 2020, 03:58:04 pm
content: Thanks to everyone who has/will contributed to this thread. This is the sort of info that would be nearly impossible to find without a forum like this one.I'll see if I can conjour up some tests with sufficiently high enough frequencies to see a difference with/without the probe's local ground connected.

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 06, 2020, 04:06:42 pm
content: Quote from: IDEngineer on November 06, 2020, 03:58:04 pmThat is relatively easy, what you need is a high electric field, not magnetic. So make a mosfet switch some high voltage with a large drain resistor. This creates fast voltages swings at low currents. The higher the voltage and the faster the falling edge the better

author: IDEngineer
author_rank: Super Contributor
timestamp: November 06, 2020, 05:21:23 pm
content: My work involves relatively low voltages. The highest supply on hand is ~60VDC and that's if I series two floating outputs. Still, I may give that a shot just to see if anything measurable happens.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 06, 2020, 06:22:23 pm
content: Yeah, long ago I did about a year's work on ESD testing and compliance. This was long before there were any sort of standards for ESD. We had some REALLY fun tools for that because we were basically figuring stuff out as we went. It's all much more formal now.You'll appreciate this story: I once did a week-long seminar with Engineers from a bunch of different companies, and to start they had us do the usual "introduce yourself" thing. Being Engineers, everyone focused on what they did professionally. It came around to this one guy and he started with "I design equipment to deliver high powered electric shocks to people." The room went silent. My first thought was he designed execution equipment for death row installations (!!!). But then he explained that he designed defibrillators, both fixed and portable. His description was 100% accurate but his delivery really made your mind go in all sorts of directions!