Cheap current probes for use with oscilloscopes - Page 1
Forum section: electronics / general

author: McPete
author_rank: Regular Contributor
timestamp: August 11, 2012, 08:09:18 am
content: Hey All,Just a quick ask around- Does anyone know of any sub-$800 scope current probes on the market at the moment that aren't utter garbage? I found this earlier;http://www.tequipment.net/InstekGCP-100.html#Datasheet;http://www.testequity.com/documents/pdf/GCP-100.pdfAnyone had a play with one of these before?P.

author: tom66
author_rank: Super Contributor
timestamp: August 11, 2012, 09:01:06 am
content: Differential probe and resistor? You can build a differential probe easily using either two probes (though it gives poor CMRR) or a diff-amp IC.

author: PChi
author_rank: Frequent Contributor
timestamp: August 11, 2012, 09:57:34 am
content: I don't have experience of the GwInstek current probe. I have only used current probes from the major players. I guess it depends what you want to use the probe for. A long time ago I used a Tektronix AC current probe on Industrial Metal Detectors which was very useful. I guess that they are cheap being only a transformer.I don't understand why the GwInstek GCP-100 bandwidth is so low. I want to know the accuracy versus frequency (hall effect at low frequency / transformer at 'high' frequency) and given the wide current range I would be concerned with how bad the drift is at 50 mA.Where is the power source for the Hall Effect device?

author: PChi
author_rank: Frequent Contributor
timestamp: August 11, 2012, 12:46:06 pm
content: One option I forgot to mention was the AIM / TTI I-Prober as reviewed by Dave in EEVblog #296

author: Unknown
author_rank: Unknown
timestamp: August 11, 2012, 07:49:34 pm
content: 100 kHz is the bandwidth of a Hall-effect sensor. Combining a Hall-effect sensor with a transformer for DC-50 MHz bandwidth is a much more complex design, invented by Tektronix. After the patent expired, LEM and Hioki have started producing similar designs. Lecroy sells some of them under their own name. The production process is extremely complex, so don't expect $10 Chinese copies. You can get either DC through a Hall sensor or tens of MHz BW with a transformer, but getting both is expensive.

author: McPete
author_rank: Regular Contributor
timestamp: August 12, 2012, 11:40:21 am
content: Ah, a Diff. probe was something I'd forgotten. I'll add that to our end of year budget surplus wishlist. As you rightly point out, that across a shunt does a fine job of measuring current.PChi, I believe the probe I linked to has batteries. Again, I'll chuck that on the wishlist. For the mains and LF stuff we do most, 100kHz is plenty.Thanks for the responses all!

author: maiakaat
author_rank: Regular Contributor
timestamp: August 16, 2012, 01:58:13 pm
content: http://www.ebay.co.uk/itm/230837571744?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649#ht_500wt_1366Tektronix AC current probe £30 or so at the moment, auction

author: elliott
author_rank: Regular Contributor
timestamp: August 16, 2012, 09:33:33 pm
content: Quote from: maiakaat on August 16, 2012, 01:58:13 pmDoesn't that require an amplifier?

author: SeanB
author_rank: Super Contributor
timestamp: August 17, 2012, 04:55:38 am
content: Just needs 15V rails to drive the active circuitry.

author: Unknown
author_rank: Unknown
timestamp: August 17, 2012, 06:43:41 pm
content: What active circuitry? The box is just a passive termination network. This is essentially just a current transformer with the wire under test as primary winding and about 60 (?) turns as secondary winding. There used to be an amplifier available (model 134) for this probe. It increased sensitivity and reduced the lower bandwidth limit by quite a bit (this is an AC only probe), but slightly reduced the upper bandwidth limit. It was discontinued long before the probe and passive termination was (it might even still be a current product).One thing I would ask is pictures of the ferrite surfaces, or at the least a careful inspection. Any cracks or chips may affect performance, and ferrite is quite easy to chip if handled carelessly.

author: SeanB
author_rank: Super Contributor
timestamp: August 17, 2012, 06:57:23 pm
content: My bad, many current probes I have seen use active amplifiers inside, to get good low current sensitivity and bandwidth. this is passive, so all you need to check is the head is not cracked, the cable is not noisy and it has a resistance of around 25 ohms ( double terminated cable) at the scope end.

author: Smokey
author_rank: Super Contributor
timestamp: August 17, 2012, 08:23:08 pm
content: We use these in the lab all the time. They are currently discontinued under the LEM name, and they suck 9V batteries like crazy, but work really well if you only need about 35A range at 100khz.http://www.tequipment.net/LEMPR30.htmlFluke seems to have bought them or something is selling them now for more than LEM did. Sucks. Here is the fluke version:http://www.fluke.com/Fluke/usen/Accessories/Current-Clamps/i30s.htm?PID=56297Like I posted in the other current clamp thread, there is this Chinese knock off I found on ebay that looks like it might have similar specs, but I haven't used it.http://www.ebay.com/itm/CP-05A-AC-DC-Clamp-Current-Probe-for-Oscilloscope-/110931036252?pt=LH_DefaultDomain_0&hash=item19d401485candhttp://www.ebay.com/itm/CP-05-AC-DC-Clamp-Current-Probe-/120965495612?pt=LH_DefaultDomain_0&hash=item1c2a1afb3c

author: chlan
author_rank: Newbie
timestamp: September 23, 2015, 07:00:46 pm
content: HiThe Labdevice current probes are made for oscilloscopes and they measure AC and DC up to 2MHz. Measurement range from low uA up to 1A. Around 300 USD...http://www.labdevice.ch/products/Cheers

author: nctnico
author_rank: Super Contributor
timestamp: September 23, 2015, 07:55:31 pm
content: I sell this current probe box (DC to 10MHz). It's frequency characteristic does have some issues between 1kHz and 20kHz though.http://nctdev.nl/page_pg%3d18.htm