Help! How to choose a proper current probe for my oscilloscope? - Page 1
Forum section: electronics / beginners

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 04, 2016, 11:50:32 am
content: Hi everyone,I was doing some repairs on a cuple of SMPS and other ac appliances and I needed a way to measure current and voltage, the way was using a 5w 1resistor and two probes across the resistor to measure the voltage potential, well it is fine if I want to measure power delivered to a load but not to great for my application so I want an expert recomendation on this subject...Thanx a lot for all help

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 04, 2016, 03:34:55 pm
content: Anyone??

author: Simon
author_rank: Unknown
timestamp: September 04, 2016, 06:10:09 pm
content: no idea to be honest I've not used current probes. If you want to effect your circuit less you could use a smaller shut like the ones used for high current and then amplify the voltage. For example the uCurrent is in effect a prtecision x100 amp so set to the nA range the input impedence would be 10K with is nothing to the micro ohms of a shunt resistor.

author: stoica adrian
author_rank: Contributor
timestamp: September 04, 2016, 08:01:56 pm
content: Depending on your application.You have to choose: Bandwidth, Attenuation ratio, Input impedance, Dynamic range, and look for compatibility with your scope.

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 05, 2016, 05:50:18 am
content: Thanx a lot for the info, is there any other parameters I have to check be for I buy the current probes

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 06, 2016, 08:04:08 am
content: Could I just make my own current probe?

author: ebclr
author_rank: Super Contributor
timestamp: September 06, 2016, 08:18:29 am
content: This little guy will help you a lothttp://pt.aliexpress.com/item/Free-Shipping-Hot-Sale-ACS712-30A-Range-Hall-Current-Sensor-Module-ACS712-Module-For-Arduino-30A/32515954572.html?spm=2114.02010208.3.10.rHrJwO&ws_ab_test=searchweb201556_0,searchweb201602_3_10057_10056_10065_10037_10055_10054_10069_301_10059_10033_10058_10032_10017_10070_10060_10061_10052_10062_10053_10050_10051,searchweb201603_2&btsid=b47076d6-b514-4047-9df3-235c2a6a8ed0

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2016, 08:56:03 am
content: Quote from: ali6x944 on September 06, 2016, 08:04:08 amYou can, I did for my first one but always yearned for a proper one.I used a small CT from an old PC PSU and roughly calibrated it using a borrowed current probe with a resistor across its output. Trouble was there was no way to measure anything without breaking the circuit and soldering a wire through the hole in the CT. Worked fine up to a few KHz.How I have a couple of P6021's, AC only, 15A max and 60 MHz rated.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 06, 2016, 08:59:14 am
content: The iProbe 520 is very nice. But as said before: list your requirements first.

author: ebclr
author_rank: Super Contributor
timestamp: September 06, 2016, 09:22:55 am
content: You can also try a ready product like this onehttp://pt.aliexpress.com/item/Hantek-CC-65-han-tai-oscilloscope-probe-current-AC-DC-AC-DC-current-clamp-measurement/32652508070.html?spm=2114.02010208.3.2.2CmG7V&ws_ab_test=searchweb201556_0,searchweb201602_3_10057_10056_10065_10037_10055_10054_10069_301_10059_10033_10058_10032_10017_10070_10060_10061_10052_10062_10053_10050_10051,searchweb201603_2&btsid=8efb74ec-cd21-46b1-ba9a-1b65366fe670

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 07, 2016, 07:09:19 am
content: Quote from: tautech on September 06, 2016, 08:56:03 amit is a good idea but dose it measure low frequency acQuote from: Ice-Tea on September 06, 2016, 08:59:14 ama frequency of 100 MHz is fineAttenuation ratio: x10measure DC as well as ACDynamic range i really did understand what is it , could u explain briefly please.

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2016, 07:31:50 am
content: Quote from: ali6x944 on September 07, 2016, 07:09:19 amAC only.How low do you want to go?

author: oldway
author_rank: Super Contributor
timestamp: September 07, 2016, 09:53:46 am
content: For ac+dc, LEM PR200 clamp.It's discontinued now but you may perhaps find a used one for cheap.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 07, 2016, 10:01:34 am
content: Quote from: ali6x944 on September 07, 2016, 07:09:19 amPretty much: what's the lowest and highest current you want to measure.And if you want 100MHz, be prepared to spend alotif money.

author: oldway
author_rank: Super Contributor
timestamp: September 07, 2016, 10:48:50 am
content: A 100 Mhz current probe fordoing some repairs on a couple of SMPS and other ac appliancesAre you kidding ?Did you not understand that 100Mhz and attenuation x10 are not especifications of a current probe but are especifications of a voltage oscilloscope probe ?ali6x944 is a beginner and he can't give especifications of what he need.You don't even need a current probe to repair SMPS...

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 07, 2016, 11:40:46 am
content: Quote from: oldway on September 07, 2016, 10:48:50 amWhich is why he is posting in the beginners section. To get advice and to learn. Probably not to be laughed at.

author: oldway
author_rank: Super Contributor
timestamp: September 07, 2016, 12:33:02 pm
content: Quote from: Ice-Tea on September 07, 2016, 11:40:46 amI'am laughing of the NON BEGINNERs who are answering at ali6x944 asking him especifications of the current probe, when he come here just because he don't know what he need and other people who would let him buy a very expensive 100 Mhz current probe that is only needed in a SMPS developping workshop.

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 07, 2016, 02:14:24 pm
content: Quote from: oldway on September 07, 2016, 10:48:50 amTrue , I might over exaggerate the value thanx for correcting me ....I'm new to all the current probe stuff... the farthest I went in measuring current was the method mentioned earlier, so please help others and me to choose the "proper" probe for their purpose.

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 07, 2016, 02:25:28 pm
content: Quote from: Ice-Tea on September 07, 2016, 10:01:34 amPretty much: what's the lowest and highest current you want to measure.And if you want 100MHz, be prepared to spend alotif money.Wait it isn't the same type of attenuation as in voltage probes?

author: oldway
author_rank: Super Contributor
timestamp: September 07, 2016, 02:56:44 pm
content: QuoteNo, the specification is how many mV or V by A or mA.A 100Mhz current probe (with power supply and amplifier) costs thousands of $ ...

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 07, 2016, 03:16:19 pm
content: Ok...I got it now

author: bson
author_rank: Unknown
timestamp: September 09, 2016, 05:39:32 pm
content: Are you measuring the mains side, the output side, or both? They require very different tools.

author: CoffinDodger
author_rank: Regular Contributor
timestamp: September 09, 2016, 06:36:34 pm
content: I'm probably completely off but what I'm thinking is an AC/DC milliamp clamp meter would be the ticket if all you care about is magnitudes on the input and output. Not the waveforms, looking for harmonics and such.. not cheap but way cheaper than trying to outfit your scope I would think. I hope I'm not missing something here.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: September 09, 2016, 10:35:31 pm
content: I bought one of the Hantek cc-65 clamps someone posted earlier. Be careful as some people sell them with banana jacks (but the photo is with BNC connector)It isn't the flashiest out there, but it has worked for all my applications so far. I'be not needed accuracy (so far) just to see the current waveform.

author: Bukurat
author_rank: Regular Contributor
timestamp: September 12, 2016, 08:21:53 am
content: Quote from: ali6x944 on September 06, 2016, 08:04:08 amYou could, but what do you want to measure? Current probes are essentially a one turn transformer with a split core and measure AC only. I have a Tektronix P6021 probe that is at least 30 years old that I use for non invasive in circuit measurements. These are still available and still pricey.If you want to measure the AC input current there are other options. I use a meter I picked up off eBayhttp://www.ebay.com.au/itm/191929341893?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITI mounted this in a plastic case and spliced the meter into a short extension cord.For measuring AC current.You can make your own current probe using one of the YHDC split core sensors. SCT-013-030 Has a built in burden resistor and gives 1V output at 30 amps.http://garden.seeedstudio.com/images/b/bc/SCT013-030V.pdfSCT-013-000 doesn't have a built in burden resistor. You can tailor the output voltage/mA with your own burden resistor.For DC you need a Hall effect current sensor. Google it, there is a lot of info out there.

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 13, 2016, 10:15:31 am
content: Quote from: bson on September 09, 2016, 05:39:32 pmI'm measuring in both

author: ali6x944
author_rank: Frequent Contributor
timestamp: September 13, 2016, 10:41:07 am
content: But I'm still confused, will it measure pulsating dc or off setted waveforms as it similar to ac but without going negative?

author: David Hess
author_rank: Super Contributor
timestamp: September 13, 2016, 10:50:08 pm
content: Quote from: ali6x944 on September 04, 2016, 11:50:32 amIf you want to measure the high speed waveforms of a SMPS, then you need something like the mentioned Tektronix P6021. Know however that the P6021 is an AC only probe and will saturate at a pretty low DC level; it can measure drive waveforms where the average DC current is low and the current through capacitors to make ripple current measurements but it cannot measure inductor current except at low average DC levels.For DC measurements you need an AC/DC probe like a Tektronix A6302/AM503 and those are more expensive. A Pintek PA-699 could work but its 1.5 MHz bandwidth is pretty low for this type of application and new they are still about $800. Someone else in the forum no doubt knows about other modern AC/DC oscilloscope current probes but none of them are cheap.A better option may be to continue using a shunt resistor and high voltage differential probe. I have a P6021 AC only probe so my usual solution for DC measurements when doing design work is to include a fast discrete current to voltage output which uses a low resistance current shunt as part of the circuit where I want to make a measurement.