Current probe for Oscilloscope - Page 1
Forum section: electronics / testgear

author: 2X
author_rank: Frequent Contributor
timestamp: July 16, 2023, 12:56:43 pm
content: Hello,I want to buy a good quality current probe for my oscilloscope to measure the pulses of a TIG (AC/DC) inverter machine. I found the two below. I look also and in the Tesetc company but I didn’t found a probe to measure 200A current. Have anyone to suggest something else?Rohde-Schwarz:R&S®RT-ZC02R&S®RT-ZC03 (This has resolution 1mA)https://www.rohde-schwarz.com/us/products/test-and-measurement/oscilloscope-probes/current-probes-for-oscilloscopes_63493-73797.htmlhttps://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_manuals/gb_1/r/rt_zcxx/RT-ZC02-ZC03_Manual_en_03.pdfTestec:https://www.testec.de/en/products/product-categories/current-probes/

author: alm
author_rank: Super Contributor
timestamp: July 16, 2023, 02:54:18 pm
content: 200A is not so common for bench scopes. That's probably why you couldn't find a Testec probe. What kind of bandwidth (lower and upper) do you need? What is the rise time and duty cycle of your pulses?I would look carefully at derating curves. For example the R&S RT-ZC02 is rated for +/- 200A or even +/- 2000A DC, or 1000A RMS AC, but if you look at the derating curve at page 40 ofthis datasheet, the rated peak current at 10 kHz (sinusoidal) is only about 50A.The TektronixTCP404XLis quite a bit better in both max current over frequency and bandwidth (see figure on page 55 ofthe manual). But you're not going to like the price. TheSiglent CP6500looks like it might also work but is not cheap either.If you can live without DC and moderate bandwidth, then there are substantially cheaper options from multimeter manufacturers as industrial current clamps with BNC or banana plug output.

author: 2X
author_rank: Frequent Contributor
timestamp: July 16, 2023, 04:22:42 pm
content: The MAX frequency as I know is about 500Hz, so I beleive it would bo ok. Siglent is quite expensive. Thanks for your reply.R&S®RT-Zxx HIGH VOLTAGE AND CURRENT PROBEShttps://scdn.rohde-schwarz.com/ur/pws/dl_downloads/premiumdownloads/premium_dl_pdm_downloads/5214_2362_22/RT-Zxx_High-voltage_dat-sw_en_5214-2362-22_v2400.pdfR&S® RT-ZC02https://www.batronix.com/shop/measurement/probes/Rohde-Schwarz-RT-ZC02.htmlSiglent CP6500 5 MHz 500 Amp Current Probehttps://www.siglent.eu/product/7962341/siglent-cp6500-5-mhz-500-amp-current-probe

author: nctnico
author_rank: Super Contributor
timestamp: July 16, 2023, 04:24:54 pm
content: Another option is to use a current shunt and an isolation amplifier. Or use a Rogowski coil. From what I've seen these are regulary used when dealing with measuring welding current waveforms.

author: 2X
author_rank: Frequent Contributor
timestamp: July 16, 2023, 04:25:44 pm
content: Quote from: alm on July 16, 2023, 02:54:18 pm"If you can live without DC and moderate bandwidth, then there are substantially cheaper options from multimeter manufacturers as industrial current clamps with BNC or banana plug output."Do you have something to suggest me from a good company or whatever do you beleive it is worth?

author: nctnico
author_rank: Super Contributor
timestamp: July 16, 2023, 04:28:51 pm
content: Random Google find:https://www.picotech.com/accessories/current-probes/200a-2000a-current-probe-bnc

author: alm
author_rank: Super Contributor
timestamp: July 16, 2023, 04:49:20 pm
content: Quote from: 2X on July 16, 2023, 04:25:44 pmAny reputable multimeter brand will do. This does not strike me as something safety critical. Try to find something that has a voltage output rather than a current output. Keep in mind that just because a particular clamp won't measure DC current does not mean DC current can't affect your measurement due to saturation of the ferrite core. If a probe is well documented, they will tell you about max permissible DC current. To get around this, you can null out the DC current by an equal current in opposite direction, or N turns of I/N current in opposite direction. See page 2-4 fromThis old Tektronix CT-5 manual.

author: Weston
author_rank: Regular Contributor
timestamp: July 16, 2023, 06:10:46 pm
content: What accuracy do you need? Do you need a split core?You can buy hall effect current transducers for equipment and use them with your scope. They come in high current ranges and are relatively cheap. They even have high accuracy versions.This was the first example I found on google:https://www.newark.com/lem/hal-400-s/current-transducer/dp/01P0338

author: Martin72
author_rank: Super Contributor
timestamp: July 16, 2023, 06:39:32 pm
content: Hi,QuoteBecause hioki made these probes..Not only for siglent, for rigol, R&S, Lecroy..The expensive behind is the mix of bandwith, accuracy and low noise.

author: 2X
author_rank: Frequent Contributor
timestamp: July 16, 2023, 06:53:36 pm
content: With same Current but different Bandwidth... the price from one to another goes up exponentially. Thanks for the reply Martin72.R&S® RT-ZC03https://www.batronix.com/shop/measurement/probes/Rohde-Schwarz-RT-ZC03.htmlR&S® RT-ZC15Bhttps://www.batronix.com/shop/measurement/probes/Rohde-Schwarz-RT-ZC15B.html

author: 2X
author_rank: Frequent Contributor
timestamp: July 16, 2023, 07:03:04 pm
content: Quote from: alm on July 16, 2023, 04:49:20 pmI didn't understand how to do this "To get around this, you can null out the DC current by an equal current in opposite direction, or N turns of I/N current in opposite direction." As I understand this refered when an AC signal contains DC offset for instance. If I put the two cables together in the clamp probe in order to null the DC current then also the AC current will null?

author: alm
author_rank: Super Contributor
timestamp: July 16, 2023, 07:18:02 pm
content: Quote from: 2X on July 16, 2023, 07:03:04 pmYes, so make sure the current in the second wire comes from a different source without the AC signal superimposed. For example a bench supply. Now finding a 100A bench supply might be tricky, but you could use a 10A current and then wind the wire carrying this 10A ten times around the clamp. Note that this is only necessary if DC current is causing you problems, otherwise you can ignore it.

author: johansen
author_rank: Super Contributor
timestamp: July 16, 2023, 11:30:19 pm
content: Buy an lem current sensor off ebay for 15 to 30$. They are typically 100 or higher khz bandwidth.

author: mkissin
author_rank: Regular Contributor
timestamp: July 17, 2023, 04:32:16 am
content: I work with very large, high frequency currents at work and (as long as you can live without true DC capability) a rogowski is the way to go. As has already been pointed out most DC current probes derate significantly with frequency due to thermal effects in the core, so you have to be careful even with your harmonics.We use various models (usually the mini and ultra-mini for the bandwidth) of these:https://www.pemuk.com/products/cwt-current-probe/cwt.aspxA handy thing is that they don't care if you go even way over the maximum voltage. The output will saturate, but no damage occurs. They only care if you violate the di/dt rating.

author: H.O
author_rank: Frequent Contributor
timestamp: July 17, 2023, 10:22:45 am
content: Be VERY careful with whatever instrument you use if you're using HF-start on the welder! If I were to use an expensive current probe on a TIG-welder I would make SURE to "connect it"afterthe arc is established.