Current probe delay adjustment - Page 1
Forum section: electronics / testgear

author: crysti
author_rank: Regular Contributor
timestamp: May 06, 2025, 01:08:15 pm
content: I'm trying to adjust it, but I can't get a clean square wave on the oscilloscope.I'm using an Owon CP024 with a 10 A PWM generator powered at 6 V, driving a 6 Ohm / 10 W ceramic resistor.I would appreciate any advice on how to obtain a well-defined rectangular current waveform.Thanks in advance!

author: Martin72
author_rank: Super Contributor
timestamp: May 06, 2025, 03:51:34 pm
content: Hi,The title says “Delay adjust,” but the post is about the “correct” square wave shape of the current signal. Which one is correct?Then:You didn't do yourself any favors with the Owon Current Probe, to put it mildly.Do you have a signal generator with a 50 Ohm output?Then you could do the following:Generate a square wave signal with it, 10Vpp, 10kHz, use a 50 Ohm terminating resistor for the scope as a load and measure the current in the line.If there is still no clean (albeit small, approx. 70mA - You can turn more wires around the core to get "more" current) current signal, the Owon is simply too poor.

author: Martin72
author_rank: Super Contributor
timestamp: May 06, 2025, 04:12:55 pm
content: I found my measurements from back then using an Owon CP05+.It's pretty likely that your model is also affected.The images show currents at 100 Hz, 2 kHz, and 22 kHz—a disaster.I would still try the experiment I described in my first post.

author: crysti
author_rank: Regular Contributor
timestamp: May 06, 2025, 04:25:14 pm
content: Thank you once again for taking the time to respond.I also tried the signal-generator method, winding ten turns of wire around the clamp to increase sensitivity, but saw no difference.At 200 kHz with a sine wave, I measured a –15 % drop in the reading, calculating current from the voltage drop across a 50 Ω resistor.I want to adjust the delay, but for that I need a square wave. Up to 1 kHz the waveform is correctly square.I believe the issue is the clamp’s size and magnetic material, which retain remanence. Every high-frequency (over 100 kHz) current clamp I’ve tried has low-iron content.What puzzles me is the frequency-dependent phase shift between current and voltage.

author: Martin72
author_rank: Super Contributor
timestamp: May 06, 2025, 04:30:40 pm
content: The phase difference will be so large that you will not be able to compensate for it with the deskew function of the scope.The Owon is simply too poor for that.Are you familiar with the Bode plot function of your scope?If so, I would make a plot from 10 Hz to 200 kHz.The phase response displayed there will speak volumes.

author: crysti
author_rank: Regular Contributor
timestamp: May 06, 2025, 04:56:55 pm
content: Quote from: Martin72 on May 06, 2025, 04:30:40 pmI have Siglent SDS824X HD and FeelTech FY6900. The Bode function is too much for me because my oscilloscope does not have this function integrated with an external generator. Can you tell me how I can do the Bode function with my configuration?

author: Martin72
author_rank: Super Contributor
timestamp: May 06, 2025, 05:17:35 pm
content: The Bode plot function of your 824X HD works directly with all external Siglent generators.However, there is a thread here in the forum where people have managed to use the Bode function with non-Siglent AWGs.You would have to search for it.Or watch this clip; I would be surprised if it didn't also work with an SDS824X HD:

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2025, 05:59:06 pm
content: The Owon CP024 is too slow by at least 2 orders of magnitude to achieve what you want. That rise time and delay are consistent, and actually better, than its claimed 200 kHz bandwidth will support.Typical current probes used for this sort of thing have bandwidths of 20 MHz or higher.

author: crysti
author_rank: Regular Contributor
timestamp: May 06, 2025, 06:01:20 pm
content: Quote from: Martin72 on May 06, 2025, 05:17:35 pmThank you very much for the tip. I’ll give it a try.

author: bdunham7
author_rank: Super Contributor
timestamp: May 06, 2025, 06:42:37 pm
content: Quote from: crysti on May 06, 2025, 01:08:15 pmA different current probe, as mentioned already. It looks like the HF response on the OWON is grossly overcompensated to try to give it some sort of passable response up to its specified BW, but only with sine waves and with a huge phase shift. How hard it might be to get a "good" result depends on how good you need it to be. This is 20kHz and 50kHz, 20Vp-pinto 50 ohms using a Fluke 80i-110s with a 100kHz stated BW with no skew adjustment or other compensation. If you want to do better than this you'll need a better current probe. The least expensive thing that I can think of that would work is the MicSig CP2100A/B.

author: Martin72
author_rank: Super Contributor
timestamp: May 06, 2025, 06:57:12 pm
content: QuoteYes, that would be my thought as well.However, I couldn't completely compensate for my Micsig at the time in terms of deskewing because its value was higher than described in the data sheet.Perhaps today's models are better in this respect – test them out.

author: tautech
author_rank: Super Contributor
timestamp: May 06, 2025, 09:36:35 pm
content: When trying to adjust for probe propagation delays, you can adjust the channel Skew in each channels menu.Because most Siglent DSO's use digital triggering we can skew one channel or the other to get them to line up.Some probes have slow risetimes but with careful trigger, waveform and channel 0V positioning, rise times can be made to perfectly intersect.A copy of the Siglent Deskew fixture was developed in this thread:https://www.eevblog.com/forum/testgear/scope-probe-deskew-fixture-pcb-project/@crystiAre you in the process of getting into the Power Analysis feature ?

author: bdunham7
author_rank: Super Contributor
timestamp: May 07, 2025, 12:40:16 am
content: Quote from: tautech on May 06, 2025, 09:36:35 pmAny idea on the rationale behind limiting deskew to 100ns?

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2025, 01:33:42 am
content: Quote from: bdunham7 on May 07, 2025, 12:40:16 amNone at all other than logically, it may have been selected as sufficient for any combination of passive/active/current probes that Siglent offer.You can adjust skew on 2 channels to obtain more, one + and the other -.Have a play around....

author: crysti
author_rank: Regular Contributor
timestamp: May 07, 2025, 07:43:59 am
content: Quote from: tautech on May 06, 2025, 09:36:35 pmI activated "Power Analysis", for this reason I would have liked to use the current clamps.Can I use it without the DF2001A? It's just a 22KHz oscillator with TL555 at a $250 premium price. I thought I could replace it with a signal generator, but my clamps start to have phase errors at frequencies above 2KHz. At low frequencies there's no point in adjusting the delay.

author: Martin72
author_rank: Super Contributor
timestamp: May 07, 2025, 07:46:04 am
content: QuoteYes, it's just a tool to make the settings easier.There is also a DIY version of it.

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2025, 08:16:27 am
content: Quote from: crysti on May 07, 2025, 07:43:59 amI see no reason why your 200kHz Owon CP024 current clamp wouldn't work.DF2001A operates @~22kHz to mimic the frequency of many common SMPS but has 2 loops of differing magnitudes for different current probes.Above is the link to the DIY thread.Phase error between current and voltage probe is from the probes propagation delay which is why we have the deskew feature to null it.If I get a chance I'll pop some screenshots up to assist you getting your head around this.....once you get that lightbulb moment you'll be good to go.

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2025, 09:04:23 am
content: A chance to show off some toys.....Channel skew adjustment with SDS6204A, SP5050A 10x 500MHz probe and SCP5030A current probe using the DF2001A Siglent deskew fixture providing ~147mA from the 1 turn loop.Ch4 = voltage probe, Ch2 = current probe < with expected longer propagation delay but not immediately apparent.Zoom in to examine the actual current probe propagation delay.Adjust to null

author: crysti
author_rank: Regular Contributor
timestamp: May 07, 2025, 10:34:52 am
content: Quote from: tautech on May 07, 2025, 09:04:23 amThank you for the example; however, the equipment you’re using is prohibitively expensive for my hobby.

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2025, 10:37:32 am
content: Quote from: crysti on May 07, 2025, 10:34:52 amThe deskew principles shown remain exactly the same for your SDS824X HD.

author: Martin72
author_rank: Super Contributor
timestamp: May 07, 2025, 02:49:25 pm
content: Quote from: tautech on May 07, 2025, 08:16:27 amThe owon is useless, at least his model is.

author: crysti
author_rank: Regular Contributor
timestamp: May 07, 2025, 05:02:41 pm
content: What do you think? Is it worth replacing the OPA2210IDRGT with ADA4896-2?It’s the first amplifier stage after the Hall sensor and, according to the datasheet, it is recommended to be powered at ±15 V.Will it still meet its specifications if powered at only ±4.5 V?

author: David Hess
author_rank: Super Contributor
timestamp: May 07, 2025, 05:11:55 pm
content: Quote from: crysti on May 07, 2025, 05:02:41 pmThe slow part is the hall sensor. Improving the amplifier and signal conditioning will not make it faster.

author: bdunham7
author_rank: Super Contributor
timestamp: May 07, 2025, 05:24:36 pm
content: Quote from: tautech on May 07, 2025, 01:33:42 amCould you ask about that? It might be handy to have a lot more deskew in some circumstances, even situations other than current measurements. I'm thinking of things like very long cables, specialized test fixtures with pre-input processing or circuits, etc.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 07, 2025, 06:15:34 pm
content: Quote from: crysti on May 06, 2025, 04:25:14 pm200 kHz is the response for a perfect sinewave and 3dB attenuated.To display a square-wave with enough details you need about 10x the bandwidth, so a 200 kHz probe can be used on a 20 kHz square-wave.I do not know the Owon probe so no clue how to improve it. I think the hall sensor could indeed be the bottle neck.

author: martin1959
author_rank: Contributor
timestamp: May 15, 2025, 03:46:21 pm
content: Quote from: tautech on May 07, 2025, 01:33:42 amI have Siglent SDS2204+, MicSig CP2100B (current) and DP10007 (differential) probes. The delay difference is ca. 140ns, so I adjust one channel to +70ns and the other channel to -70ns. It is possible to perform power analysis and other functions with this workaound. But it would be nice if Siglent could allow a little higher value (200ns) for the deskew.