SIGLENT SDS1104X-E measurement problems - Page 1
Forum section: electronics / testgear

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 24, 2020, 02:45:36 pm
content: empty, i can't seem to attach my 3 images correctly.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 24, 2020, 02:48:29 pm
content: I have some weird problems measuring with my new SDS1104X-E.This is the signal pulse I'm trying to capture in full:On the same capture as above; setting to 2V/DIV - this is the signal I'm expecting to see in the next capture, obviously with the missing peak.However this is what I get:For this capture I had to increase delay as it triggers at some preceding noise at this low trigger level.The weird thing is that if I swap CH3 with either CH2 or CH4 and set them to 10VDIV both channels work as expected. CH2 and CH4 also work as expected with the scope ref signal.I have also tried to dump the data for the 2V/DIV in the hope that the correct data was there but just not displayed correctly on the scope - alas it was not.What could be the problem?

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 24, 2020, 03:09:02 pm
content: it seems that setting CH2 and CH4 to 2V/DIV alters the signal, and that the issue is not trigger related. At least that's my current theory.Triggering on CH3 with CH2 and CH4 at 1V/DIVTriggering on CH3 with CH2 and CH4 at 2V/DIV

author: tautech
author_rank: Super Contributor
timestamp: April 24, 2020, 08:31:35 pm
content: Some suggestions if I may.Nearly always use DC trigger coupling. Then the trigger level is visible.AC channel coupling is only needed if a DC offset is present.Slow timebase down which displays more data points and captured waveforms can then be magnified both horizontally and vertically from the capture.....this is the real power of a DSO.....post capture data inspection.Use Trigger holdoff when the capture you need to see is after a previous event or adjust trigger level so to miss that event.Attempt to keep the trigger position on the display so to be able to see the actual trigger event.Further tricks are to work in Zoom mode with the primary display at a slow timebase setting, then much pre-trigger information is available in the capture and you can use horizontal position to view it in the zoomed display.You have much more power than a CRO at your fingertips so practice some to learn how to get the best from it.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 25, 2020, 09:01:58 am
content: tautech, thank you for the tips, I appreciate it.Good rule of thumb for the AC coupling, was in doubt bout that. And I will start using trigger holdoff. ;-)I agree the post capture data inspection is the rel power of DSO, I use it for the same reason. However the scope seems to alter my signal which renders it useless for my measurements. I will have to build an shielded attenuator to keep the signal within 1V/DIV as I don't have other ideas and options time being.

author: tautech
author_rank: Super Contributor
timestamp: April 25, 2020, 07:14:29 pm
content: When I look at the signal amplitude of your screenshots vs the channel input attenuation settings, at first glance all are using 10x attenuation but one channel 10V/div.Do you have one probe set to 1x by mistake ?If by chance there is, the additional capacitance loading from a 1x probe setting may be impacting on the signal fidelity.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 06:49:49 am
content: Quote from: tautech on April 25, 2020, 07:14:29 pmUnfortunately not. When fiddling with the probe it's very easy to flip the x10 button by mistake, and I have experienced several ruined days only to discover it was set on x1, so from then I'm very alert about the probe setting, even check it several times a day even if I haven't been touching the probes just in case the lab gremlins did something naughty.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 07:11:57 am
content: OK, so the question still remains what is causing the signal to be altered to what you see ?Scope settings or probing technique ?

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 09:53:51 am
content: Quote from: tautech on April 26, 2020, 07:11:57 amIf it's scope settings, then I have no clue what it could be.I currently doubt (not excluding it) it's probing technique, because CH2 and CH4 are connected to two individual scientific grade precision passive current transformers and as such are not physically connected to the circuit. CH3 is connected to the circuit, but if I disconnect CH3, the problem persists on CH2 and CH3.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 10:24:31 am
content: Quote from: Gaktyt on April 26, 2020, 09:53:51 amOK, can we do a sanity check using just the probe compensation 1 KHz square wave on all channels @2V/div.Use whatever channel you like for triggering and spread the channels apart so we can inspect each waveform.Post a screenshot.TIA

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 10:26:36 am
content: Hi,QuoteRemember, all the channels got the same gnd potential.Plus: Do you note the correct polarity of the transformers, when connecting the probes ?

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 10:28:23 am
content: Quote from: Martin72 on April 26, 2020, 10:26:36 amYes, just dawned on me too....ground loop ....but why is 1V/div OK ?

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 11:32:23 am
content: First of all, he should set the coupling to DC, all channels.Then it would be good if he explain, what he expected to measure - circuit description.And showing a screenshot wit lowered timebase, so we can see more from the signals.Nevertheless, it´s a strange behaviour.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 01:46:13 pm
content: Thank you all for your kind suggestions:The scope is powered through a isolation transformer- - no earthThe circuit is battery powered - no connection to mains or earthAll channels except CH4 are physically disconnected from scope.CH4 connected to current transformer specs herehttps://www.pearsonelectronics.com/pdf/4100.pdfCH4 set to DCCH4 connected to CT via BNC to probe adapterCH4 connected to CT via 50ohm coaxCH4 connected to CT via 50ohm coax with 50ohm terminationChanging to 2V/DIV makes it impossible to trigger due to preceding noise, no matter what I set holdoff time to, it triggers at the same noise in the beginning.It should be noted, that there are no problems when the scope is not only in 1V/DIV, but it's also fine at 500mV, 200mV etc. it's everything above 1V/DIV that presents problems.

author: 2N3055
author_rank: Super Contributor
timestamp: April 26, 2020, 02:06:39 pm
content: What is the amplitude of the top of that pulse? The fast first edge. It seems that is waay up outside of screen.If you are overloading the input that might explain wierd signal behaviour.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 03:32:01 pm
content: Quote from: 2N3055 on April 26, 2020, 02:06:39 pmI can't measure it ;-)Quote from: 2N3055 on April 26, 2020, 02:06:39 pmYes that could be a plausible explanation, but then why does it also work with 500mV/DIV and 200mV/DIV?

author: 2N3055
author_rank: Super Contributor
timestamp: April 26, 2020, 03:41:02 pm
content: Use faster timebase and find pulse top.Also, current transformers are specified to work on specific load on secondary. You have to have 50 terminator on it, so correct is to use 50 Ohm coax and termination on scope side and set ch to 1X. No other config is valid.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 03:42:52 pm
content: NOW MEASURING WITH A SIGLENT SDS2104XThe scope is powered through a isolation transformer- - no earthThe circuit is battery powered - no connection to mains or earthAll channels except CH4 are physically disconnected from scope.CH4 connected to current transformer specs herehttps://www.pearsonelectronics.com/pdf/4100.pdfCH4 set to DCCH4 connected to CT via BNC to probe adapterCH4 connected to CT via 50ohm coaxCH4 connected to CT via 50ohm coax with 50ohm terminationCompared to the SDS1104X-E (in post 01:46:13 pm) the difference in results is quite impressive, maybe even worrying.Here is the signal in full length at 500mV/DIV

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 03:49:18 pm
content: Quote from: 2N3055 on April 26, 2020, 03:41:02 pmHow will a faster timebase do that? I'm not sure I understand you.Quote from: 2N3055 on April 26, 2020, 03:41:02 pmAs I read the specs for this specific CT, all three configurations are valid, the 50ohm termination is just to avoid reflections. But perhaps I'm wrong, so if I'm wrong please tell me where in the CT documentation you find it.

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 04:11:41 pm
content: Could you share a photo from your testsetup with us ?

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 05:02:09 pm
content: Quote from: Martin72 on April 26, 2020, 04:11:41 pmSure, here you go:

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 05:35:08 pm
content: OK, thanks.QuoteIf your circuit is not top-secret, could you show the schematic from it and at which points you´re measuring ?If I remember it right, we got a such a current transformer too and a 1104X-E, maybe I can nearly reproduce it at work.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 05:44:22 pm
content: Quote from: tautech on April 26, 2020, 10:24:31 am

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 05:54:52 pm
content: Quote from: Martin72 on April 26, 2020, 05:35:08 pmIt's not top secret, it's mainly made of DIY components which took me weeks to fabricate, so you wouldn't be able to replicate it unless you had the time and machinery.Quote from: Martin72 on April 26, 2020, 05:35:08 pmI sincerely (in the original meaning of the term) appreciate your kind gesture, however I'm afraid it won't be this time. But thank you once again.

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 06:09:16 pm
content: Without further information, helping will remain a joint guessing game.OK, let´s guess again…As we don´t know the value of the current through the transformer, maybe he´s saturating or the inputs of the scope are going to clip.Hard to believe you couldn´t get the full signal (Amplitude) on the screen, with 10x probes, 400V are the maximum.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 06:42:01 pm
content: Quote from: Martin72 on April 26, 2020, 06:09:16 pmThere is no way in which, within my financial reach, that I could theoretically quantify the current that could be expected. I'm guessing just as well as you are.Quote from: Martin72 on April 26, 2020, 06:09:16 pmYes I agree, but that's only at 100V/DIV which I can't use.Regarding saturation, I find it highly unlikely, there is only one pulse and the CT is air-core good for 135MHz.That is why I think it would be a good idea if I made an attenuator or voltage clamp or both, and connected it between the CT and scope. This way I can be sure of the maximum.Could I use two e.g. 1n4148 cathode to cathode to clamp the voltage? I believe breakdown occurs at around 80V?

author: 2N3055
author_rank: Super Contributor
timestamp: April 26, 2020, 07:02:58 pm
content: I will repeat. you MUST absolutely load secondary of transformer with 50 Ohm. And than measure that voltage with scope.Otherwise you can get very high voltages when unloaded.Transformer is calibrated to give 1V per 1A with 50 OHm loading on secondary.That is first.So if you do that, and if you still can't see top of the pulse that means you have more than 40 A pulse when going it to scope 1x with just direct coax cable.If you put 50 Ohm terminator and then connect 10x scope probe, you can probe up to 400 V pulse (like Martin said), which would be 400 A pulse.That's a lot.Also first part of the pulse that contains a peak, looks very fast. On your current timebase (that is kinda slow) top of pulse is probably to fast to see. You should either go to faster timebase, or set acquisition to peak detect mode.Since you didn't say what are you measuring (it looks like some capacitor/static discharge) we don't know fast is the pulse. For static discharge test it is recommended to use at least 1 GHz scopes.... So your scope might not even be fast enough for all we know...

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 07:04:23 pm
content: QuoteOK....As I wrote it two times, a schematic of the circuit would be helpful, but I won´t ask for it again.Quote100V, but: We´re talking about the using of the current transformer mentioned before, right ?Edit: Sinisa was faster.

author: StillTrying
author_rank: Super Contributor
timestamp: April 26, 2020, 07:05:35 pm
content: Quote from: Gaktyt on April 26, 2020, 06:42:01 pmIt might be too late.The CT's proper restive load should be enough, don't try it without a connected load.When a large unknown voltage is off screen, the shape of what does appear on the screen can't really be trusted, it often takes the scope's input some time to recover from the voltage overload, especially with DSOs. 2N3055 mentioned this.[edit and more now]When capturing +ve going only waveforms you're allowed to move the 0V marker below the mid screen to fit more of the +ve on.For a +ve only waveform I often move the 0V right to the very bottom of the screen.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 07:45:49 pm
content: From the info forthcoming while sleepingI see 2 things that are of concern.As others have mentioned the CT's need termination and at those voltage levels NOT by the 50 Ohm input of SDS2000X for risk of damage to its inputs. 50 ohm feedthrough BNC terminations should be suitable.Where Ch3 reference (ground) lead is connected is commoning with the CT reference points and I believe a differential probe may be required on Ch3.Do you have a differential probe Gaktyt ?

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 07:52:20 pm
content: Quote from: 2N3055 on April 26, 2020, 07:02:58 pmYou are right, I reread the documentationhttps://pearsonelectronics.com/pdf/Application%20Notes.pdfQuoteSo only 50 ohm coax to high impedance scope input from now on. I will not use the termination as that alters the signal heavily on the 1104X.How would you explain this difference then?SDS1104X CT connected with 50 ohm coax.SDS1204X CT connected with 50 ohm coax.[sorry i attached wrong image again, will attach in new post as I can't do that when editing]Quote from: 2N3055 on April 26, 2020, 07:02:58 pmThat makes sense. Here is a scopeshot at 50nS/DIV, DC coupling, CT connected via 50ohm coax.Quote from: 2N3055 on April 26, 2020, 07:02:58 pmYou are right, but for my purpose I would be happy just seeing the signal at 10V/DIV. I don't really need the peak in it's entirety that much.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 07:57:37 pm
content: trying to attach againHow would you explain this difference then?SDS1104X CT connected with 50 ohm coax.SDS1204X CT connected with 50 ohm coax.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:01:26 pm
content: Quote from: Martin72 on April 26, 2020, 07:04:23 pmThank you.Quote from: Martin72 on April 26, 2020, 07:04:23 pmYes, inserting it between the coax and scope input, all in a shielded box. That was my intention.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 08:02:16 pm
content: 50 ohm coax by itself is NOT a 50 ohm termination.You need 50 ohm coax and a suitable 50 ohm termination to have a properly balanced signal line for the CT then probes or the scopes input will pass the correct signal. You can set the scopes input where the CT's are connected to display current measurement ....see P2 of the channel menu.

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2020, 08:03:08 pm
content: QuoteOK, I´m out of here.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:03:13 pm
content: Quote from: StillTrying on April 26, 2020, 07:05:35 pmI usually do that too, but for this thread I placed it at zero.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:10:47 pm
content: Quote from: tautech on April 26, 2020, 08:02:16 pmYes I know that, but see what the termination does to the signal on the 1104X (01:46:13 pm) compared to the 1204X (03:42:52 pm)

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:15:21 pm
content: Quote from: Martin72 on April 26, 2020, 08:03:08 pmI'm sorry about that. I wassincerelythanking you for respecting my decision, I though that was very civilized of you, therefore I felt the need to thank you. Apparently "Thank you" doesn't mean what I think it does, so I'msincerelysorry if I have offended you in any way, that was not my intention and I would besincerelyhappy to see you back.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 08:22:16 pm
content: Quote from: Gaktyt on April 26, 2020, 08:10:47 pm3 things, scope model #'s are incorrect, your time is not the same as mine(use post #) and displayed results will be wrong if the waveform is off the display.Q. Do you know the expected amplitude of the current pulse measured by the CT ?Set the scope with the waveform lower on the displayandselect Amps/div as the input and with a P-P measurement showing the expected output. Use the input attenuation settings to have this display the correct value.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:34:32 pm
content: Quote from: tautech on April 26, 2020, 07:45:49 pmNo I don't own a diff probe unfortunately. And I think from now on the setup will be as depicted in post of 05:02:09 pm, I think it's better just to focus on one single CT and be somewhat sure that it's a correct measurement.Ref termination as 2N3055 pointed out to me, from the documentationhttps://pearsonelectronics.com/pdf/Application%20Notes.pdf"The output receptacle of the current monitor is connected via the coaxial cable to the high-impedance oscilloscope or voltmeter input."and"External Termination When viewing pulse rise times below 100nanoseconds, RF currents above a few mega-hertz, or when using long cables, it is advisable to terminate the general-use current monitor output cable at the oscilloscope with 50 ohms to prevent standing waves or cable fill-time effects.With this termination the output voltage will be approximately half the unterminated value,subject to the accuracy of the termination resistance, and the attenuation of the cable."The termination seems to be produce more "correct" signals on the 1204X than on the 1104X, so I would be reluctant to use termination on the 1104X, or just use the 1104X at all.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:44:25 pm
content: Quote from: tautech on April 26, 2020, 08:22:16 pmI'm sorry i don't understand what you mean by that.Quote from: tautech on April 26, 2020, 08:22:16 pmI can't locate the post#, this is what I see in my firefox browserQuote from: tautech on April 26, 2020, 08:22:16 pmDuly noted, thank you.Quote from: tautech on April 26, 2020, 08:22:16 pmNo, it is not possible for me to quantify that, I'm just guessing.Quote from: tautech on April 26, 2020, 08:22:16 pmAlready tried that at 1V/DIV with the trace as low as possible, the peak does still not appear.Which input attenuation settings are you referring to?

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 08:49:11 pm
content: Quote from: Gaktyt on April 26, 2020, 08:34:32 pmNo matter, we can address that when we need to a bit later.QuoteYes, back to basics and then build the complete measurement system from there.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2020, 08:57:45 pm
content: Quote from: Gaktyt on April 26, 2020, 08:44:25 pm

author: StillTrying
author_rank: Super Contributor
timestamp: April 26, 2020, 09:51:21 pm
content: Can't you create a known AC current to pass through the center of the CT, 12 VAC and 12V bulb would do, winding the wire multiple times through the CT would give higher currents.www.pearsonelectronics.com/pdf/4100.pdf

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2020, 05:24:05 am
content: Gaktyt, the first step you must do is confirm scope input settings and correct termination are each correct to get accurate results from your CT's.StillTrying's idea is quite valid and you can check the CT measured value matches a AC current measurement on your DMM.So a few minutes replicating the waveforms posted earlier using an AWG, Exponential curve output into a 50 ohm load reproduced with Ch2. Inverts and such used to replicate edges of previous waveforms, ignore them.Note, this is a repetitive free running waveform so no need for Single shot capture.On Ch4 is a Tek P6021 current probe on the 2mV/mA probe termination setting so therefore needs a 0.5x channel input setting.P-P measurements added....all pretty basic stuff.I mentioned a differential probe and as you haven't got one I've also included an example of the 'poor man's' diff probe using channel subtract from the Math menu.Simply, it's done like this:Google 'DSO differential measurements' for further info.The Math trace was used to replicate the 1x cable measurement of Ch2 using two 10x probes in a 'poor man's' differential configuration with both probe reference (ground) leads removed.2 channels are needed so 1 and 3 were used and made invisible to remove unnecessary display clutter.There's a wealth of info in this screenshot so study it carefully......same DSO as yours, SDS1104X-E.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 08:34:18 am
content: Quote from: StillTrying on April 26, 2020, 09:51:21 pmThank you for your excellent suggestion. I have considered this myself previously as a way to create a reference, however I abandoned the idea since the AC would be 50Hz and the CT's minimum frequency is 150Hz. But you got me thinking, I have a square wave generator capable of up to 20V and a few amps around 40KHz, perhaps I could use that with a known induction free resistor?

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 09:08:14 am
content: Quote from: tautech on April 27, 2020, 05:24:05 amYes I agree.If you don't mind I would like to recap what I think (and what I think is not necessarily correct) the discussion has produced in ways of locating the problem. Obviously I have also learned a lot about proper scope operation which I'm very grateful for, so I'm taking this opportunity to thank everyone for their valuable input.CT connection and termination: The CT must be connect to the scope with 50ohm coax and termination, this yields a true attenuated replication of the current.Signal attenuation: In order to compensate for the attenuation, I need a know reference (which I don't have time being)Signal overvoltage: Since I can not quantify the expected peak overvoltage remains a concern. This morning I have built a voltage clamp out of two BNC plugs, two 1n4148 cathode to cathode, and a piece of alu foil for shielding, all which should clamp the voltage to about 200Vpp I believe. I'm not completely sure that it would work as intended, I don't have that experience, but in theory I think it should. If the voltage clamp works as intended and the problem persists, then overvoltage can be excluded from possible error sources.Quote from: tautech on April 27, 2020, 05:24:05 amI always wanted to measure diff with ground probes disconnected but was uncertain due to my inexperience, thank you.I have another fundamental doubt if I may, If a 50ohm coax is connected to a 50ohm output impedance, does the cable attenuate a given signal?Quote from: tautech on April 27, 2020, 05:24:05 amI sincerely appreciate your time and effort, and I will study it carefully, thank you.

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2020, 09:24:36 am
content: Quote from: Gaktyt on April 27, 2020, 09:08:14 amYes, attenuate it correctly !Sorry, no.The coax allows for correct transmission of the waveform as part of a transmission system when coupled with the correct impedance termination......a match for both the signal source and the coax impedance.It's abalancedtransmission system.Back a bit, member 2N3055 IIRC pointed out the CT need be terminated into 50 Ohms which applies the correct loading to the CT instead of the high voltage peaks you see. The scope's 1M input has no hope in hell of loading the CT enough for it to give accurate readings. Properly loaded there is no requirement for a clamp.My first current probe was a small PCB CT from an old PC PSU and it did much the same thing as you are seeing.....way too high readings so a friend lent me his Tek P6022 current probe to experiment with shunt resistors across the CT output until the readings somewhat matched. As it was a SMPS CT it was only ever designed for a few 10's of KHz and tests against the Tek current probe confirmed this however it was still useful in the time I used it......before a Tek P6021 was added to my kit....then another and another. Recently a P6022 as well !Yes I have a fetish for these current probes.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 11:00:03 am
content: Quote from: tautech on April 27, 2020, 09:24:36 amNoted, so when the CT manufacturer states"The output receptacle of the current monitor is connected via the coaxial cable to the high-impedance oscilloscope or voltmeter input ... The voltage wave-shape as displayed on the oscilloscope will then be a faithful reproduction of the actual current waveshape ..."they must be incorrect because the CT is not terminated by the suggested procedure, if I understand the implications correctly.Quote from: tautech on April 27, 2020, 09:24:36 amNoted, so when the CT manufacturer states"When viewing pulse rise times below 100nanoseconds, RF currents above a few mega-hertz, or when using long cables, it is advisable to terminate the general-use current monitor output cable at the oscilloscope with 50 ohms to prevent standing waves or cable fill-time effects.With this termination the output voltage will be approximately half the unterminated value."They must be incorrect because they are unaware that their CT must be terminated under all circumstances, and therefore the terminated output voltage is in fact the actual and true value, and not"approximately half the unterminated value"if I understand the implications correctly.Quote from: tautech on April 27, 2020, 09:24:36 amI can understand your fetish. There was a guy here on this forum who designed a diff probe with an AD8130, I took his design and adapted it to my needs and even successfully simulated it and did a PCB layout, but then my project stopped there because of the SMD's - I really dislike them, because I'm old and my hands are shaking. But the design experience was very educational.

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2020, 11:27:03 am
content: Quote from: Gaktyt on April 27, 2020, 11:00:03 amYes but we still must check if the readings it provides are correct and I suggest you set a scope channel correctly to Amp units and 1x input attenuation, then check it's accuracy against a known current draw of a sinewave P-P measurement. You might get a good enough result to prove accuracy with mains draw of a lightbulb or Stilltrying's LV method.....accuracy to prove you are on the right path.I see what may have confused you is the 1V/A that you need set as 1x and units of amps.Quote from: Gaktyt on April 27, 2020, 11:00:03 amI'm not at shaking hands yet thankfully but the eyesight is not as good as it used to be so I can't do SMD without a visor and I've not gone smaller than 0805. I place and tack but placing on paste might be an option for you.Persevere with SMD if you can but maybe still use TH silicone devices. Seems a shame that diff probe is unfinished.

author: 2N3055
author_rank: Super Contributor
timestamp: April 27, 2020, 11:55:47 am
content: Terminate at all times. Period. Because you don't know what are you measuring, and CT is serially terminated with 50 Ohm, not parallel. That means there is no load.If you apply very fast pulse, CT will ring out some crap at it's resonant frequency.So, if you were measuring 10 kHz sinewave you could be un-terminated and be ok with it.But you have very fast, very high energy pulse going into that core.. If you are not terminated you have no clue of how it is going to look..Also, you said you don't want to look at the whole pulse. Well, physics don't care what you want. You MUST put whole pulse on your screen. That ( and just a bit more) is whole dynamic range of your scope.Otherwise you are over driving scope vertical amp and all you are looking at is scope amplifier overdrive recovery curve.And also, that will give you good idea about pulse risetime (you need to know that) and also of the top of pulse (is your CT saturating for instance).After you have whole waveform and have good idea of how it looks, than you can devise way to look at parts of it. You might need to clamp the pulse if you want to see only lover part of full amplitude. In which case you will need to verify if clamp works well and on proper voltage, recovers well so part of signal you want to look at is undistorted.Basically except simple "I checked this battery with multi-meter and is above 12 V", a bit more complicated stuff in measurements must be approached as science experiment. Research the topic, learn about signal you want to measure, devise method, verify method, and then measure data and verify data. Rinse and repeat until you have trust in results.

author: StillTrying
author_rank: Super Contributor
timestamp: April 27, 2020, 12:07:00 pm
content: The pearson site and pdfs are quite bad, IMOThey swap between current transformer and current monitor randomly without giving useful details of either.It took me lots of searching to find this.How much resistance is inserted?Each Pearson CT has an internal terminating resistor that converts secondary current into an output voltage.www.pearsonelectronics.com/support/faqs

author: 2N3055
author_rank: Super Contributor
timestamp: April 27, 2020, 12:18:43 pm
content: Quote from: StillTrying on April 27, 2020, 12:07:00 pmLike I said, it has serial 50 Ohm termination. That is there to make impedance matching to 50 Ohm coax when going into 50 Ohm input on instrument.On high impedance instrument, that 50 Ohm gets in series with 1MOhm (or 10) making it pretty much unloaded.They will work on 1MOhm (or 10 MOhm with 10x probe), anything will.. But impulse response will be pretty much undefined (unless you make full characterization yourself).AFAIK, they don't even provide pulse response graph, and use words like "usable rise time".There is also a question of DC bias. If wire you are measuring has DC current on it in addition to pulse, core might badly saturate...

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 12:38:21 pm
content: Quote from: tautech on April 27, 2020, 11:27:03 amGreat, I think I will ask the manufacturer to clarify their documentation so that other less experienced like me don't go through the same trouble. I have a small 20W mono class-A audio amplifier module, I think I will feed that with a 10KHz sine and put a resistor on it's output, then I can use it as reference.Quote from: tautech on April 27, 2020, 11:27:03 amI'm still confused about that one, I thought that changing the unit on the scope actually meant to change the unit i.e. substituting V for A on the display, but I can understand it does more than that, but I don't know what.Quote from: tautech on April 27, 2020, 11:27:03 amI can't even place on pasteand in addition I got the eyesight problem as you. I don't know what a "TH" is. And yes the probe sim showed -3dB at around 70MHz which is perfect for me.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 12:51:44 pm
content: Thank you for your valuable insights, I appreciate it very much.Quote from: 2N3055 on April 27, 2020, 11:55:47 amI don't fully understand this, so it's a scope thing or a physics (as in science) thing?Quote from: 2N3055 on April 27, 2020, 11:55:47 amWell, I couldn't disagree with you on that, so true. It's just sometimes like this there are too many details to take into consideration for the inexperienced like me, and that is just confusing at start.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 01:01:21 pm
content: Quote from: 2N3055 on April 27, 2020, 12:18:43 pmDuly noted thank you. It just goes to prove that even if you like Pearson have been doing the same thing for 75 years and become a scientific plug-and-play standard, then you can still mess things up. Just think of all scientific papers out there following the operating instructions to the letter and ending up with the incorrect result because the users don't have a background in EE.

author: Gaktyt
author_rank: Regular Contributor
timestamp: April 27, 2020, 01:10:07 pm
content: Based on the guidance I have received here, I think I have managed to capture a true-ish waveform, true in form but not in amplitude I mean, I still have to make a reference.CT connected to 50 ohm coax with 50 ohm terminationUnfortunately the whole signal is not within the screen so it is not valid.CT connected to 50 ohm coax with 50 ohm termination and 16.2V voltage clampHere the peak is within the screen so the measurement must be valid, except that it seems distorted, maybe it's the diode capacitance causing it.

author: 2N3055
author_rank: Super Contributor
timestamp: April 27, 2020, 01:19:02 pm
content: Quote from: Gaktyt on April 27, 2020, 12:51:44 pmBoth. Vertical sensitivity knob is not a graphical zoom button. It controls amplification and attenuators on input. If you put it to say 1V/div, you have (on this scope ) range from -4V to +4V to work with.OK maybe -5 to +5V of full dynamic range. You input +10V into it, scope will not explode, it will put amps in saturation, and after you remove that (too high) pulse, it will have to recover first, before making any sense again. It can take few us or few ms before it gets back into linear regime and starts behaving properly again. All scopes have that limit. It will be different between any different scopes, it will even be different between different V/div on the same scope. Sometimes when you have large DC offset and small AC component on top of it, you can apply offset. Or AC couple. But you can use it only if by doing that you can pull whole vertical amplitude of pulse onto the screen.. Looking at just part of pulse by overdriving input is equivalent to say, trying to isolate triangle inside whole orchestra by pumping out the volume of the amplifier. Fact that you plan to listen only to triangle, won't mean that other louder sounds won't overdrive amplifier and create distortion or even a smoke if you go too far.

author: 2N3055
author_rank: Super Contributor
timestamp: April 27, 2020, 01:22:53 pm
content: Just to make sure, based on datasheet, probe ratio is 500mV/1A when 50 Ohm terminated.

author: StillTrying
author_rank: Super Contributor
timestamp: April 27, 2020, 03:04:07 pm
content: "CT connected to 50 ohm coax with 50 ohm termination"To correct the scope's A/div readings with the halving of the V/A sensitivity with a 50R termination, change the scopes X1-X10 to X2, 1A/div. will change to 2A/div.Surely +/- 80 Amps is enough to fit the real current spikes on the screen.

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2020, 06:11:20 pm
content: Quote from: Gaktyt on April 27, 2020, 12:38:21 pmTrust us on this.Set the CT channel to Amps unitsandselect a P-P measurement for that channel.As others have indicated CT termination is dependant on waveform type as unterminated its fast edge will ring like a mongrel while sine waves it will handle with ease.I'm not entirely comfortable with your clipping setup despite the pretty result.When pushing limits and proving designs you want to see everything so to be sure when you are approaching the point of losing control of that expensive silicon magic smoke.For the majority of power electronics fast current edges are the norm which to reproduce faithfully is also BW related hence my preference for high BW current probes.BTW, TH earlier = through hole (parts).