Oscilloscope probe loading - Page 1
Forum section: electronics / general

author: Veketti
author_rank: Regular Contributor
timestamp: October 24, 2024, 04:44:44 pm
content: Hi,I'm tempted to purchase Probemaster spring loaded probe for my Siglent scope. The question I have is, do the probe have to have same 17 pf value than the scope inputs do? Original probes seem to be 18pF Or would the Probemaster PM4913-1 with 11 pf work just fine?Thank you in advance

author: TimFox
author_rank: Super Contributor
timestamp: October 24, 2024, 04:50:32 pm
content: Normal passive probes have a trimmer capacitor to get flat response with a given ‘scope input.They are specified to work with a 1 megohm input resistance and a specified range of input capacitance.The capacitance seen at the probe tip should be smaller than the ‘scope input capacitance.What are the relevant specs of the probes and your ‘scope?

author: Veketti
author_rank: Regular Contributor
timestamp: October 24, 2024, 06:11:03 pm
content: This probe that I was looking at has 10M-ohm, 11pf, 10x attenuation and 300MHz. Scope inputs are 1M-ohm, 17pF and 200MHz BW.

author: TimFox
author_rank: Super Contributor
timestamp: October 24, 2024, 06:27:19 pm
content: In the probe spec, what range of ‘scope input capacitance will it work with?(The probe trimmer adds to that capacitance to give the “bottom end” of the probe divider.)

author: 2N3055
author_rank: Super Contributor
timestamp: October 24, 2024, 06:55:14 pm
content: Compensation Range is 10pF to 50pF for Probemaster PM4913-1.Datasheet.

author: Veketti
author_rank: Regular Contributor
timestamp: October 25, 2024, 04:52:18 pm
content: So for dummies, did I understood right that as long as the probe compensation range is within the scope input capacitance range I'm good to go?

author: 2N3055
author_rank: Super Contributor
timestamp: October 25, 2024, 05:16:39 pm
content: Quote from: Veketti on October 25, 2024, 04:52:18 pmYou didn't say which exact scope you have.Input capacitance is normally written on front panel of the scope, near inputs.You should be OK, but it might be fiddly because range is so large (10-50pf).It would be better if it was 10-25pf, for instance, it would is easier to adjust trimmer when range is smaller..

author: David Hess
author_rank: Super Contributor
timestamp: October 25, 2024, 06:22:12 pm
content: Quote from: Veketti on October 24, 2024, 04:44:44 pmThe oscilloscope input capacitance and the probe tip capacitance are unrelated, so the Probemaster PM4913-1 will work fine. The lower tip capacitance compared to your old probes will actually improve measurement accuracy.What matters is that the compensation capacitance range of the probe must match the input capacitance of the oscilloscope. For the Probemaster PM4913-1, the compensation range 10pF to 50pF so again, this will work fine with your oscilloscope.

author: Veketti
author_rank: Regular Contributor
timestamp: October 27, 2024, 07:24:23 am
content: Thanks David, that's clear.

author: Bill3745
author_rank: Contributor
timestamp: December 30, 2024, 05:23:14 am
content: Quote from: Veketti on October 24, 2024, 04:44:44 pmDid you end up buying the PM4913-1 and if so are you happy with it? I was looking to pick up one myself.

author: Veketti
author_rank: Regular Contributor
timestamp: February 20, 2025, 05:54:27 pm
content: Hi, yes indeed I did. I'm very happy with it. I really like the spring loaded tip to always get even pressure and not to damage any pads etc. Also it had the spring ground supplied. Two length of ground leads with very flexible silicone wire. It's highest quality, no doubt and very worth the price. Wouldn't hesistate a second on buying again. Previously I've updated all my multimeter leads to Probemaster as well and in my opinion it's superior to any Rigol or Siglent scope leads. I have no experience on high end scope (Tek, Keysight etc.) leads so can't compare to them. Only downside is that they use imperial thread on the multimeter leads so alligator clips need to be bought from them.

author: chp
author_rank: Contributor
timestamp: April 29, 2025, 10:36:17 am
content: Hello!Can you share a screenshot of your Probemaster PM4913-1 probe's response to a 1 kHz test signal from a Siglent oscilloscope? I'm having issues with my probe and want to compare it with others.

author: TimFox
author_rank: Super Contributor
timestamp: April 29, 2025, 02:41:03 pm
content: Did you follow the procedure (from Probemaster) to adjust the compensation?Is the DSO input DC-coupled?

author: chp
author_rank: Contributor
timestamp: April 30, 2025, 07:56:22 am
content: Quote from: TimFox on April 29, 2025, 02:41:03 pmDo you mean?https://probemaster.com/all-about-oscilloscope-probes/I've got this (Screenshot). With siglent probes all looks good and flat.

author: David Hess
author_rank: Super Contributor
timestamp: April 30, 2025, 11:44:06 am
content: Quote from: chp on April 30, 2025, 07:56:22 amThat is your result with a Probemaster probe and after adjusting compensation?Do all channels look like that?Do you have another square wave source, like a function generator, that you can use in place of the compensation output?

author: chp
author_rank: Contributor
timestamp: April 30, 2025, 04:33:12 pm
content: Yes. All channels on 2 oscilloscopes (sds1204X HD and sds1202x-e) and 2 generators (sdg2122x and rigol dg4062)

author: David Hess
author_rank: Super Contributor
timestamp: April 30, 2025, 08:37:35 pm
content: Quote from: chp on April 30, 2025, 04:33:12 pmThere is definitely something wrong. Do you have more than one Probemaster probe to check?Some probes have high frequency transient response adjustments, but not at 200 MHz.Try running the same test with a direct coaxial connection and 50 ohm termination to see what the waveform should look like.

author: chp
author_rank: Contributor
timestamp: May 02, 2025, 06:28:36 pm
content: Quote from: David Hess on April 30, 2025, 08:37:35 pmNo, I haven’t. And this is last one I bought from Probe master. They said they cant help me..Anyway, now I want to buy a PMK probe with spring.Is a PML 711A-RO probe compatible with the Siglent SDS1204X HD? And why are the ones with lower bandwidth more expensive? Is it because of the cable length?

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2025, 12:31:47 am
content: Quote from: chp on May 02, 2025, 06:28:36 pmWhy are they more expensive? I cannot tell without examples.The PML 711A-RO should be completely compatible with the Siglent SDS1204X HD, but the ProbeMaster probe should also have been.

author: bdunham7
author_rank: Super Contributor
timestamp: May 03, 2025, 04:14:51 am
content: Quote from: chp on April 30, 2025, 07:56:22 amI assume this is with the compensation adjustment maxed out in one direction? If so, can you post what it looks like if you adjust back the other way? IDK whether there are any other adjustments in the compensation box (they don't come apart AFAIK) but if it is a throwaway anyhow perhaps have a look?

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2025, 05:01:40 am
content: This is the kind of problem which would lead me to testing the oscilloscope input with a normalizer to verify that it is working properly, however modern oscilloscopes do with normalization so this is a lost art. You could still make one to test the inputs.An oscilloscope normalizer is essentially a 2x probe and is made with a 1 megohm resistor in series with the input, and a compensation capacitor in parallel with the resistor.It is possible that Siglent is relying on a custom probe to apply equalization to their high impedance input, but normally this is not required to achieve 200 MHz bandwidth. If this is the case, then no "standard" oscilloscope probe is going to work properly.

author: chp
author_rank: Contributor
timestamp: May 03, 2025, 09:26:57 am
content: Quote from: David Hess on May 03, 2025, 12:31:47 amI mean High-Z Probe Series PML ® 2.5mm.PML 711-RO, 712-RO, 713-RO.https://pmkamerica.com/collections/pml-high-z-probe-seriesBig thanks to everyone for the answers and help!

author: chp
author_rank: Contributor
timestamp: May 03, 2025, 09:56:35 am
content: Quote from: bdunham7 on May 03, 2025, 04:14:51 amNo, it is compensated.Well, I opened compensation box and there is one more hidden attenuator for HF. I captured screenshots at both ends of the adjustment range. 1 kHz and 1 MHz.

author: Veketti
author_rank: Regular Contributor
timestamp: May 09, 2025, 02:56:22 pm
content: Hi,Here are screenshots. C1 is the PM4913-1 and C2 is the 4905-1. I could compensate more, but then the line is not horizontal anymore so I think this is the best it can be.

author: tggzzz
author_rank: Super Contributor
timestamp: May 09, 2025, 04:10:40 pm
content: Quote from: Veketti on May 09, 2025, 02:56:22 pmLF compensation looks good, but need a faster timebase to see the HF compensation. "Faster" means, say, 2ns/div to 50ns/div.

author: Veketti
author_rank: Regular Contributor
timestamp: May 09, 2025, 05:33:26 pm
content: Well, the oscilloscope internal 1kHz square wave output is so slow rise time that it's useless to even try to show anything faster than 500ns/div. But I got SDG1020 with 0.01ppm TCXO hack and used that to generate 1kHz signal. It does overshoot, but that's the signal generator's fault. So below is from SDG 1020 shots.

author: chp
author_rank: Contributor
timestamp: May 10, 2025, 10:36:06 am
content: This is mine.. Same peak. So, my probe is fine i guess, and this is just a feature of ProbMaster probes. Thanks!I'll come back once I’ve made the oscilloscope normalizer...

author: David Hess
author_rank: Super Contributor
timestamp: May 10, 2025, 11:09:53 am
content: Quote from: chp on May 10, 2025, 10:36:06 amThat feature should not exist. Something is broken.

author: chp
author_rank: Contributor
timestamp: May 10, 2025, 12:19:07 pm
content: This is mine... Siglent SDG2042X (unlocked to 120 MHz).

author: chp
author_rank: Contributor
timestamp: May 10, 2025, 12:22:47 pm
content: Well, we have 3 oscilloscopes and 3 different ProbeMaster probes. And the same issue occurs everywhere. Is it possible that Siglent oscilloscopes amplify peak display at slow timebase settings?

author: 2N3055
author_rank: Super Contributor
timestamp: May 10, 2025, 12:29:29 pm
content: Quote from: chp on May 10, 2025, 12:22:47 pmNo, not really.Otherwise it would happen with every probe.I presume that ProbeMaster's very wide compensation range (up to 50pf) might be part of the reason.You can try an experiment: connect tip of the probe to signal source via 47Ω resistor... What do you see?

author: chp
author_rank: Contributor
timestamp: May 10, 2025, 04:25:26 pm
content: Nothing changes.. w (2) and w/o (3) 47 Ohm.

author: David Hess
author_rank: Super Contributor
timestamp: May 10, 2025, 07:16:49 pm
content: Quote from: chp on May 10, 2025, 12:22:47 pmNo, but it is possible that the Siglent oscilloscopes are relying on equalization from the probe to provide a flat response, in which case only specific probes are going to work properly. This can be tested with a normalizer or a verified good probe. The response should be checked with a reference level pulse generator, but applying the source with a 50 ohm termination will show what the probe response should match.In the past when Tektronix released a new line of oscilloscopes, they sometimes released an A, B, or C version of the previous probe for the higher bandwidth models. This was because the probe itself provided equalization for the high impedance input which was slightly different from the old model.I have noticed that modern low cost DSOs somehow get away without having any input capacitance or equalization adjustments somehow, which makes me suspicious about how they provide proper equalization.

author: bdunham7
author_rank: Super Contributor
timestamp: May 11, 2025, 01:58:22 am
content: Quote from: chp on May 10, 2025, 04:25:26 pmYou mentioned that your compensation is not maxed out. Can you adjust it so that the overshoot "feature" is just barely eliminated or reduced to being almost imperceptible and post that screenshot?

author: bdunham7
author_rank: Super Contributor
timestamp: May 11, 2025, 03:31:18 am
content: Quote from: David Hess on May 10, 2025, 07:16:49 pmI set up a Siglent SDS1104X-E scope w/ 200MHz BW and fed it some square waves from an AWG. I used 3 probes--a Probemaster 100X/10M 4910-2, a Tektronix P9139A and the OEM Siglent PP215. I used a BNC-probe adapter for the first and last, the P6139A doesn't have one and I had to handhold it using a ground wire attachment similar to a ground spring. I've attached screenshots of the probes overcompensated, undercompensated and then expanded or with a 10MHz square wave to zoom in on that rising edge.The Probemaster looks good and you can see that the compensation changes are in that same small area as the overshoot that is appearing in the posts bychpandveketti.The Tek P6139A, a very high performance 500MHz probe that came with the TDS520/540. It retained that little blip of an overshoot even when properly compensated. I noticed that the area affected by the compensation was broader than the small area occupied by the overshoot blip. There are several additional adjustments in the compensation box but I didn't mess with them. This probe works very well on my 2465B.The Siglent PP215 came with the scope and you can see that it works pretty nicely with no fuss.I'm not sure it really is Siglent designing scopes that only work with their probes. The Siglent probes actually work just fine on non-Siglent scopes and any number of other probes have worked fine with my Siglent scopes. I suspect that this is more of an issue of HF/phase/step/etc compensation used in probes rated for more than 200MHz. 500MHz with a 1M probe is pretty tough to pull off in the first place and I'm sure you have to make some compromises to do it. A small overshoot is just a feature of fast edges, it's just a bit surprising to see it on a 1kHz signal generated by an AWG or calibrator output.Also, I believe that Siglent did make some of their higher-BW probes specifically to work with certain scopes but I can't find that info right now. But those were all well over 200MHz.

author: chp
author_rank: Contributor
timestamp: May 11, 2025, 02:02:10 pm
content: Quote from: bdunham7 on May 11, 2025, 01:58:22 amAllready did. This is the best I could get.

author: bdunham7
author_rank: Super Contributor
timestamp: May 11, 2025, 02:08:08 pm
content: Quote from: chp on May 11, 2025, 02:02:10 pmWhat I mean is to deliberately undercompensate it like my 6139A undercomp screenshot so that the peak of the overshoot is level with the top edge. This gives you an idea of where the compensation adjustment is working vs where your overshoot is. The second HF trimmer didn't have an effect?

author: chp
author_rank: Contributor
timestamp: May 11, 2025, 03:26:32 pm
content: Quote from: bdunham7 on May 11, 2025, 02:08:08 pmI already posted screenshots on the previous page. But here’s another one. The high-frequency attenuator on a 1 kHz signal only affects the very edge, which doesn’t solve problem. At the same time, the probe becomes undercompensated at high frequencies, which is incorrect.

author: chp
author_rank: Contributor
timestamp: May 11, 2025, 03:31:37 pm
content: Quote from: David Hess on May 10, 2025, 07:16:49 pmI tried it with the normalizer.Maybe I'm doing something wrong..

author: bdunham7
author_rank: Super Contributor
timestamp: May 11, 2025, 03:37:35 pm
content: Quote from: chp on May 11, 2025, 03:26:32 pmOK, so the regular compensation adustment is working in the ~5kHz range and the HF trimmer is affecting much higher frequencies. I concur that you are unlikely to improve on that. Try compensating it properly as you did before--a flat top, ignoring the overshoot. Then change to a 1MHz square wave like my 6139A 1MHz screenshot. Is it worse than that?

author: chp
author_rank: Contributor
timestamp: May 11, 2025, 07:40:31 pm
content: Quote from: bdunham7 on May 11, 2025, 03:37:35 pm1 Mhz.

author: tggzzz
author_rank: Super Contributor
timestamp: May 11, 2025, 07:46:45 pm
content: Quote from: bdunham7 on May 11, 2025, 03:37:35 pmDon't bother to change the fundamental frequency; it is irrelevant (1Hz would be perfectly adequate!)What you need to do is change thetimebaseso that you can examine therisetimein detail. That's what indicates the high frequency response.So, reduce the time/division one step at at time until you start to see ripples after a transition. Continue to the shortest time/division; if the risetime is longer than about 1 division, then you need an input signal with a faster risetime.

author: David Hess
author_rank: Super Contributor
timestamp: May 11, 2025, 07:52:50 pm
content: Quote from: chp on May 11, 2025, 03:31:37 pmThe normalizer tests the low and medium frequency response, so that looks fine.I looked back through the photos and did not really find what is required. If you do not have a reference level pulse generator, then three photos are required:Direct coaxial connection of the reference signal with termination into the oscilloscope input, through a 10x RF attenuator so that the oscilloscope volts/div does not change. This becomes the reference waveform.Probe connections to the terminated reference signal without the 10x RF attenautor. These photos should match the direct connection. The probe connections should be coaxial, but a spring clip is acceptable. Ground lead attachments will not work for this because they have too much inductance.A reference level pulse generator makes this easier because it can be assumed that the pulse has no overshoot or undershoot, so the direct reference connection is not required unless adjusting the oscilloscope's transient response.Of course for any of this to work, your signal source must have a rise/fall time as fast or faster than the oscilloscope, but sometimes you have to do the best that you can. Since the direct connected reference waveform is being compared to the probe waveform, the speed and aberration requirements are not as strict.

author: chp
author_rank: Contributor
timestamp: May 12, 2025, 09:02:27 am
content: Quote from: David Hess on May 11, 2025, 07:52:50 pmLike this one?http://probemaster.com/6143-bnc-to-bnc-10x-attenuation-cable/Have not any yet.. Do you have a schematic, so I can make it myself?

author: tggzzz
author_rank: Super Contributor
timestamp: May 12, 2025, 11:11:27 am
content: Quote from: chp on May 12, 2025, 09:02:27 amSeehttps://w140.com/tekwiki/images/6/62/062-1146-00.pdfBefore starting, ensure you have the right cable - which isn't ordinary coax!FFI see references athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: bdunham7
author_rank: Super Contributor
timestamp: May 12, 2025, 01:37:10 pm
content: Quote from: chp on May 12, 2025, 09:02:27 amThat one is 10M impedance and you could have the same or similar issues with it. You want to use a 50 ohm 20dB attenuator followed by a 50R terminator if you scope doesn't have 50R inputs.https://www.aliexpress.us/item/1005008964999919.html

author: David Hess
author_rank: Super Contributor
timestamp: May 12, 2025, 01:43:02 pm
content: Quote from: chp on May 12, 2025, 09:02:27 amNo, like this:https://www.ebay.com/itm/296116100134https://www.ebay.com/itm/286202294464https://www.ebay.com/itm/335807794405https://www.minicircuits.com/WebStore/dashboard.html?model=HAT-20A%2BThe reason it is needed is so that the signal level is the same when testing the direct coaxial connection and the 10x probes. Otherwise the volts/div setting is changed which could be the problem. 10x in voltage is the same as 20dB.QuoteIt is just 3 resistors in a Pi or T configuration:https://docs.keysight.com/display/genesys2010/AttenuatorsBut the physical construction needs to be good to preserve the signal shape.

author: chp
author_rank: Contributor
timestamp: May 13, 2025, 06:52:58 am
content: Got it. Ordered one. Thanks a lot!