Problem with the probe compensation adjustment - Page 1
Forum section: electronics / beginners

author: OscilloscopeSeeker
author_rank: Newbie
timestamp: July 13, 2022, 01:04:22 pm
content: Hello! I recently received a new (first in my life) oscilloscope with new probes. When I was adjusting the compensation of the probes, I found that I could not get a undercompensation. It varies from overcompensation level to normal compensation. What could be the problem? Or maybe this is normal and I shouldn't be nervous about it?Probe: PP510, probe set to X10 (in channel settings also)Oscilloscope: Siglent sds1104x-u

author: Zenith
author_rank: Frequent Contributor
timestamp: July 13, 2022, 05:30:59 pm
content: I suppose if you can achieve correct compensation, that's fine. However, this seems odd. I'd expect the probes supplied with a new scope to be adjustable from definitely under-compensated, to correct compensation, to definitely over-compensated.Have you pushed in the BNC connectors and turned them so they lock? New ones can be stiff.Have you pushed on the probe's hook properly?Have you tried without the hook and holding the probe tip on the calibration terminal?Are you using the proper adjustment tool, that should have come with the probes, or are you using something like a jeweller's screwdriver that was handy? They don't include those adjustment tools for no reason.Is this one probe or both probes?Is this on one Y channel or both Y channels?Is there something else which might interfere, such as having a Y channel filter turned on?

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2022, 05:52:25 pm
content: With normal 'scope probes, the specification gives a range of input capacitances (at the 1 megohm 'scope input) to work with.Your 'scope should similarly specify the capacitance in parallel with the 1 megohm input resistance.Do these values match? If the 'scope spec is within the range of the probe specs, then one or the other is out of spec.(This assumes you did not add anything else, such as a tee or short cable after the probe connector.)

author: OscilloscopeSeeker
author_rank: Newbie
timestamp: July 13, 2022, 08:03:18 pm
content: TimFox, Zenit, Thank you for the responses!Quote from: Zenith on July 13, 2022, 05:30:59 pmYes, I push and turn them 90 degrees clockwise.Quote from: Zenith on July 13, 2022, 05:30:59 pmI think yes.Quote from: Zenith on July 13, 2022, 05:30:59 pmI just tried it, same result.Quote from: Zenith on July 13, 2022, 05:30:59 pmYes, i use the plastic screwdriver that came with.Quote from: Zenith on July 13, 2022, 05:30:59 pmYes, all probes behave the same. And each probe behave the same on all ports.Quote from: Zenith on July 13, 2022, 05:30:59 pmI think no, I press default button (the manual says that it resets the oscilloscope to default settings) before adjusting.Quote from: TimFox on July 13, 2022, 05:52:25 pmI am new to oscilloscopes, so I don't know how understand these characteristics. I need help.The following is written under the BNC connectors (on the oscilloscope):All inputs: 1MΩ/11pFAnd in the user manual of the probe:Input resistance: 1MΩ/10MΩ +-2%Input capacitance: 1X: 85pF~120pF, 10X: 18.5pF~22.5pFCompensation Range: 10pF~30pF

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2022, 08:43:36 pm
content: "Quote from: TimFox on Today at 12:52:25 pmWith normal 'scope probes, the specification gives a range of input capacitances (at the 1 megohm 'scope input) to work with.Your 'scope should similarly specify the capacitance in parallel with the 1 megohm input resistance.Do these values match? If the 'scope spec is within the range of the probe specs, then one or the other is out of spec.(This assumes you did not add anything else, such as a tee or short cable after the probe connector.)I am new to oscilloscopes, so I don't know how understand these characteristics. I need help.The following is written under the BNC connectors (on the oscilloscope):All inputs: 1MΩ/11pFAnd in the user manual of the probe:Input resistance: 1MΩ/10MΩ +-2%Input capacitance: 1X: 85pF~120pF, 10X: 18.5pF~22.5pFCompensation Range: 10pF~30pF "The probe is designed to work with 10 pF to 30 pF, and the scope input capacitance is rated at 11 pF.This should work, but it has little margin.It's not surprising that the probe just reaches "compensated" before the end of the adjustment.

author: tautech
author_rank: Super Contributor
timestamp: July 14, 2022, 12:54:29 am
content: Quote from: OscilloscopeSeeker on July 13, 2022, 01:04:22 pmI've seen this too and reported it to Siglent.Probes and channel combinations are sometimes all different and when you can't quite get proper compensation my advice is to reassign/swap that probe to another channel and try again.If you can't get them compensated with any probe/channel combination send the darn thing back and insist it's replaced with a working probe combination.

author: Zenith
author_rank: Frequent Contributor
timestamp: July 14, 2022, 08:37:28 am
content: Scope input channels have a tolerance for their capacitance, which is usually stated, say 20pF +/- 2pF. The probe compensation range will also have a tolerance - they won't all be 10pF to 30pF - some will be slightly different. Get a scope with input capacitance on the low end of the spread, and a probe with a range on the high end, and the probe could never be compensated correctly. Then there might be slight temperature and aging effects.Siglent are cutting it very fine with this.

author: tautech
author_rank: Super Contributor
timestamp: July 14, 2022, 09:55:46 am
content: Quote from: Zenith on July 14, 2022, 08:37:28 amFear not they know although there will be a good number of units around the world waiting for sales.I've done a couple of PD checks on X-U models lately and what I reported earlier has improved for probes now to be much easier to compensate properly whereas before you sometimes need swap probes around.

author: StillTrying
author_rank: Super Contributor
timestamp: July 14, 2022, 01:04:51 pm
content: Have you first done the Self-Calibration, all probes removed and done when it's warmed up.Are all the channel inputs on DC COUPLED for the compensation, and waveform height around 6 divisions.I'll be surprised if the sds1104x-u's input capacitances are only 11pF, unless there's some bits missing off the inputs.

author: TimFox
author_rank: Super Contributor
timestamp: July 14, 2022, 01:45:04 pm
content: A quick check of the capacitance range hypothesis:Add a BNC Tee connector between the probe and 'scope input: it should increase the 'scope input capacitance by a few pF (I can't find a spec quickly).

author: Zenith
author_rank: Frequent Contributor
timestamp: July 14, 2022, 02:05:40 pm
content: The characteristics of the scope input are written on the scope, They are also given in the datasheet as DC: (1 MΩ±2%) || (11 pF ±2 pF).https://telonic.co.uk/product/siglent-sds1104x-u-4ch-100mhz-1gsa-s-14mpts-super-phosphor-oscilloscope/Look under specification on that page. It seems low, but there it is.That probe has a stated compensation range 0f 10-35pF. No tolerance mentioned.https://siglentna.com//wp-content/uploads/2020/02/PP510_Users_Guide_082017.pdfAll rather tight and it's easy to see how you could end up, by the luck of the draw, with a probe and channel combination incapable of being set correctly. More likely you'd have something only just capable of being set correctly, as seems to be the case here.