How to minimize the noise from the oscilloscope probe - Page 1
Forum section: electronics / beginners

author: khtwo2002
author_rank: Contributor
timestamp: January 09, 2016, 09:35:31 pm
content: I can see that the oscilloscope probe act as antenna and introduced noise to the oscilloscope waveform. This is especially obvious when my hand move close tot he probe head. I also see that the noise is significantly reduced when putting probe on the anti static grounding mat. Are there any other ways to minimize this "antenna" effects?

author: tautech
author_rank: Super Contributor
timestamp: January 09, 2016, 09:44:26 pm
content: Minimise the length of the Reference (GND) lead.There are times when only the std lead will reach a safe reference point (usually GND) and for many circuits this is adequate, but in noisy circuits other options should be used.Alternatives include:Probe GND spring connectorsDirect coax connectionDifferential probes

author: brillopad
author_rank: Contributor
timestamp: January 10, 2016, 12:19:37 am
content: W2aew has some scope videos this one is about low noise probes.

author: MarkS
author_rank: Unknown
timestamp: January 10, 2016, 12:58:46 am
content: I've only ever used an oscilloscope once, so I have extremely limited knowledge. However, I too noticed what you are seeing. I didn't have the ground lead connected to anything as I wasn't sure what it was at the time. Once I connected it to ground, the signal cleaned up completely.

author: cdev
author_rank: Super Contributor
timestamp: January 10, 2016, 03:02:47 am
content: The late, legendary Bob Pease wrote some worthwhile reading on this and related subjects and I am pretty sure also did at least one YouTube video. Its one of those things you remember because you use it all the time.Yes, short leads are all important.

author: mtdoc
author_rank: Super Contributor
timestamp: January 10, 2016, 03:59:36 am
content: Quote from: cdev on January 10, 2016, 03:02:47 amMaybe this one:

author: cdev
author_rank: Super Contributor
timestamp: January 10, 2016, 04:37:46 am
content: Yes, thats the one!

author: khtwo2002
author_rank: Contributor
timestamp: January 10, 2016, 04:54:26 am
content: Thank you all for the information.I did some noise tests with my DS1054z, in all tests the probe head are floating in air and aren't directly connected to any signal source. Here are the vpp peak-peak value:Disconnect probe: 10.4-11.2mv (this is the oscilloscope internal noise, normal?)Connect probe with GND spring, probe head on antistatic grounded mat: 10.4-12.0mvConnect probe with GND spring, probe head on antistatic UN-grounded mat: 17-18mvConnect probe with GND spring, probe head not on antistatic grounded mat: 12-30mv depend on the different positionConnect probe without GND spring, probe head on antistatic grounded mat: 12.8-14.4mvConnect probe without GND spring, probe head on antistatic UN-grounded mat: 23.8-24.8mvConnect probe without GND spring, probe head not on antistatic grounded mat: 13.6-56mv depend on the different positionConnect probe with std hook cap, probe head on antistatic grounded mat: 46-50mvConnect probe with std hook cap, probe head on antistatic UN-grounded mat: 106-110mvConnect probe with std hook cap, probe head not on antistatic grounded mat: 34-200mv depend on the different positionSo, when working on the grounded anti-static mat and the probe with ground spring, I got the almost noise free signal input. In conclusion:1. Grounded antistatic mat significantly reduce the noise level. I'm planning buy a larger antistatic mat that can cover my whole table2. GND spring can help reducing the noise level and get almost perfect signal, but not always convenient. I think in most cases, the bare head without GND spring should be good enough.3. Try stay away from the std hook cap, which significantly amplified the noise level up to 200-300%. I think this is probably because the hook cap doesn't have a grounded metal wrap around the probe needle, thus make the unwrapped needle much longer than original. This "extended antenna" is more sensitive to the common noise waves around us, and receive more energy from those noise. I wonder if adding a grounded metal wrapper could improve the performance of the hook cap. Will do some test later.

author: jitter
author_rank: Frequent Contributor
timestamp: January 10, 2016, 07:55:45 am
content: I see no mention of limiting the bandwidth of the scope.If you don't need a bandwidth > 20 MHz, then switch on BW limit (try it anyway and see what happens).

author: tggzzz
author_rank: Super Contributor
timestamp: January 10, 2016, 10:11:32 am
content: Quote from: khtwo2002 on January 10, 2016, 04:54:26 amWhat frequency? What probe type? Those areveryimportant factors.QuoteConvenience is irrelevant. Testing has to be an integral part of design and construction.There are alternatives, e.g. a very effective homebrew tip describedhttps://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/QuoteThe probe won'tamplifyanything.QuoteThere is a lot of information pertinent to your situation in the various references athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: khtwo2002
author_rank: Contributor
timestamp: January 10, 2016, 07:54:35 pm
content: Quote from: tggzzz on January 10, 2016, 10:11:32 amIt's pure noise in the air. The probe is a passive 150Mhz probe that come with Rigol DS1054Z.Quote from: tggzzz on January 10, 2016, 10:11:32 amTrue if you already know the testing point. For the situation where you still looking for the exact point to test, convenience still a factor.Quote from: tggzzz on January 10, 2016, 10:11:32 amThanks for the link.Quote from: tggzzz on January 10, 2016, 10:11:32 amMaybe I use the wrong word. What I mean is that the probe head(antenna) receive more energy from the noise in the air, and makes the probe more sensitive to these noise.Quote from: tggzzz on January 10, 2016, 10:11:32 amThat's quite some material to read. Thanks!

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: January 11, 2016, 01:26:39 am
content: This may sound silly, but sometimes arranging/messing with the probe's excess cable can make a pretty big difference too. Try loose coils, etc.

author: jitter
author_rank: Frequent Contributor
timestamp: January 11, 2016, 06:11:22 am
content: Quote from: khtwo2002 on January 10, 2016, 07:54:35 pmYep, and that's a nuisance most of the time, but check outEEVblog #284(from about 2:30), sometimes it's useful...

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2016, 09:40:15 am
content: Quote from: khtwo2002 on January 10, 2016, 07:54:35 pmI don't know what you mean by that. Perhaps you mean "white noise" that contains all frequencies at the same power.The problem is that an improperly triggered scope display can look like white noise. If your scope has an FFT function, I suggest you capture a single sweep and do an FFT to see if there are any frequencies you have missed. Do several tests at different sweep speeds, capturing the maximum interval at each sweep frequency.That technique isn't guaranteed to show anything that is there, but nothing is when serching for noise!

author: Brumby
author_rank: Unknown
timestamp: January 11, 2016, 09:48:46 am
content: I took the phrase "pure noise in the air" as being of no particular 'colour' but simply describing all the EM that's floating around in our modern day world. Everything from lightning halfway around the world to SMPS switching transients, automotive ignition pulses and so on.

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2016, 10:21:38 am
content: Quote from: Brumby on January 11, 2016, 09:48:46 amJust so, but it could be many other things as well.Characterising them - in whatever way is possible - is the first step to understanding and amelioration.

author: khtwo2002
author_rank: Contributor
timestamp: January 11, 2016, 09:38:13 pm
content: Quote from: tggzzz on January 11, 2016, 09:40:15 am"white noise", that's that. Who knows, maybe pinky noiseAnd thanks for pointing out the FFT function, I have never thought the use of FFT function. LOL newbie