Scope Probes - Page 1
Forum section: electronics / testgear

author: Dellyjoe
author_rank: Regular Contributor
timestamp: March 20, 2020, 07:35:26 pm
content: Good Afternoon everyone,I got a Analog Discovery 2(AD2) which ya i know isn't a scope, and people are going to hate that I bought it but whatever, i'm in school and this just made sense. However this AD2 came with the words wrost probes, so I'm asking if you recommend any good probes, looking to not spend a lot of money, looking in the range of 30-40 dollar max for one probe.Whata all thinking,Thank you for reading,Joe

author: nctnico
author_rank: Super Contributor
timestamp: March 20, 2020, 07:44:00 pm
content: Personally I like the ones from Testec (a German company). Not too expensive but good quality. I have a whole bunch of them. Usually I don't use the probes which come with an oscilloscope but the probes I already have. The advantage of having one type of probe is that you can mix & match accessories and use parts of a broken probe for other probes. I have one tray with probe accessories and since they all fit it doesn't matter which one I pick. It will fit on the probe.

author: Dellyjoe
author_rank: Regular Contributor
timestamp: March 20, 2020, 08:05:13 pm
content: Quote from: nctnico on March 20, 2020, 07:44:00 pmhttps://www.testec.de/en/products/product-categories/standard-probes/weird they don't show prices. but they look nice.i will have to find someone that sells them.Joe

author: Fungus
author_rank: Super Contributor
timestamp: March 20, 2020, 09:30:36 pm
content: You can get very passable probes for $5-$6 on ebay, aliexpress, etc.

author: garrettm
author_rank: Frequent Contributor
timestamp: March 20, 2020, 10:43:08 pm
content: I'm surprised no one pointed out that probes aren't really interchangable between instruments. Each probe family is designed to operate with a particular scope input capacitance. For instance, my ancient HP 54542C (500MHz, 4Gs/s) has an input capacitance of ~7pF. The probes for this particular scope have 5 to 9pF trimmer caps for HF compensation. If I were to use a probe that had say 15 to 35pF trimming for HF compensation, it wouldn't compensate correctly for high frequency signals on my scope.The point is, when ordering probes, always check to see if the compensation range (in picofarads) will work with your scope's input capacitance. Otherwise you will have ringing or too slow of risetimes when using that probe.Another consideration is bandwidth. The total system bandwidth is given by the attached formula. For example, a 500MHz probe and a 500MHz scope do not give 500MHz system bandwidth, you actually get ~350MHz system bandwidth. So it's always lower than you would expect. This is why its advantageous to use higher bandwidth probes: they let you access more total system bandwidth and get closer to your osciloscope's actual bandwidth.Now most of this isn't very important for low frequency instruments like the AD2, but its good to know for the future when you use standard equipment in the workplace or decide to upgrade your own home lab.

author: nctnico
author_rank: Super Contributor
timestamp: March 20, 2020, 10:54:24 pm
content: The oscilloscope input capacitance is something to watch out for but most modern scopes are around 15pf nowadays. Also passive probes are not very useful beyond 100MHz due to circuit loading. All in all you'll need to look at different probing solutions for looking at signals over 100MHz. For now I don't think the OP should really worry about this.

author: garrettm
author_rank: Frequent Contributor
timestamp: March 20, 2020, 11:06:21 pm
content: @nctnico the AD2 has 24pF of input capacitance... So it does matter. But admittedly not much for low frequency stuff. And you're right, active probes with <2pF input capacitance // with 1M or 100-10kohm are generally use for higher frequency stuff.

author: tggzzz
author_rank: Super Contributor
timestamp: March 20, 2020, 11:17:24 pm
content: Quote from: Dellyjoe on March 20, 2020, 07:35:26 pmDon't be a twat.Engineering requires assessment of fitness for purpose. The AD2 is a very capable device within its specification.So, what are your "purposes"? Without that information, any recommendations are invalid.

author: egonotto
author_rank: Super Contributor
timestamp: March 21, 2020, 01:39:03 am
content: Hello,Dellyjoe wrote:"However this AD2 came with the words wrost probes"What is wrong with your probes? What is your hope that other probes can do better?AD2 is a very nice tool with a great software.Best regardsegonotto

author: Dellyjoe
author_rank: Regular Contributor
timestamp: March 21, 2020, 02:57:56 am
content: Quote from: egonotto on March 21, 2020, 01:39:03 amI agree atm I'm loving my AD2, but the probes it came with, the alligator clip already bent, and now i cant pry it open and it was never easy to do, and the probe hook is hard to press, over all just feels cheap. To be fare at work I use nice keysight probes but i'm not spending 300 dollars for a probe for a hobby that I just started.So really I would say i'm just looking for a probes that are 1/10x capability and have good quality hook, and alligator clips.do any of you have anything in mind.Thank you for taking time out of your day to help me,Joe

author: Mr. Scram
author_rank: Super Contributor
timestamp: March 21, 2020, 03:34:35 am
content: Quote from: garrettm on March 20, 2020, 10:43:08 pmWhere does that formula come from? Why do so many manufacturers supply probes that are exactly right, leading to a lower system bandwidth?

author: jjoonathan
author_rank: Frequent Contributor
timestamp: March 21, 2020, 03:57:10 am
content: Also -- not sure if this is a problem here -- the cut sheet metal style of hook (vs bent wire style) is truly awful. It doesn't fit into a third of the places where the bent-wire would, it chops small wires, and the edge rusts.

author: Fungus
author_rank: Super Contributor
timestamp: March 21, 2020, 06:42:59 am
content: Again:https://www.ebay.com/sch/i.html?_nkw=oscilloscope+probehttps://www.eevblog.com/forum/reviews/cheapest-100mhz-oscilloscope-probes-hands-on-review/

author: garrettm
author_rank: Frequent Contributor
timestamp: March 21, 2020, 07:00:24 am
content: Quote from: Mr. Scram on March 21, 2020, 03:34:35 amThat's a loaded question! But let's just say that the total rise time for various components in the signal path doesn't add linearly. Instead, they add by the root of the sum of their squares. The formula I posted earlier is just a simplification of this principle, since BW and t_rt are related. I won't go into the math, as its cumbersome to do here, but it's not too difficult to work out if you've got a mathy background.As for the probing part of the question. Well, passive probes, while great and cost effective, are limited in what they can achieve. I think 600 to maybe 1000 MHz bandwidth is really the limit for a good passive probe that isn't a 50ohm divider. We're talking 4-6.5pF input capacitance (in parallel with 1-10 Mohm) for very good 10:1 probes. But passive probe capacitive loading at and above a 100MHz is such that you wouldn't use a passive probe for HF measurements. They impose too much loading on the signal under test. Those couple of picofarads pack a punch.To access 95% of an oscilloscope's bandwidth, you'll find that the probe needs to have 3x the oscilloscope's bandwidth! Passive probes simply can't give your wide bandwidth scopes their full system bandwidth. This, of course, assumes wide bandwidth scopes, >= 300 Mhz. For 50 Mhz it’s easy to get nice 150 MHz passive probes.

author: tggzzz
author_rank: Super Contributor
timestamp: March 21, 2020, 08:28:14 am
content: Quote from: garrettm on March 21, 2020, 07:00:24 amBe aware that a so-called "low impedance" *10 Z0 resistive divider probe has ahigher impedancethan a so-called "high impedance" *10 probe. Do the arithmetic: what's the impedance of a typical 10Mohm//10pF at, say, 250MHz. Compare that with 500ohms//0.7pF.Of course with a resistive divider probe your scope needs a 50ohm input, ideally without 15pF parallel capacitance.

author: electricMN
author_rank: Regular Contributor
timestamp: March 21, 2020, 05:27:03 pm
content: Quote from: Dellyjoe on March 20, 2020, 08:05:13 pmYou can get them from Newark:https://www.newark.com/c/test-measurement/test-leads-test-probes/oscilloscope-test-probes-voltage-frequency?brand=testec

author: Dellyjoe
author_rank: Regular Contributor
timestamp: March 23, 2020, 04:41:06 pm
content: Quote from: electricMN on March 21, 2020, 05:27:03 pmTHank you sir ,They are a little over my price range, but I think I'm going to go for it, given I should have someone of good probes in my life.Thank you again,Joe

author: jacklee
author_rank: Regular Contributor
timestamp: March 24, 2020, 06:45:34 am
content: Quote from: Fungus on March 20, 2020, 09:30:36 pmAgreed, probes are consumables, after broken just get a new one...

author: Vgkid
author_rank: Super Contributor
timestamp: March 24, 2020, 07:12:02 am
content: Also look into probemaster probes, its all I own. Bought both new, and NIB ones.Unfortunately that skews the price data.

author: garrettm
author_rank: Frequent Contributor
timestamp: March 24, 2020, 10:06:16 am
content: PMK makes good probes, and can often be found for cheap on eBay. They make most of Lecroy's lower end probes and much of Pomonas line up. I've got a couple of their 100:1 and 1000:1 HV probes and some of their standard 10:1 HF probes. PMK uses pogo pins and generally come with two or three spare pins as well as a probe-tip to BNC adapter which can come in handy every once in a while.

author: hli
author_rank: Frequent Contributor
timestamp: March 24, 2020, 01:26:22 pm
content: Quote from: Dellyjoe on March 20, 2020, 08:05:13 pmReichelt has them (e.g.https://www.reichelt.de/modulartastkopf-150-mhz-10-mohm-testec-lf-212-p32415.html), and I also find them on Amazon Germany (although they are more expensive there).

author: oventech
author_rank: Contributor
timestamp: March 26, 2020, 11:49:12 pm
content: Another pitch for Probe Master.https://probemaster.com/Have been using some of their probes at work since the 90's. Still good after all these years.

author: The Chump
author_rank: Contributor
timestamp: March 27, 2020, 07:01:49 am
content: That formula only applies for probes with 1st order rollof, such as active probes. Passive probes don't have a 1st order rollof.I regularly use cheapo 100MHz x10 passive probes with my 500MHz scope and the combination gives 500MHz rise-time.The difference between 100MHz and 500MHz passive probes is in the suppression of the reflections.Practically speaking, you get a 10ns 25%overshoot lump on the leading edge. I would take a screenshot of the difference but, we're on corona virus lockdown here.So, when it comes to passive probes for < 1GHz scopes the bandwidth printed on the probe is a recommendation for the bandwidth of the scope so that the aberration is hidden.Also, pretty much all run-of-the-mill <1GHz scopes have 1Mohm in parallel with 13pF - 15 pF input impedance.Coupled to a x10 passive probe you will get 10Mohm in parallel with 13pF - 15pF. You don't get a reduction in capacitance due to the 1.2m of coaxial cable.Yous need a x100 probe to get 5pF input capacitance.For your AD2, which has a 1st order bandwidth of 10MHz, event the lowliest of 60MHz probes will do so you can buy based on cost and robustness.AlexQuote from: garrettm on March 21, 2020, 07:00:24 am

author: tggzzz
author_rank: Super Contributor
timestamp: March 27, 2020, 10:41:23 am
content: Quote from: The Chump on March 27, 2020, 07:01:49 amI would be very interested in photos of your experimental setup and scope trace.QuoteIf that's what I expect it is, the ~100MHz "ringing" isn't a reflection. FFI seehttps://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/https://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/More importantly, a principal use of a scope is to assess signal integrity of an (analogue) waveform, to assess whether it will be correctly interpreted as a digital signal by the receiver. Such assessments are greatly hampered by poor probing techniques.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 27, 2020, 11:07:13 am
content: Quote from: The Chump on March 27, 2020, 07:01:49 ammajor contributor is reflection due to impedance mismatch in the coax cable used. lossy (specialty) coax cable type will reduce this effect greatly. this is why i guess you have the sense of increased 100MHz probe's BW, its the first ringing you are seeing.Quote from: The Chump on March 27, 2020, 07:01:49 ami would say, if 10X is 15pF, 100X will be 1 tenth of that ie 1.5pF. but we will lose low voltage resolution and get increased noise. and again, the major contributor to the probe's capacitance is the coax cable (100-150pF). lossy type cable will reduce this effect greatly as well, thats why some expensive passive probe such as Tek TPP0500/1000 can achieve 4pF input at 1/10X, the lossy cable used is in the order of 40pF capacitance.

author: 2N3055
author_rank: Super Contributor
timestamp: March 27, 2020, 02:02:34 pm
content: Quote from: Mechatrommer on March 27, 2020, 11:07:13 amYou don't have to invent numbers. It is clearly specified in specifications for probes. TT-HV 250 | 100:1 is 100 MΩ, 4 pF, Bandwidth 300 MHz, Rise Time 1,2 ns

author: The Chump
author_rank: Contributor
timestamp: March 28, 2020, 01:14:15 am
content: It was done using a probe tip to BNC adaptor thingy into the end of an RG58 which was terminated with a 50R load on a tee piece. The source was the high speed reference output (not the probe cal signal) on my Rigol DS4054. The 500MHz probe and the 100MHz probe and the direct input to the scope gave easily sub 1ns rise times.The 10ns lump I refer to was definitely distinct from the edge ringing and looked like a reflection - ie a rectangular step.Not like the pictures in your second link, clearly showing an expensive 150MHz probe with circa 1ns rise time.The main point is that the formula only holds when both scope and probe have 1st order rollofs, so it doesn't apply when we're faced with a passive probe with you-get-what-you-pay-for roll-off characteristics.And it matter much less when your scope only has 10MHz bandwidth.Quote from: tggzzz on March 27, 2020, 10:41:23 am

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2020, 01:45:48 am
content: Quote from: The Chump on March 28, 2020, 01:14:15 amSo completely unrepresentative of the normal ways in which scope probes are used (ad-hoc "flying leads" probing whatever might have turned out to be interesting).That's legitimate, but it sounds like a proper 50ohm input would have been more appropriate.QuoteThat means nothing to me., and I can't be bothered to search for specifications you don't bother to provide.QuoteI can't comment on that since I don't understand that "picture".QuoteYou are missing the point; the pictures in that example are using the scope probe in a "traditional" way: an ad-hoc flying lead on a board, not carefully terminated in 50ohms.As for 150MHz <=> 1ns, no that isn't traditional. Normally 150MHz <=> 2.3ns.QuoteFalse; not first order. Decent probes and scopes have a gaussian rolloff, to avoid distortions due to differential phase delays.QuoteNo surprises there!Quote from: tggzzz on March 27, 2020, 10:41:23 am

author: TK
author_rank: Super Contributor
timestamp: March 28, 2020, 03:43:45 am
content: Keysight N2862B probe for $28.49https://www.ebay.com/itm/KEYSIGHT-N2862B-Probe-150MHz-10-1-10M-15pf/163589412379

author: Helix70
author_rank: Unknown
timestamp: March 28, 2020, 04:30:17 am
content: Quote from: TK on March 28, 2020, 03:43:45 amThat is a great deal.

author: The Chump
author_rank: Contributor
timestamp: March 28, 2020, 05:10:30 pm
content: Quote from: tggzzz on March 28, 2020, 01:45:48 amI wanted to see the difference between the probes under ideal conditions, so totally appropriate for my experiment.QuoteI can be bothered. You didn't even have to ask nicely.See 1-17 on page 47 ofhttps://res.cloudinary.com/iwh/image/upload/q_auto,g_center/assets/1/26/Rigol_DS4000_and_MSO4000_User_Guide.pdf"the oscilloscope outputs a fast edge signal with 500 ps rise time from this connector..."Just the kind of signal for this experiment.QuoteYou not commenting is, well, a comment in itself. I can't provide a picture as I'm not at my lab.And I can't get the forum to insert images so I can't even draw it.The red trace in this has a similar but smaller lump for about 2 divisions - a mismatch reflection.It was a long time ago and I honestly can't <exactly> rememberQuoteAgreed that the pictures are of 150MHz passive x10 probe with apparently >>150MHz rise time.Also the pictures are of a variety of different probing techniques, good and bad.QuoteOk, yes Gausssian (which includes 1st order).But still, passive high-impedance (at LF) probes don't have gaussian rollofs, even decent ones, so one can't apply that formula.There are rules of thumb for rules of thumb.Apologies to everyone for hijacking this thread. Time to shutup.

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2020, 05:19:19 pm
content: Quote from: The Chump on March 28, 2020, 05:10:30 pmI've seen such distortions from both scopes with an internal non-flat frequency response, and also with probes where the internal HF compensation needs to be tweaked. N.B. such tweaks are inside the probe (usually in the housing by the BNC connector) and are not the easily accessible LF compensation capacitor.

author: lastguy
author_rank: Contributor
timestamp: October 01, 2021, 04:20:36 am
content: if your people bother on high frequency, just use 560+390 ohm then 50ohm cable to 50ohm scope input (20:1). if your scope don't have 50ohm input, buy a passthrough BNC adapter.

author: hpw
author_rank: Frequent Contributor
timestamp: October 01, 2021, 02:45:16 pm
content: Quote from: lastguy on October 01, 2021, 04:20:36 amEven have a 1GHz active probe for a +/- 500ps edge using a SDS2K Plus scope, the direct 50E SMA connection convinced me even better.So the questions on square wave is: how the scope or probe or connections behaves in the 100x time regions as frequency and phase figures.In other words, not having a scope with required BW & phase behaviors, the displayed signal is in questionshp