Cheap Oscope Probe Quality - Page 1
Forum section: electronics / general

author: TopherTheME
author_rank: Regular Contributor
timestamp: January 20, 2011, 08:16:55 pm
content: Has anyone ever used some of the cheapo oscilloscope probes that you can get off ebay? For example:http://cgi.ebay.com/Two-New-100MHz-Oscilloscope-Probes-Probe-Tektronix-HP-/160499354691?pt=LH_DefaultDomain_0&hash=item255e81cc43I wrecked one of my Agilent probes last week and would like a replacement but I'm not going to pay $100+ for a new one. A lot of the cheaper probes appear to be of similar quality and have the same functionality. What is so great about the probes Agilent and Tektronix produces that makes them so expensive?

author: baljemmett
author_rank: Unknown
timestamp: January 20, 2011, 08:32:30 pm
content: Quote from: TopherTheME on January 20, 2011, 08:16:55 pmI've got a pair of what look like exactly the same thing -- they seem to work OK on my 20MHz analogue scope, at least. More than that I can't say I'm afraid!

author: Unknown
author_rank: Unknown
timestamp: January 20, 2011, 08:43:02 pm
content: Aberrations, circuit loading at high frequencies (flatness of the input impedance), mechanical quality. Tek/Agilent usually specify bandwidth at the probe tip, so the -3dB is including the standard probes. Even seemingly basic stuff like the input hybrid is complicated and proprietary technology (I believe Tek bought back the company that made them after spinning it off). Tek tunes the probe response to the front-end used in the scope, if the front-end has an impedance peak somewhere in the frequency band, the probe is designed to compensate for this. This is why they made various probes with almost identical specs. These effects tend to get magnified as you approach the bandwidth limits for Hi-Z passive probes.Random example of what can be wrong in cheap probes: dielectric absorption or leakage in the input caps can lead to funny looking waveforms, which you may not attribute to the probe until you accidentally use a different probe. I've also had a cheap probe with a bum switch, even in ground mode, it would capacitively couple the signal. Safety might be an issue if you ever use scope probes on dangerous voltages. If the trimmer cap in the head is fails shorted due to high voltage, this may be dangerous for both the user and the scope (which suddenly sees the unattenuated signal).If you're likely to kill them (I tend to treat them as delicate, expensive instruments, so I don't drop them or get the cord caught under my chair), a cheap(ish) one may be fine for simple/low-frequency use, just use a real probe for important measurements. In my experience, the cheap crap is not significantly cheaper than some used Tek probes, so I don't see the point.

author: Time
author_rank: Frequent Contributor
timestamp: January 20, 2011, 08:59:28 pm
content: I think I have a pair of the probes that you show in that auction. For 13 dollars, I thought I'd give them a whirl on my analog 40 MHz scope. I got the scope for free and needed some cheap probes so I figured even if these crappy probes dont meet their 100 MHz spec they probably still have a better response than 40 MHz. All I ever use that scope for is basic micro work and slow signal stuff when I run out of channels on my DSO.

author: saturation
author_rank: Super Contributor
timestamp: January 20, 2011, 09:28:46 pm
content: Since they have no brand, I can't say all such Chinese cheapo probes are the same. I bought a pair months ago too from ebay and they look identical, though.For the money, you can't go wrong using them, but having function generator in hand, and if you have a better probe still around, characterize them and compare them, see if they live up to their specs. I did them same to the limits of my Rigol, and they are good through at least 50 MHz.

author: TopherTheME
author_rank: Regular Contributor
timestamp: January 20, 2011, 10:16:05 pm
content: Quote from: saturation on January 20, 2011, 09:28:46 pmI think this is what I'll do. I do still have one good probe which I'll keep in a drawer for comparison.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 20, 2011, 11:17:14 pm
content: I was disappointed with the quality of the probes that came with my £6K Agilent scope, as they were big and had rather stiff cables. I much prefer the old Tek P6131'swhich are very small and have very flexible cables that have less tendancy to pull the board off the bench when you have 4 probes hanging off it.

author: qno
author_rank: Frequent Contributor
timestamp: January 21, 2011, 09:57:42 am
content: I have used these probes and they are OK.A bit flimsy switches,The designers have looked to the older Tek probes carefully.They last a long time but I have one that has a broken wire now.Best choice for $13.

author: Unknown
author_rank: Unknown
timestamp: January 21, 2011, 06:47:41 pm
content: Quote from: saturation on January 20, 2011, 09:28:46 pmFunction generators are easy, they usually have an output impedance of 50 ohm (25 ohm if you terminate them properly). Real circuits usually have a much higher output impedance, which will make them more sensitive to probe loading. Function generators also usually can't supply signals with a high slew rate (large amplitude, fast rise/fall time). You also need a known good probe to compare aberrations like over/under shoot. Most people are not able to do these kinds of tests, this allows some companies to sell some really crappy probes (can't say about these particular probes, I've never used them, and even if I had, without brand you can't be sure that they're the same).

author: saturation
author_rank: Super Contributor
timestamp: January 21, 2011, 11:30:13 pm
content: Thanks for the sage advice alm, and detailing the capabilities of more costly probes that aren't obvious unless fully tested characterized as say, a reputable scope manufacturer like Tektronix would do.Getting a used Tektronix or equivalent reputable 60-100MHz 10x passive probe isn't exactly $7 each. Ebay typicals with clear manufacturer model numbers are $15-50 each delivered, via eBay, and about $50-200, new. If you treat your probes with respect and delicacy, its anyone's guess how these eBay probes will perform without performance testing, given it could have been abused physically and/or electrically.But your insight suggests to me that getting hold of a really known good probe as a reference and doing tests comparing the cheapo to it, to make it 'good probe' traceable, is prudent. Once characterized I can compare future probes against referenced ones.I'll revise a test suite with an impedance load to give the probes a workout modeled after Tek's more simpler to implement philosophy and expose what weakness Chinese cheapos maybe are hiding.http://www.tek.com/Measurement/App_Notes/60_18324/eng/60W_18324_0.pdfQuote from: alm on January 21, 2011, 06:47:41 pmQuote from: alm on January 20, 2011, 08:43:02 pm

author: gxti
author_rank: Frequent Contributor
timestamp: January 22, 2011, 01:53:23 am
content: Those look identical to the probes I got with my Instek GDS-1062A. Guess I know where to find replacements, now. I've barely used it in the 4-5 months since I got the scope but the spring in one of the grabbers broke so it doesn't snap back correctly.

author: Unknown
author_rank: Unknown
timestamp: January 22, 2011, 09:08:28 am
content: Quote from: saturation on January 21, 2011, 11:30:13 pmTrue, although I have gotten some like-new Tek probes for something like $15 each, which IMO is close enough to $7 to skip the cheap crap. Yes, as everything you buy from a non-authorized dealer without return policy, there is a risk that they're faulty, although the most common fault with probes appears to be damaged probe cables or tips, and this will easily show up with LF tests. Most low-frequency (<150MHz or so) probes don't have any adjustments except LF compensation to mess up either.Quote from: saturation on January 21, 2011, 11:30:13 pmGood app note, thanks. Note that it does focus on multi-GHz active probes, at those frequencies there is no such thing as a high-impedance input. At low(er) frequences there is, which is why there are 10Mohm 100MHz probes, but no 10Mohm 8GHz probes. The stuff about how their philosophy is superior to Agilent is not so interesting, I think Agilent has a similar app note showing that their philosophy is better.The Tek documents 'Oscilloscope probe circuits' and 'Oscilloscope probe measurements' (from the sixties) are probably also informative, passive probes are still basically the same (8Ghz active probes probably not so much), and they contained much more technical details compared to today's app notes which are written by marketing.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 22, 2011, 10:12:14 am
content: Quote from: alm on January 22, 2011, 09:08:28 amIndeed. If you want to learn a little bit about today's GHz probes, you can look at Tek and Agilent patents in a patent archive (at the USPTO or some who republish them). Some fascinating stuff, e.g.http://www.freepatentsonline.com/7586318.pdfalthough they of course don't tell you every little dirty secret in those patents.

author: saturation
author_rank: Super Contributor
timestamp: January 24, 2011, 07:50:17 pm
content: Comparing Probes. Details later, but the simple test was revealing. Since the speed changes are consistent it suggest the speed rating of the probes are close to its electrical performance.NN = sold as no name eBay 100 MHz scope probes have namesYang Sun P6100, $14 pair [it has a name somewhere, will locate and revise post later]. Probe labels and documents suggests its CAT 1 and has a frequency to voltage derating curve.Rise time measurements are the tracing in yellow.Rigol = RP 2200[ shipped with 1052E ], 200 MHz rating,Rise time measurements are the tracing in blue.Signal Sources, used for rise timesInstek = SFG 1003 , faster source, TTL output at least to 4.8nsHantek = DDS 3x25Tektronix mentions the industry standard probe test uses a 1ns pulse with 50 ohms impedance. See image. Test probes were connected directly to the signal sources without adapters. I don't have a 1ns pulse, so the Instek and Hantek substitute for it, for now.The dot image shows the sample points, it suggests negligible aliasing or no erroneous interpolation created by an unmodded 50MHz 1052E.

author: Unknown
author_rank: Unknown
timestamp: January 25, 2011, 05:41:56 am
content: So the Rigol probe shows a faster rise time with the Instek FG, but slower with the Hantek AWG? The appears to be significant overshoot in the blue trace in the first picture, but this may also be the signal. 4.8ns shouldn't really be a hard test for these probes, it requires 70MHz or so of bandwidth, so the scope is likely to be limiting. At least in the first setup, the Rigol probe looks slightly better to me (less smooth), the opposite in the second. Note that this from a low-impedance source with a low amplitude, none are issues with Tek's current many-GHz probes, they're low-impedance inputs anyway, and won't survive a high amplitude. The scope also appears to sample too slow to really see aberrations, you should probably test one probe at a time so you can use the full 1GS/s.

author: saturation
author_rank: Super Contributor
timestamp: January 26, 2011, 03:04:49 pm
content: Yes, since I don't have a calibrated traceable reference for rise times or pulses, I have to deduce the performance.The simple test shows that an identical scope+probe setup produces different rise times from 2 different sources, one faster than another. Changing the probe causes a proportional change, with the sources consistent, Instek is faster than Hantek.One can say with certainty that the RP2200, rated at 200 MHz, is faster than the Yang Sun rated at 100 MHz. But how fast they really are quantitatively, I can't say. Since the Rigol probe provides a faster rise time vs the Sun probe, this suggests that the Instek source rise time is at <= 4.8ns, it could be better, but even if it faster than 1.8ns needed to test the 200 MHz probe to its limit, I then am limited by the scope's rise time.The question raised by the OP, is are these 'low cost' eBay probes any good?Using the Instek rise time 4.8ns for the Rigol probe, and 6.6ns for the Sun probe, and using 0.35/rise time estimates, gives applicable bandwidth between 73MHz and 53 MHz. Since my scope is only rated to 50 MHz or slightly more, either probe is suitable to 50 MHz.In addition to the rise time, you can also do a brute force sweep of sine wave frequency to check the -3dB limits of the probe+scope combination, and finally a qualitative appearance of a square wave distortion to complement all the measurements.It would be good to have a reference probe and signal source traceable to a calibrated device, but I leave that task for another day.On the sampling rate, yes, I checked each response at 1Gs/s when doing measurements, to insure I get the best results. For these photos, I combined the images mostly to avoid posting so many individual photos. I also use dot mode to confirm the scopes interpolation, and use vector to make the photos.On the overshoot, yes, I could try to correct it, but I think it will add little more to determining whether these eBay probes are adequate for a 50 MHz DSO.In summary, the probes don't limit the scope's performance, and the limiting step now is the scope. If a user has a fast rise time square wave source, they can easily check the performance of a no-name passive probe by simply connecting the probes directly to the signal source, and measuring its rise time on the scope its to be used on. The key is to insure it will allow the scope to perform at its rated bandwidth.Quote from: alm on January 25, 2011, 05:41:56 am

author: saturation
author_rank: Super Contributor
timestamp: January 26, 2011, 03:32:02 pm
content: Yes, what interested me more in that link is that Tek doesn't believe in measuring probe performance using a modeled load as Agilent does [which is what I was intending to slap together], and spends a good portion of the pdf discussing why; this reduces to the equivalent circuit I posted as an embodiment of their philosophy for characterizing probes. Thus, the tests the OP or others can use can be the Tek model: its a simpler way to confirm the bandwidth of those nameless eBay passive probes, with validity.I found those classic Tek documents and read them through as you suggested, and they are great refreshers, thank you! The newer documents carry over a lot of that, but they touch on why there are so many probes, and how to focus your need: passive, active, differential, current, etc., and are the accessories worth it. Many of those probes cost far more than the Rigol alone!The Tek documents I read summarize 4 things worth remembering when buying passive probes:500 MHz is a practical upper limit for passive probes, beyond which will likely require active probes, so that's Tek's upper limit for passive probes in their catalog. Its a long story, its detailed in "ABC of Probes."Probe+ scope should be rated 3-5x more than the bandwidth to reduce amplitude error; at the -3dB mark, there will be an amplitude error ~ 30% from the roll off.Use the shortest shortest shortest shortest ground leads possible.As always, beware the loading effects of probe capacitance and cable length.Quote from: alm on January 22, 2011, 09:08:28 am

author: jahonen
author_rank: Super Contributor
timestamp: January 26, 2011, 04:27:21 pm
content: Quote from: saturation on January 24, 2011, 07:50:17 pmCan you elaborate a bit more how the grounding was done, hopefully you did not use the long ground clip? I have always believed that when one characterizes the probe, BNC adapter (or similar) is usually used, which provides 360° ground right at the probe tip, minimizing the excess inductance.For comparison, seemy comparison between two ground connection styles.Also, it does not make any sense to make very high-bandwidth 10M passive probe because capacitive loading gets way too high. For typical 10 pF probe, probe impedance drops to 160 ohms @ 100 MHz and 32 ohms @ 500 MHz. That is comparable to transmission line impedance in digital applications (something like 80-40 ohms). Anyway, 10 M input impedance makes sense only at DC. Even at 20 kHz, loading due to capacitance has dropped down to 800 k.Regards,Janne

author: tinhead
author_rank: Super Contributor
timestamp: January 26, 2011, 06:18:50 pm
content: you can build your own cheap active FET probes, they are good enough up to 500Mhz.http://welecw2000a.sourceforge.net/docs/Hardware/Aktiver_Tastkopf_mit_OPA659.pdfI know the pdf is not in english, but in principle all you need to know is the schematics,the PCB cab be ordered by the developer for few USD.

author: Chasm
author_rank: Regular Contributor
timestamp: January 26, 2011, 06:41:18 pm
content: It's a nice active DIY probe, the only thing missing is a scope that would warrant it for me.Several measurements were taken during the development iterations of this probe.The only thing still missing is AFAIK to hit it with some really high end measuring equipment.

author: tinhead
author_rank: Super Contributor
timestamp: January 26, 2011, 07:01:36 pm
content: they are comparable with P6205 on a TDS5104B, so good enough for me.

author: saturation
author_rank: Super Contributor
timestamp: January 26, 2011, 07:24:14 pm
content: Hi jahonen:I use the spring ground clip on the Rigol's and compared the output on the 'long' alligator ground clips [its about 10cm long]. I also probed directly without the spring into the BNC adapter, making contact between the probe tip ground ring and the ground socket of the BNC adapter while probing inside the male socket. It didn't make a difference, but I did it only once. Then I just used the alligators clips clipped to the ground ring of the BNC jack for convenience.I didn't try at all for the Sun probes, hmmm, I'll try again, it doesn't take much time or effort.Quote from: jahonen on January 26, 2011, 04:27:21 pm

author: saturation
author_rank: Super Contributor
timestamp: January 26, 2011, 07:30:09 pm
content: Thanks Tinhead, have given that consideration too. When the loading becomes too much, this is the only alternative.FWIW too, the $7 100 MHz no-name Chinese probes are most cost effective. The 200 MHz no-name probes are $25-30 each, and probes below 100 MHz are about $5-6 each.Quote from: tinhead on January 26, 2011, 06:18:50 pm

author: saturation
author_rank: Super Contributor
timestamp: January 27, 2011, 03:47:34 pm
content: I just repeated some measurements with the spring clip on both the Sun and Rigol probes, all 4 of them, they ship 2 pair in a box. I also checked the spring clip's effect on a Velleman probe, rated at 60 MHz.Examining it more intensely, there is a1m400mV reduction in the over shoot, and minor ringing in now flattened out. The rise time is interestingly longer by 0.5ns on all probes compared to using the ground clip. Very odd result, but the signal quality is improved, but not much. Will post photos when able.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 04:50:34 pm
content: I've just received a pair of these Chinese probes made by Yang Xun 100Mhz, 600v CatI type P6100. Cost £8 (UK) inc p&p. Would I us them on 600v? No way but for general use on my 50meg analogue scope you can't be robbed. For absolute precision probably not much cop but for run of the mill work a no brainer and remember the old saying "You can never have too many probes". Put the money saved towards buying something useful

author: Unknown
author_rank: Unknown
timestamp: January 27, 2011, 07:21:23 pm
content: Quote from: saturation on January 27, 2011, 03:47:34 pmOver shoot will result in a faster (apparent) rise time, although I'm not sure if 1mV over shoot explains 0.5ns rise time difference. I would definitely trust these measurements over measurements with a long ground lead, those things shouldn't be let anywhere near high-speed signals (unless your scope has an extremely low input capacitance, like active or lo-Z probes). The usual way is with a probe-tip to BNC adapter, preferably with internal 50 ohm termination, otherwise with feed-through termination between it and the generator.

author: saturation
author_rank: Super Contributor
timestamp: January 28, 2011, 04:26:12 am
content: Sorry, my bad its not 1mV overshoot, its in the 360mV range, as pictured here. The rise time estimate is about there, here its 0.7ns.White = alligator ground clipYellow = spring clipQuote from: saturation on January 27, 2011, 03:47:34 pm

author: saturation
author_rank: Super Contributor
timestamp: January 28, 2011, 07:17:33 pm
content: Hi alm,Alas I don't have a 50 ohm terminated probe-tip BNC adapter nor a feed through terminator so I initially used a 50 ohm resistive load, then not noticing significant differences, did not use it for the further measurements. Will give it another look and buy adapters and these terminators.Here's a link for other regarding classic Tek Circuit Series textbooks. Scanned and free.http://www.slack.com/concepts.htmlQuote from: alm on January 27, 2011, 07:21:23 pm

author: AndersAnd
author_rank: Frequent Contributor
timestamp: November 11, 2013, 12:23:49 pm
content: Quote from: saturation on January 24, 2011, 07:50:17 pmQuote from: saturation on January 26, 2011, 03:04:49 pmRigol RP2200's bandwidth is only rated at 150 MHz. However it looks like Rigol originally rated them at 200 MHz [hence the name RP2200.The funny thing is the RP2200 User's Guide that came with my Rigol 1052E from 2009 has two tiny stickers on them that says150MHzand2.3nsfor 10X bandwidth and 10X rise time respectively.Below the 150MHz sticker it originally said200MHzand I think it says1.7nsbelow the 2.3ns sticker.http://www.rigol.com/prodserv/DS1000E/attachment/?act=view&itemid=1

author: saturation
author_rank: Super Contributor
timestamp: November 11, 2013, 01:10:10 pm
content: Thanks AndersAnd. I wonder if the materials they use now downgrade the capabilities?From my probe datasheet, enclosed.

author: Stonent
author_rank: Super Contributor
timestamp: November 11, 2013, 01:20:43 pm
content: I have a set of the 2 for $10 100MHz probes that the adjustment thing fell out so now on one probe, I can't do the x10 adjustments any more.

author: AndersAnd
author_rank: Frequent Contributor
timestamp: November 11, 2013, 05:32:18 pm
content: Quote from: saturation on November 11, 2013, 01:10:10 pmHow old are your RP2200 probes? I bought my Rigol 1052E with the RP2200 probes in June 2009.Are you probes older than that?Or maybe they just forgot to put the stickers in your user's guide. Or maybe they later found out the probe couldn't live up to the 200 MHz BW they originally specified and just put stickers in the manual instead of improving the product to live up to the specs originally planned. I don't think these probes were ever sold with any scopes above 150 MHz BW anyway. Rigol 1152E-EDU with 150 MHz BW is sold on the Chinese market, with these RP2200 150/200 MHz probes too I think.I just attached a scan of the spec sheet in my Rigol RP2200 User's Guide.Notice the 150MHz and 2.3ns stickers on it. You can see some of the 200 below the 150MHz sticker and when I hold it up against the light I can see some of the 1.7ns too.

author: Martini
author_rank: Regular Contributor
timestamp: March 29, 2016, 03:39:38 pm
content: I just ordered a set ($ 4.17) and thought I would ask my question here...The probes are rated at 100 MHz at 10x and 6 MHz at 1x. It's the same (or close) for every probe. Someone cares to explain me (in simple terms) why there is such a dramatic difference in bandwith between the two modes?

author: TheSteve
author_rank: Unknown
timestamp: March 29, 2016, 09:04:02 pm
content: Quote from: Martini on March 29, 2016, 03:39:38 pmDave would be happy to explain it:

author: saturation
author_rank: Super Contributor
timestamp: March 29, 2016, 09:08:03 pm
content: It has to do with capacitive loading by the probe cables on the circuit being tested; when you add an RC network to the probe you can compensate for the cable load to some extent, that's why there are different rated probes and ultimately passive probes have a limit to their usability.What actually can be done in compensation depends on the make of the probe.From the formula bandwidth in Hz = 0.35/rise time in secondssubstitute to the datasheet below:0.35/50ns = 7 MHzQuote from: Martini on March 29, 2016, 03:39:38 pm

author: Martini
author_rank: Regular Contributor
timestamp: March 30, 2016, 01:46:06 pm
content: Quote from: TheSteve on March 29, 2016, 09:04:02 pmBrilliant!But then, can you have a x1 only probe with decent bandwith?

author: vladk
author_rank: Newbie
timestamp: August 22, 2017, 01:46:30 pm
content: QuoteHmm... There are people exist who are not experienced enough in this particular topic of DIY.Could you please be so kind to help with a link to an english version of that PDF or, may be better, to a source of affordable knowledge which will help to consider re-building the construction from the scratch?

author: vladk
author_rank: Newbie
timestamp: August 22, 2017, 02:04:35 pm
content: At least, I would like to know - are those probes have adequate quality for the price?https://www.aliexpress.com/item/new-x1-x10-P6200-200MHz-Oscilloscope-Clip-Probe-For-Tektronix-HP-FREE-SHIPPING/32394762214.html?spm=a2g0s.9042311.0.0.BcuaFr