Why Oscilloscope Probes are expensive - Page 1
Forum section: electronics / beginners

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 26, 2016, 04:27:16 pm
content: it's just a cable with a cap and resistor, why is it expensive?for example Tektronix P2220 1X/10X 200 MHz costs $117.90

author: retrolefty
author_rank: Super Contributor
timestamp: February 26, 2016, 04:35:01 pm
content: Quote from: JustAnotherGuy999 on February 26, 2016, 04:27:16 pmPart is name brand and published and trusted specifications. However cheap Asian probes are and will be available that may vary in quality but some should work within their specification.This might make a decent 'shoot-out' amoung different price class probes Vs 'Brand' priced and see how well they all perform?

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 26, 2016, 04:38:30 pm
content: they are still expensive "in my opinion" compared to the components they contain.I mean why people don't just "hack" a probe using a wire a cap and a resistor, there something i don't know

author: TimFox
author_rank: Super Contributor
timestamp: February 26, 2016, 04:40:50 pm
content: Quote from: JustAnotherGuy999 on February 26, 2016, 04:27:16 pmIf you assemble a probe with only a 9.0 megohm resistor, a trimmer capacitor, a length of RG-58/U cable, and a BNC plug, it won't meet the 200 MHz specification. Try it: it would be a cheap experiment.

author: tggzzz
author_rank: Super Contributor
timestamp: February 26, 2016, 04:42:06 pm
content: Quote from: JustAnotherGuy999 on February 26, 2016, 04:27:16 pmNo, it isn't. Their construction is surprisingly subtle and complex.Tostartto understand, see the references inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 26, 2016, 04:44:55 pm
content: TimeFox can you explain plz what does "it won't meet the 200 MHz specification" mean

author: PA4TIM
author_rank: Super Contributor
timestamp: February 26, 2016, 05:06:47 pm
content: You think it is just a cable, capacitor and resistorDo not forget the switch a cheap 1/10x probe has. Good probes are not switchable so that should make them even cheaperA good 10x probe for , lets say, a 100 MHz scope must have a higher bandwidth. It has often 2 or more adjustable components in the compensation compensation network(s). That network is more as just a resistor an a cap. Often several resistors, inductors and capacitors. But also relative cheap parts. The probe body is a thin wall metal tube for shielding purpose. The probe cable is a complex part. It is 1 strand of very thin wire. You can see this more or less a distributed network on its own. Besides that is must not break easy. from 99% of the broken probes I had, the cause was the cable.Besides that there is often the 1x, 10x, 100x recognition mechanisme in the bnc.Then the tip, these can bend and break. But in good probes they are replaceable and for sale. This is not a universal part.A good probe is often repairable, a cheap probe often not. I have repaired several probes with succes. See some pictures from probe guts:http://www.pa4tim.nl/?p=5549By the way, an expensive probe can cost a lot more as 117 dollar and one of the increasing factors is bandwidth.

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 26, 2016, 05:13:38 pm
content: thanks guys

author: AlfBaz
author_rank: Super Contributor
timestamp: February 26, 2016, 05:23:13 pm
content: Dave did a video where he "probes" into probes. He shows the peculiar construction of the cable in itI think it's this one

author: Tom45
author_rank: Frequent Contributor
timestamp: February 26, 2016, 08:17:30 pm
content: Your question is actually a good one because scope probes do indeed look like very simple devices. But there is an amazing amount of technology that goes into the design and manufacture of such an apparently simple device.Besides Dave's video that was referenced, you can go straight to Tektronix, the inventors of high frequency scope probes:http://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdfWhether or not you understand all of the Tekronix probe document, you should at least get a feel for just how much goes into the design of a high frequency scope probe.

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 26, 2016, 08:30:43 pm
content: thanks

author: mmagin
author_rank: Frequent Contributor
timestamp: February 26, 2016, 08:39:27 pm
content: People often look at things like this and forget that the good quality product has good quality mechanical parts, and the mechanical parts are very often much costlier than the electronic components. In general, good quality test leads (and scope probes) are far more durable and will continue to perform correctly for longer than the cheapest approach. This even comes down to simple things like the plating on hooks, probes, and alligator clips, the springs specified, the design of switches, etc. And it costs even more to ensure uniform quality of those things across every production run of the product.Also, it's just not made in the quantities of consumer electronics, so you can't hope to get as much for your money as you do in say, your smartphone.

author: Howardlong
author_rank: Super Contributor
timestamp: February 26, 2016, 08:47:52 pm
content: I really liked this articlehttp://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdfWhich explains why rolling your own hi-z probe ain't so easy.

author: saturation
author_rank: Super Contributor
timestamp: February 26, 2016, 09:05:14 pm
content: Low cost Chinese passive probes are decent so long as you know and work within their limits. Its 60+ year old technology. There's a lot of data in the eevblog archives, here are some choice ones.https://www.eevblog.com/forum/reviews/scope-probe-what-the-difference-between-100mhz-and-500mhz/msg395742/#msg395742Note the frequency response to actual sweeps between an Agilent probe and a nameless cheap one:https://www.eevblog.com/forum/reviews/cheapest-100mhz-oscilloscope-probes-hands-on-review/msg100171/#msg100171

author: pickle9000
author_rank: Super Contributor
timestamp: February 26, 2016, 09:28:55 pm
content: Not a bad question.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 27, 2016, 01:44:27 am
content: Quote from: JustAnotherGuy999 on February 26, 2016, 04:27:16 pmbecause the knowledge to build it. try build it, once your get the knowledge, it will be cheaper to diy... just dont expect fancy looking probe.

author: andyturk
author_rank: Frequent Contributor
timestamp: February 27, 2016, 02:01:20 am
content: Quote from: PA4TIM on February 26, 2016, 05:06:47 pmHey PA4TIM,I've got a bad Rigol RP3500. It just seems to be open. Any suggestions on how to find the problem?

author: klunkerbus
author_rank: Unknown
timestamp: February 27, 2016, 02:04:24 am
content: I won't defend a $117 probe, but I worked for a test equipment company in the 70's and led the oscilloscope development team. On a new scope we were releasing, I was surprised at the hassles we ran into with the associated probe. Coming up with a physical design was daunting, between meeting the upper end of the 1KV voltage spec for the probe, the tooling costs of molded parts, and my god, finding a cable that would not be microphonic when you touched it or dragged it across the bench. Who wants a scope trace that jumps around as the probe cable is moved? Seriously ended up having a cable house manufacture custom cable for the probe... As a pretty green engineer at the time, that was quite the eye opener on how subtle components can really bite you in the behind. The rest of the oscilloscope design was pretty straightforward.EDIT: Also... Striving for a small design that still felt well from a human factors standpoint. Obtaining a flat frequency response. Providing the means to adjust compensation. Coming up with a means of providing a sharp point tip that had some hardness to it. Coming up with a clip accessory that would do at least a fair job across a wide range of applications.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 27, 2016, 08:00:56 am
content: Quote from: andyturk on February 27, 2016, 02:01:20 amYes, the first problem is, that it is a Rigol. >:-)Use TDR to find the location of the open. It will probably be the cable and most chance it is at the end just before the point it enters the probe.Then you have to take apart the probe and that can be a big problem. If you can take them apart you have to cut the cable and remove the crimp-ring that holds the shield of the cable. Then you have to find a way to connect the core of the cable to the probe. If you are lucky, you can solder the material, if not you need to find an other way. Then crimp a new collar to the "connector" used to couple the cable to the probe body. If there is one. I had two 100 MHz Rigol probes that lasted less as a year. I could not take them apart and was not able to repair them. But they performed so sad that I probably did not try it hard enough.

author: TimFox
author_rank: Super Contributor
timestamp: February 27, 2016, 08:23:50 pm
content: Quote from: JustAnotherGuy999 on February 26, 2016, 04:44:55 pmAttached is the result of a Spice simulation of the AC response for a simple probe.The circuit comprises:1.0 megohm and 20 pF scope input (typical values at panel BNC)6 nsec of 50 ohm coax (approximately 4 feet of RG-58/U at 66% velocity), which has 120 pF capacitance at low frequency.9.0 megohm and 15.5555 pF (140 pF/9) between probe point and coax input.Note that the attenuation at low frequency is 20 dB, as expected, but we get lower attenuation above about 20 MHz, and serious resonant problems above 50 MHz. These resonances are in the improperly-terminated 50 ohm coax.With 2 feet of cable (3 nsec), the effects kick in around 100 MHz, and still mess up the circuit at 200 MHz, as shown in the second graph.Note that Spice does not allow a frequency-dependent attenuation in the transmission-line model. In reality, the resonances won't be quite this strong, due to loss in the coax at high frequencies.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 27, 2016, 10:09:46 pm
content: Quote from: andyturk on February 27, 2016, 02:01:20 amwith press at different probe cable location, i can pinpoint where the break is, luckily (or unluckily?) its near the BNC connector, so i split them into 2 and i will reinstall new BNC connecter. but later when i have time for it...

author: andyturk
author_rank: Frequent Contributor
timestamp: February 28, 2016, 10:30:36 pm
content: Thanks Mechatrommer and PA4TIM!You guys inspired me to actually take my broken probe apart and see what was wrong. Turns out it wasn't "open", the inner conductor wire was actually shorting against the metal probe shield.There were some extra loops of the zig-zag conductor, so I desoldered it, cut it to an appropriate length and pushed a tiny bit of insulation inside the hole to keep the conductor off the shield. It works like a champ now.

author: Jbliss
author_rank: Regular Contributor
timestamp: March 01, 2016, 04:40:54 am
content: Probably because there is quite a bit of design that goes into them

author: kunzem
author_rank: Contributor
timestamp: March 01, 2016, 02:30:00 pm
content: yep design plus the quality assurance is what you pay for, i dont want to relay on a 10$ probe from some bunker in whang hang loaw when i want reliable results in my tests. (sure material wise they are overpriced x100, but thats not what you pay for).

author: borjam
author_rank: Unknown
timestamp: March 02, 2016, 07:31:21 am
content: The probes are certainly the weakest point of affordable oscilloscopes. I've got a Rigol DS1074Z and the probes are really crappy. Just tapping them with the finger shows how flaky they are.But of course if I get four decent probes at $100 each, well, it's more than 50% of the price of the oscilloscope itself. Anyway it would be great to have a shootout of reasonably cheap but modestly reliable probles, if that thing exists after all!

author: tautech
author_rank: Super Contributor
timestamp: March 02, 2016, 08:06:57 am
content: One has to ask why, with the probably millions of P6100 or similar probes that I and you can buy for ~$14/a pairdo other "branded" probes cost so much?And how many failures do these P**** probes have? Bugger all be the truth.From the same stable there's also the P2***, P4***, P5*** and P7*** ranges as well as a range of current and differential probes.Passives to 1000:1 and BW's to 500 MHz and an active 1G probe and members rubbish these P**** probes as crap.Time will decide I'm sure.

author: saturation
author_rank: Super Contributor
timestamp: March 02, 2016, 12:45:52 pm
content: As archived older forum posts may have said, use the cheap and cheerful for daily work, easy to replace, no tears for damage or loss. Buy many and stock up when you find a particular one with good specs. QC varies with no-name brands even within the same 'brand' name, for whatever brand is worth. Keep your good probes for when measurement quality is essential, but that usually is less an issue under 200 MHz. Closer to 500 MHz, good probes shine.Probes differ in actual characteristics and can alter with age, so its best to 'calibrate' a probe if you make a critical measurement to insure nothing has changed, or to find if the probe is broken is subtle ways.When making critical measurement touching or tapping probes, even high quality ones, will distort measurements, best done hands off once clamped.Quote from: it was said in the past on March 02, 2016, 07:31:21 am

author: exe
author_rank: Unknown
timestamp: March 02, 2016, 12:48:01 pm
content: Quote from: JustAnotherGuy999 on February 26, 2016, 04:27:16 pmI think car analogy is fine here: expensive spare parts is the easiest way to increase income. It's just a part of their business model. But, yeah, engineering high-frequency probes is not trivial and this also adds to cost. Particularly, when it comes above a few hundreds of MHz.I also think the volume of production matters a lot. High-freq probes are rarely needed and this makes them even more expensiveAnd lab gear is expensive in general. Fortunately, we have Rigol

author: PChi
author_rank: Frequent Contributor
timestamp: March 03, 2016, 10:01:06 pm
content: Another reason why the named brand probes are expensive problem is that mould tools to make all the little plastic parts are incredibly expensive so if you don't sell many the tooling costs make up a large part of the purchase price.The quality probes use custom coaxial cable with I believe a resistive inner core and low capacitance construction which doesn't come cheap.For general purpose use the cheap probes are adequate but at a couple of hundred MHz there is a difference.I do wonder if the likes of Rigol can actually make money. Test equipment is hardly mass market.

author: exe
author_rank: Unknown
timestamp: March 03, 2016, 10:28:00 pm
content: Quote from: PChi on March 03, 2016, 10:01:06 pmCan they just use the same plastic for all probes? Or at least for probes like in 50-500MHz range...

author: danadak
author_rank: Super Contributor
timestamp: March 03, 2016, 11:36:36 pm
content: At some point you might want a low C probe, FETs are used and those probescan be pretty expensive.Go to Linear Technology (linear.com) and Jim Williams has published ap noteson rolling your own.Another aspect of probes is in use for doing scope common mode measurementsat high frequency. Probe to probe variations can contribute significant errors toCM rejection.Regards, Dana.

author: retrolefty
author_rank: Super Contributor
timestamp: March 04, 2016, 12:03:25 am
content: Quote from: PChi on March 03, 2016, 10:01:06 pm' Compared to mass consumer electronics that is true. However with the new 'global economy' the market got/gets a lot bigger then it use to be and one gets a lot more scope per buck then ever before.

author: barry14
author_rank: Regular Contributor
timestamp: March 04, 2016, 12:33:23 am
content: It is interesting to read the responses to why some oscilloscope probes are expensive. I wonder, however, why anyone is surprised. What is true of probes is true of most products. There are ballpoint pens that cost well under a dollar (often given away as a promotion) and there are ballpoint pens that cost hundreds of dollars. There are digital cameras that cost under $100 and others that cost over $5000. One could go on but I think my point has been made. This is an old expression that may apply here: "You get what you pay for." Higher priced items, in general, use better materials, more sophisticated manufacturing methods, and have additional features (some of which may not be immediately obvious).