Why are proper current probes for scopes so expensive ? - Page 1
Forum section: electronics / testgear

author: Martin72
author_rank: Super Contributor
timestamp: January 19, 2020, 10:26:15 pm
content: Hi everyone,I want to share my thoughts coming in my mind when I´m observe the market what current probes for scopes concerns.First thought, it seems that probes for scopes aren´t much desired by customers - passive probes, active probes, differential probes for voltage are more than enough there.But current…?Either they´re for AC measuring only, because of it´s simple design you can get a couple of them on the market, no big deal.Or they´re for DC and AC measuring.Then a hall sensor is used.You can get it from hantek for a few bucks, or from owon, or by some brands using the same thing ( pintek = rigol = siglent = lecroy = keysight = rohde&schwartz).It starts from appx 50 bucks and ends at 1000 bucks, depending from the bandwith and the brand itself.But all have in common, they aren´t much precisely, in higher current ranges measures failures lies up to 15% and much more.Also by the 1000 bucks probesYou can buy a hantek cc-65 probe for 50 or a rohde&schwartz for 1000....differences between them are not so much as you would expected by the spending money.Yes, a little deviation occurs, bandwith is a little bit better, noise level also.But in general, it was crap.To get a proper probe, you must take a huge step what pricing concerns.4000, 5000, 6000 bucks...These probes can therefore costs much more than your scope itself, wtf?!And there is nothing between - Either you spend up to 1000 for a "crap probe" or you must take the big step and spend minimum 4000.Why?OK, to be honest, probes must have a proper supply, real noiseless for the small outputlevel. ( Think about good old tektronix system : Inputlevel must be 10mV on scope)And to avoid saturation of the core element ( the reason why "cheap" probes have such a great measure failure on higher currents) you must have a compensation circuit for it.Proper power supply and compensation circuits, OK, this can´t be cheap to realize.In the 1970´s....But we have 2020 now and it seems, today it can´t be affordable also.Why ?Can´t believe it...Martin

author: 0culus
author_rank: Super Contributor
timestamp: January 19, 2020, 10:34:36 pm
content: Tektronix P6042 probes can be had for not outrageous amounts. I've collected four of them. One was fully restored by the prior owner (aside from replacing the probe cable with some more modern cable bundled up with heat shrink, it's like new) and it is in spec and works. The other three are in varying levels of working and I intend to rob them for parts as needed.The probes are vulnerable to drop damage, and the cabling is prone to developing breaks in the very fine control wires that are routed with the two coaxes.

author: Electro Detective
author_rank: Super Contributor
timestamp: January 19, 2020, 11:15:01 pm
content: It appears a LOT of test gear companies may be wayyy out of touch and clueless, especially from addon/accessories profit making ,by not producing affordable TooHungLow sourced current probes and many other gadgets for oscilloscopes, be they DSO or CROMy pet beef is not having affordable TooHungLow sourced DSOs with FULLY ISOLATED SEPARATED channels and Trigger inputs, outputs,and basically anything going in and out of the oscilloscope, including the USB and comm portsIf one desires a mains or otherwise earthing/ground reference, the manufacturer SHOULD fit an array of hard switches etcor a master link or switch to save moneyInstead they continue releasing the same old tired single ended designs and overpriced corporat priced accessories to frustrate cash strapped battling owner users,as well as ignore the fact clueless or reckless death wishers will try and measure mains voltages or suspect grounded DC by thinking their DSO/CRO works like a floating multimeterAnd seriously folks, WHO doesn't want to see a current waveform on their screens as well as the voltage in real time or frozen?Why not jack the price of the DSO a bit and throw in a current probe or options to buy two, four..?Unfortunately, it's not going to change anytime soon so don't hold your breath waiting, or buying into apologist BS.China tech is cheap, we all know that, and a lot of product is good enough,there's no excuse 'isolation' and 'current probes' are -expensive because..- for whatever feeble reasons in 2020,or that Demand is low =+=

author: james_s
author_rank: Super Contributor
timestamp: January 19, 2020, 11:41:40 pm
content: There are a number of reasons. One is that the demand for current probes is far lower than for voltage probes, probably by at least two orders of magnitude. The probes are much more complex, their operation is simple in concept but the devil is in the details. Try building a clamp probe that is reasonably linear from a few tens of Hz to a few tens of MHz and see how easy that really is. If it was easy to build cheap ones that worked well someone would already be offering them.

author: HighVoltage
author_rank: Super Contributor
timestamp: January 20, 2020, 08:17:40 am
content: Even DC Probes are difficult to keep in tolerance and that makes them expensive.And, quantity sold is very low compared to voltage probes.But, if you have time you can get very good current probes on the secondary market for reasonable cost.

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 08:24:48 am
content: Quote from: Electro Detective on January 19, 2020, 11:15:01 pmState yourrealrequirements !Peak amps ?Max continuous amps ?Frequency ? Maxandmin !Insertion loss ?Conductor size ?Rigid or flexible design ?Physical size/mass ?AC or AC/DC ?Isolation rating ?Accuracy ?Resolution ?It should be plain to see that NO one size will fit all so the myriad of choices currently and historically available indicate they are specialist bits of gear and therefore not made in the millions so to be available to the masses for a few bucks like P6100 probes are.QuoteMine too but like quality current probes it's not piss simple.Fullandsafe isolation is a difficult task in a scope and just the price of isolated channel handheld DSO's reflect this without adding into the mix a mains supply, Ext Trig, Pass/Fail, USB, LAN isolation and operator safety too.Further additional cost are probes suitable for isolated channel use with NO exposed metal and reference leads with shielded plugs and heavy clip insulation.As some example just one of these costs more than four PP510 100 MHz probes:For most differential probes serve this less common use type well and at affordable cost today where they can also double for measuring currents across shunts when they might not have a gnd referenced point.QuoteAgain, a current probe you might be happy with, your mate won't as he will have different needs and even the selection of what's available pale in comparison to the decades old Tek designs like the 60 MHz P6021 or 100 MHz P6022.Then how do we check current probe calibration and voltage/current probe skew ?Add a current probe loop like in some old Teks or supply a current probe test fixture like this ?Further additional cost.QuoteYou seem to think all this ^ is a simpleone size fits allexercise however I can assure you it's not !

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 20, 2020, 09:17:47 am
content: Quote from: tautech on January 20, 2020, 08:24:48 amwe can see current using normal probe and $1 shunt resistor...if anything, if i dont like whats on the market, i'll try diy to appreciate why the price is (or is/should not).

author: BravoV
author_rank: Super Contributor
timestamp: January 20, 2020, 09:56:27 am
content: Quote from: blueskull on January 20, 2020, 09:25:12 am+1 , bookmarked this particular page if I'm in the mood just to droll->Hioki CT6700 Current Probesas I can not afford them, this one's price can buy many-many DS-1054Z scopes.

author: Electro Detective
author_rank: Super Contributor
timestamp: January 20, 2020, 10:10:20 am
content: Quote from: blueskull on January 20, 2020, 09:25:12 amThanks mateI suspected some sort of monopoly or corporat market stifling going onYou would think one of them might at the leastdangleoffer an affordable low bandwidth current probe, to keep up with multimeters and clamps which kick to 500 hzand some can stretch out to 2khzIf people want 'ludicrous bandwidth' and accuracy, they gotta pay big dollar or DIY, hey I get that

author: coppice
author_rank: Super Contributor
timestamp: January 20, 2020, 10:29:48 am
content: Quote from: Electro Detective on January 20, 2020, 10:10:20 amThe reason the current probe business is a near monopoly is its very small. Dave tried a current probe using a tiny flux gate, which is an innovative and interesting design. However, I doubt they've sold more than a handful, and had to finance the development of an entire new sensor for it.

author: Sighound36
author_rank: Frequent Contributor
timestamp: January 20, 2020, 11:45:29 am
content: Quote from: coppice on January 20, 2020, 10:29:48 amThe reason the current probe business is a near monopoly is its very small. Dave tried a current probe using a tiny flux gate, which is an innovative and interesting design. However, I doubt they've sold more than a handful, and had to finance the development of an entire new sensor for it.I have one of the ITT probes and they are quirky but bloody useful especially for tight board work and silly SMPS around 600Euro +vat use this one at least once a week.Martin the other current probe which we find very useful for sensible money is Pico Technology 30 A AC/DC precision current probe accurate to 1m/a cost is around 340 Euro'https://www.picotech.com/accessories/bnc-current-probes/30-a-precision-current-probe-bnc

author: Mr Evil
author_rank: Regular Contributor
timestamp: January 20, 2020, 05:37:03 pm
content: Quote from: BravoV on January 20, 2020, 09:56:27 amThat probe isexactlythe sort of thing I would love to have, but likewise it costs multiples of my entire oscilloscope. There's no way it can actually cost that much to manufacture.The closest I have to an affordable version of that (a low-current DC current probe) is aCP-06. It was cheap, but it's slow, too noisy to be usable for measuring currents of the order of milliamps, and the build quality is barely adequate.

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 05:40:41 pm
content: Quote from: blueskull on January 20, 2020, 09:25:12 amThat's true to a point but there are starting to be other Asian options available.PT-350Bandwidth DC-50MHzPeak current 60AMax.current 20A RMSMin.current 20mAAccuracy 1%（±5mV）Noise ≤3mA RMSRise time ≤7 nsTerminal load 50ΩCoupling AC/DCLength 1.48mClamp dia. 5mmConversion ratio 0.1V/A

author: supperman
author_rank: Regular Contributor
timestamp: January 20, 2020, 06:03:16 pm
content: You can find this one for $200 on ebay..up to 1Ghz and super sensitive. Completely passive coil..amazing how it can drive into 50 ohm..https://www.amazon.com/Tektronix-CT1-Frequency-Bandwidth-Accuracy/dp/B00A7GYISWAs a somewhat newbie I may be missing something, but it seems dead on accurate into 50 ohm over a high frequency range.. Of course will not do DC.. but I have a cheap one for that. And of course you need to wire it up.. but you kind of have to do that anyways with current probes. I use a breadboard patch cable which fits perfectly. (after removing the plug)

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 06:13:25 pm
content: Quote from: supperman on January 20, 2020, 06:03:16 pmFor most of us insertion is a PITA without a split core and high BW isn't really necessary.Often a much cheaper option if we don't mind/can put up with insertion is an off the shelf CT or one from a SMPS current feedback loop.FYI, attached is the Tek CT range spec and CT1/CT2 manual

author: joeqsmith
author_rank: Super Contributor
timestamp: January 20, 2020, 07:00:57 pm
content: Yes, probes can be expensive. I picked up an old LA a few years ago and wanted to some contactless and a few MICTOR cables for it. The cables cost about 2X more than the LA.For home, I'm way too cheap to afford a nice clamp. I have my old 1960's Tektronix that I rebuilt. It drifts around a bit until it warms up but usable. I wouldn't mind finding a new clamp with similar specs for under $100.

author: james_s
author_rank: Super Contributor
timestamp: January 20, 2020, 07:15:14 pm
content: Quote from: supperman on January 20, 2020, 06:03:16 pmThe whole point of a current probe, and part of the reason they are so expensive is that they open up to slip over conductors without having to break the circuit and disconnect anything. If you don't mind opening the circuit you can use a differential probe across a sense resistor for a lot less money.

author: supperman
author_rank: Regular Contributor
timestamp: January 20, 2020, 07:25:15 pm
content: Quote from: tautech on January 20, 2020, 06:13:25 pmWait.. I want to understand this better. There are inexpensive current measuring devices that you can place on the board for testing? Can you offer me some key words so I can do some searches? I did not get very far with the above.I'm dealing with high speed LED communications (in the 2-3ns switching range) and am having decent results with the coil.. but would totally embed components if there was a good non-invasive method. The less wire leads the better since this things wants to radiate.. The Ghz response is key.. (well.. on a 500Mhz tek scope)

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 07:36:53 pm
content: Quote from: supperman on January 20, 2020, 07:25:15 pmCT = current transformer.QuoteThis makes it difficult, really difficult and I don't know of off the shelf solutions, sorry. Others might.

author: james_s
author_rank: Super Contributor
timestamp: January 20, 2020, 07:42:56 pm
content: Quote from: supperman on January 20, 2020, 07:25:15 pmI've never even heard of a current probe with 1GHz bandwidth, even a voltage probe needs to be relatively exotic to achieve such bandwidth, I'm not aware of any DIY solutions that even come particularly close. Your best bet is probably a non-inductive sense resistor coupled with a high speed active differential probe.

author: supperman
author_rank: Regular Contributor
timestamp: January 20, 2020, 07:53:39 pm
content: I guess I'm using the correct tool then.. the Tek CT1 is responsive.. at least to what my scope can measure.. and down to very low current. I don't know how it is possible either.. I don't have it setup right now or I would share pictures.. ran tests be directly driving current with my 500mhz SDG6k

author: james_s
author_rank: Super Contributor
timestamp: January 20, 2020, 08:19:13 pm
content: The fact that you're seeing something on the scope doesn't guarantee that what you're seeing matches what is actually there.

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 10:17:39 pm
content: Quote from: supperman on January 20, 2020, 07:53:39 pmIf you're close to replicating risetime specs for the SDG6kX you can be reasonably confident with your CT1 and scopes performance.

author: supperman
author_rank: Regular Contributor
timestamp: January 20, 2020, 10:37:05 pm
content: Quote from: tautech on January 20, 2020, 10:17:39 pmYes, This. I was left with a feeling that the voltage readings correctly matched the current readings when driving into a linear resistor. (50 ohm). Diodes are then a leap of faith.. but I think it is good enough for what I need.

author: Harjit
author_rank: Regular Contributor
timestamp: May 30, 2020, 06:33:28 pm
content: I would love to find a clamp on oscilloscope current probe that went from 1mA / 10mA to 10A with a 1MHz bandwidth that was ~$200 but no luck... Any ideas?

author: Martin72
author_rank: Super Contributor
timestamp: May 30, 2020, 07:03:58 pm
content: New ? No Chance....Best offer until now :Micsig CP2100B, 1.5Mhzfor appx 375€.Actually I got this and it´s surprisingly good for it´s money.The only thing you can do, and with a little bit more money than 200$, is looking at ebay or similar platforms for a good old tektronix probe+amplifier.The A6302 probe got 20Arms/50Apk, a Bandwith up to 50Mhz (?), the probe amplifier AM502B for example allow range steps down to 1mA (!!!).As I am very confident with the micsig, when I get the chance, I would buy the tek also.It got degaussing function and compensating measure method - This you´ll find only in actual models from up to 3000 bucks and more.

author: nctnico
author_rank: Super Contributor
timestamp: May 30, 2020, 08:22:21 pm
content: Quote from: Harjit on May 30, 2020, 06:33:28 pmForget about really low currents. For that you'll be better off using a shunt + differential amplifier. Other than that the low cost probes can be reasonable but IMHO the trick is to buy one which doesn't have range settings (or at least as possible). A wider total range means needing more amplification for the lowest ranges and thus more noise.The 200kHz CP-05A I have shows 16mArms / 100mApeak-peak of noise in the 4A range.

author: Martin72
author_rank: Super Contributor
timestamp: May 30, 2020, 08:29:25 pm
content: Hmm...Maybe this is the reason why today´s tek probeamplifier got "only" two ranges….As mentioned in my micsig thread, the noiselevel comparision between tek a6302, lecroy ap011 and cp2100b, the ap011 got the lowest - and no switchable ranges.

author: Martin72
author_rank: Super Contributor
timestamp: May 31, 2020, 04:27:58 pm
content: Quote from: Martin72 on May 30, 2020, 07:03:58 pmSo I got the chance....and lost:https://www.ebay.de/itm/264738310153?nordt=true&orig_cvip=true&rt=nc&_trksid=p2546137.m43663.l10137My bid was 250€...too optimistic.

author: nctnico
author_rank: Super Contributor
timestamp: May 31, 2020, 05:44:13 pm
content: Quote from: Martin72 on May 31, 2020, 04:27:58 pmYou bid way too early and people are also in a bidding war. Don't waste time on Ebay auctions with a bidding war going on. Place a bid in the last 10 seconds with the amount you want to spend unless the price is already higher than your maximum amount. The beauty of Ebay is that there is always a better deal around the corner.

author: bson
author_rank: Unknown
timestamp: May 31, 2020, 06:33:03 pm
content: Quote from: BravoV on January 20, 2020, 09:56:27 amBut then you're probably better off buying the branded one for your specific scope, to get the full scope interface with auto-zero, demagnetization, power, gain control, firmware updates, and whatnot without having to push buttons on the probe adapter. This adds value, obviously.

author: Martin72
author_rank: Super Contributor
timestamp: May 31, 2020, 06:54:04 pm
content: QuoteNormally, I do exactly so, but today I got no possibility to wait for the last 10 seconds...

author: james_s
author_rank: Super Contributor
timestamp: May 31, 2020, 09:39:49 pm
content: Quote from: nctnico on May 31, 2020, 05:44:13 pmI see that all the time and it baffles me, I simply do not understand why people start bidding when there are DAYS left, sometimes I see something that was just listed an hour earlier that already has 30 bids. I'm left wondering if it's old guys who don't "get" how online auctions work? Unless you just want to kill the BIN option to gamble on getting a better deal there is never a reason to bid before the last day at the very earliest. The ONLY thing it does is jack up the price, the real action always happens in the final seconds. Personally I use a sniping service to bid in the last seconds, set it and forget it, if I win I win, sniping annoyed me for a long time but at some point I realized it was not going away so I joined in. Ebay could eliminate sniping by extending the auction for a period after the last bid so it ends after people stop bidding like a live auction but they've never done this.