The restive transmission line probe is my favorite way to make a built in high speed test point. Because of cell-phones there are some absolutely TINY coax connectors. Many are less than 2.5mm on a side. Add a series resistor and you've got a GHz bandwidth test point for 30-60 cents in < 10mm^2 that securely hooks to the scope with a $5-10 of coax adapters. Easy to AC couple the test point as well, just "tent" a resistor and a cap in series.
I’d love to see an automated test rig where that positional current probe is mounted on an automated XY stage and is scanned across an entire PCB to generate an image of where current is flowing.
One danger is navigating around components. To measure the probe tip needs to be in contact to trace or signal is quickly lost and also must orient to perpendicular to current path. The tip is quite fine and collision with components by an XYZ movement system could easily damage the tip. Extensive dragging over surfaces may also cause wear of the probe tip surface. I would recommend extreme caution in contemplating such setup. Maybe a robotic probing system taught exact positions of multiple test location may work, by sweeping around a board assembly is very risky
I've put one on a linear stage and tried scanning a magnetic strip. Can sort of make out the numbers, which seemed pretty impressive considering everything. For the PCB, probably would also need to turn the probe or board. I would like to see this too.
12 GHz active probe: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-KKItbyz6564.html 25 GHz probe including custom front end IC: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-jnFZR7UsIPE.html
The Siglent scopes allow you to set a custom ratio for the probe, such as a 21x if wanted, I did it today on the new SDS1104X-U which I am doing a review video on.
Save the tape. Kapton is expensive. I'd just use an IEC plug with the ground pin broken off. Used to do that with our powered PA speakers, when I worked at the school, to avoid the ground loop hum. Ideally, we could have bought a pair of in-line XLR isolation transformers, and kept the speakers properly grounded, but the school didn't like to spend money it didn't need to.
My DP20003 (5.6KV differential probe) was a real life saver when we were developing some equipment that went up do around 2.3KV. I hated that project, because you always needed to be 100% vigilant or you risked killing yourself or damaging the equipment.
some great info in these 2 vids... thanks Dave.. good job as usual! nice to see im not the only one who pulls out the magnifying glass with SMD stuff!... i need specsavers!
Certainly good coverage, in fact I have basically all such probes on hand except very high bandwidth FET active type. But also have a isolated HV Probe, with >3KV isolation. Passive probes to 750MHz, Diff probe to 1700V, current probe 600KHz 100A, current probe 100MHz 15A , I-Probe 520, RF probe set, many custom build coax, twisted pair probes, custom 10MHz low capacitance (0.3pF) 100Mohm diff, special USB cal adapter with SMA sample outputs. Also created a Mains line access box, to all three lines, with current probe loops and voltage probing access, but such that user is fully guarded from accidental contact with mains, even in case of access to miswired , swapped around lines setup. I would not want to be without much of such equipment.
The oddest probe i have seen was someone stuck a little 0805 photodiode stuck on the end of a coax with a BNC it was used for measuring PWM LED strips by someone else who shared the lab it was nifty at times but obviously its for relative measurements and the signal level was really rather low
I've made a cruder version of that. A small solar panel connected to a sound card input. It would also be useful for measuring PWM of lighting, but I used it as an easy way to read IR remote controls.
Actually a very nice wide-dynamic range optical probe is a large BP34 photo-diode clipped into an oscilloscope probe. Will pick up photo-currents from ~1nA to 40mA with a nice logarithmic response above about 50nA as the diode gets forward biased by the photo-current. But It is fairly slow.
What I did miss in this presentation is the isolated probe Tek developed for high common mode signals (IsoVu). It allows small signal measurement in the presence of high amplitude common mode with impressive CMRR @ 100MHz. This is due to all optical path between the measuring head and base unit. I had the chance to work with both generations and the level of common mode noise immunity and low ground current coupling is impressive. You do have to sell an arm and a leg to get one as they are priced in the range of top oscilloscopes.
Took a stab at designing an open loop low bandwidth fiber-optic probe a few years ago. Unfortunately the fiber attenuation is very position sensative, so I need to do a V2 with a differential fiber signal or optical feedback. hackaday.io/project/12231-fiber-optic-isolated-voltage-probe
@@martylawson1638 What you've done is very nice and the results are impressive. Considering the price of such probes I think it's worthwhile investing in a DIY project. I would say any such project should start with "know your fiber" and Tx Rx combo. Multiple issue are there. A big one I can think of is gain linearity over the measurement range. Optical feedback is a good idea but could add delay. Also the front stage can be really noisy and JFETs could yield better results. 1st generation IsoVu has a propagation delay of ~30ns while the 2nd gen is 20ns. 1st gen does have some DC bias issues (LF fluctuations and there's thermal drift for the first 1-1.5h after powering up) and the measurement can be disturbed when wiggling the fibers in a specific way. 2nd gen is much improved. BTW the power for the measuring head is also via optical fiber. No battery is used. 1st gen has 5 fibers. There's no switchable attenuator like for a regular scope input. The measurement range with the fixed attenuators they offer is wide enough though for daily use.
@@pipbogdan I'm leaning towards differential fiber open loop for V2 due to round trip delay conserns. Common mode signal would directly measure losses while differential mode signal would minimize dc offset errors. Would need a PGA driven by the fiber losses to stabilize gain errors. Noise wasn't super impressive. So V2 would get plug in input attenuators. Sounds like J-fets are a good idea too. Still I think the hardest part is finding the right LED and photo-diode pair with connectors at a reasonable price. Have since gotten a 3D printer so might roll my own connectors on V2.
I always wondered what makes these differential probes so expensive. They contain the same basic electronics as a 1970's transistor radio thats costs $ 5, yet they cost a 100-fold...
Low volume. You can spread out all the cost of the business making the radios over millions or tens of millions of units per year. For an active differential probe you're spreading all your costs (non-recurring engineering costs, things like plastic moulds, usual business costs) over perhaps low thousands of units a year in a market with not a lot of competition.
@dave, could you do a small explanation on why, or why not, setting my scope up for differential measurement with two passive probes and the math trick would be as good, or not, aa a true differential probe? Yes i you loose one channel but if thats ok would there be other benefits to buy a rather expensive diff probe?
You can do this, it's quite safe as long as you don't exceed the voltage ratings of the scope and probes. The disadvantages are the long single ended connection path and the poor CMRR. The signal integrity is very bad. But for some low frequency measurements it can be useful.
I tried to measure current on a shunt once that way. IIRC max common mode voltage was about 10-20V, resistor voltage under 1V. First, my low-end chinese scope couldn't keep up, the refresh rate was terrible. Second, because of the relatively high input voltage setting, the effective resolution was useless.
I've made a couple of current sense probes for indication using old VCR head-drum heads or audio erase heads, may not be as fancy as the AIM but are a hell of alot cheaper, have made some probes using infrared LEDs just to see signals from IR remotes, was also hoping to see the large high voltage probes used for CRT testing.
This is why I started soldering on wire wrap fly leads. You can also twist them to get quite better high frequency performance than the typical grounding wire. The tiny 26-28 AWG works best.
Really appreciate the coupon code for the CP2100B ! That will help So, we use a LOT of diff probes in our power conversion circuits. The issue that ALL scope probes have is common mode noise. Working in power electronics with the high rise/fall times causes a LOT of non-real signals. Always having to check to make sure what I am seeing is real. Connecting both ends of the probe input together and then connecting that combination to the common or ground point of the circuit under investigation. If the signals show up, then they are not real. Also, running the coax or the differential input wires through a ferrite or maybe wrapping it around a couple of times can sometimes help. Major issue in power conversion with fast times and higher voltages and high currents. Awful stuff ! :) You (Dave) are very good with this stuff but I don't think I've seen you probe power circuits with high CM noise inducing into the probes ??? Maybe you have and I have forgotten ? Yeah, maybe you did. But differential probes are always used in these circuits and are almost always a problem
Thank you for the video, I think this is the most concise and accurate description. But completely on a different topic, can we measure switching transients which measure upto 4KV with a time duration of 50ns using 10X CAT II probes , or should we be using Differential probes. For your kind information I am measuring these transients that are effecting near GPIO pins of the micro controller. Any help or advice is most appreciated.
20Vpeak translates to 40 dBm into 50 ohm load. If you are not measuring high power PAs, 20Vp/40Vp is plenty enough for medium fast digital signals or low power RF for which they are probably designed for anyway.
This really opened my eyes to the whole new worlds of higher end probes. I never realized there were so many types of them, and the I-Prober is indeed interesting to see in action.
Dave, I'm an electrical engineering college student, and I have been using an ampclamp that was originally intended to be connected to a multimeter. I found it in the trash bin at work. They were just getting rid of it because they got a bunch of new multimeters for our field battery technicians and the new meters all have amplamps built in. It would be really interesting to see how an ampclamp that was designed to connect to a multimeter compares to an ampclamp that is actually for an O-scope. I have been curious about this but have no way to compare myself as I cant afford a CP2100B
Maybe you could write a little thing to correct the data from the coax discharging into correct data. It may not be possible on the scope, but if the data was downloaded.
Curious if you considered the type of your resistor for the 1k DIY probe. My reason is because ages ago I read somewhere that low ohms resistors appeared as inductive, while high ohmic resistors appeared as capacitors, both of course in series or in parallel with the ideal resistor. That was when the (through hole ) resistors were of the Allen-Bradley type -- element buried at the center of "hot molded" mass insulation. Going further, Philips and probably others introduced the type that had a resistive film on top of a ceramic cylinder and overall "paint" on top. That structure reduced the thermal resistance, so higher power dissipation rating in the same size resulted. But there was another benefit -- the resistor element could be grooved to trim the resistance on the production line. Instead of +/- 20% tolerance, the common tolerance then became 5% and even better were available for a minimal price increase. So far so good, BUT the spiral grooving created additional inductance. O.K, all that applied to the through hole type components. I believe present surface mount resistors are likely also trimmed , but depending on the trimming pattern there may be little or no effect to the inductance. So after all this background -- did you use a surface mount or a through hole resistor?
Why these things are so expensive is beyond me... There are actually a few bucks worth of parts inside and definitely don't have a very complicated design that needed a fleet of very high payed engineers to come up with. It has to be the fancy carry case I suppose.
I would really like to make an active probe (100x )to use at work for 455 kHz IFs. It would need to be high impedance and output to a oscilloscope. I only need enough bandwidth if maybe 60 kHz. I just have no idea how to pull it off.
Is there a reason you couldn't use a cheap passive probe? The cheap P4100 probe you can find online has an input capacitance of only 5pf. If you need lower capacitance but don't care as much about accuracy you can just hold a normal probe up to your IF.
In addition to what supernumex said, 3) money in Keysight/Tektronix/Sigilent/...'s pocket, and more seriously 4) the active FET probes also have a higher input impedance. If those aren't problems then just go with the resistive probe.
Today we are just spoiled by high performance digital scopes from China and used scopes from EBay. Not a long time ago high performance devices that can benefit from the high performance probes were only really available to companies and the users of the devices and accessories probes included did not care how much they cost as long as they help to speed up a product design at least a tiny bit or make it somewhat easier. Combined with the limited demand and very high quality expectations it allows the suppliers to charge almost as much as they want. For high performance probes it is still the case even today and I would not expect the sutuation to change any time soon.
Same reason Snap On gets $30 for a wrench made from a dollar's worth of steel. It's trusted that it's made correctly, will perform better than advertised, keep doing it a long time and be promptly dealt with by the manufacturer if it doesn't.
It is almost never uncertain how the signal changes if you connect another probe or a multimeter lead to a circuit. In many cases it is very easy to predict and compensate for. The only reason it may seem strange is because today we are just spoiled by cheap 1M input impedance test gear that in most cases allows to just ignore the effect of the extra load.
So does anyone have any idea which of the PI's ddr pins he was probing? If I had to guess, I would say that it was probably a DQ or a DQS pin. I can't think of any other DDR3/4 inouts off of the top of my head, but there are probably others.
@@EEVblog They _claim_ to have schematics for at least some of the boards at www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/README.md, but a moment's glance at any of them reveals that they've omitted most of the interesting stuff, including the DDR signals. The Raspberry Pi foundation always has just given lip service to open source, so it's not surprising.
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I have one question coming up 6x in my head because you showed the cheap passive 1K resistive load probe solution you build yourself 6x: what if you would use a 1MΩ resistor there ? Since the scope impedance is als 1MΩ you would only load it down to half the sensitivity, so would that be more useful for high frequencies ? I cannot check, I have no scope other than 5MHz bandwith, and no generator that is capable of that.
One usage example would be high-frequency noise away from analog components. By having a good connection at one point, as Dave shows here, you can have a solid ground as well as keeping the analog section GND-plane clean.
I dont understand why the lead (or scope) would get vaporized with the non isolated probe. Thats where the rcd is for, isnt it? That trips by 300mA or so?
Even with a GFCI/RCD you will still have high currents flowing for tens of milliseconds because the mechanism takes some time to open the circuit. Also your RCD can only sense faults on mains-referenced circuitry. If you connect your ground to multiple points on an isolated supply your mains RCD won't see anything out of the ordinary. If your secondary supply is grounded that's already one connection, so just connecting a single ground lead to a power rail can damage your equipment.
@@eDoc2020 I don't think those tens of milliseconds will vaporize the lead or vaporize the ground plane inside the scope. I've tripped loads of RCD's due to faulty equipment and the energy flowing is so short that it barely warms up. And as a electronics lab is a dry area, you can fit a 30mA RCD. In fact, I can't imagine someone working without an RCD. Where I live, it has been legaly mandatory in houses for 50 years or so, so having power in your house without RCD seems very archaic and unsafe to me. Especially as they cost peanuts. Sure it's not 100% foolproof, nothing ever is. Can't fix stupid. But for a few bucks it goes a long way, so I've always been puzzled why Dave never mentioned this.
@@mrpetit2 Here in the US GFCIs are only standard in wet locations. Yes, it is a bit archaic. For testing live mains equipment I'd definitely recommend adding a GFCI or even better an isolation transformer. For what would happen, I agree the fault current won't vaporize any wiring. However it likely could vaporize part of your clip right where it touches and arcs for those few milliseconds. It's worth noting that here in the US neutral and ground are bonded inside electrical service panels, so fault currents from shorting live to ground are likely much greater than you'd find in Europe. But while the chances of blowing up your scope by connecting the ground to something live are fairly low, there are other dangers. Depending on where your ground touches you could send hundreds of volts into the electronics you are testing. And like I said earlier, your RCD will only protect in case of one fault. Say you touch your scope ground to a PC's 12v power supply. Current will flow from the 12v rail, through the probe lead, through the scope's AC cord, through the PC's AC cord, and back to the power supply's DC ground. Lots of current will flow but to your RCD all will be normal.
@@eDoc2020 Yes connecting ground to neutral inside the electrical service panel is also a really dangerous thing imho; this is a TN-C system and afaik not allowed here in europe and I don't even think in CENELEC countries . TNC gives risk that with 1conductor failure neutral is rerouted through earth, and puts a live voltage on earthed metal appliences. As for the PC power supply: that would only happen if the minus of the power supply is connected to mains ground. Is that normal? True you're then basically shorting the powersupply out through the earth mains. But still that's only 12V, I think the spark will scare your hand away and only 12V means there isn't a lot of energy present (so I wonder if real damage is done). Not like when you have 230V. Without protection that will give a blow. Using an isolation transformer for your DUT is of course the best thing, but there is quite a difference in price between an RCD (~$15 for all power requirements in your lab) and a say 1000W isolation transformer for powering up most DUT's you're working on. I mean I think it's kind of stupid when building a workbench for your electronics lab with all the outlets, and not put an RCD and manual switch in there. But maybe that's just me (or europeans) not knowing anything else than always having an RCD (required by law) in the electrical system. A simple & cheap device like an RCD also prevents most tragedies like these: www.news.com.au/lifestyle/real-life/cause-of-12yearolds-tragic-electric-shock-revealed-after-the-child-was-left-brain-damaged/news-story/8d60948c20675e647236b2bc2e9e5a3d
Your cable has a 50 ohms impedance (L/C), the 50 ohms is based on the wire inductance and capacitance to the shield, if you want a correct signal put a 50 ohms input resistors assuming the source is a perfect 0 ohms source or none if the source is a 50 ohms generator. A 1k resistor is an impedance mismatch, calling for serious cable standing waves. Any spacing variation between ground and lead will mismatch the impedance seen by the source, creating weird signal on the transitions. In cable or pcb electrons travel at about half a foot per ns, a few inches of impedance mismatch like in those 2 wires probes can seriously affect your reading.
All this is fine theory, but on practice all probing is a non ideal system. Here the system is not a controlled impedance source fedding to a controlled impedance load, like a typical antenna were mismatch causes reflection at either or both feed point to source or at load end back to source. In practice as presented the probe works very well. Reflection in this case is not happening from scope end, as it IS correctly 50 ohm terminated, so no reverse signal flow, so no standing wave from that and at input side the 1K or any other value used is accessing a signal from a complex signal source, usually totally unknown characteristics, anyway that is not a 50 ohm matched source, so reflection there is no issue on the probe lead. Mere attaching ANY probe to a circuit can, and to varying degree does, affect the actual signal, thus ideally probe has very large resistance at no capacitance, at least smallest possible capacitance, thus active probes.... For this probe arrangement your normal RF matching theory plays zero roll.
The explanation is already given above but as people say it is better to see once than to hear 10 times. It is actually very easy to test how exactly the 1k resistor decouples the source from the coax cable in the probe and how the larger its value is the less reflection goes back to the board from the connection point. All you need for the experiment is a signal gen, an oscilloscope, 3 BNC-terminated pieces of coax, a T-connector, 2 50Ohm terminators and a tin can with 2 BNC sockets and a variable resistor.
@@helmuthschultes9243 with the 1k resistor we see the slowly raising edge caused by cable capacitance in complete mismatch with its inductance. Well balanced transmission lines have only an ohmic loss worsen by skin effect (where similar electrons repulse each others), a transmission line is a distributed L/C circuit which will not disturb the signal only attenuate it with length when impedance is matched, otherwise its another L/C circuit on the way messing up the signal.
@@johnkubik8559 Sadly you are hung up on your transmission line practices. They are correct for the circuit design, to function correctly, but the probecmust introduce minimal disturbance. As Dave pointed out the simple probe works provably to high bandwidth and as I explained in probing a circuit you have very deviant behaviour from transmission line. Mostly, except special cases like impedance controlled lines, circuits are logic paths and other analog signals. Rarely are circuits some pure matched impedances, and even if so the probe goes into a well matched circuit putting it out, made worse the lower resistance and higher the capacitance. Do your self a real favour, and analyse the measuring practice of such probes, by actual observation. Another view is even if you have a matched impedance path on a circuit board, with a source driving, for example a 50 ohm differential trace. You now wish to observe the signal, which input impedance probe will cause maximum disturbance a largely 1K ohm probe, or hanging a 50 ohm probe on the trace. As I already explained, any access to a active working circuit WILL suffer some disturbance, but aim is to observe normal circuit function with least disturbance/distortion. You do not remove the normal circuit load and replace it with the probe, you ADD the probe across the actual working circuit. If you have a well matched circuit and stuff another 50 ohm load across it you gurantee maximised disturbance as the circuit matching is totally stuffed, 50//50 is now 25 ohm load. Yes ideally you have an infinite resistance, zero capacitance probe but that is impossible, so highest resistance lowest capacitance, so an very expensive active probe. If you can afford it, if not as Dave correctly showed the dynamic response of a simple "coax" probe is excellent. The rise and fall times observed match the expensive active probe, the falling RC decay is another matter, while the digital line is tri state, so high impedance, thus with 1.05 K load of the simple probe pulls down the floating signal not actively driven high. You really are missing out being hung up on matched impedance theories/rules that apply within the circuit design to make it work optimally and now being observed, but probe must view it at minimised additional load put in parrallel.
Good luck trying to match the FETs and keeping the thing linear through the whole operational voltage and frequency range. Even copying an existing design that is known to work completely with PCB layouts and all the part names and dimentions is going to require a significant amount of effort and that is not even touching the calibration process. For a thing that you probably not really going to ever need I would not even bother but you are free to try if you have some free time and if you are brave enough.
@@EEVblog in fact I build a measuring preamplifier during my PhD. It should not fullfill industry standards, but work for the student and laboratory rat who cannot afford it.
