Homemade HV Low Frequency Differential Oscilloscope Probe
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- Опубликовано: 29 сен 2024
- Video showing a few of the the basics of building a home made high voltage differential oscilloscope probe.
Possible future efforts on a higher frequency version may be found here:
www.eevblog.co...
Links to the RUclips vidoes:
• MicSig DP10013 times t...
• Video
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Is there a reason not to configure the two input opamps of the instrumentation amplifier as voltage followers? I can still set any gain I want with R2 and R3. Is the system bandwidth higher when the gain is distributed among two opamp stages?
Good question. I think it deserves the pin. If you wanted to change the gain, it is easier to change the one resistor. Symmetry is VERY VERY VERY important. This applies to EVERY part of the design. In the case of this fixed gain probe, had I buffered the input and used unity gain throughout the amplifier, I would achieve a bit higher BW. Like any design, there are trade offs. Goal with this video was really just to show some basics.
Thanks. I didn't think about symmetry. That makes a lot of sense.
As always, thanks for sharing your wealth of knowledge. Much appreciated, best wishes from Northern Ireland.
Glad you enjoyed it Derek.
Very informative video. Thanks for making such an interesting video. I would definitely plan for making one/two such probe to measure my power supplies primary side. Its always pain to measure high voltage side if you dont have a differential probe. It would be nice if you share some more details about your prototype that you made.
Making educational videos for an unknown audience is a bit like rolling the dice. Just how much detail to provide is a hard one to sort out. There are risks when you start to work with line voltages. You would be better served buying a probe that is certified to be safe for your application. Consider also that if you wanted a probe to do power supply design, you would need something with a lot higher bandwidth than I show. Designing and constructing such a probe would not be trivial or cheap. Depending on your skills, it may also prove not to be safe.
joe smith Thank you for kind reply in this regard. I understand the self made one would cost more than buying a new one from the market, but there are many peoples who loves to use self made gadgets. It also gives more insight about the product. My requirement is just for viewing the waveform, but yes need more bandwidth to see the ringing at switching actions. There are plenty of high bandwidth opamps available which could be used for this purpose. Front end frequency compensation is tricky unless we have the measurement tools to verify that as well as the skills to design it properly. You have thrown the proper light in right direction. If you have plan for making something like DIY kind then it would help many peoples around the world. I am not sure how much worth would it be for your time, but I feel a low cost differential probe would initiate many buyers from youtube community. I feel you have tools too to characterising the product. Decision is yours and its just my feeling about this.
Assuming we are talking about something that could be used to measure potentially lethal circuits, I suspect you could be held liable and would need to have the product certified. You may also want to consider insurance and forming a corporation. Maybe just start by talking with an lawyer and get some advice. With it being a kit, who is liable if the builder has no clue what they are doing and gets injured? I suspect you could be. You may be able to make a low voltage kit but hobbyists may find it less useful. Me personally, for the small amount of money we could potentially make, the risks far outweigh the gains. You could just sell an end product but again, I would start by talking with a lawyer to get some idea on how to protect yourself.
Very interesting probe and very informative video. Thanks
Glad you enjoyed it.
Thanks Joe.
Great stuff! I'm constantly amazed how you fiddle around with hundreds of volts without a care in the world. I would probably last about five seconds in your lab before I was declared deceased.
Hey Jack, hows the yellow plastic experiments going? I was looking at an old APC UPS I have and noticed how yellow it is getting.
Well, it's finally summer here in Sweden, so there is sunlight for 17 hours a day. I'll keep you posted after summer. I'm having high hopes for my Renaissance Wax treatment.
Jack, I'm looking forward to your results with the wax, too.
Thanks for the educational video about instrumentation amplifiers, excellent improvisation . Nowadays there are some pre-built instrumentation amplifiers such as the INA333 , AD8221 with the only Rg external but with less bandwith than this.
Diff amps have been around for a while. I've used the old Burr-Brown INA111 for a few projects.
Well 2MHz bandwith for medical instrumentation that's very good indeed alongside it's partner AD8421. I trully never used an instrumentation amplifier or a differential probe but your video has the discrete application, from a pratical perspective and open for the experience.
The opamp block has been putted in sponge on the box... mistery ... I think i have a use for this circuit , for current sensing of a resistor . Is this implementation prone to amplify also the noise if higher gains applied?
Noise is always a concern. lol. Circuit under sponge is the same as what was on the white board, only better parts used.
Nice, but I got distracted by all the marker bleed-thru thinking, "if only he completed that dang thumbnail happy-face.." ;-)
BTW, you may want to check the Pace thread - a US member posted he has 17 ST Sodr-Pens looking to do a horse-trade.
I am still using the original PS90/heater that was supplied with the unit. It's a shame that PACE would not respond to my question about quality.
The ST 45 was already 11-years old in the original post. I'm not defending them, but maybe consider the initial email was sent on a Thursday and perhaps didn't get a viewing until the following week. Also, I see no way Aaron could have given a public forum answer with a commitment to longevity.. there is always failure rate (especially on new gear). Maybe we should cut him some slack, after all it is rare these days to field questions on a forum like that.
That's their choice to make if the want to ignore the question. Telling that they responded to pretty much every question except on quality. PACE was a company built on quality and I would have thought this would be the one topic they would be all over. Seeing the initial problems with the roll out does not give me a lot of comfort in their ability. I wouldn't mind getting a new station from them but I want the tweezers and they don't offer them yet.
setting the standard, as per usual. much thanks!
I don't know about that, but thanks!
Thanks for yet another excellent video.
Excellent probe to be homemade what OPAMP are using?
I suggest if you want to try some experiments, start with what ever op-amp you have. Read the data sheets. See how they perform. My goal here was to show some basics on how to design a probe so you can design your own for your own needs.
2K-Ohm from input to ground? Wouldnt that influence the signal big time?
With it being a half hour video, I have no idea what you are referring to. Provide a time stamp and I may be able to help.
Great video.
Nice. I saw my own kitchen desk in your video. The two differential probes and my famous clock tick in the background..... :-)
And you have a nice new PACE station.
Would something like this be suitable for measuring the noise in a DC power supply?
I suppose the absolute values would not be the most reliable, but the waveform should give an idea about the noise.
Off the top of my head, I don't think this is what you want. You may want something that you can have an adjustable offset in the range of what you are trying to measure. There are probes like this.
this video deserves more like and views
I WAS TOLD THERE WOULD BE NO MATH 🤤
I was told practically all the "plastic box" high voltage diff amps used a video amplifier IC.
stefantrethan Yeah they have good bandwidth. It was probably an AD part which I forgot the number. But yeah it's just a normal opamp with high BW and high price at about 9 bucks or so
I enjoyed this video. One question: the output of the probe is always ground referenced (3min 15 sec). Can I work with two probes at different circuit points not connected to the same ground spot of DUT on 2 channels scope?
I am not 100% sure what you are asking when you as about "two probes". There are all sorts of different probes. Most scopes use a common connection for all of its channels and these are normally connected to the chassis ground. Depending how your lab is wired, the chassis ground my be ties to the AC line's neutral. The ground lead for your standard 1X / 10X passive probes are then connected to that same chassis ground. I imagine more than one scope probe and/or scope was damaged by it's user not understanding this basic concept. If that is what you are asking, I suggest doing a little reading before using your scope.
If you are asking if with the homemade differential probe I am showing but using two of them could I attach each of their references to a different potential, then yes, as long at it stays within the common mode range of the probe.
@@joesmith-je3tq Thanks a lot for your answer. I was asking for differential probes (I did not mention in the question). I wish you a successful and happy New Year !:)
Hello, I really liked your video. I just wanted to confirm if I can use this for 100kHz with 250V input to give 3.3v output?
To be clear, you don't have this probe. You would have to attempt to replicate it and I would have no way of knowing your skill set. It also implies you understand the risks involved. IMO, you would be far better off buying a ready made probe. However, if you do decide to attempt to design, construct and use a high voltage probe, don't skimp on the front end. Saving $40 in parts may cost you an oscilloscope or worse.....
@@joesmith-je3tq The thing is i am trying to make a differential voltage probe that would input 250V and output 3.3V. so i was wondering if I can use this video and circuit to make one, but by using different values of the resistor to get the gain (or attenuation) that i want. can i?
@@ummeylabibahaque5881 How would I know your level of education, construction abilities or what equipment you have available? There is a second video showing how I designed a higher frequency differential probe. One thing you may want to consider if you don't care about the lower frequencies is using a transformer to reduce the voltage. ruclips.net/video/0thOfk4I3qs/видео.html
What op-amps did you use?
The goal of this video was not to provide kids with a turn key, copy this schematic and plug it into your wall outlet. Rather these diff probe videos show some of the basic design concepts. You can design in what ever op-amp you need to meet your requirements.
So do we have a circuit diagram for this please.
Sadly, only if you watched the video. Or was it too difficult to follow along?
@@joesmith-je3tq Yeah you can quit with the sarcasm, perhaps I should have asked a more complete circuit diagram but never mind found one anyway.
@@markgray1089 There was no sarcasm intended. This series of videos was to show some of the basic design steps and considerations when designing a differential probe. Designing and copying are not the same. I considered this a fairly simple project. There wasn't a lot of math involved and my question was if you were having a hard time following that math. Based on your response, it seems you were looking for something to copy without giving any thought. This isn't the channel for that.
im designing one right now that will use some LMH6624 op amps, should be fine with a gain of 10 to 20mhz and it claims 700uV max offset over temp range and a claimed 90db of CMRR ... but we will have to see in practice
I was going to attempt a DC coupled GHz+ probe but never made it out of the paper/SPICE stage. Good low voltage diff probes for digital work now show up on eBay at reasonable prices. For higher voltages, 100MHz+ would not be too bad, depending what all constraints you level on the design. I'm interested in seeing what you come up with. If you have a blog or something, post a link.
Im at the stage of calculating out the optimal AC divider path (more like brute forcing it in LTspice as my math has failed me), im planning this out as a 400v AC diff probe with a 40v option (with a higher gain in the instamp as i tend to use these for switching power supplies), than im going to proto that out on perf than ill have a PCB made up for me
at that point ill be updating my blog and posting on the EEVBlog, ill send you a message when i finish in the upcoming month or two
after watching this i did add in some MOV protection and some rated safety resistors and tossed in a diode rail clamp at the end to prevent overloading the opamps before the 800v of MOVs kick in and im looking in to adding in a PTC
so once again thanks for the video as usual, these videos are very useful when it comes to safety and making me think to myself "what would joe smith think of the safety of this"
Sounds like a fun project. Looking forward to reading more about it. Doing a search on EEVBLOG, it looks like there have been a few who have attempted to make some sort of MHz + 100V+ diff probes but they seemed to have abandon them.
100MHz with opamps is as far as I know (I'm not really uptodate here) pretty hard because you'll have to dig deep to find some opamp at whatever extreme pricepoint. 10MHz should be doable, above that it's RF territory and the price you pay just increases exponentially as with anything more better like constructing a source meter for very low currents in the picoamps is much worse than just nanoamps.
Also what about just using a differential amplifier? Like an IN196 thing (not that that thing should be used) which are integrated instrumentation amps. For 10MHz maybe you'll find some? Dunno if it works but everything in a smaller package could make the design easier and reduce price even though these things cost a pretty penny