Multimeter probe (banaba connector) used with oscilloscope - Page 1
Forum section: electronics / beginners

author: Mm
author_rank: Contributor
timestamp: November 26, 2023, 12:40:07 pm
content: Hello,Is it generally bad to even think of using probes for multimeter with oscilloscope? Is there actual danger to damage your scope and will using banana to bnc adapter affect the measurement negatively?Situation is this. I need hv probe for my o-scope. HV probes for o-scopes seems to cost significantly more than for multimeter. I was thinking of buying 1000x hv probe for multimeter, use banana to bnc adapter and use it with o-scope. Is this bad idea?HVP-40https://eleshop.eu/pintek-hvp-40.htmlHVP-80https://eleshop.eu/pintek-hvp-08.htmlYes, Im not pro with these - so educate me if this is just stupid.

author: radiolistener
author_rank: Super Contributor
timestamp: November 26, 2023, 01:13:03 pm
content: Quote from: Mm on November 26, 2023, 12:40:07 pmYou can use it for DC voltage measurement and may be for low frequency measurement up to about 1-100 kHz.But you're needs to understand that such probe will distort/attenuate high frequency components.Before use, make sure that such a probe has output voltage below 40 V, because DMM input often can survive from 1-2 kV, but oscilloscope input can be damaged with AC voltage above 40 V.Also note that such high voltage probe voltage limit is specified for DC, if you're planning to measure AC voltage, then it's max limit will be much smaller depends on the frequency, higher frequency == lower max limit.It will be more safe for oscilloscope to use standard 1:10 probe with this 1:1000 high voltage probe.

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 26, 2023, 04:22:51 pm
content: DMM is typically 10 megaohm input impedance, oscilloscopes are typically 1 megaohm. So probes with attenuation built in will not interchange properly, voltage will read wrong. For DC/near DC use I suppose it would work terminated to a 10:1 probe like radiolistener suggests, also protects the scope somewhat as mentioned.The DMM probe you linked is only rated to 60Hz, rather than 40Mhz. As a rule of thumb you don't want to run probes at higher AC frequency than specified.There's really no way around how passive oscilloscope probes work and how that makes for an expensive piece when you want an AC/DC voltage divider flat to 40 megahertz, AND good for 8kV DC.

author: Thunderer
author_rank: Regular Contributor
timestamp: November 26, 2023, 06:00:00 pm
content: One can build a differential probe (you make it 100: or 1000:1 or more if you like and put the right insulation) and be adapted to the scope.If you do not need bandwidth of MHz, then it is pretty simple to build one.An example here:https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/If you need help with calculations, simulation, I can help, as I built one linear to 1MHz.

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2023, 06:48:56 pm
content: Quote from: Mm on November 26, 2023, 12:40:07 pmYes, that would probably be a bad idea for many reasons. To really answer your question, we'd need to know the specific voltage range that you want to measure, both peak voltage and bandwidth.

author: Mm
author_rank: Contributor
timestamp: November 26, 2023, 07:10:36 pm
content: Fair enough.So far I have seen about 4500V (peak to peak) and I doubt frequency will ever go over 2MHz. I suspect that voltage will go higher than 4500V all the way maybe to 10kV.And of course I know I cannot use 50/60Hz rated probes in my situation. What is added to probe to be able to handle e.g. 2MHz instead of 60Hz?

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 26, 2023, 08:00:21 pm
content: See the derating curve for the scope probe you linked, at 2MHz it's only good for about 300 volts, high frequency probes are sold with a "one or the other" rating, both at once will fry it. E.G. For the probe linked, per the manual input capacitance is 3pF, at 40MHz that's about 1300 ohms, dissipating a cool 49.2kW@8kV.

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2023, 08:24:00 pm
content: Quote from: Mm on November 26, 2023, 07:10:36 pm10kVp-p@ 2MHz would be beyond the capabilities of most HV probes, way beyond what you've listed. The Tektronix P6015/P6015A would manage it with a little room to spare and you can find those used if you don't like the price of new. Even the fairly robust-looking Cal Test CT4025 wouldn't quite measure up, 10kVp-p@ 1MHz appears to be its limit. At those levels, you need very low input capacitance and an input resistor that can dissipate some heat, as well as very robust insulation and a complex compensation circuit.

author: Mm
author_rank: Contributor
timestamp: November 26, 2023, 08:44:07 pm
content: I appreciate you taking ur time to explain this to me.I need to be able to measure high impulses. Like I said - so far I have seen 4.5kV impulses with frequency 50-300kHz.What if I say that I would like to have probe capable of 500kHz and 10kV impulses. What kinda options do I have?

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2023, 08:47:51 pm
content: Quote from: Mm on November 26, 2023, 08:44:07 pmIs that the bandwidth of the impulses (and if so how have you determined that) or the repetition rate? If it is the repetition rate, what is the rise time of your impulses, or do you even know that yet?The Tektronix P6015A I mentioned would be the obvious choice, whether lesser options would be suitable depend on a little more detail on the characteristics of your impulses.

author: Mm
author_rank: Contributor
timestamp: November 26, 2023, 09:05:43 pm
content: The device Im developing is not ready yet and I do not know what is going to be optimal for it's performance. The mentioned 500kHz is something I think might be maximum I ever need, but it might be much lower too - like I said Im not sure yet. I have seen great results with 50kHz.Again I cannot say anything precise about the rise time. So far the rise time has been 4.2uS (slow still), but idea is to make the rise time to be hopefully ~100-500ns. Fall time is relatively slow.About the amplitude of the impulses - I think I need to get more voltage than 4500V, hopefully not more than 10kV.

author: radiolistener
author_rank: Super Contributor
timestamp: November 26, 2023, 09:19:54 pm
content: Quote from: Mm on November 26, 2023, 07:10:36 pmI think this 1:1000 high voltage probe cannot handle 4500V at 2 MHz. This is too high.I bet it will be burned...

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2023, 10:19:48 pm
content: Quote from: Mm on November 26, 2023, 09:05:43 pmOK, so I forgot to ask what the source impedance would be here--is this a high energy circuit that won't mind the 100M/3pF loading of the P6015A probe or is that a problem?Assuming it doesn't mind that load and since you don't actually know what the pulse will be and thus the need for some margin, I think the P6015A that would be suitable. I'm not aware of alternatives to it, so if someone else has some they can chime in.

author: Mm
author_rank: Contributor
timestamp: November 27, 2023, 07:11:44 am
content: The source impedance is very low. This source is basically a capacitor terminal which is not attached to anything - it is a copper plate. The impedance of the probe should not be a problem at all, but the price of the P6015A is.

author: BeBuLamar
author_rank: Super Contributor
timestamp: November 27, 2023, 12:49:40 pm
content: I use my scope only for audio frequency range and the probes really don't make much of a difference.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 27, 2023, 02:12:52 pm
content: Micsig has a few hv differential probes. Can you use those? They're not too pricey. ~€200.