Budget 2 isolated channel bench oscilloscope? - Page 1
Forum section: electronics / testgear

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 23, 2020, 10:20:19 pm
content: I've been having issues with my Rigol DS1054Z when measuring audio signals and rectified mains voltage on many occasion so I'm not using it any more in fear of damaging something.It occurred to me that I would much rather lose 2 of those 4 channels and get the remaining 2 isolated so I no longer have to worry about shorting equipment and ground loops.Would you recommend any bench scopes under 600$ with two isolated channels? If I find an appropriate model, I will put up for sale my Rigol.

author: thanasisk
author_rank: Regular Contributor
timestamp: April 23, 2020, 10:23:47 pm
content: Perhaps one of the micsig oscilloscopes or using an active differential probe as an alternative?

author: nctnico
author_rank: Super Contributor
timestamp: April 23, 2020, 10:27:15 pm
content: For mains: get a differential probe. For audio purposes it is not difficult to make a differential amplifier from an instrumentation amplifier. I also think that $600 might not be enough to get an oscilloscope with isolated channels (many of the cheap handhelds don't have isolated channels!). Besides that most handheld scopes are crappy; they are extremely limited compared to a regular bench top oscilloscope. The ones from MicSig are rare exceptions but these don't have isolated channels.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 23, 2020, 10:46:59 pm
content: Quote from: nctnico on April 23, 2020, 10:27:15 pmI have heard of differential probes, however I believe they are extremely expensive if I'm correct. Will these isolate the scope from the mains?Not sure about the differential amplifier you talked about. Maybe some more info would be useful as I am not familiar with the idea.

author: tautech
author_rank: Super Contributor
timestamp: April 23, 2020, 10:49:42 pm
content: 200 MHz 2ch SDS1202X-E coupled with ISFE for 2 fully isolated channels costs $ 379 + $ 135https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/https://siglentna.com/product/isfe-isolated-front-end/User manual:https://int.siglent.com/u_file/document/ISFE_User_Manual.pdfIts drawbacks are 200:1 attenuation and 1 MHz max frequency.ISFE couples directly onto Siglent DSO inputs while other brands use different input spacings so short BNC cables are also required for use with other scopes.

author: nctnico
author_rank: Super Contributor
timestamp: April 23, 2020, 10:55:22 pm
content: Quote from: drummerdimitri on April 23, 2020, 10:46:59 pmAround $180 from MicSig for example. These will isolate the scope from mains (the ones from MicSig have a CAT rating).QuoteJust look at analog devices, TI, etc for an instrumentation amplifier chip. This will take a differential signal and create a single ended output. The bonus is that you can choose to amplify the signal too.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 23, 2020, 10:56:50 pm
content: Quote from: tautech on April 23, 2020, 10:49:42 pmCan't I used that ISFE isolated front end on my Rigol?Not an issue regarding the 1 Mhz frequency as most of my work involves audio, PWM signals and mains voltages etc.If that's the best option I will seriously consider it.

author: nctnico
author_rank: Super Contributor
timestamp: April 23, 2020, 11:00:45 pm
content: Quote from: drummerdimitri on April 23, 2020, 10:56:50 pmYes but the 200x attenuation ratio makes it utterly useless. Just get the MicSig differential probe for mains use. Best bang for the buck.

author: tautech
author_rank: Super Contributor
timestamp: April 23, 2020, 11:03:40 pm
content: Quote from: drummerdimitri on April 23, 2020, 10:56:50 pmYou can as it only requires USB power however unless you have a 200:1 channel input attenuation setting amplitude values will need to be calculated in your head.There’s a thread about ISFE here on EEVblog you can hunt out for further info.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 05:31:50 am
content: Just get a diff probe and call it a day. Use it for mains and directly probe audio. The probe is made for any scope and the isfe isnt, even though you can make it work. Listen to nctnico and save yourself trouble.

author: james_s
author_rank: Super Contributor
timestamp: April 24, 2020, 05:38:36 am
content: I will second this. I picked up a Tektronix P5205 differential probe for $120 after reading about them on here, it's been so useful I wish I'd bought one sooner. I was only vaguely aware they existed before that and now I use it all the time.

author: Fungus
author_rank: Super Contributor
timestamp: April 24, 2020, 05:54:09 am
content: Quote from: drummerdimitri on April 23, 2020, 10:20:19 pmFor sale: Rigol DS1054Z, one careful owner.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 06:04:51 am
content: Haha, never abused, barely used. Like new.I blew up a probe a while back though not thinking. Technically the probe still worked but the short ground attachment was MIA after a loud noise, assumed vaporized. So I can't laugh too much.

author: BravoV
author_rank: Super Contributor
timestamp: April 24, 2020, 06:06:54 am
content: Quote from: drummerdimitri on April 23, 2020, 10:20:19 pmJust get HV diff probe as many already suggested above, it will relief you big times at your above worries, and also as time goes by, when you decided you want to replace your current Rigol, you still can use it for your upcoming new scope in the future.Just an example on how stress free to probe directly anything at AC mains voltage level, as below example the scope was probing straight at the AC mains that powered the scope it self.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 09:06:58 am
content: Sounds good. Will be getting a differential probe then but as there are so many on the market, what specifications should I be looking for?

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 09:15:11 am
content: Just make sure it's capable of the voltages you'll be using it at. I prefer lower ratios. The HVP 70(NLA I think) has 1/10 and 1/100 ratios and +-700V range which works well for me. The micsig probe(DP10013) is pretty popular here. You can also just search on ebay and find one that fits your needs.http://www.micsig.com/html/41.html

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 09:23:56 am
content: Will lower ratios be more accurate in terms of absolute voltage measurements? Surely the relative waveforms will be of the same shape.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 09:32:54 am
content: Higher division ratios mean more noise from the probe itself but different probes have different levels there too. Yes the waveforms will, but if your division is too high and/or the measurement too low you're relying even more on the scope having a good low noise floor. The 1054Z is not a good low noise scope. For mains it's not a problem but who knows when you'll need to probe other lower voltage mains referenced signals. Just for mains you're probably safe with most probe that are ok with the voltage.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 24, 2020, 11:14:28 am
content: First up, this time I checked that the OP is using a Rigol and not a Siglent,as per a previous king sized post blunder on my partThat said, would running the scope in ch 1 and ch 2 differential mode, with its limitations,plus two external differential probes on ch 3 and ch 4yield a poor mans three channel isolated DSO ?Can't see why it won't work, and ch 1 and ch 2 differential mode could double as an isolated trigger

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 03:26:26 pm
content: I did some digging and found the Pintek DP-25 to be a more suitable option for my uses as the minimum of 50x attenuation of the Micsig will not be so great for audio measurements but the 200x for mains will be the same on the Pintek DP-25 and the Micsig.I like the x20 of the Pintek DP-25 better for low level signals as it will give me less noise and since I don't realistically need over 1 MHz of bandwidth I think the Pintek is the better option unless someone can prove otherwise.

author: thanasisk
author_rank: Regular Contributor
timestamp: April 24, 2020, 05:00:48 pm
content: You can have a look also at the differential probes by Testec.Pay attention to the maximum voltage specs depending on the range. Some diff probes offering also 1:1 have very low max voltages for those modes.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 05:30:41 pm
content: Quote from: thanasisk on April 24, 2020, 05:00:48 pmI just did and it is the equivalent of the Testec TT-SI-7002 which looks exactly the same so my guess is they are just re-branded probes and is a bit more expensive so would rather get the Pintek in this case as it is available on Aliexpress for 225$ shipped!

author: nctnico
author_rank: Super Contributor
timestamp: April 24, 2020, 06:53:30 pm
content: Quote from: drummerdimitri on April 24, 2020, 03:26:26 pmYou shouldn't use differential probes like the DP-25 for audio anyway. Just go the differential amplifier route for that.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 07:06:35 pm
content: Yea standard diff probes add enough noise that it's not a great idea for audio. I'd prefer direct probing or proper LNA which gives you the bigger signal without the added noise. I've usedhttps://www.alphalabinc.com/product/lna10/and it's typically been pretty good the seller is also responsive.You could also make your own if you'd like to go that route.

author: tautech
author_rank: Super Contributor
timestamp: April 24, 2020, 07:28:15 pm
content: Quote from: drummerdimitri on April 24, 2020, 03:26:26 pmYep, you're onto it.DP-25 is a well priced option that I also stock.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 07:31:15 pm
content: Quote from: nctnico on April 24, 2020, 06:53:30 pmI am only interested in seeing waveforms and not measure the noise of an amplifier if that's what you were thinking. (ex. clipping)Not interested in a DIY solution for this so either I get one differential probe or two for my purposes.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 07:39:48 pm
content: How about this... You definitely want that probe for watching the mains. If you want to test it for your audio waveform you can do that too, by itself, but if the added noise of the diff probe is a hindrance you can search further. However, I suspect just standard probe for signal and diff probe for mains is the cheapest and easiest way for you to go.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 07:47:59 pm
content: Quote from: maginnovision on April 24, 2020, 07:39:48 pmThat sounds quite reasonable. So I would have better chance of being able to measure 220 V AC and audio signals with the DP-25 than I would with the DP10013 correct?

author: rstofer
author_rank: Super Contributor
timestamp: April 24, 2020, 07:59:37 pm
content: Quote from: maginnovision on April 24, 2020, 06:04:51 amAnd this is why I try to discourage anyone from buying a used scope! A ground fault through the BNCs just can't be good for the scope.

author: rstofer
author_rank: Super Contributor
timestamp: April 24, 2020, 08:03:34 pm
content: Quote from: maginnovision on April 24, 2020, 07:39:48 pmOk, given that you can now watch the mains, what exactly can you do about it? If there is noise, a) you can't fix it and b) you will have an opportunity to deal with the noise at the lower voltages. Just assume the mains are trash and deal with it later.Why all the interest in jamming a scope probe into a wall outlet? There simply must be another way to get things done!

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 08:07:55 pm
content: Quote from: drummerdimitri on April 24, 2020, 07:47:59 pmFor 220V ac I don't think it's going to matter which probe you get. For the micsig you'd have to be on the 500X mode, the 50x won't support 220V AC so technically the pintek would be better but I don't know if the difference would matter to YOU if you're not at all interested in measurements. For audio I don't think either probe is good but the pintek again would be BETTER than the micsig.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 08:08:39 pm
content: Quote from: rstofer on April 24, 2020, 08:03:34 pmI don't know, it's not my requirement. Maybe he's looking for mains noise rejection.

author: james_s
author_rank: Super Contributor
timestamp: April 24, 2020, 08:15:25 pm
content: There's more than one source of something that could be called mains. I've used my differential probe to look at the output of inverters and generators on occasion.

author: maginnovision
author_rank: Super Contributor
timestamp: April 24, 2020, 08:25:58 pm
content: Yea, realistically it's useful for anything mains referenced as well which is not a small number of things.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 11:47:00 pm
content: I had totally forgotten that I had used the software MATH function on my scope in the past to probe around things I wasn't really sure of.What are the benefits of a DP over the A-B function?

author: tautech
author_rank: Super Contributor
timestamp: April 24, 2020, 11:50:19 pm
content: Quote from: drummerdimitri on April 24, 2020, 11:47:00 pmIt uses just one channel.There are less voltage restrictions compared to probe ratings.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 24, 2020, 11:52:10 pm
content: Quote from: tautech on April 24, 2020, 11:50:19 pmWell I've never had the need to use more than 2 out of the 4 available channels.I will need to investigate this further...

author: MustardMan
author_rank: Contributor
timestamp: December 22, 2020, 03:30:37 am
content: I started a thread asking about Isolated vs Differential, and ended up making a list of all the isolated scopes I could find... probably too late for the OP.https://www.eevblog.com/forum/testgear/isolated-or-differential-for-floating-measurements/msg3380586/#msg3380586Before starting that particular topic I found this discussion through a web search, and although I used several pointers from it, it didn't helping me much (hence I started a new one).

author: exe
author_rank: Unknown
timestamp: December 22, 2020, 01:39:24 pm
content: Analog discovery 2 has two differential inputs. But it's only up to 25V.For audio, depending what you do, an audio analyzer (or even just a sound card) can also be useful if you want to measure THD. Oscilloscopes usually don't have enough resolution for THD measurements.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 22, 2020, 01:53:42 pm
content: Isn't the advantage of a differential probe is a known CMRR over the entire bandwidth? Whereas a isolated scope only gives you the CMRR for 50/60 (sometimes 400) Hz.Scopes are isolated for safety where diff probes are isolated for function.

author: MustardMan
author_rank: Contributor
timestamp: December 22, 2020, 09:57:54 pm
content: I *think* one of the reasons that there is a niche for isolated scopes is because (as David mentions inhttps://www.eevblog.com/forum/testgear/isolated-or-differential-for-floating-measurements/msg3379970/#msg3379970) differential probes and differential input scopes (there is at least one of those out there) are range limited by the noise floor of the differential amplifier. The bigger the offset voltage, the less detail you can get.From what I gathered (and I'm new to this stuff), is that isolated means you can see the detail even with a large offset. The downside is loss of CMMR at higher frequencies (mind you, that also happens with differential probes too, but not as badly/quickly). The Cleverscope device/design has done a spectacular job at making an Isolated Scope that has an exceptional CMMR at higher bandwidth. If only it was an integrated 'scope and not require a PC/USB connection I'd buy one today!Maybe if a cleverscope was integrated with a tablet like MicSig have done...