EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: trevwhite on March 31, 2017, 10:11:49 am
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Hi, I have a project coming up that will involve long runs of RS485 - 100ft end to end at least. Probably more. I will need to get a scope to at least measure signal integrity. I already have some USB logic analysers so decoding is not so important. It would though probably be useful but not the main requirement.
I have looked at Micsig, Picoscope, Analog Discover 2. They all have their strengths and weaknesses. Anyone got some real-world experiences to share of what they use for such testing/debugging in the field?
Thanks
Trev
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I would get a
https://www.eevblog.com/forum/testgear/tek-ths720a-portable-scope-teardowndiscussion/ (https://www.eevblog.com/forum/testgear/tek-ths720a-portable-scope-teardowndiscussion/)
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Although RS485 debug is mostly about signal integrity, decode may be quite useful to have in the same package. Decode is promised soon on the Micsig so may be worth waiting for that.
If I were looking for a portable scope now, I think Micsig would be top of the list overall due to big screen, responsiveness and 4 channels. If smallest size is important, e.g. single handed use up a ladder, then the Owon HDS3104M-N is probably still a pretty good contender.
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I was considering the MS220T MicSig but the tablet type have so much more memory. I can see that being useful for startup conditions. If they do release the decoders would it be a free firmware upgrade or would we need to pay for it?
The Analog Discovery and Pico scopes have lots of memory and also the decoders already done. Bit of a hassle needing a laptop but they seem to suggest enough performance?
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I was considering the MS220T MicSig but the tablet type have so much more memory. I can see that being useful for startup conditions. If they do release the decoders would it be a free firmware upgrade or would we need to pay for it?
They haven't said yet. I was referring to teh Tbook mini tablet scope, not the handhelds. I suspect the architectures are very different so no idea if they will also do decodes on the handheld.
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I did assume you were talking about the tBook. I watched your review, Mike. It was really useful, thanks.
I saw one of the unbranded Micsig handhelds going cheap ( the multimeter feature is faulty/disabled). It looked a good spec for the money but the thing that caught me was the idea of measuring startup conditions. The handheld has very limited memory compared to the tBook - I think its 240kpts versus the tBook which has 14M? 240kpts is not terrible for startup conditions but more memory the better I suppose.
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The Analog Discovery and Pico scopes have lots of memory and also the decoders already done. Bit of a hassle needing a laptop but they seem to suggest enough performance?
AD2 has maximum 2x16kSa, but then lose pattern gen. With pattern gen 2x8kSa. €273.7 w BNC adapter and w/o probes.
Cheapest Pico for RS485 debug should be 2204A, 10MHz, 8kSa shared memory. Price €95.00 w/o probes.
First modern Pico is 2206B, 50MHz, 32MSa shared memory. Price €299.00 with probes.
"In the old days" I remember successfully debugging VFD RS485 link with 2010my 2205, 25MHz, which has 16kSa shared.
Picos usually do about ~1.5x rated bw measured directly on BNC, so probably in analog speed department AD2 and 2204A are about the same. AD2 is expensive because all the digital stuff, pattern gen, 2x signal gen. As actual analog scope 2206B wipes floor with both. Also it's so small and light that can essentially considered as probe adapter - can just velcro it anywhere. All usability comes down to choosing suitable laptop. There is some touch functionality in latest software version but not very polished yet. Suggest try it first (Demo works w/o scope).
Edit: Forgot, with 2204A you can stream into 100MSa software buffer at 1MSa/s, with 2206B at 9.6MSa/s. Also none of the above has isolated inputs.
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R&S Scoperider? I have a 4-ch one on order, and from everything I've seen so far, they seem like really nice scopes for industrial troubleshooting applications (eg: CAT IV isolation up to 600V). I can post a mini-review once I get my hands on it. It has serial decode options, but like other R&S scopes, they are quite spendy.
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As this is for occasional use I am not going to blow the budget on it. I looked more into the MS220T and it has serial triggering which seems to be able to trigger on a data byte value. I think that's not a bad halfway house. I really want to check electrical signals are good primarily. Last thing I want is to be out in the field debugging actual code so the triggering should give me some electrical signal sync on data but not go into extremes of decoding all the packets.
I have logic analyzers already so if I really need to be debugging actual data then I can get that stuff out.
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There's generally some good deals on older models of Picoscopes on eBay, direct from the manufacturer. I got a 200MHz MSO for £300 (with 500MSa/s).
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100' on RS485 is like being in the next room. The bus is good to at least 4000' at 100k baud and 2.5M baud (or more) at 100'. Assuming good cable...
http://www.chipkin.com/cable-lengths-and-baud-rates-fro-rs485-or-bacnet-mstp/ (http://www.chipkin.com/cable-lengths-and-baud-rates-fro-rs485-or-bacnet-mstp/)
http://cds.linear.com/docs/en/datasheet/486fc.pdf (http://cds.linear.com/docs/en/datasheet/486fc.pdf)
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In an ideal world but if there are problems with an installation due to installation guys 'using their initiative' or say someone did not use the right cable, I will need to be able to see what is going on and check everything is good.
Until I find the problem everyone will say it's the design that doesn't work rather than it being an installation issue.
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Hi, I have a project coming up that will involve long runs of RS485 - 100ft end to end at least.
Meh, that's nothing. I've run RS232 over longer wires than that*. I can't imagine you'll have signal integrity problems.
(depending on your frequency, obviously, but that's classified information)
* It was proper 12V RS232
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There's generally some good deals on older models of Picoscopes on eBay, direct from the manufacturer. I got a 200MHz MSO for £300 (with 500MSa/s).
https://www.picotech.com/picoassured (https://www.picotech.com/picoassured)
No 4ch but various 2ch models with discounts.
Also they have new 4ch differential (or 8ch depends how look at it) 12/14bit model which has proprietary CATIII probes:
https://www.picotech.com/oscilloscope/4444/picoscope-4444-overview (https://www.picotech.com/oscilloscope/4444/picoscope-4444-overview)
But must keep in mind all Picos good for in-depth analysis with low wfm/s (because analysis mode is default mode), or single shot. If want (very) high wfm/s ("glitch hunters" approach) must go into several special modes. I'll try to cover that sometimes in my 2000 series review thread. Quite complex subject (...to understand every little detail for review).
With AD2 there is no high wfm/s modes at all, but unloaded "regular mode" is bit faster... until you start cranking up analysis functions... which will make slower again.
If this is a problem depends very heavily on subject at hand and how lazy you are to click special mode buttons.
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100' on RS485 is like being in the next room. The bus is good to at least 4000' at 100k baud and 2.5M baud (or more) at 100'. Assuming good cable...
And correct termination.
And ( sometimes ) biasing
And grounding on non-isolated systems
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If you have the space I would consider any of the DSOs that have a battery vs the hand helds. I have an Owon SDS7102V and it is a full-width DSO but not that deep. It seems like the battery lasts forever. It costs about 1/4th that of the Tek handheld, maybe less. I looked at all of them and finally just decided to use my Owon. The micsig is a great scope as well as the others mentioned but they aren't significantly smaller than the SDS7102V and some of the other battery enabled scopes and you don't have to squint at it.
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I was considering the MS220T MicSig but the tablet type have so much more memory. I can see that being useful for startup conditions. If they do release the decoders would it be a free firmware upgrade or would we need to pay for it?
They haven't said yet. I was referring to teh Tbook mini tablet scope, not the handhelds. I suspect the architectures are very different so no idea if they will also do decodes on the handheld.
Yes, you are right. Now Only handheld oscilloscope MS300 and MS500 have the 5 kinds serial bus trigger and decode.
And i think MS300 is not expensive to compare with others. ;)
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MS200 series do not support bus decode upgrade.
We will have it in our tBook mini.
Handheld oscilloscope MS300 and MS500 have decode already. :)