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| How does waveform updates on an oscilloscope work? Why do they work that way? |
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| tautech:
--- Quote from: Someone on April 18, 2023, 10:26:22 pm --- --- Quote from: pdenisowski on April 18, 2023, 06:52:23 pm --- --- Quote from: 2N3055 on April 18, 2023, 06:27:45 pm ---Trigger event is start of capture event, it cannot happen again until scope fills the whole requested time period + rearm time... --- End quote --- Yes. People sometimes forget that the waveform update rate may also be limited by the user settings: if you have 100 ms/div and 10 divisions, the maximum waveform update rate for any oscilloscope is < 1 waveform per second -- it will take 1 full second just to perform a single acquisition :) --- End quote --- While datasheets like to publish the lowest achievable dead time (and highest update rates) they are always with the little * or acknowledgement that they are the best case. Often re-arm time changes with parameters like memory depth, or it has a minimum that can occur between some acquisitions but that is not guaranteed with occasional longer gaps. The re-arm time is rarely (never?) a constant. For many complex questions like these the only option is to test in the specific application, oscilloscopes being such complex and configurable devices that they cannot detail/explain every possible use case (or might not want to talk about their shortcomings). --- End quote --- Quite but unless someone (not you :P) does the work and prepares tables of how sampling rates and mem depths are managed by the scopes acquisition process we are all just guessing. :horse: Then we also have user selectable memory depths which of course impact on rearm times...is that any surprise and user selectable sampling rates too so we must be careful to carefully compare apples with apples with instruments running in a default auto sampling/memory management configuration. Here is where user skill and knowledge come into their own for each and every use case....there are no hard and fast rules and the experienced user like this, we need to be in charge of how a scope acquisition works, not the manufacturer thinking they know best. |
| Someone:
--- Quote from: tautech on April 18, 2023, 10:37:14 pm --- --- Quote from: Someone on April 18, 2023, 10:26:22 pm --- --- Quote from: pdenisowski on April 18, 2023, 06:52:23 pm --- --- Quote from: 2N3055 on April 18, 2023, 06:27:45 pm ---Trigger event is start of capture event, it cannot happen again until scope fills the whole requested time period + rearm time... --- End quote --- Yes. People sometimes forget that the waveform update rate may also be limited by the user settings: if you have 100 ms/div and 10 divisions, the maximum waveform update rate for any oscilloscope is < 1 waveform per second -- it will take 1 full second just to perform a single acquisition :) --- End quote --- While datasheets like to publish the lowest achievable dead time (and highest update rates) they are always with the little * or acknowledgement that they are the best case. Often re-arm time changes with parameters like memory depth, or it has a minimum that can occur between some acquisitions but that is not guaranteed with occasional longer gaps. The re-arm time is rarely (never?) a constant. For many complex questions like these the only option is to test in the specific application, oscilloscopes being such complex and configurable devices that they cannot detail/explain every possible use case (or might not want to talk about their shortcomings). --- End quote --- Quite but unless someone (not you :P) does the work and prepares tables of how sampling rates and mem depths are managed by the scopes acquisition process we are all just guessing. :horse: Then we also have user selectable memory depths which of course impact on rearm times...is that any surprise and user selectable sampling rates too so we must be careful to carefully compare apples with apples with instruments running in a default auto sampling/memory management configuration. Here is where user skill and knowledge come into their own for each and every use case....there are no hard and fast rules and the experienced user like this, we need to be in charge of how a scope acquisition works, not the manufacturer thinking they know best. --- End quote --- And when you have a particular application that needs some performance measure not in the specifications, hopefully your local distributor can test it for you or loan a unit for evaluation ;) |
| tautech:
--- Quote from: Someone on April 18, 2023, 10:43:48 pm ---And when you have a particular application that needs some performance measure not in the specifications, hopefully your local distributor can test it for you or loan a unit for evaluation ;) --- End quote --- Of course however many need review the way they think about using a DSO and better utilise their best feature: Storage ! Of course you can use a DSO just like a CRO and for those that do they are missing so much capability....and members still advise newbies to buy such outdated stuff. ::) Really they do them no favours when they are better served to get into this century and learn how to use the modern feature set rather than some thing that just displays wiggly lines in real time. With a DSO we can overlook retrigger rates to some degree and use a slow timebase, capture the waveform/s of interest and zoom in to deeply inspect them in detail. Hardly advanced use just properly utilising a DSO's basic features. |
| Someone:
--- Quote from: tautech on April 19, 2023, 01:35:23 am --- --- Quote from: Someone on April 18, 2023, 10:43:48 pm ---And when you have a particular application that needs some performance measure not in the specifications, hopefully your local distributor can test it for you or loan a unit for evaluation ;) --- End quote --- Of course however many need review the way they think about using a DSO and better utilise their best feature: Storage ! Of course you can use a DSO just like a CRO and for those that do they are missing so much capability....and members still advise newbies to buy such outdated stuff. ::) Really they do them no favours when they are better served to get into this century and learn how to use the modern feature set rather than some thing that just displays wiggly lines in real time. With a DSO we can overlook retrigger rates to some degree and use a slow timebase, capture the waveform/s of interest and zoom in to deeply inspect them in detail. Hardly advanced use just properly utilising a DSO's basic features. --- End quote --- I think you are walking off (and back around on the loop) from the point of that comment. There are people on this forum who like to take a (best case and/or asterisked) specification and then try to use that as evidence of some performance related to but not actually specified. Oscilloscopes have many non specified performance and features, that can only be determined by testing. To state blankly that retirgger rates are generally not important as deep memory can do the job..... we're back at the start of that stupidity again. Both have valid uses and neither is better for all cases. They are not replacements for each other and result in radically different workflows/results for the cases that could use either. |
| 2N3055:
--- Quote from: Someone on April 18, 2023, 09:55:41 pm --- --- Quote from: 2N3055 on April 18, 2023, 01:49:53 pm --- --- Quote from: Someone on April 18, 2023, 11:57:37 am --- --- Quote from: 2N3055 on April 17, 2023, 11:53:59 pm ---I don't know of any current production scope that has software triggers (out of mainstream brands i know off). I certainly don't know them all naturally. --- End quote --- --- Quote from: 2N3055 on April 18, 2023, 09:57:14 am --- Pico 3406D has less than 0.6 µs [blind time] --- End quote --- Arent Picoscopes in that category of software based serial triggers? At which point the best case blind time of captures is irrelevant when talking about sustained throughput. --- End quote --- There is no software triggers in Picoscope.. You have wrong information. Do better research before stating something as a fact.. --- End quote --- Really? where do they advertise hardware serial triggers? where are examples or documentation of that? Why do they not correct people on their own forums who say the serial triggers are software? --- End quote --- I don't know what and why happens on their forums, that is a question for them. I imagine they cannot police every word and correct every wrong thing ever said there... Picoscope has no serial triggers software OR hardware. It has only analog and parallel digital triggers. Triggering is triggering. Decoding is post processing like math channels and measurements. It has decoders for 30+ protocols.. |
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