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| How to trigger a combined signal |
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| RAPo:
Recently I acquired a 3-channel isolating amplifier switch. Basically it generates from 3 signals a new wave signal, where the first signal rides on the top of the wave, the second signal is in the middle and the third signal rides on the bottom. See the attached images. The question is: how can one best trigger such a combined signal? The apparatus has a selectable trigger-out signal, but that achieves triggering of the input signal, not the combined signal. |
| EPAIII:
I have used oscilloscopes for over 56 years. I have never seen anything like that. What is the purpose/use of such a thing? Your "3-channel isolating amplifier switch" seems to have three Voltage steps and each of your input signals is SWITCHED on during and superimposed upon one of these three levels. It appears to be a type of combined time and Voltage level multiplexing. But WHY? WHY would you want to do that? ?????????????????????????????????????? Or, if that is not what it is doing, then WHAT? As for triggering, you do not give enough information to allow an answer. I see several possibilities: 1. You have access to all three of the initial signals, which appear to be phase locked together as well as the combined signal from your "3-channel isolating amplifier switch" which also appears to be phase locked to the input(s). In that case, I would simply choose one of the input signals, the triangle waveform seems like a good choice, and use that for your trigger signal. But this ASSUMES that the input signals are what you show and not something else (like stereo audio and composit video, perhaps or maybe R, G, B video or whatever). 2. Your input signals are not always what you show (sine, triangle, and ???) but can be any arbitrary waveforms including random noise. In that case, you need to look to your "3-channel isolating amplifier switch" for the possibility of a trigger signal. Perhaps as a separate output. Or you may need to modify it's circuitry to bring out such a trigger signal. (Side question: How is the frequency of the three steps generated? From one of the input waves? Which one? From some combination of all three? How are they combined? More questions along this line.) 3. Your input signals are not available and you do not have a trigger from the "3-channel isolating amplifier switch" and you can not modify it's circuitry to obtain one so you must trigger from that mess of a combined waveform. In that case and if your input signals do not change over time, then PERHAPS a low frequency filter or band pass filter can produce a trigger signal. I have been in similar situations and getting a good trigger was NOT EASY. 4. Oh heck, there are just too many more possibilities to keep going through all of them. Perhaps you can be more SPECIFIC. But I have heard that things will be different, things will be BETTER when we have digital oscilloscopes. ................. Oh, wait, wait ... we DO have digital oscilloscopes. So, what's the next iteration? Analog, digital, then _____! And when do we get IT? I can't wait. |
| EPAIII:
OK, upon rereading I see another interpretation here. You ask, "how can one best trigger such a combined signal?" Does this mean what it says? Are you looking for a trigger that PRODUCES the input signals in some other apparatus? Is that how they are generated in a phased locked condition with the three steps of the "3-channel isolating amplifier switch"? But you seem to have those signals already. I see them on the scope's display. And if it IS triggering the generation of the input signals, then why can't be also used to trigger ----- but here I do not know what to say because your words, once again, seem not to make sense. You say, "The apparatus has a selectable trigger-out signal, but that achieves triggering of the input signal, not the combined signal." By that do you mean that it triggers the beginning of the steps in your "3-channel isolating amplifier switch"? That is what it seems to say. But that would be obvious. Something must trigger those steps. Or do you mean that it is a trigger that is available to use on a scope to view the combined signal? But, in that case, aren't your photos showing scope waveforms that are properly triggered on/in the scope? What exactly are you trying to trigger? The input waveforms? The step waveform in the "3-channel isolating amplifier switch"? The scope display? But all of them seem to be nicely triggered in your photos. So WHAT? And in what piece of equipment do you wish to trigger that? In the "3-channel isolating amplifier switch"? In the waveform generator that generates the inputs? In a scope? In some other piece of equipment? Be specific please. Frankly your photos seem to show that everything IS being well triggered! So I really must ask. --- Quote from: RAPo on October 12, 2022, 06:56:33 pm --- ...<snip>... The question is: how can one best trigger such a combined signal? The apparatus has a selectable trigger-out signal, but that achieves triggering of the input signal, not the combined signal. --- End quote --- |
| jonpaul:
schematic or block diagram no idea what you are doing j |
| RAPo:
--- Quote from: EPAIII on October 13, 2022, 03:49:35 am ---I have used oscilloscopes for over 56 years. I have never seen anything like that. What is the purpose/use of such a thing? Your "3-channel isolating amplifier switch" seems to have three Voltage steps and each of your input signals is SWITCHED on during and superimposed upon one of these three levels. It appears to be a type of combined time and Voltage level multiplexing. But WHY? WHY would you want to do that? ?????????????????????????????????????? Or, if that is not what it is doing, then WHAT? --- End quote --- The apparatus is just in. I'm exploring it now. As for the why, it seems to do two things: a poor man's extension to an oscilloscope in order to get more channels. I've seen an article where there were 4 inputs calling it a quad tracer. In that article, the channels were not isolated, in this apparatus it is. The second thing seems to be the isolation amplifier part (https://www.google.com/search?q=isolation+aplifier+switch) but I haven't done any tests on that. --- Quote from: EPAIII on October 13, 2022, 03:49:35 am ---1. You have access to all three of the initial signals, which appear to be phase locked together as well as the combined signal from your "3-channel isolating amplifier switch" which also appears to be phase locked to the input(s). --- End quote --- The phase locking is in reality not necessarily there, I just showed some easily recognizable signals. --- Quote from: EPAIII on October 13, 2022, 03:49:35 am ---2. Your input signals are not always what you show (sine, triangle, and ???) but can be any arbitrary waveforms including random noise. In that case, you need to look to your "3-channel isolating amplifier switch" for the possibility of a trigger signal. Perhaps as a separate output. Or you may need to modify it's circuitry to bring out such a trigger signal. (Side question: How is the frequency of the three steps generated? From one of the input waves? Which one? From some combination of all three? How are they combined? More questions along this line.) --- End quote --- Indeed it is meant to work with different input signals (different waveforms, different amplitudes, different frequencies, and different phases). As described the apparatus has a switch 'Trig-out' where you can select one of the input signals, the BNC-out connector shows the corresponding original signal. However, that doesn't trigger the yellow combined signal. More on that later, but my question is: if you only have the yellow signal how can you achieve a stable signal on a (digital) oscilloscope. I can set a trigger on the overall signal that shows the yellow signal more or less triggered but not the different signals in the respective regions. It all looks like it is triggered because it is a screenshot, in reality, there is no locking in the regions even if I use the same frequencies. Good questions on how the yellow signal is generated. I'm still exploring don't know yet. --- Quote from: EPAIII on October 13, 2022, 03:49:35 am ---3. Your input signals are not available and you do not have a trigger from the "3-channel isolating amplifier switch" and you can not modify it's circuitry to obtain one so you must trigger from that mess of a combined waveform. In that case and if your input signals do not change over time, then PERHAPS a low frequency filter or band pass filter can produce a trigger signal. I have been in similar situations and getting a good trigger was NOT EASY. --- End quote --- As described I have the separate signals available, but I would like to work only with the yellow signal. I have seen video's on how to trigger an oscilloscope if you have two separate signals with different frequencies. That indeed is not easy. This case is different, I have one signal with three regions, and just putting an edge trigger with a trigger level in one of the regions does not give a stable image. --- Quote from: EPAIII on October 13, 2022, 03:49:35 am ---4. Oh heck, there are just too many more possibilities to keep going through all of them. Perhaps you can be more SPECIFIC. But I have heard that things will be different, things will be BETTER when we have digital oscilloscopes. --- End quote --- I'll try to give answers to your posts. |
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