Trying to take oscilloscope voltage data

[RTSLVU]

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@sahurley wrote:

Unfortunately, I don't think that'll work for this because I need to have it record how many pulses I'm getting over a course of (around) 8 hours.

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Originally you stated you had a NI-DAQ of some sort, forget the scope and just use the DAQ.

It is probably better suited for this purpose.

[RTSLVU]

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@RTSLVU wrote:

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@sahurley wrote:

Unfortunately, I don't think that'll work for this because I need to have it record how many pulses I'm getting over a course of (around) 8 hours.

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Originally you stated you had a NI-DAQ of some sort, forget the scope and just use the DAQ.

It is probably better suited for this purpose.

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Or if you are set on using the scope think about doing this instead.

1. Setup the scope to take the measurements you want on the waveform
2. Set the scope to trigger a single sweep on a pulse.
3. Arm the trigger so it is ready and waiting
4. IF the scope is triggered:
5. Save the waveform and the measurements data along with a time stamp
6. Goto 3

[sahurley]

So if I were to use the DAQ could I make an oscilloscope in LabVIEW that output the waveform and saved the voltage vs. time data?

[NIquist]

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@sahurley wrote:

So if I were to use the DAQ could I make an oscilloscope in LabVIEW that output the waveform and saved the voltage vs. time data?

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Don't confuse the issue with incorrect terminology.  You do NOT want an oscilloscope, you want a data logger.  

Yes, almost any simple DAQ card can do this.  There are several ways depending on the signal you need to monitor.  You said it's a pulse.  How long is the pulse?  Is it always the same amplitude?  Is it a digital standard like TTL?

[sahurley]

Pulse is probably confusing here, so basically there is a spark.  The spark causes a spike in the voltage, otherwise it is steady.   The spark should be steady a steady pulse of 1hz, but I don't think it is so that's why I need to log the data.   The amplitude is also not necessarily the same.

[NIquist]

Well of course the faster in time and the smaller in amplitude the spike is, the harder it will be to reliably detect.  Can you post an image from your scope?

Also, what kind of DAQ card(s) do you have available?  Do you have knowledge enough in electronics to build a signal conditioning circuit if you need to?

[NIquist]

I hate to even bring this up since it makes it seem like we're going around in circles, but now that you've better described the signal you're trying to monitor you could actually use your scope for an analog signal conditioner and make it very easy to log whether or not the spikes are firing consistently.  If you can set your scope to reliably trigger every time the spike occurs you could just log the easy to read digital TRIG OUT of your scope.  This technique would combine the best parts of both worlds:

1)  The high speed analog triggering front-end of your fast scope and,

2)  The long-term data collection abilities of the DAQ card and PC.

You can try this out easily if you can borrow a spare scope.  Set the best scope to trigger on your spike and then connect the other scope's channel 1 to the TRIGGER OUT jack of the first scope with a BNC cable.  You should see your spike on the first scope and a much longer TTL pulse on the second scope every time the first scope triggers on the spike.  Now you can use a much slower, simpler DAQ to read the nice TTL pulse instead of sampling at a very high rate trying to catch the spike.  Look at some of the Digital Input examples for recording the TTL TRIG OUT.  Some of them can also log to a file for you.  You should be able to do it with Signal Express as well.

[sahurley]

Using the DAQ seems to have worked , but I'm not actually seeing the curve just spikes every so often (that don't line up with what the oscilloscope is showing; I connected them separately).  Also, the time axis is still not running in real time.  Is this because it's too much data and I have to break it down?

[billko]

I'm still having a difficult time understanding what it is that you really want to do.  Instead of concentrating on how to get the data, let's concentrate on what you expect to see.  For instance, are you expecting a LabVIEW chart to duplicate what you see on the screen?  Or maybe you are only interested in when the spikes occur and at what amplitude?

It seems to me that you aren't quite sure what want to do yet.  Please sit down for a minute and really think about what you expect the results to look like and then we can give you better advice.

[sahurley]

I want to see the spike at the corresponding time interval.