Capture of 4 analog chanels, using one of them as a trigger

[MikN]

Thanks again for getting back to me.

That is really dissapointing news.. not sure what I'm going to do now.

You say that the start trigger would be do-able..? Do you think it would be simple to implement what I said, but in a simpler way to that the channels are just captured for a specified number of samples, after receiving the trigger edge?

Many thanks,
Mike

[jasonhill]

Mike,

Take a look at the DAQmx Trigger function.  I use the Start Analog Edge option in a system very similar to yours.  I do not know a way to simultaniously read and monitor the trigger for a "stop" signal. 

What you could do is set your number of samples high enough that you have a resonable certanty of capturing all the required data, scan the trigger channel data for the third downward edge, then truncate all the signals at that point, and output to file / graph.  I recomend you change the DAQmx Read to output a 1D waveform.  Labview has a wide variety of tools for analyzing waveforms and they can also be easily truncated and written to file.

I might be able to rig up a sample if you need it.

=jason

[MikN]

Hi there,

thanks very much for the reply.

I had decided that what you suggested was probably the best (simplest option): i.e. to set up a digital trigger that then runs the signal capture of 3 or 4 analog input channels. I've been messing around with this all afternoon here.. I went through some examples and tried to modify them, but haven't got it to work yet. This may be because I've screwed up trying to (physically) wire in a digital channel to connect my pulse generator to. I'll attatch an example, perhaps you could suggest what's wrong with it..??

Many thanks,

mike

[MikN]

oops, I meant to say that the capturing of the analog channels will last for a pre-specified number of samples, that should allow all the data (probably up to 10 seconds worth) to be sampled... This is instead of the crazy start/stop thing I was going on about which I think is probably a bad idea for my sanity..

[MikN]

Well,
in case anyone finds this useful, I have now got the system working correctly (touch wood). In fact the VI i posted does the job nicely with our setup. The key was wiring in the trigger input to the correct terminals on the interface box.

Many thanks,
mike