How can I trigger a waveform chart in LabView RT?

[BenSparkes]

Hi, I'm trying to trigger a waveform chart to a sawtooth function (created inside LV) to make something analogous to a CRO inside labview RT. Can anyone help me?

Ben

[Christian Mergl]

Hey,

Would be helpfull if you could be a little bit more specific.

Christian

[ColeTrain]

Ben, 

I am also confused with what you are working to accomplish here.  Are you saying that you would like to build in a trigger so that you can display a sawtooth function once the trigger is tripped? 

[BenSparkes]

Specifically we are scanning an optical cavity using a sawtooth function (created on an FPGA card) and looking at the reflection signal. We would ideally like to be able to look at this detection signal using LabView RT instead of a CRO. We can currently do this using a Waveform Chart but, as the chart is not triggered to the sawtooth function as we can do simply with the CRO, this is not very useful. Ideally we would like to graph on the screen using RT a full scan (up and down) of the sawtooth function and have it triggered to start again at either top of bottom (i.e. rising or falling edge). So far I have not been able to find a way to do this and any help would be most appreciated!

Cheers, Ben

[ColeTrain]

Ben, 

The FPGA IO points can specifically be targeted from within the RT system.  From the RT system, through either TCP/IP or sharved variables, you can port the data from the RT system to a host PC.  In general, graphs and indicators in general are used from the host PC, while the data collection and processing are done in the RT environment.  

From what it sounds like, you would like to read in this sawtooth wave and display it on a graph.  But I am still unclear on what you are referring to with the triggering off of the sawtooth signal.  Are you reading only one "tooth" of the wave at a time and are looking to plot the response of just one tooth at a time?

[BenSparkes]

Yes, thats exactly what I want to do - plot one tooth at a time and look at the detector signal for that tooth.

Cheers

[ColeTrain]

Ben,

If you're going to read this directly into RT, you will need DAQmx.  You can set up a trigger based on a digital pulse and then record for a number of samples or set it up to stop sampling once the value gets low enough.  Although, each of these functions will depend on what card you are trying to read in on.  So... which card are you working with?

[BenSparkes]

I thought I might need something like that but couldn't get it to find any inputs when using the DAQ Express.

I am working with a PXI-7852R card on a PXI-1042Q Chasis.

Ben

[ColeTrain]

Ben, 

All of the R-Series cards have to go through the FPGA to access the card's IO.  You will not see any of these IO Variables using DAQmx (which includes the DAQ Assistant).  You will need a non-R-Series card to use DAQmx.

[BenSparkes]

Ah, thats a bit of a problem then, I guess we'll have to go back to some more old fashioned technology to look at the signal. Thank you for your help though!

Cheers, Ben