Generate a Trigger on a M series DAQ from SCXI data

[bensteve]

I have a combination PXI SCXI chassis (PXI-1050) that is using a SCXI-1102 to get temperature data (in conjunction with a SCXI-1581).  A PXI-6259 M Series Daq is in the last PXI slot of the PXI Chassis to communicate with the SCXI-1102.  Since the SCXI data is aquired in the PXI-6259 across the backplane, can the PXI-6259 send a trigger on a level received from the SCXI-1102.  I want a trigger sent if any temperature data exceeds a set threshold.

[John_P1]

Hi bensteve,

Thanks for posting!  You should be able to do this by setting a Reference Trigger and Exporting the Signal, but I would have to actually try it out myself to make sure.

What is your application?  Do you absolutely need a hardware-timed trigger based off of a temperature reading which should be slowly varying anyway?  It might be sufficient to simply check for the threshhold in software and write a digital line based offf of this information.  What is the trigger being used for?  Any additional information about your application would be helpful so we can make the best decision about how you should implement it.

-John

[bensteve]

Due to uncertainty of timing of a non realtime operating system, we would like to perform the triggering without Windows involved.  We don't care if there are mutiple triggers, since we can handle that with the FPGA.  We would only trip if the temperature gets to a dangerous level at which time the FPGA would inhibit the operation of power supplies.  It will be the responsibility of the operators to get the temperature to a safe range and then send a reset to the FPGA circuitry.  So during normal operatioon it should never trip.  We also don't care which temperature channel trips, any channel that goes above the level threshold should provide a trigger to the FPGA.  We figured we could use the built in level trigering of the M series DAQ, but were unsure of the interaction with the SCXI device since multiple SCXI channels are associated with one daq channel.  If the daq will still be able to provide a trigger on any of the scxi channels then I think we are good to go.

[John_P1]

Hi bensteve,

Doing this without using software is actually more difficult than I first imagined (if not impossible).  I would really suggest looking into checking for the threshhold in software--how quickly would the temperature rise beyond your cutoff in a few milliseconds?

While the SCXI inputs are multiplexed into AI0 of your DAQ device, I don't believe the driver will allow you to trigger off of it as a single channel.  If you could connect the output of the SCXI to APFI then you could set up a dummy task to trigger off of the level on APFI and export the Analog Comparison Event on a PFI line.  However, I don't believe you can do this since all of the signals are routed through the backplane of your chassis.

While I don't believe there is a hardware limitation to prevent you from triggering off of your multiple SCXI channel levels, the driver does not seem to provide a way to accomplish this.  If you absolutely need the trigger signal on your current setup to be hardware timed you would have to likely use register-level programming and invest a great deal of time learning the intricacies of the DDK. 

Again, I am not even positive if it is possible to do what you need even with the DDK.  There is also not a straightforward way to do what you need with DAQmx--my recommendation would be to use software timing for the trigger signal if possible.

-John