Waveform Triggering - APFI Versus AI

[Pie566942.0]

Hi All,

I have a PXIe-6366 simultaneous X-Series DAQ that supports analog triggering on AI<0..7> or APFI0.  System Explorer in VeriStand 2013 SP1 does not support analog triggering on terminals other than APFI0 or APFI1.  Why does System Explorer impose this limitation?  Is there any way to use an analog input as a start trigger for a VeriStand waveform task?  I don't want to modify the XML to point to an analog input for the Start.Source property without knowing how this property is interpreted by the engine.

IMHO, the differences between AI and APFI inputs prefer AI channels for analog triggering.  For example, APFI cannot be differential, it's with respect to AGND when used as an analog input.  The X-Series UM states, "you should drive the [APFI] terminal with a low impedance signal source (less than 1 kΩ source impedance)".  APFI channels are not amplified so they can be less accurate than AI channels for analog input.

Thanks,

-Steve K

[Jarrod_S.]

You can type a custom value into the Trigger Source field. You don't have to pick one of the APFI lines. The reason the drop-down list is limited to the APFI lines is that it is fairly complicated to populate the actual full list of available trigger sources for the task. For instance (and I'm not the biggest DAQ expert, so this example could be wrong), on some cards you can only pick the first channel in a task to trigger off of.

You won't need to edit any XML. You can just type in the value that you want to trigger off of. If that line is not valid, you should get an intelligible run-time error.

[Pie566942.0]

Thanks Jarrod,

Apparently I didn't dive deep enough into the VeriStand help, because one more link and I would have read, "This menu lists common trigger sources for the device(s) whose channels you assign the task. You also can enter the names of other terminals."  This is a good start.

Now I'd like to know if there's a way to configure the AI waveform trigger channel's terminal configuration and input range.  These are the PXIe-6636 hardware features I'd like to take advantage of.  System Explorer's start trigger section exposes trigger type, source, slope and level.

-Steve K

[Jarrod_S.]

Just add the AI line to the Analog Inputs section linked to the DAQ task like any other and configure it there. I assume you're doing a buffered measurement?

[Pie566942.0]

Thanks Jarrod,

Yes, sorry for the gap.  I'll be doing HIL on 4 ins and 4 outs.  I want to do an independent, retriggerable, high speed buffered waveform acquisition on another input.  I assumed if I added the waveform input to the AI list it would be implemented as HTSP.

-Steve K

[Jarrod_S.]

One DAQ board can only run one AI task, so all its lines must be used for either HWTSP or a buffered acquisition. Does your setup have more than one DAQ board? If so, is the trigger source for the buffered task on the same board that is being used for the buffered task?

[Jarrod_S.]

... At least that's how it traditionally works. I am not 100% sure if simultaneously sampling boards have this limitation.

[Pie566942.0]

Hi Jarrod,

As long as instanciating the AI channel under the DAQ (to configure the terminal mode and range) doesn't force the waveform channel into HTSP mode, we're in business.  I guess it's strange to me that I can configure the AI in waveform mode yet still have access to it as a mappable channel.  I'd think it would be one or the other.

-Steve K

[Jarrod_S. · Accepted solution]

The Analog Inputs section under the DAQ device has a setting where you select either the standard HWTSP or Waveform. If you select Waveform, then you have a chance to select the Waveform Task that will control the Analog Inputs section.

When you change the Analog Inputs section to Waveform, the items under it are no longer channels, but rather waveforms. Waveforms behave a little differently than channels. For instance, you can't map waveforms or use them in calculated channels. You can access waveforms from the Workspace using the Waveform Graph control, or programmatically using the execution API. You can also access waveform values in Custom Devices using a special API.

[Pie566942.0]

Bingo, I missed that drop-down.  I even read the "Setting Up Timing and Logging Properties for Waveform Acquisitions" help page at least three times.  D'uh.  Thank you!  I owe you one.

-Steve K