Continuous and On Demand Sampling

[pyro61]

Hello,

I've got an SCXI system set up in which I acquire and monitor 64 different channels continuously.  I have set up the acquisition using the DAQ Assistant.  I also have a Daqpad 6070E in which I'd like to sample the 8 analog inputs "on demand" for short periods of time (whenever the user presses a button).  However, I'm having difficulty setting this up in LabView.

I tried placing the VI for the Daqpad inside a case structure (which is inside the main while loop) that executes when a button is pressed, but this does not really work.  After the data has been acquired from the Daqpad, I receive an error from the DAQ Assistant (trying to read samples that are no longer available) which I'm assuming is due to the fact that the Daqpad acquisition took too much time, in effect stalling the continuous acquisition of the DAQ Assistant.

Is there a way to continuously acquire the one signal while acquiring the other signal on demand (in parallel)?  Since separate devices are being used, I assume this can be done easily, however I can't quite get it.

Thanks in advance,

Scott

[e-Cash-Money]

Hello Scott,

In the last sentence it sounded like you have two different DAQ devices but you only mention the DAQpad 6070E.
Is the SCXI connected the DAQpad 6070e or some other DAQ device?

It would also be helpful if you posted your code so we can take a loot at what you are doing

[pyro61]

Yes, I've got two separate DAQ devices, the Daqpad and a separate SCXI chassis containing an 1100 and 1102 module to sample 32 BNCs and 32 thermocouplers.  I want to sample the SCXI system continously (connected to a SCXI-1600 through a USB port) while sampling the analog in of the Daqpad "on demand," but in parallel with each other.

I am currently out of the lab so I do not have the code I am using.

Thanks!

Scott

[Tom_W_[DE]]

Hi Scott-

I think you are right on track with the "parallel" suggestion-  the method you will want to employ for your application in LabVIEW is to use two parallel loops for your two acquisitions.

Rather than using one large loop, you should place your continuous acquisition in one loop and your on demand acquisition in a second loop with either a case structure or (ideally) an event structure to sense button presses and react accordingly.  This should allow you to avoid the error you are seeing and to perform both acquisitions concurrently yet independent of one another.

Hopefully this helps-