Managing Tasks on Ethernet cDAQ - Best Practice

[dankaroll]

Hi all,

I'm currently working on a multi-station machine to perform functional product tests using an NI cDAQ 9188. Each station in the machine performs the same function but is intended to run independently. Basically a given station is loaded with a part, tested, sorted, a new part is installed and repeats. During this process other stations are undergoing the same procedure and sharing the same cDAQ. 

During this testing digital signals (48) are turned on/off and analog signals (24) are being read between all stations. I've found that in contrary to a PCI task, the ethernet cDAQ tasks have quite a delay (~750 ms) when starting / stopping. Prior to this project I've only had experience using PCI tasks where I could read N Samples when needed without much start-up delay. Same goes for writing digital samples.

The solution I've implemented for this is to create a continuous analog read VI that reads all analog signals and loops in the background continuously writing to a global variable. When a given station gets to a point where it needs to read signals, it pulls the desired index from the global array at that point in time. I also have a similar solution set up for the digital task, except it is reading a global variable for digital states and applies that to the task on each loop iteration. Normally I try to avoid continous loop senarios but the PC I'm using lets me get away with it. 

Basically what I really need is subVI that starts the analog or digital task, but is idle until called by any module and returns N samples. This VI needs to act as a gate for analog read requests to avoid any reserved resource issue. I can't really think of how to accomplish this. 

Any ideas?

[KeaneSenses]

If you're looking for more control over the DAQmx task, perhaps you could utilize the DAQmx Control Task VI to control which state the task is in?

http://digital.ni.com/public.nsf/allkb/3D9CF4F4A0549F40862574420029ECCD

http://zone.ni.com/reference/en-XX/help/370466V-01/mxcncpts/taskstatemodel/