Simple Timed IO control with continous data aq

[RickCSM]

Hello,

I have a set of 5 relays used to control cycling/sequencing of events on an industrial system.  The system operates on a cycle with the various relays being activated or deenerginzed at specific and adjustable times.  I need to have fairly continuous display of 10 analog inputs combined with data logging at a specified interval.  I would also like to have some of the analog inputs log data continuously over a number of cycles once or twice a day.

I currently have a good control loop that uses a sequence structure with timed loops.

I understand that a timed loop preempts the execution of other commands during its iteration, and therefore interferes with input monitoring and display.

What other ways of programming labview are there for this type of application?  I have tried operating two seperate VI's for control and Analog input display but the two vi's appear to effect each others execution. 

Any example VI's on the support page?

[TroyK]

When you say "fairly continuous display" and "data logging" what kind of sample rates are you talking about?
What kind of accuracy do you require? <1ms?
What kind of DAQ hardware are you using and what OS are you running it on? Is it an RT target?

[RickCSM]

Sample rates and accuracy shouldnt be an issue.  I need to have the analog input connections update every few seconds, just so that the system operator can get an idea of the systems response when adjusting valves, flowrates, etc.

I would like to have the analog input values logged to a file say, once every hour.  Additionally, the system will be running on a 4-10 minute cycle.  I need to have a few (perhaps 5) cycles recorded each day.  This recording could be in the ballpark of once every few seconds for 20-40 minutes and only needs to include 3 of the input connections.   

I am using two LabJack U12 USB boards which as I believe means I can only have 2 executions through the USB port at the same time. (?)

The OS is windows XP

If it helps, Im operating a biological treatment system which needs only a cycling of two pumps, and on/off for a few valves.  The system should take 4-8 weeks to reach a steady state of operation, so the sampling rate does not need to be fast.

I can put VI's together that would do all of these things, but I can't get them to work together.

Thanks, Rick

Message Edited by RickCSM on 07-08-2008 11:01 PM

[TroyK]

From what you have described, you should be able to accomplish all of this in a single vi.
You just need to choose the right architecture and implement the functions correctly.

For such slow sample and control requirements you don't need to use timed loops or a real time OS.
I don't think you even need hardware timed data acquisition. It can all be software timed "on demand".

OS timestamps should be accurate enough to control your timing.

Perhaps it is just your implementation that is causing the functions to interfere with each other.

If you attach your vis we may be able to suggest a fix.