Better than 1s time resolution on Red Lion Graphite?

We often use the Red Lion Graphite series as a PLC since it can easily handle the extra workload in scripts. So far it's worked out nicely. But now, needing to do PID control with less than 1s update rate. I know I can run this in the On Update section, which is supposedly run 10 times/second, but I don't want to just say each update is exactly 100 ms apart because I know that's not going to be the case. Is there any way to get more accurate time resolution on these? Without the control module....

Should've added, do not have a PID module. Doing the PID myself with the analog output module.

You're correct about On Update, it runs each time the display is redrawn. This is usually around 10 times a second, but can vary depending on how loaded down the system is and how complex the display is.

You could try running a background program with an infinite loop, and use the Sleep function at the end of the loop body. This gives "millisecond" resolution, but I wouldn't push it too low and also expect some jitter.

Here's something you can try...

Make a program with this code
Add it to the global On Startup action to get it running. Be sure to set the Execution Task to Background or it will lock up your unit. Replace 50 with whatever time you want in milliseconds; ThisTag will now toggle at this rate continually.

That's an interesting question. Haven't tried it, but maybe this would work:

Use the Comms Delay in the PLC protocol; say 500ms.
Create a tag that reads from a ms counter in the PLC, so the HMI tag will always change every 500ms update.
On that tag, use the Trigger On Change to run your PID code.

kolyur said:

Here's something you can try...

Make a program with this code

Code:

while(true){
    Sleep(50);
    ThisTag := !ThisTag;
}

Add it to the global On Startup action to get it running. Be sure to set the Execution Task to Background or it will lock up your unit. Replace 50 with whatever time you want in milliseconds; ThisTag will now toggle at this rate continually.

Click to expand...

Just curious.
If it's set to background, do you think that it will run every 50ms?
Ie. would it get way off if you load a screen with heavy PLC comms, or when another (non-background) task runs?

I just assumed background to be random, unreliable. But maybe all the code runs so fast that it doesn't really matter.