PID's from DH+ to Ethernet

hi guys,

I am newbie in the forum and in plc so please bear with some of my terms and language I use.

We have just successfully switched one of our node (SLC 5/04)from DH+ to ethernet but all our PIDs started playing up and wont stabilize. I was thinking because now that the processor is running through the ethernet that it is now communicating faster and in return a small difference in the PV and CV makes the control a bit harder. how can I stabilize my PIDs? Did i missed something that I need to adjust on the PIDs?

Any answer is much appreciated.

Thanks,

Winston

this is just a guess based on what you've posted so far ...

it sounds like your PIDs are configured for STI mode – but you're not actually using an STI to schedule the PIDs ...

when that situation happens, the PID (incorrectly) gets executed on each and every scan ...

so ...

when the speed of the scan speeds up (or slows down) the tuning of the PID becomes "skewed" for the Integral and for the Derivative actions ... those actions are "time related" – the Proportional action won't be affected ...

in simplest terms, any change in scan speed causes your PID to become "detuned" ...

again - this is all just guesswork at this point ...

suggestion:

post your complete RSS program files (original and new if possible) ... you'll have to zip the files before posting – forum rule ...

we'll be glad to take a look and see if we can provide a detailed answer ...

Sounds like a pretty good guess, Ron. It's also possible that a version of the program with different tuning values stored in the data tables could have been installed when the processor was swapped.