hi all,

i need to run a control loop always faster than others.

this would be done on DCS and it should be right the first time (manager knows about the plan). i am doing it with control parameters. should i also consider altering the scan time? any benefit?
any other suggestion?

 

Hi,

Altering the scan time would make it fast for all loops on that cycle.

You can actually call PID function more than once in one scan, that way you make sure it runs faster(?!). at least pid parameters will update more than once.

Andy

 

Altering the PID paramaters will make your loop response better and smoother. But if you need the field value to update faster on your controller, then you can change the scan time of that particular loop alone. On doing these will increase your CPU load.

 

What type of DCS or PLC are you using? How you change the scan time of a loop depends on your PLC. On some DCS or PLCs its very simple - on others it's a minefield.

Have you bump tested the control loop to check the response time? Whether you even need to change the scan time depends on your process.

What is the current CPU load of your controller and what will you affect if you change the scan time of more than just one PID loop?

Rob
www[.]lymac.co.nz

 

i skipped the scan time alternative. it needs a little more effort than i expected earlier.

what is bump testing? (is it step response?)

 

> what is bump testing? (is it step response?)

Yes