Dear All,
There is a requirement of one of our customers where there is a temperature controller (TC1) whose PV will never cross 305 degrees but the remote SP it gets is 307 degrees.
This is because there is another upstream temperature controller (TC2) which makes sure that the PV dosent cross 305 degrees for the downstram controller TC1.
Now, my issue is that i need to take care of Anti reset Windup in my TC1. There fore i have asked my customer to provide me with the actual process conditions C1 when i can "ACTIVATE" the Anti Reset Windup and not calculate the error in my PID any more.
I want to ask you guys for help in how i can achieve this "ACTIVATION" of Anti Reset Windup in our DeltaV PID?
**** My solution to the above problem was that during the process condition C1 where we need to "ACTIVATE" the anti reset windup i will "BYPASS" the PID through logic and the turn off the BYPASS when the condition C1 becomes false. This was the PID will not calculate anymore during C1 = TRUE. ****
But my customer dosent like this solution. Please Advice.
Thanks in advance guys,
Chitti
There are various built-in ways for the DeltaV PID block to mitigate integral wind-up, so I question whether you need to develop a strategy to "activate" it dynamically at run-time. The PID algorithm can detect and properly handle the situation if set up properly.
The following BOL article describes how proper initialization setup can ensure integral wind-up is nullified (PID function block advanced topics):
www3.emersonprocess.com/.../c_pid_function_block_advanced_topics.html
Look into use of the ARW_HI_LIM and ARW_LO_LIM parameters which cut reset when output becomes limited (PID function block parameters) :
www3.emersonprocess.com/.../r_pid_function_block_parameters.html
Then look into the FRSI add-on option for Dynamic Reset Limit (FRSI add-on options):
www3.emersonprocess.com/.../c_frsi_add-on_options.html
Interesting problem. But you describe this as a need to activate Anti Reset Wind up. Anti-Reset Windup is used to allow the output to saturate past the limit, but as soon as the output demand moves back out of limit, the reset value is "reduced by a factor of 16", moving the output more quickly out of the limit. The limit value is fixed. So this feature would not prevent wind up of TC1. The Output Limit would stop the signal and prevent wind up, but at what value to place the limit?
During this C1 condition, what do you need the output of TC1 to do? should it freeze? Follow TC2? Follow a different value? Still respond to TC1 error if PV fluctuates. Placing it in bypass would pass the CAS_IN to the OUT parameter. Would the CAS_IN be changing or fixed to 307?
Maybe you simply need to track the TC1 output. This disables the PID altogether, and in MAN you can set the option to allow user to change output, or not. You could track the PID to its OUT value, locking the PID in place when TRACK_IN is true.
You've only described part of your process and control requirement, so its difficult to see what you truly need.
Andre Dicaire