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Old October 23rd, 2009, 09:43 AM   #1
The Plc Kid
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PID Single Loop Controller Vs. PLC

What are the pro's and con's of doing a psi or temp control pid loop in the processor vs a single loop controller?

Which method is best?
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Old October 23rd, 2009, 09:54 AM   #2
curlyandshemp
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Quote:
Originally Posted by The Plc Kid View Post
What are the pro's and con's of doing a psi or temp control pid loop in the processor vs a single loop controller?

Which method is best?
In the PLC you can alter parameters based on what is happening in the process.

In some processes, such as sterilization of an HTST , differential level control loops in a flash chamber have different parameters for startup, cooldown and process.
Based on what the program is doing, parameters can be altered or the PID put in Manual Mode all under program control without an operator.

Advantage of stand alone PID controllers, the Auto Tune feature usually works.
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Old October 23rd, 2009, 10:06 AM   #3
The Plc Kid
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Is there an autotune for the plc pid loops. AB slc 5/04?
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Old October 23rd, 2009, 10:35 AM   #4
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Is there an autotune for the plc pid loops. AB slc 5/04?
No.
Only AB product with built in autotuning is the Contrologix PIDE instruction used in Function Block Diagram
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Old October 23rd, 2009, 12:57 PM   #5
russrmartin
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Kid,

There are advantages to both, and that really is why there are both. Typically the need for the autotune isn't required in the PLC, because the PLC controls the whole process, and at time the desired response from the loop controller is specific to the process. I've personally never used the autotune on the PIDE. Usually, if anything, I've seen PLC PIDs tuned to be overdamped, due to other conditions that made the overdamped response from the PID ideal for the process.

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