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6/18/2008 7:49 AM | |
Joined: 9/27/2006 Last visit: 9/8/2024 Posts: 12282 Rating: (2682) |
Hello AppSupportGuy; The basic implementation of the PID cascade loop with Siemens' FB41/42 is relatively simple (see the attached illustration, taken from the Standard and System Functions manual). The setpoint of the inner loop is the output of the outside loop controller; the PVs for each loop comes from their own process transciever. I suggest you look at the following document http://www.essproducts.com/download/PIDprimer.PDF I have used in the past; I especially like the Cascade control checklist provided starting page 7.It is general enough to be applicable on any number of processors (I have used it with Rockwell and Siemens controllers). One point that is not mentionned: place the loop with the fastest response time as the inside loop. For example, if you have a level/temperature cascade control to implement, the level will in most cases respond much quicker than the temperature controller; so I would place the level loop insiode and the temperature loop outside n the cascade loop. This leads to more stability in the system. Hope this helps, Daniel Chartier |
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