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The control in Fieldbus philosophy is more distributed then DCS, at field instruments level. Advance Process Control comes in whenever upgradation of ammonia plant is concerned. The APC is based on Predictive Multivariable Controller which takes some really critical and performance affecting variables from different sections of the plant and in turn generates setpoints for the conventional DCS, within some predefined constraints, which are otimized economically and from an operational point of view.

This seems OK in DCS but in Fieldbus it needs some serious thought as the PID control is implemented in field devices by incorporating the functional blocks.

The question is: How would it be possible for APC algorithim to first of all gather var. values from plant and then generate optimized setpoints to field devices?

Your replies are requested...

Hello,

There should be no difference whether you use Fieldbus or not. Even without APC, the operator is able to change the setpoints of those PIDs. The ammonia plant is very likely to have a supervisory facility (probably a DCS), and so you should have the means to access the necessary data there. To identify your models, you can access a plant historian or a real-time database if there is one in the system.

Please let me know if we can be of any help regarding MPC.

Best Regards, Andrey Romanenko // Ciengis Advanced Process Control

When using fieldbus the pid control does not have to be done in the instruments but it can, and with fieldbus instruments thru your dcs you can still gather that information to update the setpoints in other device or other plants but you can get other information from the fieldbus devices such as if the instrument fails you would not want another device using the data if any comming from that device and it could alarm you and switch to another device or go into failsafe reading