PROBLEM 1:
(a) Figure P1.1 shows a feedback control scheme for blending process that is subject to significant
disturbances. It is desired to augment this scheme with feedforward control. Of the four
potential locatio
...
PROBLEM 1:
(a) Figure P1.1 shows a feedback control scheme for blending process that is subject to significant
disturbances. It is desired to augment this scheme with feedforward control. Of the four
potential locations for the feedforward measurement indicated in the diagram, A, B, C, or D,
which would be the best? (The θ values noted in the diagram correspond to the average
residence time in the indicated hollow pipes). Justify your answer briefly.
If the system is to be pure feedforward control, the best location for the measurement would be location
A.The control mechanism receives information from the composition measurement of the right hand feed
stream and the composition controller on the left feed stream can adjust its value opening to ensure
correct product composition. Placing the analyzer at A instead of B will allow amble time for the
composition controller to respond to a disturbance (given the delays of both feed streams). Although a
feedforward controller can also be implemented at location D (not C because of the delay).
Although if a feedforward-feedback control strategy a different scheme can be used placing the
feedforward measurement at positon D:
This scheme allows for disturbances in the left side feed stream before the delay (to catch disturbance
early and adjust flow to an adequate value) to be detected and compensated for, along with the product
composition be detected and compensated for as well. These measurements can both be used in order
to be composition controller to be adjusted for an ideal product composition. Although A would still be
an appropriate choice depending on what you believe is the larger potential disturbance.
Delay compensation can be implemented on the system and any of the locations could be used (more
complex but possible).
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