Lecture 5

Question 1

Supple Side Disturbance

Answer 1

Related to the stream being manipulated by the feedback controller, such as supply pressure, temperature or flowrate - Cascade can be used to avoid these disturbances

Question 2

Load Side Disturbance

Answer 2

Disturbances related to the main process stream or ‘load’ that is to be processes, including its flow rate, temperature or, composition. - Feed forward control is used to mitigate these

Question 3

Flow Ratio Control

Answer 3

Two types of flow in a flow ratio control system - wild (which will vary) and controlled (which is manipulated to maintain the set point)
A ratio controller is used to calculate the set point for the controlled flow by multiplying the wild flow by a desired ratio
A flow controller manipulates the controlled flow to match the calculates set point

Question 4

Reverse Action

Answer 4

Increasing measurement - Decreasing output

Question 4

Direct Action

Answer 4

Increasing measurement - Increasing output

Question 5

Material Balance Control

Answer 5

It is essential that a plant’s inventory is within safe limits, between the maximum and minimum.
Precise control of level is not always necessary as they can fluctuate within a range
Scheme favoured when there is a large reflux ratio

Question 6

Product Quality Control

Answer 6

Maintaining the product specifications, most importantly composition, is crucial
PID controllers, tuned to tightly hold variables that impact the product quality close to their set point are employed
Cascade or feedforward control is implemented if disturbances are known to cause deviations in product quality.