Question

1)How does the feed forward control loop anticipate disturbance ? Elaborate with an example.
2)It is well known that PLC is used for batch processes; however, SCSADA can be used for continuous processes as well;though, it is built on PLC. How is that possible ?
3) A good example of the application of proportional derivative ( PD ) controller is

please solve the questions at least two questions

Answer 1

1) A feedforward control loop is based on the idea of predicting the effect of a disturbance and taking the preventive action prospectively so as to negate the effect of a disturbance. The success of a feedforward control mechanism largely rests upon two factors:

1. The ability of the sensing system to quickly and accurately measure the disturbances creeping into the system, and
2. The exhaustiveness and robustness of the predictive model which estimates the effect of the measured disturbance on the process.

This loop anticipates a disturbance in advance by measuring the key properties relevantly affecting the controlled variables.

For example, in a CSTR, if the controlled variable is the outlet concentration, then the key disturbances which could affect this are the inlet flow rate, the temperature of the reactor, and the mixing. These three disturbances can be proactively detected upstream by keeping a check on the flow rate of the inlet mixture, any disturbances in the coolant flow rate and temperature, as well as the homogeneity of the reaction mixture by appropriate sensors. Thus, instead of measuring the outlet concentration and then taking a feedback control action, the feed-forward control mechanism can be triggered based on the anticipated disturbance measurements as described above.