1. (a) What is proportional control? (b) Explain the function of proportional control? (c) How fail safe arrangement is encored in control values?

 

(a) It is the mode of control where controller output is directly proportional to the deviation.

 (b) Function:

                           1. A set value of pressure (P_s) is established in one bellow & the measuring value (P_m) in feed into the opposing bellows.

                           2. Measured value (P_m) could be proportional to the temp flow etc.

                           3. Any difference between two pressures causes movement of the flapper.

                           4. Then alteration in air flow out of the nozzle & hence variation in output pressure (P_o) to the control system.

                           5. If upper end of the flapper is fixed no proportional action.

                           6. And if the top end of the flopper will move in the opposite direction to the lower end. This reduces the senility & windiness the promotional band.

                           7. Finally proportional action result in a steady herd after a change out as a different value of desire value.

(c) Fail safe arrangement arranges to move the value to a position that allows the plant continue to operate safely that is fully open fully closed.