A speed control system has an amplifier-motor-control element capable of maintaining a speed of 4000 rpm at the output shaft with no external load and an input of 8 mV to the amplifier. A tacho-generator coupled to the output shaft gives 120 mV per 100 rpm and provides the feedback signal of the closed loop system.

a) Draw a Block diagram of the control loop (Use the block diagram of a closed-loop process control system in Figure 1.7 of the textbook as a guide)

b) For an output shaft speed of 4000 rpm, determine the values of the following signals on the Block diagram:

i) feedback signal C_m

ii) actuating (error) signal, E

iii) reference input (set point) signal, R

c) A load is now applied to the output shaft such that if the actuating (error) signal remained constant, the speed would fall to 3000 rpm (ie open loop). Calculate the approximate output speed in the closed-loop system.

d) A replacement motor is fitted and this produces a no-load speed of 2500 rpm for a 8 mV input. What must the reference input (set point) signal be to provide a speed of 4000 rpm.