Question

A control system that anticipates load 7 Problem 1: Select the most correct answer disturbances and controls them before they can impact the process variable is of this type Open loop controllers have this characteristic: 1 They don't use feedback Open loop control system Feedback control system a b. They don't observe the output Can't compensate for disturbance All of the above b. Feedforward control system d. None of the above This is an example of an open-loop system 8. in the following way feedforward controllers deal with disturbance a Stepper motor b. Light bulb Compensate for measured disturbance before it impacts the system a TV remote control d. Any of the above Compensate for measured disturbance after it impacts the system b 3. A motor which rotates to one of a number of Compensate for unmeasured disturbance before it impacts the system c. fixed positions by sending a stream of electrical pulses to it causing it to rotate by exactly that Compensate for unmeasured disturbance after it impacts the system d. many steps is of this kind: a. DC motor When comparing feedforward and feedback control systems, measuring the disturbance is b. AC motor c. Stepper motor None of the above necessary in those systems d. Feedforward control systems a A control system which measures a process 4. Feedback control systems Both feedforward and feedback control b. variable and sends the measurement to a c. controller for comparison to setpoint. If the systems Neither feedforward not feedback control process variable is not at setpoint, control action d. is taken to return the process variable to setpoint is of this type: systems 10. When comparing feedforward and feedback control systems, a mathematical understanding (model) for the effect of disturbance on process variable is necessary in those systems Open loop control system Closed loop control system Feed forward control system C. None of the above d. Feedforward control systems This is a closed loop control system 5 b. Feedback control systems Temperature controlled toaster Both feedforward and feedback systems a c. d Neither feedforward nor feedback systems Cruise control Elevator C 11. Ratio control is a special kind of those control All of the above d systems Feedforward control systems have this 6 Feedforward control systems Feedback control systems limitation: b. a. Effect of disturbance must be predicted b. May not generalize to other conditions Will not be accurate if the system changes d Open loop control systems d Digital control systems c. All of the above

Answer 1

1. d

2. d

3. c

4. b

5. d

6. d

Based on a given mathematical model, effect of disturbance must be predicted. Also it cannot be generalized as each system needs a specific mathematical model. Mathematical model defined for system may not perform well if the system changes

7. c

8. a

Process variables such as pressure, level, flow, temperature are interrelated and so one variable may affect another as a disturbance in the process. Feedforward system measure important disturbance variables and take corrective action before they upset the process.

9. a

Feedforward system measure important disturbance variables and take corrective action before they upset the process whereas in feedback system corrective action is taken after the disturbance causes a change in the system (hence not measured)

10. a

Unlike feedback control systems where the disturbance causes a change in the system so as to reach the setpoint, in feedforward the setpoint in the system is set by setting up a suitable mathematical model assuming that a given disturbance will cause an expected change in the system by considering the mathematical model.

11. a

In ratio control of feed forward control, disturbances are measured and their ratio is held at a desired set point by controlling one of the streams