Questions: Introduction to Control Systems

Question 1

A cruise control system in a car maintains speed by adjusting the throttle. What are the four elements of this control system?

• A. Engine, wheels, road, driver
• B. Set point (desired speed), sensor (speedometer), controller (cruise control computer), actuator (throttle)
• C. Gas pedal, brake pedal, steering wheel, speedometer
• D. Battery, alternator, fuel pump, transmission

Answer: (B)

The driver sets the desired speed (set point). The speedometer measures actual speed (sensor). The cruise control computer calculates the needed throttle adjustment (controller). The throttle mechanism adjusts fuel delivery to the engine (actuator). The loop runs continuously: measure speed, compare to set point, adjust throttle.

Question 2

On-off control produces the same result as proportional control -- it just uses simpler hardware.

• T. True
• F. False

Answer: False

On-off control produces oscillation around the set point because the actuator is always at maximum or zero. Proportional control produces a smoother response by adjusting the actuator output proportionally to the error. The control quality is fundamentally different, not just the hardware.

Question 3

What would happen to a room temperature control system if the temperature sensor broke and always reported 18°C regardless of actual temperature?

Model answer: If the set point is above 18°C, the controller would think the room is always too cold and run the heater continuously, overheating the room dangerously. If the set point is below 18°C, the heater would never turn on and the room would get cold. The system has lost its feedback connection to reality and can no longer regulate properly.

This illustrates why sensor reliability is critical in control systems. A faulty sensor breaks the feedback loop -- the system no longer knows its actual state and makes corrections based on false information. Safety systems often include redundant sensors or plausibility checks to detect sensor failures.