Questions: Sensors and Feedback in Engineering Systems

Question 1

A robot arm uses a position sensor to verify it reached the correct location after each move. What type of system is this?

• A. Open-loop system
• B. Closed-loop (feedback) system
• C. Analog system
• D. Binary system

Answer: (B)

The system measures its actual output (arm position) and compares it to the desired output (target position). If there is a difference, the controller adjusts. This measure-compare-adjust cycle is the definition of a closed-loop feedback system.

Question 2

An open-loop system (no feedback) typically performs worse than a closed-loop system.

• T. True
• F. False

Answer: False

Open-loop systems can be adequate when the process is highly predictable and disturbances are minimal. A toaster uses an open-loop timer -- it heats for a set duration regardless of the toast's actual color. For simple, predictable tasks, open-loop is cheaper and simpler. Feedback adds value when conditions vary or precision is critical.

Question 3

A greenhouse heating system uses a temperature sensor but the heater runs at full power whenever the temperature is below the set point. What problem might this cause?

Model answer: The system will overshoot the target temperature because the heater does not reduce its output as the temperature approaches the set point. The temperature will rise past the target, then the heater turns off, the temperature drops below the target, the heater turns on again, and the cycle repeats. This oscillation (called 'bang-bang' or on-off control) wastes energy and never achieves a stable temperature.

On-off control is the simplest form of feedback but causes cycling around the set point. More sophisticated control (like proportional control, which reduces heater power as the temperature approaches the target) can achieve smoother, more stable temperature regulation.