Which control strategy switches the control signal abruptly between two distinct limits and uses hysteresis to avoid chattering?

• A. Proportional Controller
• B. Derivative Controller
• C. On-Off Controller
• D. Integral Controller

Answer: (C)

The main idea is a bang-bang control with a deadband. An On-Off controller drives the actuator to one of two extreme states, not a varying output. To prevent rapid flipping, it uses hysteresis: you switch on when the process variable crosses a lower threshold and switch off only after it crosses an upper threshold (or the reverse). This creates a clear gap between the two switching points, so small fluctuations around the switch point won’t cause chattering. A familiar example is a thermostat that turns a heater on at a low temperature and off at a higher temperature, keeping the room within a comfortable range without continuous on/off cycling. Proportional, derivative, and integral controllers adjust outputs continuously based on error, rate of change, or accumulated error, rather than jumping between two fixed limits with a deadband.