What is hysteresis in thermostat control?

• A. Hysteresis refers to data logging intervals.
• B. Hysteresis is when thermostat always switches to opposite state instantly.
• C. A zone maintains the current state until the measured value passes the opposite threshold, preventing rapid cycling.
• D. Hysteresis is a time delay in sensor reading.

Answer: (C)

Hysteresis in thermostat control is the use of two different temperature thresholds to switch heating or cooling on and off, creating a deadband. The system stays in its current state until the measured temperature crosses the opposite threshold, which prevents rapid cycling. For example, when heating is active, it stays on until the temperature reaches an upper threshold and then turns off; when cooling is active, it stays off until the temperature drops to a lower threshold and then turns on. This approach reduces wear on equipment, saves energy, and avoids jittery on/off behavior around the setpoint. The other ideas don’t capture this two-threshold switching rule: data logging intervals don’t define hysteresis, instantaneous switching isn’t how hysteresis works, and a simple sensor-reading delay describes lag rather than the purposeful two-threshold control.