How is hysteresis defined in the context of control systems?

Hysteresis in the context of control systems refers to the phenomenon where the output response of the system differs based on the direction of the input change. This means that when you apply an increasing input, the system may behave differently compared to when you apply a decreasing input. This characteristic is essential in various applications, such as in thermostats, where the temperature needs to change significantly to switch the heating or cooling systems on or off, preventing rapid cycling that can lead to wear and tear.

In this scenario, the definition captures how hysteresis manifests as a gap between the outputs for rising and falling inputs, resulting in a non-linear relationship. It highlights the inherent lag or delay in the system's response due to external factors such as friction, mechanical play, or the time it takes for a system to stabilize after a change.

The other choices describe different concepts. The instantaneous response relates to immediate system behavior without accounting for this differential lag. Measurement of data fluctuations describes noise or variability in the data rather than the intentional behavior seen in hysteresis. The ability to ignore minor input variations is more related to filtering or deadband behavior in control systems, which is separate from the hysteresis effect.