Explain the concept of hysteresis in sensors and give an example scenario where it degrades measurement.

• A. Hysteresis is dependency of output on the previous input path; e.g., a temperature sensor shows different readings when heating vs cooling due to material lag.
• B. Hysteresis is when input increases and output lags by a fixed amount.
• C. Hysteresis is a measure of accuracy only.
• D. Hysteresis is noise in signal.

Answer: (A)

Hysteresis in sensors is the idea that the output depends on the history of the input, not just the current input value. The system stores energy or experiences lag so the path taken to reach a given input matters. As a result, the response when the input is increasing can follow a different route than when the input is decreasing, forming a loop in the output versus input.

A typical scenario is a temperature sensor with finite thermal mass. When you raise the environment temperature, the sensor reads gradually as heat diffuses into it. If you then cool the environment, the sensor’s reading at the same ambient temperature can differ from what you saw during heating because the sensor and its surroundings take time to respond, and the path (heating versus cooling) changes the output.

This path-dependent behavior degrades measurement by introducing bias and lag. It harms accuracy and repeatability, makes the transfer relationship nonlinear, and can destabilize control systems that expect a single-valued response. To reduce hysteresis, engineers choose materials with low hysteresis, improve thermal design to lessen lag, or calibrate and design control strategies that account for the direction-dependent response.