Understanding Hysteresis in Sensors

In sensor engineering, hysteresis means that the sensor gives different outputs for the same input value depending on whether the input is being increased or decreased.3 Therefore, among the options given, the correct answer is (ii) Difference in output when input increases vs. decreases.2

This behavior occurs because many sensing systems have a form of memory effect caused by material elasticity, internal friction, magnetic effects, mechanical backlash, or structural relaxation.2 As a result, the sensor’s output is not determined only by the present input; it also depends on the path by which that input was reached.2

A simple example is a pressure sensor measured at 50 kPa. On the way up, it may read 49.95 kPa; on the way down, at the same true pressure, it may read 50.05 kPa. The difference between those two readings is hysteresis.2

Footnotes

1. Hysteresis in pressure calibration: What you need to know - Explains hysteresis in pressure instruments and gives an ascending-versus-descending reading example. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

2. Hysteresis 101 - Interface - Defines hysteresis as the algebraic difference in sensor output at the same load for increasing versus decreasing direction. ↩ ↩² ↩³

3. Calibration Error Hysteresis Non-linearity Saturation Dead Band - Lecture material distinguishing hysteresis from dead band and dynamic response characteristics. ↩ ↩²

4. Hysteresis - Wikipedia - Describes hysteresis as dependence of system behavior on input history and discusses rate-dependent versus rate-independent forms. ↩

Why option (ii) is correct

The defining signature of hysteresis is a direction-dependent output.2 In calibration and instrumentation, this is often evaluated by moving the input upward through a range and then downward through the same range, recording the sensor reading at identical input points.2 If the readings differ, the sensor exhibits hysteresis.2

This is different from purely dynamic delay. A sensor can have hysteresis even under slow, quasi-static testing, because the issue is not only speed of response but path dependence.2 In practical specifications, hysteresis is often reported as a percentage of full scale or as the maximum difference between ascending and descending readings at the same input.2

A useful conceptual model is a hysteresis loop: the upward and downward calibration paths do not coincide.2

Footnotes

1. Hysteresis 101 - Interface - Defines hysteresis as the algebraic difference in sensor output at the same load for increasing versus decreasing direction. ↩ ↩² ↩³ ↩⁴ ↩⁵

2. Calibration Error Hysteresis Non-linearity Saturation Dead Band - Lecture material distinguishing hysteresis from dead band and dynamic response characteristics. ↩ ↩² ↩³ ↩⁴ ↩⁵

3. Hysteresis in pressure calibration: What you need to know - Explains hysteresis in pressure instruments and gives an ascending-versus-descending reading example. ↩ ↩² ↩³ ↩⁴

4. Hysteresis - Wikipedia - Describes hysteresis as dependence of system behavior on input history and discusses rate-dependent versus rate-independent forms. ↩

5. Sensor Resolution vs Accuracy vs Repeatability - Clarifies repeatability and shows hysteresis as a distinct contributor to sensor accuracy. ↩ ↩²

Distinguishing hysteresis from similar sensor behaviors

Several sensor concepts are often confused:

• dead time is a temporal delay between input change and observable output response.
• dead band is an insensitive range where output does not change despite changing input.
• repeatability concerns consistency under repeated identical tests, not necessarily opposite-direction tests.
• noise refers to irregular random fluctuations.

These distinctions matter because each error type has different causes and mitigation strategies.3

Footnotes

1. Calibration Error Hysteresis Non-linearity Saturation Dead Band - Lecture material distinguishing hysteresis from dead band and dynamic response characteristics. ↩ ↩² ↩³

2. Sensor Resolution vs Accuracy vs Repeatability - Clarifies repeatability and shows hysteresis as a distinct contributor to sensor accuracy. ↩ ↩² ↩³

3. Hysteresis in pressure calibration: What you need to know - Explains hysteresis in pressure instruments and gives an ascending-versus-descending reading example. ↩

Practical interpretation for the multiple-choice question

If a sensor shows one reading while the measured quantity is increasing and a different reading at the same actual value while the quantity is decreasing, that is the classic definition of hysteresis.2 Therefore:

$$\text{Correct answer} = \text{(ii)}$$

This can be expressed conceptually as:

$$H = y_{\uparrow}(x) - y_{\downarrow}(x)$$

where $y_{\uparrow}(x)$ is the output at input $x$ during increasing input, and $y_{\downarrow}(x)$ is the output at the same input during decreasing input.2 If $H \neq 0$, hysteresis is present.

In contrast:

• option (i) describes dynamic response behavior,
• option (iii) describes an insensitivity or saturation-type condition,
• option (iv) describes noise or instability.

Footnotes

1. Hysteresis in pressure calibration: What you need to know - Explains hysteresis in pressure instruments and gives an ascending-versus-descending reading example. ↩

2. Hysteresis 101 - Interface - Defines hysteresis as the algebraic difference in sensor output at the same load for increasing versus decreasing direction. ↩ ↩² ↩³

3. Calibration Error Hysteresis Non-linearity Saturation Dead Band - Lecture material distinguishing hysteresis from dead band and dynamic response characteristics. ↩ ↩² ↩³

4. Sensor Resolution vs Accuracy vs Repeatability - Clarifies repeatability and shows hysteresis as a distinct contributor to sensor accuracy. ↩