The static characteristics of a sensor refer to the relationship between the sensor's output and input signals when the input signal is static. Since both the input and output are independent of time, their relationship—the sensor's static characteristics—can be described by an algebraic equation without a time variable, or by a characteristic curve plotted with the input signal on the x-axis and the corresponding output signal on the y-axis.
The main parameters characterizing the static properties of a sensor include linearity, sensitivity, hysteresis, repeatability, and drift.
1. Linearity: refers to the degree to which the actual relationship curve between the sensor's output and input deviates from the fitted straight line. It is defined as the ratio of the maximum deviation between the actual characteristic curve and the fitted straight line over the entire range to the full-scale output value.
2. Sensitivity: Sensitivity is an important indicator of a sensor's static characteristics. It is defined as the ratio of the increment in the output quantity to the corresponding increment in the input quantity that caused that increment. Sensitivity is denoted by S.
3. Hysteresis: Hysteresis is the phenomenon that the input-output characteristic curves of a sensor do not coincide during the changes in input quantity from small to large (forward stroke) and from large to small (reverse stroke). For the same input signal, the output signal magnitudes of the sensor are not equal during the forward and reverse strokes; this difference is called the hysteresis difference.
4. Repeatability: Repeatability refers to the degree of inconsistency in the characteristic curves obtained when the input quantity of a sensor changes continuously multiple times in the same direction across its full range.
5. Drift: Sensor drift refers to the change in sensor output over time when the input remains constant. There are two main causes of drift: one is the sensor's own structural parameters; the other is the surrounding environment (such as temperature and humidity).
6. Resolution: When the input of a sensor slowly increases from a non-zero value, the output changes observably after exceeding a certain increment. This input increment is called the resolution of the sensor, or the minimum input increment.
7. Threshold: When the input of a sensor slowly increases from zero, the output changes observably after reaching a certain value. This input value is called the threshold voltage of the sensor.
