What are the characteristics of physical sensors?

1. Static characteristics of sensors

The static characteristics of sensors refer to the relationship between the output and input of sensors for static input signals. Because both the input and output are independent of time, the relationship between them, i.e., the static characteristics of sensors, can be described by an algebraic equation without time variables, or by a characteristic curve drawn with the input as the horizontal coordinate and the corresponding output as the vertical coordinate. The main parameters that characterize the static characteristics of sensors are: linearity, sensitivity, hysteresis, repeatability, drift, etc.

(1) Linearity: refers to the degree to which the actual relationship curve between the output and input of the sensor 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 within the full range to the full-scale output value.

(2) Sensitivity: Sensitivity is an important indicator of the static characteristics of sensors. It is defined as the ratio of the increment of the output to the corresponding increment of the input that causes the increment. S represents sensitivity.

(3) Hysteresis: The phenomenon that the input-output characteristic curve of the sensor does not overlap when the input changes from small to large (positive stroke) and from large to small (reverse stroke) is called hysteresis. For the same input signal, the output signal of the sensor in the positive and reverse strokes is not equal. This difference is called the hysteresis difference.

(4) Repeatability: Repeatability refers to the degree of inconsistency of the characteristic curve obtained when the input of the sensor changes continuously in the same direction over the full range.

(5) Drift: The drift of the sensor refers to the change of the sensor output over time when the input remains unchanged. This phenomenon is called drift. There are two reasons for drift: one is the structural parameters of the sensor itself; the other is the surrounding environment (such as temperature, humidity, etc.).

2. Dynamic characteristics of sensors

The so-called dynamic characteristics refer to the characteristics of the output of the sensor when the input changes. In actual work, the dynamic characteristics of the sensor are often expressed by its response to certain standard input signals. This is because the sensor's response to the standard input signal is easy to obtain experimentally, and there is a certain relationship between its response to the standard input signal and its response to any input signal. Often, knowing the former can infer the latter. The most commonly used standard input signals are step signals and sinusoidal signals, so the dynamic characteristics of the sensor are often represented by step response and frequency response.

3. Linearity of the sensor

Under normal circumstances, the actual static characteristic output of the sensor is a curve rather than a straight line. In actual work, in order to make the instrument have a uniform scale reading, a fitting straight line is often used to approximate the actual characteristic curve, and linearity (nonlinear error) is a performance indicator of this approximation. There are many ways to select a fitting straight line. For example, the theoretical straight line connecting the zero input and full-scale output points is used as a fitting straight line; or the theoretical straight line with the smallest sum of squares of deviations from each point on the characteristic curve is used as a fitting straight line. This fitting straight line is called the least squares fitting straight line.