1. Linearity: The degree to which the actual relationship between sensor output and input deviates from the fitted straight line. Defined as the ratio of the maximum deviation from the full-scale output value between the actual characteristic curve and the fitted line over the full scale range.
2. Sensitivity: Sensitivity is an important indicator of the static characteristics of the sensor. It is defined as the ratio of the increment of the output to the corresponding increment of the input that caused the increment. Use S for sensitivity.
3. Hysteresis: The phenomenon that the input/output characteristic curve of the sensor does not coincide during the change of the input amount from small to large (positive stroke) and input amount changes from large to small (anti-stroke) becomes hysteresis. For the same size input signal, the sensor's positive and negative stroke output signal size is not equal, this difference is called hysteresis difference.
4. Repeatability: Repeatability refers to the degree of inconsistency in the resulting characteristic curve when the sensor continuously changes the full range of the input in the same direction.
5. Drift: The drift of the sensor means that the output of the sensor changes with time when the input volume is unchanged. This phenomenon is called drift. There are two reasons for the drift: one is the sensor's own structural parameters; the other is the surrounding environment (such as temperature, humidity, etc.).
6. Resolution: When the input of the sensor slowly increases from a non-zero value, the output changes observable beyond a certain increment. This input increment is called the resolution of the sensor, ie, the minimum input increment.
7. Threshold: When the input of the sensor slowly increases from the zero value, the output will have an observable change after reaching a certain value. This input value is called the sensor's threshold voltage.
Sensor dynamic characteristics
The so-called dynamic characteristic refers to the characteristic of the output of the sensor when the input changes. In practice, the dynamic characteristics of a sensor are often expressed in terms of its response to certain standard input signals. This is because the response of the sensor to the standard input signal is easily found experimentally, and there is a certain relationship between its response to the standard input signal and its response to any input signal, and the former is often known to be able to estimate the latter. The most common standard input signals are step signals and sinusoidal signals, so the dynamic characteristics of the sensor are often expressed by step response and frequency response.
The linearity of the sensor
In general, the actual static characteristic output of the sensor is a curve rather than a straight line. In actual work, in order to make the meter have a uniform scale reading, a commonly used straight line approximates the actual characteristic curve, linearity (non-linearity error) is a performance index of this approximate degree.
There are several ways to select a straight line. For example, the theoretical straight line connecting the zero input and the full-scale output point is used as a fitting straight line; or the theoretical straight line whose sum of squared deviations from each point on the characteristic curve is the minimum is used as a fitting straight line. This fitting straight line is called a least-squares method. Straight line
It is like ordinary diodes, the reverse current is very small (<μA), called the dark current of the photodiode; when there is light, the carriers are excited to generate electron-holes, called photoelectric photoelectric sensor carriers. Under the action of an external electric field, the photo-carriers participate in conduction, forming a much larger reverse current than the dark current, which is called photocurrent. The size of the photocurrent is proportional to the light intensity, so that an electrical signal that changes with the light intensity can be obtained on the load resistance. In addition to photodiodes that have the ability to convert optical signals into electrical signals, phototransistors also have the ability to amplify electrical signals. The appearance of the phototransistor is almost the same as that of a normal triode. In general, the phototransistor only leads to two poles—the emitter and the collector, the base is not led out, and the shell also opens the window so that the light can enter. In order to increase the illumination, the base area is made large, the emission area is small, and the incident light is mainly absorbed by the base area. During operation, the collector junction is reversed and the emitter junction is positive. In the absence of light, the current flowing through the tube is the dark current Iceo=(1+β)Icbo (small), which is less than the penetration current of a normal triode; when there is light, a large number of electron-hole pairs are excited, making The current Ib generated by the base increases, the current flowing through the tube at the moment is called photocurrent, and the collector current Ic=(1+β)Ib. It can be seen that the phototransistor has higher sensitivity than the photodiode.
The static characteristics of the sensor refer to the static input signal to the sensor (Figure 4)
There is a correlation between the output and the input of the sensor. Since both input and output are independent of time, the relationship between them, ie, the static nature of the sensor, can be used as an algebraic equation without a time variable, or as an abscissa with the input, and the corresponding output is used as The ordinate shows the characteristic curve. The main parameters that characterize the static characteristics of the sensor are: linearity, sensitivity, hysteresis, repeatability, drift, etc.
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