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How to choose the sensor, what is the structure of the sensor?
One, selection of sensitivity
1, usually, in the linear range of the sensors to the sensitivity of the sensor is good, because only the high sensitivity, and the output signal of the measured changes corresponding to the value is relatively large, is conducive to signal processing, but it is important to note that the sensor has high sensitivity, and is independent of external noise measurement can easily mix that will be also amplified by the system, affect the measurement accuracy, therefore, requires the sensor itself should have high SNR, minimize the interference signal from the outside into the;
2, the sensitivity of the sensor is directional. When the measurement is a one-way quantity and has a high requirement for its directivity, we should choose other direction sensitive sensors. If the measurement is multi-dimensional vector, then the smaller the cross sensitivity of the sensor is, the better.
Two, frequency response characteristics
1, the frequency response characteristic of the sensor determines the frequency range to be measured. It must remain undistorted in the allowable frequency range. In fact, there is always a definite delay in the response of sensors, and the shorter the delay is, the better.
2, the higher the frequency response of the sensor, the wider the frequency range of the measurable signal.
3. In dynamic measurement, the response characteristics of the signal should be based on the characteristics of the signal (steady, transient, random, etc.) so as to avoid excessive error.
Three. Linear range
1, linear range sensor refers to the range of the output is proportional to the input, in theory, in this range, the sensitivity is kept constant, the linear range of the sensor is wide, its range is larger, and can guarantee a certain accuracy, in the selection of the sensor, when the determination of types of sensor first look at the range meets the requirements;
2, in fact, any sensor can guarantee absolute linear, its linearity is relative, when the required measurement accuracy is relatively low, in a certain range, the sensors can be considered linear nonlinear error is smaller, it will bring great convenience to measurement.
Four, stability
1, the sensor used for a period of time, its performance remains unchanged is called stability, factors affecting the long-term stability of the sensor in the sensor itself is the main sensor structure, the use of the environment, therefore, the sensor has good stability, the sensor must be a strong ability to adapt to the environment;
2, before choosing the sensor, we should investigate the environment and choose suitable sensors according to the specific environment, or take appropriate measures to reduce the environmental impact.
3, the stability of sensors has quantitative indicators. After exceeding the service life, the calibration of sensors should be done again to determine whether the performance of sensors is changing.
4, in some occasions that require sensors to be used for a long time, and can not be easily replaced or calibrated, the stability of the selected sensors is more stringent, and it is able to stand the test for a long time.
Five. Precision
1, the accuracy is an important performance index of the sensor, it is very important to take a measurement accuracy of the measurement system, the precision of the sensor is high, its price is more expensive, therefore, the precision of the sensor as long as meet the measurement accuracy requirements can be, does not need to be so high, so that it can be in to meet the many sensor with one measurement in sensor selection Atlas air compressor accessories is relatively cheap and simple;
2, if the purpose of the measurement is qualitative analysis, the sensor with high repeatability and accuracy can not be selected, and the absolute value is high. If we want to get the accurate measurement value for quantitative analysis, we need to select the sensor with accuracy level to meet the requirement.
3. For some special occasions, it is impossible to choose the appropriate sensor, and the sensor is designed by itself. The performance of the self-made sensor should meet the requirements of use.
The composition of the sensor
The sensor is usually composed of three parts, the sensitive element, the sensing element and the conversion circuit.
1, sensitive element
It is a pre transformation device that can be converted into physical quantities that can be easily measured, and there is a definite mathematical relationship between input and output (preferably linear), for example, an elastic sensing element converts force into displacement or strain output.
2, sensing element
It is to transform the non electrical physical output of sensitive components into electrical signals, such as resistors, inductors, capacitors, etc., such as converting temperature into resistance change and converting displacement into inductor or capacitor.
3, the basic conversion circuit
The electrical signal conversion to measure power, such as voltage, current, frequency, some sensors (such as thermocouple) only sensitive components, feelings are measured when the direct output electromotive force, some sensors composed of sensitive components and conversion components, without basic circuit, such as piezoelectric acceleration sensor, some sensors composed of sensitive components and basic circuit, such as capacitive displacement sensor, some sensors, not only to a conversion element, after several times of conversion to the output power, most of the sensor is an open loop system, but also individual is a closed-loop system with feedback.