Sensor model selection

Modern sensors vary greatly in principle and structure. How to reasonably select sensors according to the specific measurement purpose, measurement object and measurement environment is the first problem to be solved when measuring a certain quantity. Once the sensor is determined, the corresponding measurement method and measurement equipment can also be determined. The success or failure of the measurement result depends largely on whether the sensor is selected reasonably. 1) Determine the type of sensor according to the measurement object and measurement environment To carry out a specific measurement, we must first consider what principle the sensor is to be used, which requires analysis of many factors before it can be determined. Because even if the same physical quantity is measured, there are sensors of various principles available for selection. Which principle of sensor is more suitable requires consideration of the following specific issues based on the characteristics of the measured quantity and the use conditions of the sensor: the size of the range; the requirements of the measured position for the volume of the sensor; whether the measurement method is contact or non-contact; the signal extraction method, wired or non-contact measurement; the source of the sensor, domestic or imported, whether the price is affordable, or self-developed. After considering the above issues, we can determine what type of sensor to use, and then consider the specific performance indicators of the sensor 2) Selection of sensitivity Usually, within the linear range of the sensor, the higher the sensitivity of the sensor, the better. Because only when the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is conducive to signal processing. However, it should be noted that the high sensitivity of the sensor makes it easy for external noise unrelated to the measured value to be mixed in, and it will also be amplified by the amplification system, affecting the measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio to minimize the interference signal introduced from the outside world. The sensitivity of the sensor is directional. When the measured value is a single vector and its directionality is required to be high, a sensor with low sensitivity in other directions should be selected; if the measured value is a multi-dimensional vector, the cross sensitivity of the sensor is required to be as small as possible. 3) Frequency response characteristics The frequency response characteristics of the sensor determine the frequency range of the measured value, and the measurement condition must be maintained without distortion within the allowable frequency range. In fact, the response of the sensor always has a certain delay, and it is hoped that the delay time is as short as possible. The higher the frequency response of the sensor, the wider the frequency range of the measurable signal. However, due to the influence of the structural characteristics, the inertia of the mechanical system is large, and the frequency of the measurable signal of the low-frequency sensor is low. In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.) to avoid excessive errors. 4) Linear range The linear range of the sensor refers to the range in which the output is proportional to the input. Theoretically, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger its range, and it can guarantee a certain measurement accuracy. When selecting a sensor, after the type of sensor is determined, the first thing to look at is whether its range meets the requirements. But in fact, no sensor can guarantee absolute linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with a smaller nonlinear error can be approximated as linear, which will bring great convenience to the measurement. 5) Stability The ability of the sensor to maintain its performance unchanged after a period of use is called stability. In addition to the structure of the sensor itself, the factors that affect the long-term stability of the sensor are mainly the use environment of the sensor. Therefore, in order to make the sensor have good stability, the sensor must have a strong ability to adapt to the environment. ? Before selecting a sensor, its use environment should be investigated, and appropriate sensors should be selected according to the specific use environment, or appropriate measures should be taken to reduce the impact of the environment The stability of the sensor has quantitative indicators. After the use period is exceeded, it should be recalibrated before use to determine whether the performance of the sensor has changed. In some occasions where the sensor is required to be used for a long time and cannot be easily replaced or calibrated, the stability requirements of the selected sensor are more stringent and must be able to withstand the test of a long time. 6) Accuracy Accuracy is an important performance indicator of the sensor, and it is an important link related to the measurement accuracy of the entire measurement system. The higher the accuracy of the sensor, the more expensive it is. Therefore, the accuracy of the sensor only needs to meet the accuracy requirements of the entire measurement system, and it does not need to be selected too high. In this way, a relatively cheap and simple sensor can be selected from many sensors that meet the same measurement purpose. If the measurement purpose is qualitative analysis, a sensor with high repeatability accuracy can be selected, and it is not advisable to select a sensor with high absolute value accuracy; if it is for quantitative analysis and accurate measurement values ​​must be obtained, a sensor with an accuracy level that meets the requirements must be selected For some special use occasions, it is impossible to select a suitable sensor, so it is necessary to design and manufacture the sensor by yourself. The performance of the homemade sensor should meet the use requirements.