How should we choose sensors
Modern sensors vary widely in principle and structure. How to properly select sensors based on the specific measurement purpose, measurement object, and measurement environment is the first problem to be solved when measuring a certain quantity. After the sensor is determined, the measurement method and measurement equipment to be matched with it can be determined. The success of the measurement results depends to a large extent on the selection of the sensor.
1.Determine the type of sensor according to the measurement object and the measurement environment
To carry out a specific measurement work, we must first consider what kind of sensor to use. This needs to be determined after analyzing various factors. Because, even if measuring the same physical quantity, there are multiple principles of sensors to choose from, which one is more suitable, you need to consider the following specific issues according to the characteristics of the measurement and the conditions of use of the sensor: the size of the range; Requirement of the measured position on the volume of the sensor; the measurement method is contact or non-contact; the method of signal extraction, wired or non-contact measurement; the source of the sensor, domestic or imported, whether the price can be afforded, or developed by ourselves After considering the above issues, we can determine what type of sensor to choose, and then consider the specific performance indicators of the sensor.
2.Selection of sensitivity
Generally, within the linear range of the sensor, it is desirable that 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 sensitivity of the sensor is high, and external noise that is not related to the measurement is also easily mixed in, and it is also amplified by the amplification system, which affects the measurement accuracy. Therefore, the sensor itself is required to have a high signal-to-noise ratio, and every effort is made to reduce plant disturbance signals introduced from the outside.
The sensitivity of the sensor is directional. When the measured is a single vector, and its directivity requirements are high, you should choose a sensor with low sensitivity in other directions; if the measured is a multi-dimensional vector, the smaller the cross-sensitivity of the sensor, the better.
3.Frequency response characteristics
The frequency response characteristic of the sensor determines the frequency range to be measured. It must maintain undistorted measurement conditions within the allowable frequency range. In fact, the response of the sensor always has a fixed delay. It is hoped that the shorter the delay time, the better.
The frequency response of the sensor is high, and the measurable signal frequency range is wide. Due to the influence of structural characteristics, the inertia of the mechanical system is large, and the frequency of the measurable signal of the sensor with a low frequency is low.
In the dynamic measurement, the response characteristics of the signal (steady state, transient, random, etc.) should be used to avoid overheating errors.
The linear range of the sensor is the range where the output is proportional to the input. In theory, 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, when the type of sensor is determined, first of all, it depends on whether its range meets the requirements.
But in fact, no sensor can guarantee absolute linearity, and its linearity is relative. When the required measurement accuracy is relatively low, within a certain range, a sensor with a small non-linear error can be regarded as approximately linear, which will bring great convenience to the measurement. 5.Stability
The ability of a sensor to remain unchanged after a period of use is called stability. In addition to the structure of the sensor itself, the factors affecting the long-term stability of the sensor are mainly the environment in which the sensor is used. Therefore, to make the sensor have good stability, the sensor must have strong environmental adaptability.
Before selecting a sensor, it should investigate its use environment, and choose the appropriate sensor according to the specific use environment, or take appropriate measures to reduce the environmental impact.
There is a quantitative indicator for the stability of the sensor. After the period of use, the calibration should be performed before use to determine whether the performance of the sensor has changed.
In some cases where the sensor can be used for a long time, but cannot be easily replaced or calibrated, the stability of the selected sensor is more stringent, and it must be able to withstand the test of a long time.
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. As long as the accuracy of the sensor meets the accuracy requirements of the entire measurement system, it does not have to be selected too high. In this way, you can choose a cheaper and simpler sensor among many sensors that meet the same measurement purpose.
If the measurement purpose is qualitative analysis, a sensor with high repeat accuracy can be used, and it is not appropriate to use a sensor with high absolute accuracy. If it is for quantitative analysis, accurate measurement values must be obtained, and a sensor with an accuracy level that meets the requirements must be selected. For some special applications, it is impossible to select a suitable sensor, so you need to design and manufacture the sensor yourself. The performance of the homemade sensor should meet the requirements for use.