Modern displacement sensors vary widely in principle and structure. How to select a displacement sensor according to a specific measurement purpose, measurement object, and measurement environment is the first problem to be solved when performing a certain amount of measurement. When the displacement sensor is determined, the matching measuring method and measuring equipment can also be determined. The success or failure of measurement results depends to a large extent on the rationality of the choice of displacement sensor.
1 , determine the type of displacement sensor according to the measurement object and measurement environment
To carry out a specific measurement work, we must first consider the principle of the use of sensors, which need to analyze many factors before you can determine. Because, even if it is to measure the same physical quantity, there are many kinds of principle sensors available for selection. Which kind of principle sensor is more appropriate, then we need to consider the following specific problems based on the characteristics of the measured and the use conditions of the sensor: the size of the range; The measured position of the sensor volume requirements; measurement method is contact or non-contact; signal extraction method, wired or non-contact measurement; sensor source, domestic or imported, the price can withstand, or self-developed.
After considering the above issues, it is possible to determine which type of sensor to use, and then consider the specific performance indicators of the sensor.
2 , the choice of sensitivity
Generally, in the linear range of the sensor, it is desirable that the sensitivity of the sensor be as high as possible. Because only the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is advantageous for 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 easily mixed in, and it is also amplified by the amplification system, which affects the measurement accuracy. Therefore, it is required that the sensor itself should have a high signal-to-noise ratio, and the dedication should reduce the plant disturbance signal introduced from outside.
The sensitivity of the sensor is directional. When it is measured as a single vector and its directionality is higher, sensors with smaller sensitivity in other directions should be selected; if the vector is measured, the cross sensitivity of the sensor is required to be as small as possible.
3 , frequency response characteristics
The frequency response characteristic of the sensor determines the frequency range to be measured. It must maintain the undistorted measurement condition within the allowable frequency range. Actually, the response of the sensor always has a certain delay. 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 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 the dynamic measurement, the characteristics of the signal ( steady-state, transient, random, etc. ) response characteristics should be used to avoid overheating errors.
4 , linear range
The linear range of the sensor refers to the range of the output proportional to the input. In theory, in this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger the range, and can guarantee a certain measurement accuracy. When selecting a sensor, when the type of the sensor is determined, it first depends on whether or not the range satisfies the requirement.
But in fact, any sensor cannot guarantee absolute linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with smaller nonlinear error can be approximated as linear, which will bring great convenience to the measurement.
5 , stability
The ability of the displacement sensor to remain unchanged after a period of use is called stability. The factors affecting the long-term stability of the sensor are not only the structure of the sensor itself, but also the environment in which the sensor is used. Therefore, for the sensor to have good stability, the sensor must have a strong environmental adaptability.
Before selecting the sensor, it is necessary to investigate its use environment, select the appropriate sensor according to the specific use environment, or take appropriate measures to reduce the impact of the environment.
There are quantitative indicators of the stability of the sensor. After the period of use is exceeded, calibration should be performed again before use to determine if the performance of the sensor has changed.
In some applications where the sensor can be used for a long period of time and cannot be easily replaced or calibrated, the selected sensor requires more stringent stability and can withstand long-term tests.
6 , accuracy
Accuracy is an important performance index of the sensor, and it is an important link related to the measurement accuracy of the entire measurement system. The higher the precision of the sensor, the more expensive it is. Therefore, the accuracy of the sensor can be satisfied as long as it satisfies the accuracy requirements of the entire measurement system. It does not have to be selected too high. In this way, a relatively inexpensive and simple displacement sensor can be selected among many sensors that satisfy the same measurement purpose.
If the purpose of the measurement is qualitative analysis, select a sensor with high repeat accuracy, and it is not appropriate to use high absolute value accuracy; if it is for quantitative analysis, accurate measurement must be obtained, and a displacement sensor that meets the required accuracy level must be used. .
For some special occasions, the proper sensor cannot be selected, so the displacement sensor must be designed and manufactured by itself. The performance of self-made sensors should meet the requirements for use.
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