Modern sensors vary widely in principle and structure. How to select sensors reasonably according to specific measurement purposes, measurement objects and measurement environment is the first problem to be solved when measuring a certain quantity. When the sensor is determined, the matching measurement method and measuring device can be determined. The success or failure of the measurement results largely depends on whether the sensor's selection is reasonable.
1. Determine the type of sensor according to the measured object and measurement environment
To carry out a specific measurement work, we must first consider the principle of the sensor,which needs to be determined after analyzing various factors.Because, even if measuring the same physical quantity, there are also many kinds of sensors to choose, which principle of sensor is more suitable, then we need to consider the following specific problems according to the characteristics of the measured quantity and the use conditions of the sensor: the size of the measurement range; the requirements of the measured position on the volume of the sensor; the measurement method is Contact or non-contact; signal extraction method, wired or non-contact measurement; the source of the sensor, domestic or imported, the price can withstand or not,or self-developed.
After considering the above issues, you can determine which type of sensor to use and then consider the specific performance of the sensor.
2. Sensitivity selection
Generally, in the linear range of the sensor, the higher the sensitivity of the sensor is, the better. Because only the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is beneficial to signal processing.However, it should be noted that the sensitivity of the sensor is high, and the external noise that is not related to the measurement is easily mixed in, and is amplified by the amplification system, which affects the measurement accuracy. Therefore, the sensor itself should be required to have a high signal-to-noise ratio, and the interference signal introduced from the outside is reduced.
The sensitivity of the sensor is directional. When the measurement is a single vector and its directivity requirements are high, other sensors with small sensitivity should be selected; if the measurement 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 to be measured.The measurement conditions must be kept undistorted within the allowable frequency range. In fact, the response of the sensor always has a certain delay, and the shorter the delay time, the better. The frequency response of the sensor is high, the measurable signal frequency range is wide. Due to the structural characteristics, the inertia of the mechanical system is large, and the frequency of the measurable signal is low because of the sensor with low frequency.
In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.) to avoid excessive error.
4. Linear range
The linear range of the sensor is the range in which 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 the range and the guaranteed measurement accuracy. When selecting a sensor, when the type of sensor is determined, it is first necessary to see if its range meets the requirements. But in reality, any sensor can't guarantee absolute linearity, and its linearity is relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with less nonlinear error can be approximated as linear, which will bring great convenience to the measurement.
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 use environment of the sensor. Therefore, in order to make the sensor have good stability, the sensor must have strong environmental adaptability.
Before selecting a sensor, investigate the environment in which it is used, select the appropriate sensor according to the specific use environment, or take appropriate measures to reduce the environmental impact. The stability of the sensor has a quantitative index, and it should be calibrated again before use to determine whether the performance of the sensor has changed.In some cases where the sensor is required to be used for a long period of time and cannot be easily replaced or calibrated, the selected sensor has stricter stability requirements and can withstand the test for a long time.
Accuracy is an important performance index of sensor, it is an important link related to the measurement accuracy of the whole measurement system.The higher the accuracy of the sensor, the more expensive it is. Therefore, the accuracy of the sensor can be as long as meets the accuracy requirements of the entire measurement system, and it is not necessary to select too high. This makes it possible to select a cheaper and simpler sensor among the many sensors that meet the same measurement purpose.
If the purpose of the measurement is qualitative analysis, with high repetition accuracy can be selected.but the sensor with high absolute value accuracy is not suitable. If it is for quantitative analysis, it is necessary to obtain precise measurement values, it is necessary to select a sensor with an accuracy class that meets the requirements.For some special applications, if you can't choose the right sensor, you need to design and manufacture the sensor yourself.The performance of the home-made sensor should meet the requirements for use.