Modern sensors vary 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. After the sensor is determined, the corresponding measurement method and equipment can be determined. The success or failure of the measurement results, to a large extent, depends on whether the sensing is reasonable.
1. Determine the type of sensor according to the measurement object and measurement environment
To carry out a specific measurement, it is necessary to first consider which principle of sensor to use, which needs to be determined after analyzing various factors. Because, even if the same physical quantity is measured, there are many kinds of sensors for selection. Which one is more suitable, you need to consider the following specific issues according to the characteristics of the measurement and the use conditions of the sensor: the size of the range; Requirements of the measured position on the sensor volume; Whether the measurement mode 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 is affordable, or self-developed.
After considering the above problems, you can determine which type of sensor to choose, and then consider the specific performance indicators of the sensor.
2. Selection of sensitivity
Generally, in 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 sensitivity of the sensor is high, and the external noise irrelevant to the measurement is easy to mix in, which will also be amplified by the amplification system, affecting the measurement accuracy. Therefore, it is required that the sensor itself should have a high signal-to-noise ratio to minimize the interference signals introduced from the outside.
The sensitivity of the sensor is directional. When the measured quantity is unidirectional and requires high directivity, other sensors with low sensitivity in direction shall be selected; If the measured vector is multidimensional, the smaller the cross sensitivity of the sensor is, the better.
3. Frequency response characteristics
The frequency response characteristic of the sensor determines the frequency range to be measured, which 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 higher the frequency response of the sensor, the wider the measurable signal frequency range.
In the dynamic measurement, the response characteristics (steady state, transient, random, etc.) of the signal shall be considered to avoid excessive error.
4. Linear range
The linear range of the sensor refers to the range where the output is proportional to the input. Theoretically, the sensitivity remains constant within this range. The wider the linear range of the sensor is, the larger its range is, and certain measurement accuracy can be guaranteed. When selecting the sensor, after the type of sensor is determined, first check 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, the sensor with small nonlinear error can be approximately regarded as linear, which will bring great convenience to the measurement.
5. Stability
The ability of a sensor to maintain its performance after a period of use is called stability. In addition to the structure of the sensor itself, the main factor affecting the long-term stability of the sensor is 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 sensors, the use environment shall be investigated, and appropriate sensors shall be selected according to the specific use environment, or appropriate measures shall be taken to reduce the environmental impact.
The stability of the sensor has quantitative indicators. After the service life 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 but cannot be easily replaced or calibrated, the stability of the selected sensor is more strict and should be able to withstand the test for a long time.
6. Precision
The accuracy is an important performance index of the sensor, which 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, as long as the accuracy of the sensor meets the accuracy requirements of the entire measurement system, it is not necessary to choose too high. In this way, cheap and simple Atlas air compressor accessories can be selected among many sensors that meet the same measurement purpose.
If the measurement purpose is qualitative analysis, the sensor with high repeatability accuracy can be selected, and the sensor with high absolute value accuracy should not be selected; If it is necessary to obtain accurate measurement value for quantitative analysis, it is necessary to select sensors with accuracy grade meeting the requirements.
For some special use occasions, if it is impossible to select a suitable sensor, you need to design and manufacture the sensor by yourself. The performance of self-made sensor shall meet the operating requirements.