Modern sensors in the principle and structure vary widely, according to the specific measurement purposes, measurement of objects and measurement of the environment to choose a reasonable sensor, is a measure of the amount of the first to solve the problem.
When the sensor is determined, the matching measurement method and measuring equipment can be determined. The success or failure of the measurement results depends to a large extent on whether the selection of the sensor is reasonable.
1. Determine the type of sensor based on the measurement object and the measurement environment
To carry out a specific measurement work, we must first consider the principle of the sensor should be used, which need to analyze a wide range of factors to determine.
Because, even if the measurement of the same physical quantity, there are a variety of principles of the sensor available, which principle of the sensor is more appropriate, you need to be measured according to the characteristics and conditions of use of the sensor to consider the following specific issues:
The size of the range;
② the measured position of the sensor volume requirements;
③ measurement methods for contact or non-contact;
④ signal leads to the method, wired or non-contact measurement;
⑤ the source of the sensor, domestic or imported, the price can afford, but also self-developed. After considering the above problems, you can determine what type of sensor you choose, and then consider the specific performance indicators of the sensor.
2. The choice of sensitivity
Usually, in the linear range of the sensor, it is desirable that the sensitivity of the sensor is as high as possible. Because only the sensitivity is high, and the measured changes in the corresponding output signal value is relatively large, is conducive to signal processing. However, it is important to note that the sensitivity of the sensor is high and the external noise, which is independent of the measurement, is easily mixed and 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, to minimize the interference signal from the outside world.
The sensitivity of the sensor is directional. When the measurement is a single vector, and its direction of the higher requirements, you should choose other sensors with low sensitivity; if the measurement is multidimensional vector, the sensor requires a smaller cross-sensitivity as possible.
3. Frequency response characteristics
The frequency response characteristic of the sensor determines the frequency range to be measured, and must keep the measurement condition without distortion within the allowable frequency range. In fact, the response of the sensor always has the delay and the delay time is as short as possible.
The frequency response of the sensor is high, the frequency range of the measurable signal is wide, and the inertia of the mechanical system is large due to the influence of the structural characteristics, so the frequency of the sensor can be low.
In the dynamic measurement, should be based on the characteristics of the signal (steady state, transient, random, etc.) response characteristics, so as to avoid excessive errors.
4. Linear range
The linear range of the sensor is 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 greater the range, and to ensure a certain measurement accuracy. In the choice of sensors, when the type of sensor after the first to determine whether the range to meet the requirements.
But in fact, any sensor can not guarantee absolute linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, in a certain range, the nonlinear error of the sensor can be approximated as a linear approximation, which will bring great convenience to the measurement.
The ability of the sensor to use for a period of time after its performance remains unchanged is called stability. Factors that affect the long-term stability of the sensor in addition to the sensor itself structure, the main use of the sensor environment. Therefore, to make the sensor has good stability, the sensor must have a strong environmental adaptability.
Before selecting a sensor, investigate the use of the environment, select the appropriate sensor according to the specific use environment, or take appropriate measures to reduce the impact of the environment.
The stability of the sensor has a quantitative indicator, after more than the use of the period, should be re-calibrated before use to determine whether the performance of the sensor changes. In some applications where the sensor can be used for a long time and can not be easily replaced or calibrated, the stability of the selected sensor is more stringent and can withstand long periods of time.
Accuracy is an important indicator of the sensor, it is related to the entire measurement system measurement accuracy of an important part. The higher the accuracy of the sensor, the more expensive the price, so the accuracy of the sensor as long as the accuracy of the entire measurement system can meet the requirements, do not have to choose too high. This makes it possible to select relatively inexpensive and simple sensors in a number of sensors that meet the same measurement purpose.
If the purpose of the measurement is qualitative analysis, the use of high repeatability of the sensor can be used, should not use the absolute value of high precision; if it is for quantitative analysis, must obtain accurate measurement values, you need to use the accuracy level to meet the requirements of the sensor.
For some special use, can not choose the appropriate sensor, you need to design and manufacture of sensors. Self-made sensor performance should meet the requirements.