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With the advent of the information age, sensors have become the main way and means for people to obtain information in the fields of nature and production. Especially in the modern industrial production process, various sensors must be used to monitor and control various parameters in the production process to make equipment Work in normal condition and make the product reach better quality. Today, sensors have long penetrated into a wide range of fields such as industrial production, space development, marine exploration, environmental protection, resource surveys, medical diagnostics, biological engineering, and even cultural relic protection. It can be seen that the important role of sensor technology in economic development and social progress is very obvious.

However, modern sensors vary widely in principle and structure. How to properly select a sensor according to the specific measurement purpose, measurement object and measurement environment is the first problem to be solved when measuring a certain quantity. Let ’s work with you to learn about the six key points and principles of sensor selection.

First: determine the type of sensor according to the measurement object and the measurement environment.

To carry out a specific measurement, we must first consider what kind of sensor to use. This requires analysis of many factors before it can be determined. Because, even when measuring the same physical quantity, there are many kinds of sensors to choose from. Which one is more suitable, you need to consider the following specific issues according to the characteristics being measured and the conditions of use of the sensor:

  1. the size of the range;
  2. Requirement of the measured position on the volume of the sensor;

3.Whether the measurement method is contact or non-contact;

  1. Signal extraction method, wired or non-contact measurement;
  2. the source of the sensor, domestic or imported, whether the price can be afforded, or developed by ourselves.

For example, there are electromagnetic flowmeters, vortex flowmeters, and ultrasonic flowmeters. We need to select flowmeters for specific targets. In addition, we need to refer to which output mode is required, such as 2-wire system. It is also a four-wire current signal, 0-20ma, 4-20ma, 0-10v voltage signal or some kind of protocol communication. After considering the above issues, we can determine what type of sensor to choose, and then consider the specific performance indicators of the sensor.

Second: selection based on sensitivity.

Generally, in 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 to minimize interference 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.

Third: judge the frequency response characteristics.

The frequency response characteristic of the sensor determines the frequency range to be measured, and it must remain undistorted within the allowable frequency range. In fact, there is always a certain delay in the response of the sensor. 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 response characteristics of the signal (steady state, transient state, random, etc.) should be used to avoid overheating errors.

Fourth: According to the stability of the sensor.

The ability of a sensor to maintain its performance after a period of time 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 long-term test.

Fifth: the linear range of the sensor. 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 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 also relative. When the required measurement accuracy is relatively low, within a certain range, sensors with small non-linear errors can be approximated as linear, which will bring great convenience to the measurement.

Sixth: The range and accuracy of the sensor are the most difficult to coordinate.

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. Therefore, 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 repetition accuracy can be used, and it is not suitable to use a high absolute value accuracy. If it is for quantitative analysis, accurate measurement values ​​must be obtained, and a sensor with an accuracy level that can meet the requirements is required. For some special use occasions, 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.

 

However, the accuracy of the sensor is limited by the range. Generally, the larger the range, the lower the accuracy. However, it is very likely that the range of the high-precision sensor is not sufficient, which results in a high-precision, long-range sensor that is very expensive. So you need to adjust their relationship appropriately when choosing.

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