Analysis of six elements in sensor selection

Modern sensors vary greatly in principle and structure. How to select sensors reasonably according to the specific measurement purpose, measurement object and measurement environment is the first problem to be solved when performing a certain amount of measurement. After the sensor is determined, the matching measurement method and measurement equipment can be determined. The success or failure of the measurement results depends to a large extent on whether the selection of sensors is reasonable.

1. Determine the type of sensor according to the measurement object and measurement environment

To carry out a specific measurement work, we must first consider what kind of sensor is used. This needs to be determined after analyzing many factors. Because, even when measuring the same physical quantity, there are multiple principles of sensors to choose from, which principle of the sensor is more suitable, you need to consider the following specific issues according to the characteristics of the measured and the use conditions of the sensor: the size of the range; The requirements of the measured position on the volume of the sensor; whether the measurement method is contact or non-contact; the signal extraction method, wired or non-contact measurement; the source of the sensor, whether it is domestic or imported, whether the price can bear, or developed by itself. 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. The choice 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 external noise that is not related to the measurement is also easily mixed in, and it 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, so as to reduce the factory disturbance signals introduced from the outside.

The sensitivity of the sensor is directional. When the measured value is a single vector, and its directivity is higher, you should choose a sensor with less sensitivity in other directions. If the measured value is a multi-dimensional vector, the smaller the cross-sensitivity of the sensor, the better.

3. Frequency response characteristics

The frequency response characteristic of the sensor determines the frequency range to be measured. It must maintain undistorted measurement conditions within the allowable frequency range. In fact, 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 frequency range of the measurable signal is wide. However, due to the influence of structural characteristics, the inertia of the mechanical system is large, and the frequency of the measurable signal of the sensor with low frequency is low.

In the dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.), so as to avoid excessive fire errors.

4. Linear range

The linear range of the sensor refers to 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 it can ensure a certain measurement accuracy. When selecting a sensor, when the type of sensor is determined, it is first necessary to see 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, the sensor with small nonlinear error can be regarded as linear, which will bring great convenience to the measurement.

5. Stability

After a sensor is used for a period of time, its ability to keep its performance unchanged is called stability. In addition to the structure of the sensor itself, the factors that affect 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 a strong ability to adapt to the environment.

Before selecting a sensor, the environment in which it is used should be investigated, and the appropriate sensor should be selected according to the specific use environment, or appropriate measures should be taken to reduce the environmental impact.

There are quantitative indicators for the stability of the sensor. After the period of use is exceeded, the calibration should be re-calibrated before use to determine whether the performance of the sensor has changed.

In some occasions where the sensor can be used for a long time and cannot be easily replaced or calibrated, the stability of the selected sensor is more stringent, and it must be able to withstand the test for a long time.

6. Precision

Accuracy is an important performance index of the sensor, 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, it is possible to select a cheaper and simpler sensor among many sensors that meet the same measurement purpose.

If the measurement purpose is qualitative analysis, use a sensor with high repeat accuracy. It is not appropriate to use a sensor with high absolute value accuracy. If it is for quantitative analysis, accurate measurement values ​​must be obtained, and a sensor with an accuracy level that meets the requirements must be selected. For some special use occasions, it is not possible to select a suitable sensor, you need to design and manufacture the sensor yourself. The performance of self-made sensors should meet the requirements of use.

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