Basic knowledge of temperature sensor

Three, the selection of sensors

The national standard GB7665-87 defines a sensor as: “A device or device that can sense the specified measurement and convert it into a usable signal according to a certain rule, usually composed of sensitive components and conversion components.” A sensor is a detection device that can feel the information to be measured, and can transform the detected and felt information into electrical signals or other required forms of information output according to certain rules to meet the needs of information transmission, processing, storage, and Display, record and control requirements. It is the first link to realize automatic detection and automatic control.

(1) Modern sensors differ greatly in principle and structure. How to select a sensor reasonably according to the specific measurement purpose, measurement object and measurement environment is the first problem to be solved when performing a certain quantity. When the sensor is confirmed, the measuring method and measuring equipment that match it can also be confirmed. The success or failure of the measurement result depends to a large extent on whether the sensor selection is reasonable.

1. Determine the type of sensor according to the measurement object and the measurement environment: To perform a specific measurement, first consider the principle of the sensor, which needs to be determined after analyzing many factors. Because, even if measuring the same physical quantity, there are sensors with multiple principles to choose from, which principle 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 location requires the volume of the sensor; the measurement method is contact or non-contact; the signal extraction method, wired or non-contact measurement; the source of the sensor, whether imported or domestic, whether the price is acceptable, or self-developed.

2. Sensitivity selection: Generally, within the linear range of the sensor, it is hoped that the higher the sensitivity of the sensor, the better, because only when the sensitivity is high, the output signal corresponding to the measured change is larger and beneficial to signal processing. But it should be noted that the sensitivity of the sensor is high, and external noise that has nothing to do with the measurement is also easy to mix in, and it will be amplified by the amplification system, which affects the measurement accuracy. Therefore, the sensor itself is required to have a high signal-to-noise ratio, and minimize the introduction The factory worry signal. The sensitivity of the sensor is directional. When the measured is a single vector, and its directivity requirements are higher, you should choose a sensor with less sensitivity in other directions. If the measured is a multi-dimensional vector, the smaller the cross sensitivity of the sensor, the better.

3. Frequency response characteristics: The frequency response characteristics of the sensor determine the frequency range to be measured, and the measurement conditions must be kept undistorted within the allowable frequency range. In fact, the response of the sensor always has a certain delay. It is hoped that the shorter the delay, the better. The frequency response of the sensor is high, the signal frequency range that can be measured is wide, and due to the influence of the structural characteristics, the inertia of the mechanical system is larger, and the frequency of the measurable signal is lower due to the low frequency sensor. In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, random, etc.) to avoid over-fire errors.

4. Linear range: The linear range of the sensor refers to the range where the output is proportional to the input. Theoretically speaking, within this range, the sensitivity remains constant, and the wider the linear range of the sensor, the larger the range, and a certain measurement accuracy can be guaranteed. 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, the sensor with less nonlinear error can be approximated as linear within a certain range, which will bring great convenience to the measurement.

5. Stability: The ability of the sensor to remain unchanged after a period of use 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 use environment of the sensor. Therefore, to make the sensor have good stability, the sensor must have strong environmental adaptability. Before selecting a sensor, investigate its use environment, and select the appropriate sensor according to the specific use environment, or take appropriate measures to reduce environmental impact. In some occasions where the sensor can be used for a long time but can be easily replaced or calibrated, the stability of the selected sensor is more stringent and must be able to withstand the test for a long time.

6. Precision: Precision is an important performance index 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, the accuracy of the sensor only needs to meet the accuracy requirements of the entire measurement system. It is not necessary to select too high, so that you can choose the cheaper and simpler among many sensors that meet the same measurement. sensor. If the measurement purpose is for qualitative analysis, select a sensor with high repeatability accuracy. It is not advisable to use a sensor with high absolute value accuracy; if it is for quantitative analysis and accurate measurement values ​​must be obtained, a sensor with an accuracy level that can meet the requirements should be selected. For some special occasions, if you can’t choose a suitable sensor, you need to design and manufacture the sensor by yourself. The performance of the self-made sensor should meet the requirements of use.