Issues to be considered in the purchase of sensors
Release date: June 6, 2019
Modern sensors vary 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 measuring a certain quantity. When the sensor is determined, the matching measurement method and equipment can be determined. The success or failure of the measurement results largely depends on the selection of sensors. The purchase reference of sensor is as follows:
1. The type of sensor is determined according to the measurement object and measurement environment
In order to carry out a specific measurement work, we should first consider what kind of sensor is used, which needs to be determined after analyzing various factors. Because, even if it is to measure the same physical quantity, there are many kinds of sensors to choose. Which one is more suitable, we need to consider the following specific problems according to the characteristics of the measurement and the conditions of the sensor: the size of the measuring range; the requirements of the measured position on the sensor volume; whether the measurement method is contact or non-contact; and whether the sensor is more suitable; The signal extraction method is wired or non-contact measurement; the source of the sensor is domestic or imported, and whether the price can bear or not is self-developed.
After considering the above problems, we can determine which type of sensor to choose, and then consider the specific performance index of the sensor.
2. Selection of sensitivity
Generally, in the linear range of the sensor, the higher the sensitivity, 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, which will affect the measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio (SNR) to minimize the plant disturbance signal introduced from the outside.
The sensitivity of the sensor is directional. When the measured is a unidirectional quantity and requires high directivity, the sensor with low sensitivity in other directions should be selected; if the measured is a multi-dimensional vector, the smaller the cross sensitivity of the sensor is, 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, and the shorter the delay time, the better.
The frequency response of the sensor is high, and the measured 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 signal measured by the sensor with low frequency is low.
In the dynamic measurement, the response characteristics (steady state, transient, random, etc.) of the signal should be taken into account to avoid excessive error.
4. Linear range
The linear range of the sensor refers to the range in which the output is proportional to the input. In theory, the sensitivity remains constant within this range. The wider the linear range of the sensor is, the larger the range is, and the measurement accuracy can be guaranteed. When selecting the sensor, when the type of sensor is determined, the first thing to see is whether its range meets the requirements.
But in fact, no sensor can guarantee the linearity of * * and its linearity is also relative. When the required measurement accuracy is relatively low, the sensor with small nonlinear error can be approximately regarded as linear in a certain range, which will bring great convenience to the measurement.
The ability of the sensor to keep its performance unchanged after a period of time 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 operating environment of the sensor. Therefore, in order to make the sensor have good stability, the sensor must have strong environmental adaptability.
Before selecting the sensor, the environment 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.
The stability of the sensor has quantitative indicators. After the service life is exceeded, it should be calibrated again before use to determine whether the performance of the sensor changes.
In some cases where the sensor is required to be used for a long time and cannot be replaced or calibrated easily, the selected sensor is required to be more stable and able to withstand the test for a long time.
Accuracy is an important performance index of the sensor, which is an important link related to the measurement accuracy of the whole measurement system. The higher the accuracy of the sensor, the more expensive its price. Therefore, as long as the accuracy of the sensor meets the accuracy requirements of the whole measurement system, it is not necessary to select too high. In this way, the cheaper and simpler sensor can be selected among many sensors which can meet the same measurement purpose.
If the purpose of measurement is qualitative analysis, the sensor with high repetition accuracy can be selected instead of the sensor with high measurement accuracy; if it is necessary to obtain accurate measurement value for quantitative analysis, it is necessary to select the sensor whose accuracy grade can meet the requirements.
For some special occasions, it is necessary to design and manufacture the appropriate sensor. The performance of the self-made sensor should meet the use requirements.