Modern sensors vary in principle and structure.
How to reasonably select sensors 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 corresponding measurement method and equipment can also be determined.
The success or failure of measurement results largely depends on whether the selection of sensors is reasonable.
1. Determine the sensor type according to the measurement object and measurement environment
To carry out a specific measurement job, we must first consider what type of main sensor should be used, which can only be determined after analyzing several factors.
Because even when measuring the same physical quantity, there are many types of sensors with different principles for you to choose from.
Which one is more suitable, we need to consider the following specific problems according to the measured characteristics and service conditions of the sensor:
① Range size;
② Requirements of the measured position in the sensor volume;
③ Whether the measurement method is contact or non-contact;
④ Signal extraction method, contact or non-contact measurement;
⑤ The origin of the sensor, national or imported, whether affordable or self-developed.
After considering the above issues, we can determine which type of sensor to choose and then consider the sensor's specific performance indicators.
2. Sensitivity selection
Generally, within the linear range of the sensor, the higher the sensitivity of the sensor, the better.
Because only when the sensitivity is high, the output signal value 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 irrelevant to the measurement is easy to mix, which will also be amplified by the amplification system and affect the measurement accuracy.
Therefore, the sensor itself must have a high signal-to-noise ratio to minimize the interference signal introduced from outside.
The sensitivity of the sensor is directional.
When the measured quantity is unidirectional and has high requirements for its directivity, the sensor with low sensitivity in other directions must be selected;
If the measured vector is multidimensional, the lower the sensor's cross sensitivity, the better.
3. Frequency response characteristics
The frequency response characteristic of the sensor determines the measured frequency range, and distortion-free measurement conditions must be maintained within the allowable frequency range.
In fact, the sensor response always has a certain delay, and 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.
Due to the influence of structural characteristics, the inertia of the mechanical system is large, so the frequency of the sensor's measurable signal with low frequency is low.
In dynamic measurement, the response characteristics (steady state, transient, random, etc.) must be based on the signal characteristics to avoid excessive errors.
4. Linear range
The linear range of the sensor refers to the range in which the output is proportional to the input.
Theoretically, within this range, sensitivity remains constant.
The greater the linear range of the sensor, the greater its range and a certain measurement accuracy can be guaranteed.
When selecting a sensor, when the sensor type is determined, we must first check 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 small nonlinear error can be considered linear within a certain range, which will bring great convenience to measurement.
5. Stability
The ability of a sensor to maintain its performance unchanged after being used for a period of time is called stability.
In addition to the structure of the sensor itself, the main factor that affects the long-term stability of the sensor is the service environment of the sensor.
Therefore, in order for the sensor to have good stability, the sensor must have strong environmental adaptability.
Before selecting the sensor, its use environment must be investigated, and the appropriate sensor must be selected according to the specific use environment, or appropriate measures must be taken to reduce the impact of the environment.
The stability of the sensor has quantitative indicators.
After exceeding its useful life, it must be recalibrated before use to determine if the sensor performance has changed.
In some occasions where the sensor needs to be used for a long time and cannot be easily replaced or calibrated, the stability of the selected sensor is more rigorous and can withstand the test for a long time.
6. Accuracy
Accuracy is an important index of sensor performance. It is an important link related to the measurement accuracy of the entire measurement system.
The greater the accuracy of the sensor, the more expensive it will be.
Therefore, as long as the sensor accuracy meets the accuracy requirements of the entire measurement system, it is not necessary to choose a value that is too high.
In this way, cheaper and simpler sensors can be selected among many sensors that serve the same measurement purpose.
If the measurement purpose is qualitative analysis, the sensor with high repetition accuracy can be selected, and the sensor with high absolute value accuracy should not be selected;
If it is necessary to obtain accurate measurement values for quantitative analysis, it is necessary to select the sensor whose degree of accuracy can meet the requirements.
For some special occasions, if it is impossible to select a suitable sensor, the sensor must be designed and manufactured by you.
The performance of the homemade sensor must meet the usage requirements.
