To perform a specific measurement task, the first step is to consider which type of sensor principle to use. This requires analyzing various factors before making a decision.
Even when measuring the same physical quantity, there are multiple sensor principles available. Which sensor principle is more suitable depends on the characteristics of the measured quantity and the operating conditions of the sensor. Specific issues to consider include: the magnitude of the measurement range; the size requirements of the sensor based on the measurement location; whether the measurement method is contact or non-contact; the signal output method (wired or wireless); and the sensor's origin (domestic or imported), affordability, or whether it needs to be custom-designed.
After considering these issues, the type of sensor can be determined, and then the specific performance indicators of the sensor can be considered.
Sensitivity Selection
Generally, within the linear range of the sensor, it is desirable for the sensor's sensitivity to be as high as possible. This is because higher sensitivity results in a larger output signal value corresponding to changes in the measured quantity, which is beneficial for signal processing. However, it should be noted that high sensor sensitivity also makes it easier for external noise unrelated to the measured quantity to be introduced and amplified by the amplification system, affecting measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio, minimizing interference signals from the external environment.
Sensor sensitivity is directional. When the measured quantity is a single vector, and its directionality is critical, a sensor with low sensitivity in other directions should be selected; if the measured quantity is a multi-dimensional vector, the cross-sensitivity of the sensor should be as small as possible.
Frequency Response Characteristics
The frequency response characteristics of the sensor determine the frequency range of the measured quantity, which must remain undistorted within the allowable frequency range. In reality, the sensor's response always has a certain delay; ideally, this delay time should be as short as possible.
The higher the frequency response of the sensor, the wider the range of measurable signal frequencies.
In dynamic measurements, the response characteristics should be considered based on the characteristics of the signal (steady-state, transient, random, etc.) to avoid excessive errors.
Linear Range
The linear range of a sensor refers to the range where the output is proportional to the input. Theoretically, within this range, the sensitivity remains constant. A wider linear range means a larger measurement range and ensures a certain level of measurement accuracy. When selecting a sensor, after determining the type of sensor, the first thing to check is whether its measurement range meets the requirements. However, in reality, no sensor can guarantee absolute linearity; its linearity is always 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 greatly simplifies the measurement process.
Stability
The ability of a sensor to maintain its performance unchanged after a period of use is called stability. Factors affecting the long-term stability of a sensor, in addition to the sensor's own structure, are mainly the sensor's operating environment. Therefore, to ensure good sensor stability, the sensor must have strong environmental adaptability.
Before selecting a sensor, the operating environment should be investigated, and a suitable sensor should be selected based on the specific environment, or appropriate measures should be taken to minimize environmental influences.
Sensor stability has quantitative indicators. After exceeding the service life, recalibration should be performed before use to determine whether the sensor's performance has changed.
In some applications where sensors need to be used for a long time and cannot be easily replaced or calibrated, the stability requirements for the selected sensor are more stringent, and it must be able to withstand prolonged use.
Accuracy
Accuracy is an important performance indicator of a sensor, and it is a crucial link in the overall measurement accuracy of the entire measurement system. The higher the accuracy of the sensor, the more expensive it is. Therefore, the sensor's accuracy only needs to meet the accuracy requirements of the entire measurement system; there is no need to choose one that is excessively accurate. This allows for the selection of 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 repeatability is sufficient; a sensor with high absolute value accuracy is not necessary. If the purpose is quantitative analysis and precise measurement values are required, a sensor with an accuracy level that meets the requirements must be selected.
For some special applications where a suitable sensor cannot be found, it is necessary to design and manufacture the sensor oneself. The performance of the self-made sensor should meet the usage requirements.