A sensor is a detection device that can sense the information being measured and convert that information into electrical signals or other required forms of output according to certain rules, to meet the requirements for information transmission, processing, storage, display, recording, and control. It is the primary link in achieving automatic detection and automatic control.
The development of modern science and technology continuously raises new demands on detection technology, while also promoting its advancement. New sensors are constantly emerging, leading to significant changes in detection technology. Therefore, how to reasonably select sensors based on specific measurement purposes, measurement objects, and measurement environments has become a common issue faced by engineering technicians.
1. Determine the Type of Sensor Based on Measurement Object and Environment
To carry out a specific measurement task, the first consideration is what type of sensor principle to use, which requires analyzing multiple factors before a decision can be made. Even when measuring the same physical quantity, there are various principles of sensors available for selection. The most suitable sensor principle needs to be determined based on the characteristics of the measured object and the conditions of sensor use, considering the following specific issues: the range of measurement; the size requirements of the sensor in relation to the measurement location; whether the measurement method is contact or non-contact; the method of signal extraction, whether wired or non-contact measurement; the source of the sensor, whether domestic or imported, whether the price is affordable, or if it needs to be self-developed.
After considering the above issues, the type of sensor to be selected can be determined, followed by consideration of the specific performance indicators of the sensor.
2. Selection of Sensitivity
Generally, within the linear range of the sensor, a higher sensitivity is preferred. This is because only with high sensitivity will the output signal value corresponding to changes in the measured quantity be larger, which is beneficial for signal processing. However, it is important to note that high sensitivity in a sensor can also lead to the inclusion of unrelated external noise, which can be amplified by the system, affecting measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio to minimize the introduction of external interference signals.
The sensitivity of a sensor is directional. When the measured quantity is a unidirectional vector and has high directional requirements, a sensor with lower sensitivity in other directions should be selected; if the measured quantity is a multidimensional vector, the cross-sensitivity of the sensor should be as low as possible.
3. Frequency Response Characteristics
The frequency response characteristics of a sensor determine the frequency range of the measured quantity. It is essential to maintain undistorted measurement conditions within the allowable frequency range; in practice, the sensor’s response always has a certain delay, and a shorter delay time is preferred.
A sensor with a high frequency response can measure a wider range of signal frequencies, but due to structural characteristics, mechanical systems tend to have larger inertia, which means that sensors with lower frequencies can measure lower signal frequencies.
In dynamic measurements, the response characteristics should be based on the nature of the signal (steady-state, transient, random, etc.) to avoid excessive errors.
4. Linear Range
The linear range of a sensor refers to the range in which the output is proportional to the input. Theoretically, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger its measurement range, and it can ensure a certain level of measurement accuracy. When selecting a sensor, once the type of sensor is determined, the first thing to check is whether its range meets the requirements.
However, in reality, no sensor can guarantee absolute linearity; its linearity is also relative. When the required measurement accuracy is relatively low, a sensor with small non-linearity errors can be approximated as linear within a certain range, which greatly facilitates measurement.
5. Stability
The ability of a sensor to maintain its performance without change after being used for a period of time is referred to as stability. Factors affecting the long-term stability of a sensor, aside from its structural design, mainly include the sensor’s operating environment. Therefore, to ensure good stability, the sensor must have strong environmental adaptability.
6. Accuracy
Accuracy is an important performance indicator of a sensor, and it is a crucial aspect that affects the overall measurement accuracy of the measurement system. The higher the accuracy of the sensor, the more expensive it tends to be; therefore, the sensor’s accuracy should only meet the requirements of the entire measurement system without being excessively high. This allows for the selection of relatively inexpensive and simple sensors among many options that meet the same measurement purpose.
If the measurement purpose is qualitative analysis, a sensor with high repeatability should be selected, rather than one with high absolute accuracy; if the goal is quantitative analysis, precise measurement values are required, and a sensor with an accuracy level that meets the requirements must be chosen.
In some special use cases where suitable sensors cannot be found, it may be necessary to design and manufacture custom sensors. The performance of custom-made sensors should meet the usage requirements.