How to select a sensor

Modern sensors vary widely in principles and structures. How to reasonably select a sensor based on specific measurement objectives, objects, and environments is the first problem to solve when measuring a quantity. Once the sensor is determined, the supporting measurement methods and equipment can also be identified. The success of measurement results largely depends on whether the sensor is reasonably selected.

First, determining the Sensor Type Based on the Measurement Object and Environment

To carry out a specific measurement, the first step is to consider which principle of sensor to use, which requires analyzing multiple factors. Even for measuring the same physical quantity, there are multiple sensor principles available. The suitability of a sensor principle depends on the characteristics of the measured quantity and the sensor's operating conditions, requiring consideration of the following specific issues: measurement range, requirements for sensor size based on the measured position, contact or non-contact measurement method, signal output method (wired or non-contact), sensor origin (domestic or imported), cost affordability, or self-developed. After considering the above, the type of sensor can be determined, followed by specific performance indicators.

Second, Selection of Sensitivity. Generally, within the linear range of a sensor, higher sensitivity is preferred. Higher sensitivity results in larger output signals corresponding to measured quantity changes, facilitating signal processing. However, it should be noted that high sensitivity may easily introduce external noise unrelated to the measured quantity, which can be amplified by the system and affect measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio to minimize interference from external sources.
Sensor sensitivity is directional. For single-directional measurements with high directional requirements, select sensors with low sensitivity in other directions; for multi-dimensional measurements, choose sensors with minimal cross-sensitivity.

Third，response Characteristics (Reaction Time). The frequency response characteristic of a sensor determines the measurable frequency range of the measured quantity, which must maintain distortion-free measurement within the allowable frequency range. In practice, sensor response always has a certain delay, and shorter delay times are preferred. Higher frequency response allows broader measurable signal frequency ranges, while mechanical systems with large inertia (due to structural limitations) are suitable for sensors with lower natural frequencies and narrower measurable frequency ranges. In dynamic measurements, match the response characteristics to the signal type (steady-state, transient, random, etc.) to avoid excessive errors.

Forth，Linear Range. The linear range of a sensor refers to the range where output is proportional to input. Theoretically, sensitivity remains constant within this range. A wider linear range enables a larger measurement range and ensures measurement accuracy. When selecting a sensor, first check if its range meets requirements after determining the sensor type.
In practice, no sensor is absolutely linear, and linearity is relative. For low-precision measurement requirements, sensors with small non-linear errors can be approximated as linear within a certain range, greatly simplifying measurements.

Fifth，Stability. Stability refers to a sensor’s ability to maintain performance unchanged after a period of use. Factors affecting long-term stability include not only the sensor’s structure but also its operating environment. Therefore, to ensure good stability, sensors must have strong environmental adaptability.
Before selecting a sensor, investigate its intended use environment and choose an appropriate sensor or adopt measures to mitigate environmental impacts. Stability has quantitative indicators; after exceeding the service life, re-calibrate the sensor before use to confirm whether performance has changed. In applications requiring long-term use without easy replacement or re-calibration, sensor stability requirements are more stringent, needing to withstand prolonged testing.

Sixth，Accuracy. Accuracy is a critical performance indicator of sensors and a key factor in the measurement accuracy of the entire system. Higher accuracy sensors are more expensive, so sensor accuracy only needs to meet the system’s requirements—no need for excessively high precision. This allows selecting cheaper and simpler sensors among those satisfying the same measurement objectives. For qualitative analysis, choose sensors with high repeatability rather than high absolute accuracy. For quantitative analysis requiring precise measurements, select sensors with suitable accuracy grades.
In special applications where no suitable sensor is available, self-design and manufacturing may be necessary, with homemade sensors must meeting performance requirements.