Gas sensors represent a broad category of chemical sensors. From their working principles, characteristic analysis, and measurement techniques, to the materials used, manufacturing processes, detection objects, and application fields, each can constitute an independent classification criterion, leading to a complex and intricate classification system. Particularly, the lack of a unified classification standard makes it quite challenging to perform a strict systematic classification. Next, let's explore the main characteristics of gas sensors:

Stability

Stability refers to the basic response stability of the sensor throughout its operating time, which depends on zero-point drift and span drift. Zero-point drift is the change in the sensor's output response over the entire operating time when there is no target gas. Span drift is the change in the sensor's output response when continuously exposed to the target gas, characterized by a decrease in the sensor's output signal over the operating time. Ideally, a sensor under continuous operating conditions should have less than 10% zero-point drift per year.

2. Sensitivity

Sensitivity refers to the ratio of the sensor's output change to the measured input change, primarily dependent on the technology used in the sensor's structure. The design principles of most gas sensors employ biochemical, electrochemical, physical, and optical methods. The first consideration is to select a sensitive technology that has sufficient sensitivity to detect the percentage of the threshold limit value (TLV) or the lower explosive limit (LEL) for the target gas.

3. Selective

The selectivity is also known as cross-sensitivity. It can be determined by measuring the sensor response caused by a certain concentration of interference gas. This response is equivalent to the sensor response produced by a certain concentration of target gas. This characteristic is very important in applications for tracking multiple gases, as cross-sensitivity can reduce the repeatability and reliability of measurements. An ideal sensor should have high sensitivity and high selectivity.

4. Corrosion resistance

Corrosion resistance refers to the sensor's ability to withstand exposure to high concentrations of target gas. During large gas leaks, the probe should be capable of withstanding up to 10 to 20 times the expected gas concentration. Under normal operating conditions, sensor drift and zero-point calibration should be as minimal as possible.

The fundamental characteristics of gas sensors, such as sensitivity, selectivity, and stability, are primarily determined by the choice of materials. Selecting appropriate materials and developing new ones optimize the sensitive properties of gas sensors.