Gas sensors are a major category of chemical sensors. From working principles and characteristics analysis to measurement techniques, from materials used to manufacturing processes, and from detection objects to application fields, each can constitute an independent classification standard, giving rise to a complex and diverse classification system. Particularly, due to the lack of unified classification criteria, it is quite challenging to carry out a strict systematic classification. Next, let's understand the main characteristics of gas sensors:
1. 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 annually.
2. Sensitivity
Sensitivity refers to the ratio of the sensor's output change to the input change being measured, primarily dependent on the technology used in the sensor's structure. The design principles of most gas sensors utilize biochemical, electrochemical, physical, and optical methods. The first consideration is to choose 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
Selective sensitivity, also known as cross-sensitivity, can be determined by measuring the sensor response caused by a specific concentration of interference gas. This response is equivalent to the sensor response produced by a certain concentration of the target gas. This characteristic is crucial in applications tracking multiple gases, as cross-sensitivity can reduce the repeatability and reliability of measurements. An ideal sensor should possess high sensitivity and high selectivity.
4. Corrosion resistance
Corrosion resistance refers to the sensor's ability to withstand exposure to high-volume fraction target gases. In the event of a large gas leak, the probe should be able to endure a gas volume fraction 10 to 20 times the expected level. Under normal operating conditions, the sensor drift and zero-point correction should be as minimal as possible.
Basic 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 characteristics of gas sensors.
