Standard JJG 551-2021 specifies the calibration procedures for sulfur dioxide Gas detectors. This standard applies to the first verification, subsequent verification and in-use inspection of sulfur dioxide Gas detection alarms and sulfur dioxide Gas Analyzers. Sulfur dioxide Gas detection alarms are used to monitor the concentration of sulfur dioxide gas in the workplace environment. They are detected by electrochemistry and have sound, light or vibration alarm functions. According to the Sampling method, they can be divided into diffusion type and pump suction type. They can be portable and fixed according to the way of use. According to the working mode, they can be continuous and discontinuous measurement. The sulfur dioxide Gas Analyzer is mainly used for the detection of sulfur dioxide gas concentration in the production process and the workplace environment, using the principles of Light spectrum method or thermal conductivity method. According to the Sampling method, it can be divided into positive pressure conveying type and pump suction type, which can be continuous and discontinuous measurement according to the working mode. These characteristics ensure that the sulfur dioxide Gas detector can accurately and reliably monitor the sulfur dioxide concentration, thus ensuring the safety and stability of the working environment and production process.