Independent air chamber structure, fast response, good long-term stability Three-wire system 4-20mA standard signal output, voltage output, 1 group of relay switches. Each unit can be switched with each other, automatically track the zero point to prevent drift, and multi-level calibration. Anti-explosion, lightning protection, anti-static, anti-reverse connection, anti-EMI, EMC electromagnetic interference, anti-impulse surge current impact. It can communicate with the computer, monitor the concentration of the on-site probe in real time through the host computer on the computer, and store, analyze and print the data on the computer.