Automatic zero tracking to prevent drift. Three-wire 4-20mA standard signal output, voltage output, 2 groups of relay switches. Anti-explosion, lightning protection, anti-static, anti-reverse connection, anti-EMI, EMC electromagnetic interference, anti-impulse surge current impact. It can be connected to the computer to monitor the concentration of the field probe in real time through the host computer, and store, analyze and print the data on the computer. It is used for concentration detection and concentration exceeding alarm, can detect the content of toxic and harmful gas and output standard signal, signal stability, three-wire or four-wire flameproof wiring, suitable for all kinds of dangerous places.