Since the 1980s, the United States, Germany and other developed countries have promulgated decrees to require gas stations to evaporate and leak oil and gas, install oil and gas recovery and treatment devices (secondary oil and gas recovery), and realize zero-emission of oil and gas. In order to confirm the operation effect of the oil-gas recovery and treatment plant, the U.S. Environmental Protection Agency (EPA) conducted testing on gas stations equipped with oil-gas recovery and treatment facilities and found that the average recovery efficiency of the oil and gas recovery system was only about 60%. Through the analysis of the indicators we can see that because of A / L caused by inefficient recovery of oil and gas accounted for 24% of the low, high pressure tank caused by gas leaks emissions, low recycling efficiency accounted for 29% of the tank or pipeline leak caused Oil and gas leak recovery inefficient 34%. In 1999, the California Air Resources Board (CARB) conducted field test on gas stations and found that 90% of the oil and gas recovery systems leaked, the equipment failure rate of the gas recovery system was 4.8% ~ 47.4%, and a considerable portion of the gas stations in California recovered oil and gas The system is operating below the certification efficiency. In 1998, Germany conducted a comprehensive inspection on the application of gas recovery systems at gas stations. Similar to the situation in the United States, most of the equipment deviated from normal working conditions. Therefore, the EPA considers that it is not enough to solve the oil and gas leakage and emission problems at gas stations only through the completion of gas station recovery and modification. Long-term and continuous monitoring of the oil and gas recovery system is required by on-line monitoring, and the unqualified treatment units are subject to monitoring results Repair treatment, in order to effectively ensure the operation of the oil and gas recovery system and oil and gas recovery efficiency. At present, the on-line monitoring equipment for commercialized oil and gas recovery is dominated by foreign products such as the ISD system from the U.S. Veeder-Root company and the VAPORIX system from Germany's FAFNIR company. US Veder-Root's ISD system is the only CARB-certified gas station online monitoring device, consisting of Roots flowmeter, pressure sensor, ISD memory expansion card and ISD interface module, the working principle is to flowmeter and The pressure sensor collects the data and transmits to the tanker TLS console, meanwhile collects the fueling pulse signal to calculate A / L. The Roots flowmeter can automatically compensate the error caused by the tank pressure and the temperature change. It has the abnormal working status alarm and forced locking Tanker features, supervise gas station management personnel to repair the fault, keep the system stable operation.