Development Of On-site Gas Flow Calibration Instrument

Gas flowmeters are important industrial metrology meters.Currently,lots of gas flowmeters on the market need calibration to keep their measurement accuracy,the traditional calibration devices are usually fixed at a location waiting for meter's calibration and can't meet the market's multiple demand.Majority of mobile gas flow calibration devices at home and abroad are truck-mounted,those calibration devices that can be pushed manually are in the minority,and their performance indicators still need to be improved.People expect a more convenient and easier way to simplify the calibration process.How to make the calibration devices civilian use and on-site calibration is the goal of this paper.In order to break through the limitations of laboratory calibration,and for those gas meters that can't have remote calibration,the on-site gas flow calibration instrument was designed.The device belongs to standard gas flow facilities based on master meters method,two high precision roots flowmeters were used as master meters,supplemented not only by the data acquisition and control module,but also by the steady flow device and gas source.By comparising with master meters we could get the measurement performance of the gas meters.The device is designed with negative pressure method,air as test gas,variable frequency fan controls flow rate.The lower computer deals with data collection and uploading,the upper computer deals with data processing,display and report generation,and the operation of mechanical structure involved.The lower computer includes frequency acquisition module and ADAM-4117 data acquisition module,responsible for collecting frequency,temperature,pressure and timing.Finally,sending data to upper computer through the serial port.Calibration interface was completed by LabVIEW software on the upper computer.Double timing method improves the measurement accuracy of frequency and Time,and data processing algorithms are based on verification regulation.The results show that the device can be used to calibrate gas meter whose precision grade is less than 1.5 ranged from0.5m~3/h to 400m~3/h.The expanded uncertainty of the device is better than 0.5%.