Ultrasonic Gas Flow Meter

With the development of national economy, the accurate measurement of largeflow rate gas becomes more and more necessary in metallurgy and chemicalengineering. The purpose of accurate measurement is energy conservation, safety inproduction, pollution control and so on. Because of more strict requirements aboutthe measurement of gas flow rate, ultrasonic technology has been used in gas flowrate measurement. Gradually, a new kind of gas flow meter is produced in the world,which is ultrasonic gas flow meter. The ultrasonic gas flow meter is a kind of latesttechnology, which measures gas current rate and flow rate by measuring two types ofpropagation times of ultrasonic pulse. The first time is what ultrasonic pulse costs totransmit in the direction of forward flow. The second one is what ultrasonic pulsecosts to transmit in the direction of opposite flow. The ultrasonic gas flow meterattracts a lot of attention and it's blueprint is very beautiful, because it has fewrelation with physical feature of gas fluid and there is no resisting force and pressureloss in the pipe of flow meter.Based on the system feature, the high-accurate digital counter circuit has beendesigned in the topic, which is the same with ultrasonic gas flow meter and isdesigned in the FPGA. The errors of digital counter is 0.25%. The hardware structureof the system is microcontroller + FPGA. The microcontroller is control center, andmost of digital circuit has been designed in FPGA. This kind of design structuremakes the circuit more simple, and makes the system more dependable. The digitalcircuit design belongs to flexible design, and can be upgraded more easily. If youchange the program in the memory in the configuration circuit of FPGA, some partsof hardware can be upgraded.The ultrasonic transducer that is used in the system can transmit and receiveultrasonic wave. The center frequency of the ultrasonic transducer used in the systemis 125KHz. The transducer is fixed in the pipe wall of DN150, and the mode offixing are single track and Z type. The angle between sound track direction and flowdirection of gas is 45o. The frequency-difference method is used in the measurementof gas current rate, which can avoid the effect of temperature.Simulative circuit is responsible for the emission, reception and procession ofthe ultrasonic signal. It is very important in the system, one character of which ismodularization design. The modularization circuit can not only implement thesystem function, but also have steady interface with other modularizations.After system debugging, test has been completed in gas flow rate experimentaldevice in the process measurement and control laboratory in Tianjin University.When the flow rate is low, the uncertainty is high. With the increment of flow rate,the uncertainty is lower and lower. The test conclusion accords with systemrequirement.