The Development Of DN80 Industrial Ultrasonic Natural Gas Flow Meter

Ultrasonic flow measurement technology, which develops rapidly in recent several years, is a new-style flow measurement technology. It uses the liquid velocity information carried by the ultrasonic to measure the flow of liquid. The advantage is non-contact, high accuracy, wide measuring scope, so it is especially acceptable for measurement of large flow, or flow in dangerous environment. In recent years, with the development of LSIC and DSP, research for new style probe material and technology, and research for acoustic configuration and hydrodynamics, ultrasonic flow measurement has showed its strong technical advantage. The paper introduces basic principle firstly. By absorbing and referring to the domestic and foreign advanced technology, the system structure is designed, and the hardware and software is also implemented. Taking into account the difficulty of the gas flow measurement, following several problems are mainly discussed and solved:Stability and reliability. Firstly, delay window is used to reduce the influence of pulse disturbance. Secondly, according to the feature of width of receiving signal, pulse width detect circuit is utilized to distinguish receiving signal and disturbing signal. Thirdly, most of digital circuits are integrated into Xilinx XC2C128 CPLD so as to simplify design and to improve the stability and reliability of the system.Accuracy and measuring scope. Firstly, better matching emitting and receiving circuits is designed to improve work efficiency and SNR. Secondly, programmable amplifier circuit is used to enhance amplifier dynamic scope, and special pipe with reflect focus structure is used, to adapt to different Gas velocity. Thirdly, double threshold method, high speed ADC and DSP are adopted to eliminate the error caused by different amplitude of receiving signal and noise. Forth, flow revision coefficient is studied and analyzed.Low power. As the system is powered by battery, some measures from hardware and software are taken to reduce the power loss. As to hardware, select low power IC and circuit, low work voltage and suitable clock frequency. As to software, use dynamic power management, alterable instantaneous flow sample cycle and low power work mode.Test showes that the flow meter is stable and low power, accuracy of the system is high in a wide measuring range.