Research On Key Technologies For Vortex Flowmeter With Special Requirements

With the development of technology and production,vortex flowmeter is required to measure the high temperature fluid,perform digital signal processing with the low-power consumption and in two-wire mode,and measure the small flow whose Reynolds number in the range of 5000 to 20,000.Therefore a signal conditioning circuit for vortex flow sensor with high temperature resistant,a digital vortex flow transmitter with two-wire HART,and a vortex flowmeter with cross-correlation analysis algorithm for measuring low Reynolds Number flow rate are developed so as to satisfy these special requirements.High-temperature vortex flow sensor made of piezoelectric crystal material can be used to measure the high-temperature fluid,but it has the problem of low sensitivity and high output impedance.For this reason a signal conditioning circuit for vortex flow sensor with high temperature resistant is developed.It has two-stage charge amplifier and two-stage low-pass filter,and can amplify and filter the low amplitude signal outputted by the high temperature vortex flow sensor to obtain a stable flow signal.The method of shielding the signal lines of sensor output and signal conditioning circuit is used to prevent the signal of the signal conditioning circuit as a result of increasing resistance from electromagnetic interference,especially the impact of power frequency interference.The introduction of HART communication increases the power consumption of the digital vortex flowmeter in the two-wire mode,and the communication stability is susceptible to power fluctuations.To this end the digital vortex flow transmitter with two-wire HART is developed.The power supply is designed by combining the voltage regulator with isolated DC/DC to ensure the stability of HART communication.The design scheme of two isolated power supplies is adopted to improve the power supply load capacity and system anti-jamming capability,which also achieves two-wire HART communication while in the digital signal processing.Combined with signal conditioning circuit of high-temperature vortex flow sensor,a complete signal vortex flow transmitter with two-wire HART is built for the high-temperature vortex flow sensor.The experimental results show that the current consumption of the transmitter is only 3.3378 mA,and reaches 0.5 level accuracy for measuring liquid flow rate.It is difficult for the conventional vortex flowmeter to measure small flow rate whose Reynolds number in the range of 5000 ~ 20000.For this purpose the vortex flowmeter with the cross-correlation analysis function is developed to measure low Reynolds number flow rate.The cross-correlation analysis method is utilized,and the similarity of two vortex flow signal is fully used to realize the measurement of low Reynolds number flow rate.The primary instrument of the vortex flowmeter is redesigned to meet the requirement of cross-correlation analysis.A fast calculation method of delay time based on cross-correlation analysis is proposed to ensure the real-time performance of the meter.The cubic spline interpolation method is adopted to improve the calculation precision of delay time.The low power single-chip MSP430F6459 is used as the core to design the system and meet the low power consumption requirements.The water flow calibration results show that the vortex flowmeter can measure accurately small flow whose Reynolds number as low as 6649 and achieve one-level accuracy.