Implementation of High Precision Time Measuring Method of Travel Time Ultrasonic Flowmeter

On the basis of analyzing the error of traditional time measuring method,a new high precision time measuring method was presented to improve the precision of time measuring of travel time ultrasonic flowmeter.Combining the theory of PLL with the technique of edge detecting,this new method made the spread time of ultrasonic just consist of integral units of timing pulse,which could minimize the phase error of timing pulse;meanwhile,implemented the circular measurement of spread time through logical programming,which could reduce the edge detecting error and system error.The result of simulation experiment shows that the method raises the precision of time measuring to ns level even sub-ns level and meets the demand of precision of time measuring in the small pipe diameter situation.The core function of this method has implemented on the FPGA chip of Xilinx XC2S100e.