Research On Built-In Ultrasonic Flowmeter Based On Correlation Method

In people'S production mad life,ultrasonic flow-measurement is widely usedUltrasonic waves contain a fluid information when propagate in a medium,thatinformation can be converted into required physical quantity such as velocity and flow-rate through different measuring means This thesis is based on the correlation method ofvertical ultrasonic flow-measurement The probe is placed in the pipe which is paralleledto the direction of the fluid medium in pipe Using of the principle that the ultrasonictravel time from transmitting probe to receiving probe is different w-hen downstream madupstream,the velocity can be measured by calculating the time difference and then thenOW"rateThe key parameter to affect this type of flow-measurement is accuracy ofpropagation time measurement The traditional method to calculate the time difference isdetection threshold the received w-aveforlTl by setting a threshold voltage,and then countsthe processed signals Due to various interferences that cause the w-aveforlTl instability inthe medium,there exists some error when counting To solve the problem,cross．correlation method is used to calculate the time difference in the time differencemeasurement Because correlation method itself has a certain denoising filtercharacteristics,the various disturbances in the received signal do not affect themeasurement accuracy after sampling and correlating calculation In this paper the FPGAwhich is designed as the core provides a drive pulse through it is used as the emittingsource The transmitting signal with amplitude modulation is designed to solve themultiple values calculation of the time difference after correlation The whole systemincludes the corresponding receiving alnplifying filter circuit,the probe switch circuit,and sampling circuit In this system the ultrasonic transceiving probes are placed relativeat a certain distance,two receiving probes axe placed at the transceiver probes side toreceive the transmitting end signal The analog switch is controlled by the FPGA timingto switch probe transmitting mad receiving on downstream and upstream The received signal at the transmitting end and the received signal at the receiving end on thedownstream and upstream are amplified and filtered and other processed and thensampled The data are uploaded to PC,SO the time difference can be obtained aftercorrelation calculationThe experimental device is tested and the experimental environment factors andtime difference error that caused by distance measurement are analyzed and testedAccording to the designed system in the laboratory conditions,the measurement data ofthe time difference aJ'e measured and verified The results show-that the calculation timedifference error of the ultrasonic flow meter is smaller than 2its compared with thetheoretical value...