Panametrics, Inc.

Saul A Jacobson

Lawrence C Lynnworth

James M Korba

Chang Shen

A clamp-on ultrasonic measurement system for a gas or fluid of low acoustic impedance, such as steam, two phase fluid or flare gas includes an ultrasonic signal transmitter which clamps to the steam or gas conduit, and first and second receiving transducers clamped in the shadow zone of the transmitter. The transmitter signal skips within the conduit wall with a characteristic skip distance L,so ultrasonic signal energy is launched across the flow along plural paths over a region, and at an angle to the direction of flow. The receivers are positioned to receive the signal energy along different ones of said paths, modulated by tags or inhomogeneities in the flowing fluid. Cross correlation of the received signals then yields a peak correlation time interval or time delay from which the flow velocity is accurately determined. The transducers preferably employ air-backed crystals to generate a continuous shear wave signal of about 100 kHz-1 MHz, which reflects within the pipe wall and transmits a portion of its energy into the fluid with each skip. A structure or material mounts with an acoustically-matched impedance coupling to the pipe between two receiver transducers to absorb or block quasi-coherent signals that have passed through the fluid and have entered and propagated along the wall, thus eliminating phantom correlation peaks in the signals received downstream. Preferably, the receiving transducers are coupled with wedges to the conduit along a length nL,, and have an actual diameter less than L,or are otherwise configured to receive energy along a spatially limited path spread with high sensitivity to small scatterers in the fluid path. In a second aspect of the invention, a system employs two transmitters at different frequencies, opposed to a corresponding pair of similarly-spaced receivers. The receiver outputs are demodulated at the separate frequencies and then correlated to determine the flow time between receiving stations.

Coherent multi-path flow measurement system

A sensor system includes an ultrasonic transducer head with plural transducing elements. The elements are arranged in pairs with the first one of each pair lying in a first plane and the second one of each pair in a second plane spaced a half wavelength away. For transmission, the two are driven out of phase, while for reception their outputs are combined differentially. By changing the drive frequency the transmitted beam is steered to compensate for changes in transducer alignment, or changes in acoustic path caused by abnormal temperature, pressure or flow velocity. In another embodiment, an assembly has a plurality of transducers aligned along slightly divergent paths. Preferred systems employ an upstream and a downstream transducer assembly, each of which is used to alternately transmit and receive signal energy.

Flow measurement system including ultrasonic transducers

A flow meter, or flow path intervalometer, transmits a transmission signal modulated with digital pseudo-noise or similar code. The received signal is correlated with the transmitted signal at successive times to produce a correlation function having a peak at a time to equal to the propagation time. The code is selected such that the side lobes of the correlation function are small. An interpolator determines a precise time of maximum correlation. In one embodiment, upstream and downstream correlation functions are defined and are correlated to determine an upstream-downstream propagation time difference interval .DELTA.t. In a preferred embodiment the digital code is a Barker code, and the transmitted signal is a finite interval wave which is phase modulated by the Barker code. In another embodiment, the received signal is a reflected signal which is range gated so as to represent flow data originating from a desired region within the conduit. The signal is sampled in phase quadrature and transformed to determine its frequency domain representation, and the devide derives local flow rate information from Doppler information. In yet another embodiment, a plurality of transducers are arranged to provide a number of sampling paths across the conduit, and the flow meter varies the range gating interval for the signal received along each path to derive a Doppler frequency, hence flow rate, for each of many sample intevals or bins along the path. The total flow in the conduit is then obtained by summing the flow in each bin times a cross-sectional area weighting factor.

Growing community of inventors

Medford, MA, United States of America

Saul A Jacobson