Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1994-01-28
1996-06-18
Chilcot, Richard
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
7386127, G01H 500
Patent
active
055266991
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION
The invention relates to gas velocity or flow monitors wherein the transmit time of an ultrasonic pulse between an ultrasonic sender and receiver changes according to the velocity of the gaseous medium flowing between the sender and receiver.
Typically, a pair of ultrasonic transducers is mounted at an oblique angle to gas flow in a duct and on a common ultrasonic axis. The transducers operate as both senders and receivers and transmit time measurements are made with and against the direction of flow so that factors affecting sonic velocity such as temperature, pressure, etc. are eliminated and, only the transmit times, when the ultrasonic pulses are transmitted in the direction of flow and the sonic transit time against the direction of flow, are measured to determine gas velocity. These are denoted transit time flow meters as opposed to ultrasonic measurements which are based on Doppler effect.
The object of the present invention is to provide an improved transit time gas flow meter which is more accurate, easier to install and of lower cost.
In particular, an object of the invention is to provide a transit time ultrasonic measuring system for measuring gas flow which may be calibrated for zero flow bias. Further, a feature of the invention is that the up stream and down stream ultrasonic transducer reflector assemblies incorporate acoustically reflective surfaces which are easily mounted in acoustic view of each other. The upstream and downstream transducer assemblies incorporate a rectangular housing which includes a mounting bracket for orienting a transducer, particularly a low-cost narrow beam electrostatic transducer of the Polaroid.RTM.-type which are pre-oriented relative to a Teflon.RTM. coated reflective surface and includes a reference wire target which is positioned at the edge of the flow path of the gas being monitored. While the reference targets could advantageously be located along the acoustic axis of the reflective surfaces and the transducers, it preferably is located at the edge of the respective reflectors so that it is out of the path of any side lobes of the transducer and, even though it may not be in the right place, since it is a known distance, the signal microprocessor can easily attend to the fact that it is not on the acoustic axis. The reference targets provide for increased accuracy in flow measurement and zero flow calibration of the instrument. High temperature sound absorbing foam is applied to all non-reflecting surfaces to eliminate ringing.
DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages and features of the invention will become more apparent when considered with the following specification and accompanying drawings wherein:
FIGS. 1a and 1b are illustrations of prior art transit time monitors,
FIG. 2 is a schematic diagram illustrating the present invention,
FIG. 3 is a sectional view of one transducer arrangement mounted in an existing flue-gas attachment,
FIGS. 4-10 are views of the transducer and reflector assembly incorporating the invention,
FIG. 11 is a block diagram of the electronic circuitry incorporated in the invention, and
FIG. 12 is a simplified graph showing the transmission and reception signals of the two transducers.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the prior art illustrated in FIG. 1a, ultrasonic transducers 10 and 11 are mounted on a common canted acoustic axis in the sidewalls 12 and 13 of a gas flow duct 14 and have a distance L between the transducers defining the path through the moving fluid medium whose velocity V is to be measured. Evaluator 15 solves the equation: ##EQU1## where K is a constant that results from the mounting geometry and used to calibrate the evaluator, T.sub.v is the ultrasonic pulse transit time in the flow direction, and T.sub.r is the sonic transit time against flow. The signals from the evaluator are supplied to a recorder 16 which may include a strip chart recorder and to a computer 17 which receives measured emission value
REFERENCES:
patent: 4373401 (1983-02-01), Baumoel
patent: 5001936 (1991-03-01), Baumoel
patent: 5275060 (1994-01-01), Lynnworth
patent: 5277070 (1994-01-01), Dorr
Biegel Rongald L.
Chilcot Richard
Xecutek Corporation
Zegeer Jim
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