Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-02-26
2001-07-31
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S334000, C310S326000, C310S312000
Reexamination Certificate
active
06268683
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to transducers and, more particularly, to a transducer suited for use in ultrasonic gas flow meters and a method of manufacturing such a transducer.
Meters which utilize ultrasonic transducers to measure the flow of a fluid are well known. For example, in one technique the difference between the time of travel of an ultrasonic wave upstream in a flowing gas and the time of travel of an ultrasonic wave downstream in the flowing gas is used to determined the flow rate of the gas. Ultrasonic transducers are utilized in such technique for receiving and transmitting the ultrasonic waves. Successful introduction of such gas flow meters requires that all manufacturing and production costs be carefully considered. Ultrasonic transducers are also utilized to establish the speed of sound within a gas by transmitting sound waves from the transducer, reflecting them off of a surface at a known distance, and receiving them back by the same transducer. Another technique for establishing the speed of sound within a gas involves transmitting sound waves from one transducer and receiving them at another transducer at a known distance. The time between transmission, reflection and reception in the case of a single transducer, or transmission and reception in the case of multiple transducers, can then be used to calculate the speed of sound within the particular gas.
In known meters the transducer is one of the most costly components for a variety of reasons. Known transducers suffer from a relatively low production yield due to, among other factors, a complex structure and fabrication procedure leading to noticeable property variations. One known type of transducer used in such gas meters includes a quarterwave matching plate covered by a foil cap. Production problems such as inconsistent foil cap pleats and widely varying quarterwave plate dimensions and material properties lead to uncorrectable variations. Further, known transducers are somewhat limited in terms of the gas pressures under which they may be utilized and are not hermetically sealed from the gas stream.
Accordingly, it would be desirable to provide a simple transducer configuration and related method of manufacture which results in higher production yields and lower transducer costs. It would also be desirable to provide a transducer capable of operating under higher gas pressures. A method of manufacturing such transducers for operation within a predetermined frequency range would further be desirable.
SUMMARY OF THE INVENTION
The present invention is a transducer configuration suited for use in ultrasonic gas flow meters, as well as in other types of systems. In a preferred embodiment of the invention the transducer includes a housing having an outer open end and an inner closed end with a side wall extending therebetween. The closed end of the housing is shaped to receive and transmit ultrasonic waves when positioned within the gas flow meter. A resonator is positioned within the housing and has a transmitting and receiving end facing the closed end of the housing. A thickness of the housing side wall at the closed end is less than at a position further toward the open end so that spurious vibrations that might otherwise occur near the resonating frequency of the transducer are reduced. Generally, such vibration reduction is best achieved when the thickness of the side wall housing gradually decreases toward the closed end of the housing.
In another aspect of the present invention a transducer for use in an ultrasonic gas flow meter includes a housing having an outer open end and an inner closed end with a side wall extending therebetween, the closed end being shaped to receive and transmit ultrasonic waves. A resonator is positioned within the housing with a transmitting and receiving end facing the closed end of the housing. An outer diameter of the housing side wall gradually decreases toward the closed end of the housing in order to suppress the magnitude of undesirable incidental housing vibrations.
A further aspect of the present invention provides a transducer mountable in a gas flow meter, including a housing having an open end and a closed end with a side wall extending therebetween, the closed end for receiving and transmitting sound waves. A resonator is positioned within the housing with a transmitting and receiving end facing the closed end of the housing. A resonator support positioned within the housing includes a base portion and a plurality of arm members extending from the base portion toward the closed end of the housing. At least a portion of the plurality of arm members contacts a side surface of the resonator and at least a portion of the base portion contacts an inner surface of the housing side wall for positioning the resonator within the housing. The resonator support provides a simple device for properly positioning the resonator centrally within the housing for improved performance and operation.
The subject transducers can be formed with a plastic housing suited for use in lower pressure applications or with a metal housing which is better suited for higher pressure applications. The closed end of the housing is used for transmitting and receiving sound waves such that in gas meter applications the matching plate and resonator can be isolated from the gas. Such transducer configurations may also include a damping medium within the housing in the space defined between the inner surface of the housing side wall and the outer surface of the resonator.
A method of manufacturing a transducer in accordance with the present invention involves providing a support member having a base portion and a plurality of arm members extending from the base portion. A resonator is positioned within a space defined by the plurality of arms of the support member. A housing having an open end and a closed end with a side wall extending between the ends is provided and a matching material is introduced into the housing from the open end such that the matching material lies adjacent the closed end of the housing. The resonator and support member are simultaneously loaded into the open end of the housing such that a first end of the resonator contacts the matching material. A damping medium is thereafter introduced into a space defined between an outer surface of the resonator and an inner surface of the housing side wall. Prior to curing the matching material, the resonator can be pressed slightly into the matching material to achieve a desired distance between an inner end of the resonator and the outer surface of the closed end of the housing.
In order to increase the number of transducers suitable for operation within a predetermined frequency range, a method of manufacturing a given transducer for operation within the predetermined frequency range involves providing a housing having an open end and a closed end with a side wall extending between the ends. A resonator is positioned within the housing such that a transmitting and receiving end faces the closed end of the housing and an opposite end faces the open end of the housing. A determination is made as to whether an initial operating frequency of the transducer is outside the predetermined frequency range and a thickness of the closed end of the housing is adjusted if the initial operating frequency of the transducer is determined to be outside the predetermined frequency range. In particular, the thickness of the closed end of the housing is reduced if the initial operating frequency is determined to be below the predetermined frequency range, and the thickness of the closed end of the housing is increased if the initial operating frequency is determined to be above the predetermined frequency range. This method results in a relatively high production yield of suitable transducers and therefore less waste and a lower per unit cost.
Accordingly, it is an object of the present invention to provide a simple method of manufacturing a transducer; a method of manufacturing a transducer for operation within a p
Dougherty Thomas M.
M&FC Holding Company
Thompson Hine LLP
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