Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1990-02-09
1992-02-25
Ruehl, Charles A.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
G01F 166
Patent
active
050902520
DESCRIPTION:
BRIEF SUMMARY
The invention concerns an ultrasonic flow measuring device according to the echo time method having a measuring tube traversed by the flow of a medium, whereby the measuring tube has two ultrasonic transformers designed as combined transmit and receive transformers stagger-mounted in the direction of flow of the medium and at least one reflector reflecting the ultrasound between the ultrasonic transformers.
This kind of an ultrasonic flow measuring device is known e.g. from the teachings of DE-A1-35 39 948. In the known arrangement, a medium flows through the measuring tube, which has a fundamentally rectangular inner cross-section. Two ultrasonic transformers are stagger-mounted in the direction of flow on two opposing, parallel measuring tube walls. Two combined transmit and receive transformers, which are designed as interdigital transformers according to DE-A1 30 20 282, serve the purpose as ultrasonic transformers.
Interdigital transformers have a direction of radiation or reception, respectively, lying at an angle to the surface. The ultrasound radiated from a first ultrasonic transformer is transmitted to a first reflector, which is mounted in the direction of flow on the measuring tube wall lying opposite the first ultrasonic transformer and staggered with the first ultrasonic transformer. From there, the ultrasound is reflected to a second reflector which is mounted in the direction of flow on the measuring tube wall lying opposite the first reflector and is staggered with the first reflector. The second reflector directs the ultrasound to the second ultrasonic transformer. The flow velocity of the medium flowing in the measuring tube is in principle detected in that one measures the differences of the echo times of ultrasonic waves in and against the direction of flow. The difference of the echo times thereby serves as a measure for the flow velocity in the measuring tube.
The disadvantage of the known arrangement is that interdigital transformers are costly to manufacture and therefore expensive. A further disadvantage consists in that the inner walls of the measuring tube in the region of the reflectors are coated with an ultrasound-reflecting material or, respectively, outside of this region with an ultrasound-absorbing material.
According to a specific embodiment according to DE-A1-28 28 397, two ultrasonic transformers are mounted at an angle to the measuring tube wall and in a direction towards each other, and are staggered in the direction of flow on opposing measuring tube walls of the measuring tube through which a medium is flowing. In this manner, both ultrasonic transformers are designed as combined transmit and receive transformers having a transmit and receive direction perpendicular to the surface. The ultrasonic transformers are operated alternately as a transmitting transformer or a receiving transformer, respectively. Thus, ultrasonic waves are transmitted in and against the direction of flow and without interconnection by means of reflectors directly to the respective ultrasonic transformer lying opposite. The adjusting echo time difference serves as a measure for the flow velocity of the medium flowing in the measuring tube.
The disadvantage of this known specific embodiment is that the ultrasonic transformers must be mounted at an angle to the surface of the measuring tube and thus to the direction of flow. Therefore, resistances to flow arise at the location of the mounting of the ultrasonic transformers either in that the ultrasonic transformers jut out into the measuring tube and thus into the flow, or in that the ultrasonic transformers are mounted set back from the measuring tube wall and thus form niches. In both cases, changes are caused in the flow which can lead to deposits on the ultrasonic transformers. In addition, eddies can arise as a function of the velocity of the flowing medium, which falsify the measuring signal.
It is the task of the invention to design a measuring tube such that one can dispense with the use of expensive interdigital transformers, whereby
REFERENCES:
patent: 3906791 (1975-09-01), Lynnworth
patent: 3964308 (1976-06-01), Scarpa
patent: 4103551 (1978-08-01), Lynnworth
patent: 4555951 (1985-12-01), Gutterman
patent: 4610167 (1986-09-01), McShane
Ruehl Charles A.
Siemens Aktiengesellschaft
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