Vortex flowmeter

• US 5,736,649 A
• Filed: 08/22/1996
• Issued: 04/07/1998
• Est. Priority Date: 08/23/1995
• Status: Expired due to Term

• Current Assignee: Tokico Limited (Hitachi, Ltd.)
• Original Assignee: Tokico Limited (Hitachi, Ltd.)
• Inventors: Tashiro, Koichi, Kawasaki, Kazumasa, Inada, Yutaka
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): Biegel, Ronald L.
• Application Number:
  US08/701,447
• Time in Patent Office: 593 Days
• Field of Search: 73/861.22, 73/861.23, 73/118.2
• US Class Current: 73/861.23
• CPC Class Codes: G01F 1/3282 for detecting variations in infrasonic, sonic or ultrasonic waves, due to modulation by passing through the swirling fluid
• CPC Class Codes: G01F 1/3287 circuits therefor

Abstract

In a Karman vortex flowmeter according to the present invention, first and second ultrasonic transmission/reception devices are offset from each other along a flowing direction of fluid, and a switching device alternately switches the ultrasonic transmission/reception devices so that the ultrasonic transmission/reception devices can alternately perform transmission and reception. There is also provided a propagation time difference detector for determining a time difference between an ultrasonic wave propagation time when one of the ultrasonic transmission/reception devices performs the transmission, and an ultrasonic wave propagation time when the other of the ultrasonic transmission/reception devices performs the transmission, and for determining a flow rate of the fluid on the basis of the time difference. When no Karman vortex is generated or when the number of generated Karman vortices is greatly reduced, the minute flow rate of the fluid is measured by the propagation time difference detector.

Claims

1. A vortex flowmeter comprising:

a vortex shedder provided in a flow path;

an ultrasonic transmitter and an ultrasonic receiver disposed on both sides of said flow path in a portion downstream of said vortex shedder and spaced apart from said vortex shedder by a predetermined distance, said transmitter and receiver being offset from each other along a flow direction of said flow path and said transmitter emits ultrasonic waves as consecutive pulses of a regular interval;

a memory means for storing first data representative of a relation between generation frequency of Karman vortices generated by said vortex shedder and a flow rate of fluid flowing in said flow path and second data representative of a relation between (a) a difference of an ultrasonic wave propagation time relative to the reference propagation time when the flow rate of fluid flowing in said flow path is substantially zero; and

(b) the flow rate of the fluid flowing in said flow path;

a first calculation means for determining the generation frequency of the Karman vortices on the basis of a detection signal obtained from said ultrasonic receiver and for determining the flow rate on the basis of the first data;

a second calculation means for measuring the ultrasonic wave propagation time between said ultrasonic transmitter and said ultrasonic receiver, for determining a difference between the ultrasonic wave propagation time when the flow rate of the fluid is substantially zero and the measured ultrasonic wave propagation tie and for determining the flow rate of the fluid flowing in said flow path from the difference between the ultrasonic wave propagation times on the basis of the second data; and

an output switching means for switching an output so that, when the flow rate of the fluid is greater than a predetermined value, the flow rate of the fluid determined by said first calculation means is outputted and, when the flow rate of the fluid is smaller than the predetermined value, the flow rate of the fluid determined by said second calculation means is outputted.

2. A vortex flowmeter according to claim 1, wherein said output switching means effects the switching so that, when the flow rate of the fluid determined by said second calculation means is greater than the predetermined value, the flow rate of the fluid determined by said first calculation means is outputted and, when the flow rate of the fluid determined by said second calculation means is smaller than the predetermined value, the flow rate of the fluid determined by said second calculation means is outputted.

3. A vortex flowmeter according to claim 1, further comprising a temperature measuring means for measuring the temperature of the fluid, and wherein

said memory means stores third data representing a relation between an ultrasonic wave propagation time from said ultrasonic transmitter to said ultrasonic receiver when the flow rate of the fluid flowing in said flow path is substantially zero and the temperature of the fluid;

and

said second calculation means measures the ultrasonic wave propagation time between said ultrasonic transmitter and said ultrasonic receiver and the current temperature of the fluid from said temperature measuring means, determines a difference between the ultrasonic wave propagation time when the flow rate is substantially zero and the measured ultrasonic wave propagation time on the basis of the third data, and determines the flow rate of the fluid flowing in said flow path from the ultrasonic wave propagation time difference on the basis of the second data.

6. A vortex flowmeter according to claim 1, wherein said predetermined distance is equal to a vortex generating distance for the Karman vortices from said vortex shedder.

7. A vortex flowmeter according to claim 2, further comprising a temperature measuring means for measuring the temperature of the fluid, and wherein

said memory means stores third data representing a relation between an ultrasonic wave propagation time from said ultrasonic transmitter to said ultrasonic receiver when the flow rate of the fluid flowing in said flow path is substantially zero and the temperature of the fluid;

and

said second calculation means measures the ultrasonic wave propagation time between said ultrasonic transmitter and said ultrasonic receiver and the current temperature of the fluid from said temperature measuring means, determines a difference between the ultrasonic wave propagation time when the flow rate is substantially zero and the measured ultrasonic wave propagation time on the basis of the third data, and determines the flow rate of the fluid flowing in said flow path from the ultrasonic wave propagation time difference on the basis of the second data.

8. A vortex flowmeter according to claim 2, wherein said predetermined distance is equal to a vortex generating distance for the Karman vortices from said vortex shedder.

9. A vortex flowmeter according to claim 3, wherein said predetermined distance is equal to a vortex generating distance for the Karman vortices from said vortex shedder.

4. A vortex flowmeter comprising:

a vortex shedder provided in a flow path;

an ultrasonic sensor means comprised of a pair of transmission/reception portions disposed on both sides of said flow path in a portion downstream of said vortex shedder and spaced apart from said vortex shedder by a predetermined distance, said transmission/reception portions being offset from each other along a flow direction of said flow path and each of said transmission/reception portions emits ultrasonic waves as consecutive pulses of a regular interval;

a memory means for storing first data representative of a relation between generation frequency of Karman vortices generated by said vortex shedder and a flow rate of fluid flowing in said flow path and second data representative of a relation between (a) a difference in an ultrasonic wave propagation time between the case when one said pair of transmission/reception portions performs transmission and the case when the other transmission/reception portion performs transmission; and

(b) the flow rate of the fluid flowing in said flow path;

a first calculation means for determining the generation frequency of the Karman vortices on the basis of a detection signal obtained from a reception portion of said ultrasonic sensor means and for determining the flow rate on the basis of the first data;

a second calculation means for determining a difference between an ultrasonic wave propagation time when said ultrasonic sensor means performs transmission from the upstream side to the downstream side and an ultrasonic wave propagation time when said ultrasonic sensor means performs the transmission from the downstream side to the upstream side and for determining the flow rate of the fluid flowing in said flow path on the basis of the second data; and

an output switching means for switching an output so that, when the flow rate of the fluid is greater than a predetermined value, the flow rate of the fluid determined by said first calculation means is outputted and, when the flow rate of the fluid is smaller than the predetermined value, the flow rate of the fluid determined by said second calculation means is outputted.

5. A vortex flowmeter according to claim 4, wherein said output switching means effects the switching so that, when the flow rate of the fluid determined by said third calculation means is greater than the predetermined value, the flow rate of the fluid determined by said first calculation means is outputted and, when the flow rate of the fluid determined by said third calculation means is smaller than the predetermined value, the flow rate of the fluid determined by said third calculation means is outputted.

10. A vortex flowmeter according to claim 4, wherein said predetermined distance is equal to a vortex generating distance for the Karman vortices from said vortex shedder.

11. A vortex flowmeter according to claim 5, wherein said predetermined distance is equal to a vortex generating distance for the Karman vortices from said vortex shedder.