JP3465100B2 - Vortex flow meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter for measuring a flow rate of a fluid. 2. Description of the Related Art As an example of a conventional vortex flowmeter, a vortex generator for generating Karman vortices is provided in a pipe through which a fluid flows.
There is a type in which a pair of ultrasonic transceivers are arranged to face each other with a Karman vortex generation region therebetween. In this vortex flowmeter, when a fluid flows in a pipe, Karman vortices are alternately and regularly generated by a vortex generator with a period proportional to the flow velocity, and ultrasonic waves are propagated in the Karman vortex generation region. By detecting the amount of modulation received by the ultrasonic wave from the Karman vortex, the flow velocity of the fluid, and thus the flow rate, is obtained. [0004] In the above-mentioned prior art, when the flow rate of the fluid is reduced, the number of generated Karman vortices becomes extremely small, or the Karman vortices are not generated, so that the flow rate can be measured. There was a risk of disappearing. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vortex flowmeter capable of measuring a flow rate over a wide range from a high flow rate to a very small flow rate. In order to achieve the above object, the present invention provides a vortex generator for generating a Karman vortex in a pipe through which a fluid flows, and interposes a Karman vortex generation region between the vortex generators. In a vortex flowmeter that includes a pair of ultrasonic transceivers opposite to each other and measures the flow rate of the fluid by determining the generation frequency of the Karman vortex by the pair of ultrasonic transceivers, the pair of ultrasonic transceivers , Arranged at a predetermined distance in the flow direction of the fluid, a pair of ultrasonic transceivers respectively transmit,
A switching unit that alternately switches to perform reception is provided, and the ultrasonic propagation time between the pair of ultrasonic transceivers when one of the pair of ultrasonic transceivers performs transmission, and the other performs transmission. In this case, there is provided an auxiliary flow rate detecting means for obtaining an ultrasonic wave propagation time between the pair of ultrasonic transmitter / receivers and calculating a flow rate of the fluid based on the propagation time difference. An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In the figure, a triangular prism-shaped vortex generator 3 for generating a Karman vortex 2 is provided in a tube 1, and the Karman vortex 2 is alternately provided downstream of the vortex generator 3 at a period proportional to the flow velocity. It occurs regularly. Vortex generator 3
Is not limited to a triangular prism, but may be a trapezoidal column or the like. A pair of ultrasonic transceivers (hereinafter, referred to as first and second, respectively, for convenience) are opposed to each other with a Karman vortex 2 generation region (Karman vortex generation region) A therebetween and spaced a predetermined distance in the fluid flow direction B. 4) and 5) are arranged. The first and second ultrasonic transceivers 4 and 5 include:
First and second switches 7 and 8 constituting the switch 6 are connected to each other. A pulse oscillator 9 and an ultrasonic detector 10 are connected to the first and second switches 7 and 8, and the first and second ultrasonic transceivers 4 and 4 are opened and closed by opening and closing operations.
The connection between the pulse generator 5, the pulse oscillator 9, and the ultrasonic detector 10 can be selectively switched. The first switch 7 includes a transceiver-side first fixed contact 7a connected to the first ultrasonic transceiver 4 and an oscillator-side first fixed contact 7b connected to the pulse oscillator 9.
Detector-side first fixed contact 7 connected to ultrasonic detector 10
c, one end of which is connected to the transceiver-side first fixed contact 7a, the other end of which is the oscillator-side first fixed contact 7b, and the detector-side first fixed contact 7b.
And a first movable piece 7d which is switched and connected to the fixed contact 7c. The second switch 8 includes a transceiver-side second fixed contact 8 a connected to the second ultrasonic transceiver 5, an oscillator-side second fixed contact 8 b connected to the pulse oscillator 9,
Detector-side second fixed contact 8 connected to ultrasonic detector 10
c, one end of which is connected to the transceiver-side second fixed contact 8a, the other end of which is the oscillator-side second fixed contact 8b, and the detector-side second fixed contact 8b.
And a second movable piece 8d that is switched and connected to the fixed contact 8c. The first and second movable pieces 7d and 8d are interlocked. A timing signal generator 12 is connected to a switch 6, a pulse oscillator 9, and a propagation time detector 11 to be described later.
Is provided. The timing signal generator 12 outputs a timing signal (hereinafter, referred to as a main timing signal) D.
Is output to the switch 6 so that the first and second
Switches 7 and 8 are opened and closed. When the main timing signal D is at H level, the first and second switches 7 and 8 are in the state shown in FIG. The first ultrasonic transmitter / receiver 4 is connected to the first ultrasonic transmitter / receiver 4 and the second ultrasonic transmitter / receiver 5 is connected to the ultrasonic detector 10, and the first ultrasonic transmitter / receiver 4 is used as a transmitter and the second ultrasonic transmitter / receiver. Device 5 as a receiver,
The transmission and reception of the ultrasonic wave E are performed. When the main timing signal D is at the L level, the first and second movable pieces 7d and 8d are switched, and the pulse oscillator 9 and the second
The first ultrasonic transceiver 4 and the ultrasonic detector 10 and the second ultrasonic transceiver 5 as a transmitter and the first ultrasonic transceiver. 4 is set as a receiver, and transmission and reception of the ultrasonic wave E are performed, respectively. The pulse oscillator 9 oscillates a pulse signal in synchronization with the main timing signal D, and the one set as the transmitter of the first and second ultrasonic transceivers 4 and 5 (see FIG. 1). In this case, the first ultrasonic transceiver 4) is driven, thereby causing the ultrasonic transceiver set as the transmitter to emit ultrasonic waves E (pulses) into the tube 1. In addition, when the main oscillator D receives the main timing signal D, the pulse oscillator 9 outputs a transmission timing signal F to the propagation time detector 11 and the propagation time difference detector (flow rate auxiliary detector) 13. As described above, the ultrasonic wave E radiated from one of the first and second ultrasonic transceivers 4 and 5 set as a transmitter propagates through the tube 1 and then propagates through the other ultrasonic wave. The sound wave is transmitted and received by the ultrasonic wave transmitter / receiver (the second ultrasonic wave transmitter / receiver 5 in the case of FIG. 1) and is input to the ultrasonic wave detector 10 through the switch 6 (the second switch 8 in the case of FIG. 1). The ultrasonic detector 10 receives a signal from the one of the first and second ultrasonic transmitters / receivers 4 and 5 which is set as a receiver via the switch 6 to amplify and input the input signal. The waveform is shaped, and when the value is equal to or larger than a predetermined value, an ultrasonic wave arrival timing signal G indicating that the ultrasonic wave E has arrived.
Is output to the propagation time detector 11 and the propagation time difference detector 13, and the occurrence frequency of the Karman vortex is detected. When the value becomes equal to or lower than a preset reference value, a Karman vortex reduction signal indicating that fact is propagated. Output to the time difference detector 13. The propagation time detector 11 detects the time from the input of the transmission timing signal F to the input of the ultrasonic arrival timing signal G, that is, the time between the first and second ultrasonic transceivers 4 and 5. The ultrasonic wave propagation time T is obtained, the ultrasonic wave propagation time T is made to correspond to the time, a propagation time signal H as shown in the lower part of FIG. 2 is obtained, and this propagation time signal H is output to the measuring unit 14. Here, the Karman vortex 2 is regularly generated in the Karman vortex generation region A, and its generation cycle is proportional to the flow velocity of the fluid. On the line connecting the sound wave transceivers 4 and 5, the direction of the Karman vortex 2 with respect to the propagation direction of the ultrasonic wave E changes according to the generation cycle of the Karman vortex 2. On the other hand, when the propagation direction of the ultrasonic wave E and the direction of the Karman vortex 2 match, the propagation time of the ultrasonic wave E becomes shorter, and when the direction is opposite, the propagation time becomes longer. For this reason, since the magnitude of the ultrasonic wave propagation time T also changes with the generation of the Karman vortex 2, for example, the flow velocity of the fluid and the flow rate thereof can be obtained from the frequency of the propagation time signal H as shown in FIG. The measuring unit 14 calculates the frequency of the input propagation time signal H and measures the flow rate of the fluid. FIG. 2 shows a case where the first and second ultrasonic transceivers 4 and 5 (corresponding signals are indicated by solid lines and thin lines, respectively) alternately transmit and receive. ,
In order to detect the Karman vortex 2, one of the first and second ultrasonic transceivers 4 and 5 may be set as a transmitter.
In this embodiment, the propagation time detector 11 transmits the ultrasonic wave when the first ultrasonic transceiver 4 transmits (shown by a solid line in FIG. 2), that is, when the main timing signal D is at the H level. T is obtained, and a propagation time signal H is obtained as shown in FIG. The propagation time difference detector 13 is an ultrasonic detector 1
The operation starts when a Karman vortex lowering signal is input from 0, and the time from inputting the transmission timing signal F to inputting the ultrasonic arrival timing signal G is measured alternately,
First and second transmissions performed by the first ultrasonic transceiver 4
The ultrasonic propagation time T between the ultrasonic transceivers 4 and 5, and the ultrasonic propagation between the first and second ultrasonic transceivers 4 and 5 when the second ultrasonic transceiver 5 performs transmission. The time T is obtained, the transit time difference is obtained, and the flow rate of the fluid is obtained based on the transit time difference. The determination of the flow rate of the fluid from the difference in the propagation speed is based on the following relationship between the flow speed of the fluid and the propagation speed. That is, when the ultrasonic wave E propagates through the fluid, the propagation speed increases when the ultrasonic wave E moves from the upstream side to the downstream side, and decreases when the ultrasonic wave E moves from the downstream side to the upstream side. The flow rate of the fluid can be obtained from the difference between the propagation speeds because the difference between the two propagation speeds (the difference between the propagation speeds) is proportional to the flow speed. In this embodiment, when the flow rate of the fluid is small and the Karman vortex 2 is not generated, or when the Karman vortex 2 is generated and the measurement cannot be performed,
An output signal from the propagation time difference detector 13 is output as a flow signal. In the vortex flowmeter configured as described above,
When a predetermined number or more of the Karman vortices 2 are generated, the propagation time detector 11 detects the first and second ultrasonic transceivers 4 and 5.
An ultrasonic propagation time T is obtained, a propagation time signal H is obtained, and this propagation time signal H is output to the measuring unit 14. In response, the measuring unit 14 determines the frequency of the propagation time signal H and measures the flow rate of the fluid. In the case where the Karman vortex 2 is not generated or the Karman vortex 2 is reduced, the Karman vortex 2 cannot be measured, and the Karman vortex reduction signal is input from the ultrasonic detector 10. This causes the propagation time difference detector 13 to operate, alternately measures the time from the input of the transmission timing signal F to the input of the ultrasonic arrival timing signal G, and the first ultrasonic transceiver 4 transmits the signal. And the ultrasonic propagation time T when the second ultrasonic transmitter / receiver 5 performs transmission,
The propagation time difference is determined, and the flow rate of the fluid is determined based on the propagation time difference. As described above, when the Karman vortex 2 is not generated or is extremely small, the propagation time difference detector 13
Operates to enable the measurement of the minute flow rate of the fluid, and the flow rate measurement over a wide range from a high flow rate to a minute flow rate can be performed. When the Karman vortex 2 is not generated, since the fluid in the pipe 1 flows in a laminar flow state, the propagation from the first ultrasonic transceiver 4 to the second ultrasonic transceiver 5 is performed. The average flow velocity in the pipe 1 is determined by calculating the time, the difference in the propagation time from the second ultrasonic transmitter / receiver 5 to the first ultrasonic transmitter / receiver 4, and making corrections in consideration of the flow velocity distribution in the laminar flow. You can ask. Since the flow rate is measured by calculating the propagation time difference, it is possible to cancel the influence of the change in sound speed due to a change in temperature or the like. Since the first and second ultrasonic transceivers 4 and 5 used for detecting the Karman vortex 2 perform the flow measurement at a small flow rate so that the Karman vortex 2 is not generated, the apparatus configuration is provided. Can be measured over a wide range from a high flow rate to a minute flow rate without complicating the flow rate. Since the minute flow rate can be measured, it is possible to detect a slight change in the flow rate such as a leak in the pipe 1, and the vortex flow meter can be provided with a leak detection function. In the above embodiment, the ultrasonic wave detector 10 detects the frequency of occurrence of Karman vortices, and outputs a Karman vortex reduction signal when the detected frequency falls below the reference value, thereby activating the propagation time difference detector 13. However, instead of this, the signal amplitude of the Karman vortex is detected, and based on the fact that the value has decreased to a predetermined value or less, the propagation time difference detector 1
3 may be configured to operate. According to the present invention, when a predetermined number or more of Karman vortices are generated, the generation frequency of the Karman vortices is determined based on transmission / reception data of a pair of ultrasonic transceivers. Measures the flow rate, measures the flow rate above the specified flow rate, and if the Karman vortex is no longer generated or the Karman vortex is reduced so that the Karman vortex cannot be measured, the flow assist The detecting means is an ultrasonic propagation time between the pair of ultrasonic transceivers when one of the pair of ultrasonic transceivers transmits, and between the pair of ultrasonic transceivers when the other transmits. Find the ultrasonic propagation time,
Since the flow rate of the fluid is obtained based on the difference in the propagation time and the flow rate can be measured at a minute flow rate, the flow rate can be measured over a wide range from a high flow rate to a very small flow rate. When the Karman vortex is not generated, the fluid in the pipe flows in a laminar state, so that the propagation time from one of the pair of ultrasonic transceivers to the other, the other ultrasonic transceiver, The average flow velocity in the pipe can be obtained by calculating the difference in propagation time from the ultrasonic wave to one of the ultrasonic transceivers and performing correction in consideration of the flow velocity distribution in the laminar flow. Since the flow rate measurement is performed by calculating the propagation time difference, the influence of the change in sound speed due to a change in temperature or the like can be canceled.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing a vortex flowmeter according to an embodiment of the present invention. FIG. 2 is a timing chart showing the operation of the vortex flowmeter. [Description of Signs] 1 tube 2 Karman vortex 3 vortex generator 4 first ultrasonic transceiver 5 second ultrasonic transceiver 6 switch 7 first switch 8 second switch 10 ultrasonic detector 11 Propagation time detector 13 Propagation time difference detector 14 Measurement unit

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-172599 (JP, A) JP-A-4-296622 (JP, A) JP-A-6-34417 (JP, A) JP-A-7- 77442 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01F 1/66 G01F 1/00 G01F 1/32 G01F 7/00 G01F 1/66 101

Claims (1)

(57) [Claims 1] A vortex generator for generating a Karman vortex is provided in a pipe through which a fluid flows, and a pair of ultrasonic transmission / receptions are opposed to each other with a Karman vortex generation region therebetween. A vortex flowmeter for measuring the flow rate of a fluid by determining the frequency of occurrence of the Karman vortex by the pair of ultrasonic transceivers, wherein the pair of ultrasonic transceivers are separated by a predetermined distance in the fluid flow direction. And a pair of ultrasonic transceivers each transmit,
A switching unit that alternately switches to perform reception is provided, and the ultrasonic propagation time between the pair of ultrasonic transceivers when one of the pair of ultrasonic transceivers performs transmission, and the other performs transmission. A vortex flowmeter provided with flow rate auxiliary detection means for determining an ultrasonic propagation time between a pair of ultrasonic transceivers at the time of the transmission and calculating a flow rate of the fluid based on a difference in the propagation time.