1. Field of the Invention
The present invention relates to a wedge and a wedge unit for use in an ultrasonic Doppler flow meter which is mounted (i.e., clamped) on the outer wall of a pipe having a fluid flowing inside thereof, supplying an ultrasonic wave (ultrasound) to the fluid, receives the reflected wave and supplies the reflected wave to a flow rate calculation unit.
2. Description of the Related Art
One of a conventional ultrasonic Doppler flow velocity profile meter is a clamp-on ultrasonic flow meter. The clamp-on ultrasonic flow meter is for measuring a flow rate of a flowing fluid inside a pipe by mounting (i.e., clamping) a material for propagating a wave into the pipe, i.e., a wedge, on a part of the outer circumference of the pipe and emitting the wave into the pipe by way of the wedge. Let it be assumed herein that a fluid is flowing horizontally in the pipe unless otherwise noted.
Clamp-on type ultrasonic flow meters include a propagation time difference and a Doppler method types.
In a propagation time difference-method clamp-on type ultrasonic flow meter, the ultrasonic wave is diagonally injected to the flowing fluid and returned therefrom, thereby measuring the flow rate by the difference in propagation time between the outward and homeward propagations.
While in a Doppler-method clamp-on type ultrasonic flow meter, the velocity of the fluid is measured (i.e., calculated) by that of suspended particles, et cetera, based on the assumption that suspended particles and air bubbles contained in a fluid flow at the same velocity as the fluid. In the Doppler method, an attention is focused on the fact that the frequency of an ultrasonic wave injected into a fluid is changed by the Doppler Effect as a result of being reflected by a suspended particle, and therefore the velocity of the particle is measured by detecting the frequency of the reflected ultrasonic wave.
FIG. 1 shows a configuration of a conventional Doppler-method clamp-on type ultrasonic flow meter.
In FIG. 1, the Doppler-method clamp-on type ultrasonic flow meter for example comprises a wedge 14 on one surface thereof being mounted on a part of the outer circumference of a pipe 31 and on another surface thereof being equipped with an ultrasonic oscillator 13 for generating an ultrasonic wave in response to an electric signal and receiving the reflecting ultrasonic wave back from a fluid within the pipe 31, a transmitter/receiver circuit 12 for generating a pulsed electric signal and supplying the signal to the ultrasonic oscillator 13 for driving it and a flow rate calculation unit (including an amplifier 21, A/D converter 22, velocity profile measurement unit 23, computer 24 and display unit 25).
The transmitter/receiver circuit 12 is, for example, comprised of an oscillator and a pulse generation circuit. The oscillator generates an electric signal having a basic frequency of f0, and the pulse generation circuit outputs a pulsed electric signal at a prescribed interval (i.e., 1/F rpf). The ultrasonic oscillator 13 generates an ultrasonic pulse by application of the pulsed electric signal thereto. The ultrasonic pulse is then transmitted to the pipe 31 by way of the wedge 14.
Note that the basic frequency f0 is essentially a required frequency defined in inverse proportion to the inner diameter of the pipe 31. Also, the ultrasonic pulse is a beam of translatory movement having a pulse width of approximately 5 mm for example.
Meanwhile, the surface of wedge 14 on which the ultrasonic oscillator 13 is mounted is inclined by a certain angle so that the normal line to the surface crosses with the direction of the normal line to the transverse section surface of the pipe 31 at an angle smaller than 90 degrees.
Meanwhile, the ultrasonic oscillator 13 functions as receiver for receiving the echo ultrasonic wave generated by an ultrasonic wave emitted by the ultrasonic oscillator 13 being reflected from a reflecting body suspended in a fluid 32 flowing in the pipe 31, in addition to the function of transmitter.
Such reflecting bodies in the fluid 32 include an air bubble consistently contained in a fluid, a particle such as aluminum particulate, a foreign material having a different acoustic impedance from the fluid subjected to measurement, et cetera.
An operation of the Doppler-method clamp-on type ultrasonic flow meter shown in FIG. 1 is then described as follows.
First, an ultrasonic pulse is injected into the fluid 32 in the pipe 31 from the ultrasonic oscillator 13 by application of a pulsed electric signal thereto, the ultrasonic pulse is reflected by a reflecting body suspended in the fluid 32, is received by the ultrasonic oscillator 13 as an ultrasonic echo, and then converted into an echo electric signal.
The echo electric signal is amplified by the amplifier 21, and the amplified echo electric signal is digitized by the A/D converter 22.
The digitized echo electric signal is then input to the velocity profile measurement unit 23. While FIG. 1 does not delineate clearly, the velocity profile measurement unit 23 receives an electric signal having the basic frequency of f0 from the oscillator of the transmitter/receiver circuit 12, measures velocity changes based on a Doppler shift according to the frequency difference between an echo electric signal and the electric signal having the basic frequency, calculates a velocity profile along the line of measurement in the respective area; and accordingly calculates a flow velocity profile across the transverse section of the pipe 31 by modifying the flow velocity profile calculated for the measurement area with the angle of the above described inclination.
The configuration of the flow rate calculation unit and the transmitter/receiver circuit shown in FIG. 1 is an example, and other types (of transmitter/receiver and calculation unit) are applicable.