JP2011038870A - Ultrasonic flow meter and flow rate measuring method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flow meter which can perform high-precision, stable flow rate measurement by determining a non-resonance condition by determining from a waveform obtained by changing an actual transmission frequency. <P>SOLUTION: The ultrasonic flow meter in an ultrasonic flow rate/flow measuring apparatus having an ultrasonic transmitter/receiver provided on a pipe under measurement includes: a frequency-variable ultrasonic transmitter; a plate-thickness propagation ultrasonic receiver which is provided in the vicinity of or integrally with the frequency-variable ultrasonic transmitter to receive an ultrasonic wave which has been transmitted from the frequency-variable ultrasonic transmitter and has propagated through the plate thickness of the pipe; and a waveform division means which divides a burst or pulse ultrasonic wave which has been oscillated with a preset frequency, has passed through the pipe wall, and has been received into at least three in the time domain. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flowmeter using ultrasonic waves that measures the flow rate of a fluid together with the propagation speed of ultrasonic waves propagating to a tube.

  2. Description of the Related Art An ultrasonic flowmeter that measures flow rate using ultrasonic waves is known. The most widely used principle in ultrasonic flowmeters is the propagation time difference method, which measures the measured flow velocity V of the fluid as a change in the propagation speed of the ultrasonic wave in the fluid, that is, the propagation time difference Δt, The flow rate Q is measured by multiplying the known running water cross section S.

FIG. 4A is a diagram showing a configuration of a general ultrasonic flow meter. In the figure, 1 is a measurement tube through which the measurement fluid FL flows, 2 is an ultrasonic transmitter provided in the measurement tube 1, and 3 is an ultrasonic receiver provided in the measurement tube 1.
4 is an ultrasonic wave propagation material provided between the measurement tube 1 and the ultrasonic transmitter 2, and 5 is an ultrasonic wave propagation material provided between the measurement tube 1 and the ultrasonic receiver 3.

In the above-described configuration, the ultrasonic wave transmitted from the ultrasonic transmitter 2 passes through the ultrasonic wave propagation material 4 and the measurement tube 1 to the ultrasonic wave receiver 3 via the ultrasonic wave propagation material 5 installed to face the ultrasonic wave. And propagate.
In this case, some of the transmitted ultrasonic waves undergo multiple reflection at the boundary between the measurement tube 1 and the measurement fluid FL due to the acoustic impedance, and the multiple reflected waves also propagate to the ultrasonic receiver 3 in the same manner.

In FIG. 4A, when the flow velocity is measured only by the ultrasonic wave a (referred to as a normal wave) propagated to the receiver 3, the flow velocity can be calculated from an ideal refraction angle.
If the refraction angle at this time is θ, the ultrasonic path direction component of the flow velocity V is obtained by V × sin θ.

  On the other hand, since the incident angle to the liquid when the ultrasonic wave b that has caused multiple reflections reaches the ultrasonic receiver 3 is smaller than the incident angle of the normal wave, as a result, as shown in FIG. If the flow velocity is measured by multiple reflected waves, the incident angle θ is smaller than that of the normal wave, and therefore the flow velocity measured by the multiple reflected waves is estimated to be lower than that of the normal wave.

  These received waves are observed as shown in FIG. 4 (c). When the flow velocity is obtained from the correlation between both waves using the correlation method, the normal wave and the multiple reflection are shown in FIG. 4 (b). A wave superposition error (minus error) E occurs.

Such an error can be achieved by limiting the sampling window to only the normal wave if the normal wave and the multiple wave are completely separable on the time axis. Thus, separation such as detecting only the wave that reaches first on the time axis becomes difficult.
Since the measured flow velocity is determined in proportion to the propagation time difference Δt of the ultrasonic pulse in the fluid, if the average flow velocity is υ and the proportional coefficient between the measured flow velocity V and the propagation time difference Δt is kt, the flow rate Q is expressed by the following equation: Can do.
Q = υ · S = (V / k) · S
= (Kt · Δt / k) · S

  The ultrasonic transducer mounting method for transmitting and receiving ultrasonic waves based on such a principle includes a V method in which an ultrasonic pulse is once reflected on the inner surface of a measurement tube, a Z method in which an ultrasonic pulse is transmitted over one diameter, and the like. There is.

  In the ultrasonic flowmeter that receives the reflection signal from the particles and bubbles in FIG. 5A and obtains the flow velocity distribution based on the received signal, the flow velocity detected by the normal wave a propagating in the measurement tube 1. FIG. 5 (b) is a diagram showing a flow velocity distribution synthesized with a normal wave and a multiple wave, and shows a flow velocity distribution of only the normal wave to be originally detected. Indicates a state in which an error occurs.

Thus, if there is multiple reflection inside the material of the pipe, a problem arises in accuracy. For example, in the measurement using the transmission method, the propagation path of the received waveform is shifted, causing an error in the measured value, or misjudging a multiplexed wave as a normal wave (wave to be detected) and causing a large error.
In the reflection method, a similar phenomenon causes a flow velocity profile observed with multiple waves to be superimposed on a flow velocity profile observed with normal waves to form an incorrect flow velocity profile.

From the above contents, it is necessary to prevent multiple waves from being generated as much as possible inside the pipe. This multiple wave is known to increase when the frequency of the ultrasonic wave satisfies the resonance condition consisting of the speed of sound of the pipe material, the plate thickness, and the incident angle of the ultrasonic wave. Therefore, in order to avoid the resonance condition, it is desirable to change the transmission frequency of the ultrasonic wave to be a non-resonance condition.
In order to obtain this non-resonant condition, the resonance frequency is calculated based on the information on the sound speed and the thickness of the pipe.

JP 2006-220534 A JP 2006-250666 A JP-A-2-260532

  In order to obtain the non-resonant frequency, it is necessary to know the thickness and speed of sound. Generally, an ultrasonic thickness meter is used for the thickness, but the sound speed in this case is generally a sound speed (fixed value) stored in a database. In practice, the speed of sound differs depending on the manufacturing method, subtle material differences, and piping depending on the temperature, and there is a problem that there is a difference from the generally known sound speed.

For this reason, it is difficult to obtain accurate non-resonance conditions, and incorrect settings may be made.
In addition, there is a problem that a material whose sound speed is unknown (not present in the database) cannot be handled.
Accordingly, an object of the present invention is to realize an ultrasonic flowmeter capable of measuring a flow rate with high accuracy and stability by determining non-resonance conditions by determining from a waveform obtained by changing an actual transmission frequency. Yes.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In an ultrasonic flow velocity / flow rate measuring device equipped with an ultrasonic transmitter / receiver provided in a measurement tube,
Thickness to receive a frequency variable ultrasonic transmitter and an ultrasonic wave transmitted from the variable frequency ultrasonic transmitter provided near or integrally with the variable frequency ultrasonic transmitter through the thickness of the pipe. Providing a propagation ultrasonic receiver and a waveform dividing means for dividing a burst or pulsed ultrasonic wave oscillated at a frequency of an initial setting value and propagated through a pipe wall into at least three parts in a time domain. Features.

The invention of claim 2
In an ultrasonic flow velocity / flow rate measuring device equipped with an ultrasonic transmitter / receiver provided in a measurement tube,
Thickness to receive a frequency variable ultrasonic transmitter and an ultrasonic wave transmitted from the variable frequency ultrasonic transmitter provided near or integrally with the variable frequency ultrasonic transmitter through the thickness of the pipe. A propagation ultrasonic receiver, and a waveform dividing means for dividing a burst or pulsed ultrasonic wave oscillated at a frequency of an initial setting value and propagated through a pipe wall into at least three parts in a time domain,
1) The waveform dividing means receives means of an ultrasonic wave emitted from a frequency variable ultrasonic transmitter and propagated through a pipe thickness, and calculates the amplitude of each of at least three areas divided by the waveform dividing means. And changing the oscillation frequency so that the ratio of the amplitude becomes a predetermined value;
2) a step of changing the oscillation frequency so that the ratio of the amplitude An of the nth reflected wave to the amplitude An + 1 of the (n + 1) th reflected wave, and the amplitude An + 2 of the n + 2nd reflected wave is maximized or minimized;
3) It includes a step of measuring a flow velocity at a frequency determined by the step 1) or 2).

According to claims 1 and 2 of the present invention, there are the following effects.
Since the non-resonance condition can be determined and determined from the waveform obtained by changing the actual transmission frequency, an ultrasonic flowmeter capable of highly accurate and stable flow velocity measurement can be realized.

It is the principal part section lineblock diagram and flowchart which show an example of the embodiment of the present invention. It is explanatory drawing which shows the relationship between time and amplitude in a resonant frequency and a non-resonant frequency. It is a block diagram which shows another Example. It is a block diagram and an operation principle diagram of an ultrasonic flowmeter showing a conventional example. It is explanatory drawing which shows the comparison with the true flow velocity distribution profile in resonance conditions and non-resonance conditions.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram (a) and a flowchart (b) of an ultrasonic flowmeter showing an embodiment of the present invention.

  In FIG. 1A, 2 is fixed to the outer periphery of the measurement tube 1 and transmits ultrasonic waves from an oscillation element (not shown) to the fluid flowing in the measurement tube 1 through the ultrasonic wave propagation material 7a. This is a variable frequency ultrasonic transmitter. Although not shown in the figure, the ultrasonic wave emitted from the variable frequency ultrasonic transmitter propagates to an ultrasonic receiver that is installed facing the downstream side. In the case of the reflective type, a variable frequency ultrasonic transmitter / receiver is used instead of the variable frequency ultrasonic transmitter, and in that case, no ultrasonic receiver is required.

A receiving plate thickness propagation ultrasonic receiver 6 is provided at an angle at which only the ultrasonic wave propagating the plate thickness can be received.
The ultrasonic transmitter 2 has a low Q and can be oscillated by changing the frequency within a specific range in combination with an oscillation circuit (not shown) that can change the frequency. The transmission waveform is a burst wave of several shots and has a width that can interfere with time to some extent (for example, a wave of about 3 to 5 bursts is oscillated at 1 MHz).

  The ultrasonic wave propagation member 7b of the plate thickness propagation ultrasonic receiver transmits the vibration propagated through the plate thickness of the pipe to a receiving element (not shown). The received signal is divided into three parts in the time domain based on the sound velocity, plate thickness, and incident angle of the pipe material previously input as approximate values by a time division unit (not shown).

FIG. 1B is a flowchart for determining the non-resonant frequency by receiving the frequency at which the ultrasonic wave emitted from the ultrasonic transmitter 2 is multiple-reflected by the plate thickness of the measurement tube 1 by the plate thickness propagation ultrasonic receiver 6. is there.
This will be described according to the flow.

The ultrasonic wave generated by the transmission circuit (S1) enters the measurement tube (S3) through the transmission element (S2).
Here, the multiplexed wave propagating through the plate thickness of the measuring tube is received by the receiving element (S4) of the plate thickness propagation ultrasonic receiver, and AD (S6) conversion is performed via the receiving circuit (S5), and the piping parameters and the incident are previously entered. This is divided by the time width calculated by the angle, the amplitude in each area is obtained by the amplitude measuring means, the waveform area is divided using the piping parameters obtained in advance by the dividing means (S7), and the result is subjected to the amplitude determination. It is determined whether or not a non-resonant frequency is transmitted in the program (S8).

  When the amplitude is large in all three divided regions, the resonance frequency is used, for example, NO. When 2 is small, the phase when the multiple reflection occurs once is NO. This state is opposite to the first wave (direct wave) and becomes smaller because they cancel each other, so this state is determined as a non-resonant frequency that is reversed from the non-resonant frequency.

  2A and 2B are explanatory diagrams showing the relationship between time and amplitude at the resonance frequency and the non-resonance frequency. In FIG. 2A, the region divided into three by the waveform dividing means is the region An considered as the nth reflected wave, the region An + 1 considered as the n + 1th reflected wave, and the region considered as the n + 2th reflected wave, respectively. It is named An + 2, and the amplitude is obtained by digital processing from the envelope in each region.

Here, as shown in FIG. 1, the time division width (tw) is the pipe plate thickness (t), the incident angle to the pipe (θs), the refraction angle at the pipe (θp), and the sound velocity of the pipe (Vp). )
tw = 2t / cos θp / Vp
The value is based on.

When the amplitude is obtained, the frequency is changed and the amplitude is obtained by the same method. This is repeated in a certain frequency range.
Next, as shown in FIG. 2B, by looking at the amplitudes in the region, a frequency in which the amplitude becomes extremely small due to interference in the non-resonant condition is specified as a frequency having the resonance condition. From this, the non-resonant condition can be regarded as a change in amplitude. In addition, when the amplitude in all the divided regions is large, the resonance condition is satisfied. Therefore, the m-th (m is an integer) resonance condition and the m + 1-order resonance condition are determined, and the intermediate frequency is determined as the non-resonance condition. It is also possible.

According to the above, it is possible to know the non-resonant condition without clearly knowing the speed of sound. In addition, since ultrasonic plate thickness meters generally measure the time by transmitting and receiving short pulses, transmission / reception elements and circuits with a frequency higher than the frequency used in ultrasonic flow meters are required, and the plate thickness is thick. Although it is difficult to measure with high accuracy only by piping, the wavelength may be long because interference is used here, and the frequency may be as high as that used in an ultrasonic flowmeter.
In addition, the plate | board thickness propagation ultrasonic receiver 6 used for this invention can be easily added to the conventional ultrasonic flowmeter.

  FIGS. 3A and 3B show another embodiment of the plate thickness propagation ultrasonic receiver. 3 (a) shows a single ultrasonic wave propagation material 4a attached with an ultrasonic transmitter 2 and a plate thickness propagation ultrasonic wave receiver 6, and FIG. 3 (b) shows a single ultrasonic wave propagation. An ultrasonic transmitter and a plate thickness propagation ultrasonic receiver 2a are attached to the material 4b.

That is, by devising the reflection angle, multiple reflections can be received even by one ultrasonic wave propagation material (transmission / reception element). In short, it is only necessary to measure a plurality of multiple reflected waves propagating through the pipe thickness.
In the present invention, the case of obtaining the non-resonant frequency has been described. However, for example, the resonance frequency (in which the amplitude is increased in the multiple interference region) is obtained in order to increase the signal strength in order to increase the sensitivity even at the expense of accuracy. May be.

The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

1 Measurement Tube 2 Ultrasonic Transmitter 3 Ultrasonic Receiver 4, 5, 7 Ultrasonic Propagation Material 6 Plate Thickness Propagation Ultrasonic Receiver

Claims (2)

In an ultrasonic flow velocity / flow rate measuring device equipped with an ultrasonic transmitter / receiver provided in a measurement tube,
Thickness to receive a frequency variable ultrasonic transmitter and an ultrasonic wave transmitted from the variable frequency ultrasonic transmitter provided near or integrally with the variable frequency ultrasonic transmitter through the thickness of the pipe. Providing a propagation ultrasonic receiver and a waveform dividing means for dividing a burst or pulsed ultrasonic wave oscillated at a frequency of an initial setting value and propagated through a pipe wall into at least three parts in a time domain. The characteristic ultrasonic flowmeter. In an ultrasonic flow velocity / flow rate measuring device equipped with an ultrasonic transmitter / receiver provided in a measurement tube,
Thickness to receive a frequency variable ultrasonic transmitter and an ultrasonic wave transmitted from the variable frequency ultrasonic transmitter provided near or integrally with the variable frequency ultrasonic transmitter through the thickness of the pipe. A propagation ultrasonic receiver, and a waveform dividing means for dividing a burst or pulsed ultrasonic wave oscillated at a frequency of an initial setting value and propagated through a pipe wall into at least three parts in a time domain,
1) The waveform dividing means receives means of an ultrasonic wave emitted from a frequency variable ultrasonic transmitter and propagated through a pipe thickness, and calculates the amplitude of each of at least three areas divided by the waveform dividing means. And changing the oscillation frequency so that the ratio of the amplitude becomes a predetermined value;
2) a step of changing the oscillation frequency so that the ratio of the amplitude An of the nth reflected wave to the amplitude An + 1 of the (n + 1) th reflected wave, and the amplitude An + 2 of the n + 2nd reflected wave is maximized or minimized;
3) A method for measuring a flow rate of an ultrasonic flowmeter, comprising the step of measuring a flow rate at a frequency determined by the step 1) or 2).

Images