JP3386334B2 - Ultrasonic vortex flowmeter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter for calculating the flow rate of a measurement fluid flowing in a flow path by using an ultrasonic signal whose propagation time is changed by a Karman vortex, and more particularly to this ultrasonic signal. The present invention relates to an ultrasonic vortex flowmeter improved so as to effectively remove noise superimposed on the vortex and output a stable vortex signal.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a structure of a converter of a conventional vortex flowmeter of this type. This configuration is disclosed, for example, in Japanese Utility Model Publication No. 6-26814. Therefore, as a conventional technique, an outline of relevant parts in the technique disclosed herein will be described below.

In a detector (not shown), a column-shaped vortex generator is inserted in the center of the measuring pipe through which the measuring fluid flows, and the measuring fluid becomes a vortex generating body corresponding to the Karman vortex generated by passing over the vortex generating body. The number of Karman vortices is detected as the generated stress by a pair of piezoelectric elements fixed to the vortex generator as a change in charge.

In FIG. 7, one piezoelectric element 10 is shown for simplicity.
Charge Q generated by Karman vortex at _VWhen the
The configuration on the converter side is shown. This charge Q_VIs charged
The voltage is converted into a voltage by the converter 11 and the vortex signal S_V0Out as
Output to the rectifier circuit 13 after being amplified by the amplifier 12.
Be done.

The rectifier circuit 13 rectifies this signal and outputs it as a direct current vortex signal S _A1 to one end of the input of the comparator 14 which functions as noise discrimination means in the next stage. The vortex signal S _A1 is a value that depends on the amplitude of the vortex, and is given by the following equation (1), where K _A1 is a constant, ρ is the density, and f _V is the vortex frequency. S _A1 = K _A1 ρf _V ² (1)

On the other hand, the vortex signal S _V0 is supplied to the low-pass filter 15
Is output to the output terminal of the filter and is output as an AC vortex signal S _V1 to the output end of the filter. This vortex signal S _V1
Also depends on its amplitude, but changes to SIN-like in response to the Karman vortex generated by the vortex generator.

If K _V1 is a constant, this vortex signal S _V1 is given by the following equation: S _V1 = K _V1 ρf _V ² sin2πft (2) Then, this vortex signal S _V1 is transmitted to the amplifier 1
It is amplified by 6 and output to the Schmitt trigger 17.

Here, the Schmitt trigger 17
This vortex signal S with the width ΔH as the boundary _V1Is the vortex pulse P_VTo
It is converted and output to the gate circuit 18. Furthermore, this vortex
Pulse P_VIs converted to the amplitude of the vortex by the frequency / voltage converter 19.
Is irrelevant and the vortex frequency f_VAnalog vortex signal S corresponding to
_V2Is converted to and output to the other input terminal of the comparator 14.
To be done.

The vortex signal S _{V2 in} this case is expressed by the following equation, where K _V2 is a constant: S _V2 = K _V2 f _V (3) Then, the comparator 14 outputs the vortex signal S _A1 output from the rectifier circuit 13 and the frequency / voltage converter 19
The output of S _V2 is compared.

As a result of the comparison, when the relationship of S _A1 <S _V2 is established, this vortex frequency f _V is discriminated not to be actually caused by the vortex but due to noise, and the off signal S
Outputs _off to the gate circuit 18 to output the Schmitt trigger 17
Turn off the output of. When the relationship of S _A1 > S _V2 is established, the switch of the gate circuit 18 is turned on and the vortex pulse P _V is output.

Next, the operation of the above circuit will be described with reference to the characteristic diagram shown in FIG. In FIG. 8, the horizontal axis represents the vortex frequency f _V , and the vertical axis represents the vortex signals S _A1 and S _V2 . In this case, the constants K _A1 and K _{V2 in the} equations (1) and (3) are the amplifier 1
At the point Z where the vortex signal appearing at the output of 6 has reached the magnitude corresponding to the trigger level S _T of the Schmitt trigger 17, the vortex signal S
_A1 and S _V2 are selected to be equal. And
The value of the trigger level S _T at this time is selected as the magnitude of the vortex signal corresponding to the lower limit of the measured flow velocity.

When the constants K _A1 and K _V2 are selected as described above, when the measured flow rate Q _M is flowing and the flow velocity in the measurement range equal to or lower than the lower limit of the measurement flow velocity is as shown in FIG.
As can be seen from the above, S _A1 > S _V2 , and the comparator 14 outputs the vortex pulse P _V measured by turning on the switch of the gate circuit 18.

On the other hand, even if a large noise is generated due to, for example, pipe vibration when the measured flow rate Q _M is zero, this is not due to the measured flow rate Q _M , so the density ρ in the equation (1) is Lacking the coefficient of S _A1 <
It becomes S _V2 . Therefore, an OFF signal is output from the output terminal of the comparator 14, the switch of the gate circuit 18 is turned off, and no pulse is output from the gate circuit 18.

As described above, the comparator 14 functioning as a noise discrimination means discriminates between the pulse signal due to the vortex signal and the pulse signal due to the noise, and in the case of the pulse due to the noise, this can be removed.

[0015]

However, since the vortex flowmeter as described above uses the piezoelectric element as the vortex detecting element, the relationship between the amplitude A of the vortex signal and the flow velocity V is A∝ρV ² (4 ).

Since the magnitude of the vortex signal actually changes depending on the diameter D, the amplitude A is represented by A∝ρV ² S (D) (5) with S as a function symbol.

Therefore, when the density ρ and the aperture D are different, the noise discrimination curves are different from each other, so that there is an inconvenience that a corresponding number of noise discrimination curves are required, and the density ρ Since a fixed value is used, there is a problem that an accurate amplitude A cannot be obtained, and noise discrimination becomes inaccurate.

[0018]

In order to solve the above-mentioned problems, the present invention calculates the flow rate of a measuring fluid flowing in a flow path using an ultrasonic signal modulated by a Karman vortex and calculates the vortex. In the ultrasonic vortex flowmeter that outputs as a flow rate signal, a modulation coefficient calculation means for calculating a modulation coefficient obtained in relation to the ratio of the phase shift amount of the ultrasonic signal and the vortex frequency, and Whether the preceding modulation coefficient falls between the lower limit of allowable phase shift and the upper limit of phase shift relative to the previous vortex frequency. Noise determining means for determining whether or not the vortex flow rate signal is output when the modulation coefficient is between the allowable lower limit value and the allowable upper limit value, and the allowable lower limit value and the allowable upper limit value are output. Output permission hand that cuts the previous output when it is not between It is obtained so as to comprise and.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of the overall configuration of an embodiment of the present invention. In this case, the configuration of the ultrasonic vortex flowmeter of the type in which the flow rate of the measurement fluid is calculated by detecting the change in the propagation time obtained by radiating the ultrasonic wave as a burst wave to the vortex is shown.

In this type of ultrasonic vortex flowmeter which restores vortices using burst waves, ultrasonic waves are intermittently sent and received as compared with the case where vortices are restored using continuous waves. When the ultrasonic wave is transmitted from the ultrasonic wave transmitter to the measurement fluid, there is an advantage that the noise reaching the ultrasonic wave receiver via the metallic measuring conduit can be separated and removed.

FIG. 2 is a waveform diagram for explaining the operation of the configuration shown in FIG. Hereinafter, an outline of the entire configuration will be first described with reference to the waveform diagram shown in FIG. 2 as appropriate. The reference clock circuit 20 outputs the reference clock CL ₁ to the drive circuit 21 and the timing circuit 22, respectively. Timing circuit 2
2 outputs a timing signal TG ₁ for transmitting a burst wave to the drive circuit 21.

The timing circuit 22 also sends a sampling signal S _P1 for sampling the ultrasonic signal, a timing signal S _P2 for sampling and holding the ultrasonic signal, and the like.

The drive circuit 21 outputs the reference clock CL ₁ to 1 /
A clock CL ₂ (FIG. 2A) divided by _{2 is} generated and a drive signal DS ₂ (FIG. 2A) is generated by a timing signal TG ₁ .
A burst-wave drive signal DS ₂ for controlling the repetition period t ₁ of the burst wave is applied to the ultrasonic transmitter 23.

The repetition cycle t ₁ of the burst wave is set shorter than the vortex generation cycle because it is necessary to restore the vortex signal, and the clock CL ₂ is halved from the reference clock CL _{1 because of the} relationship of forming the reference wave signal. The frequency is divided.

The piezoelectric element of the ultrasonic transmitter 23 causes a voltage / distortion conversion by applying a drive signal DS _{2 in the form} of a burst wave,
Ultrasonic waves are sent into the measurement fluid filled inside the measurement conduit 24.

This ultrasonic wave is phase-modulated by the Karman vortex generated by the vortex generator 25, is received by the ultrasonic receiver 26, and is further output to the amplifier 27 as an ultrasonic signal S _U3 (FIG. 4 (B)). Here, the gain is adjusted by a gain adjustment value G _V by a variable resistor or the like and output to the pulsing circuit 28.

In addition, in the ultrasonic signal S _U3 shown in FIG. 2B, in addition to the main waveform that captures the Karman vortex, the measurement line 2
4 appears as a waveform that is multiple-reflected or a waveform on which reverberation waves are superimposed.

[0028] In the gain adjustment ultrasonic signal S _U3 are using a variable resistor or the like predetermined threshold S _h (see FIG. 2 (B)) pulsing circuit 28 is set, pulses the threshold S _h as a reference And is output to the sampling circuit 29 as an ultrasonic signal S _U4 (FIG. 2 (C)).

The sampling circuit 29 is repeatedly given the sampling signal S _P1 (FIG. 2 (D)) from the timing circuit 22 with a predetermined delay with respect to the transmission of the burst wave. The sampling signal S _P1 As a result, the ultrasonic signal S _U4 (FIG. 2 (C)) is sampled each time and output to the phase detection circuit 30.

On the other hand, to the reference wave circuit 31, the reference clock CL ₁ is applied from the reference clock circuit 20, and the reference wave signal S _R is phased from the reference wave circuit 31 with a predetermined delay with respect to the transmission of the burst wave. It is output to the detection circuit 30.

Here, for the sake of simplicity, the reference wave signal S _R is explained as a single signal, but the phase shift of the multi-reference type in which the phase shift due to the vortex is detected for each phase using a plurality of reference waves is detected. The same can be applied to.

Then, the phase detection circuit 30 phase-detects the ultrasonic signal S _U5 (FIG. 2 (E)) output from the sampling circuit 29 based on this reference wave signal S _R ,
It is output to the sample hold circuit 32.

The sample and hold circuit 32 samples the output of the phase detection circuit 30 by the sampling signal S _P2 sent from the timing circuit 22 and smoothes it, then
The vortex signal is reproduced as a staircase waveform by holding each sampling period and output to the filter 33.

The filter 33 is a Schmitt trigger circuit 34.
The filter signal to the Schmitt trigger circuit 34.
Outputs the vortex waveform reproducing the Karman vortex obtained at the output end of the filter 33 to the counter 35 as a pulse-shaped waveform with a predetermined threshold as a reference.

The counter 35 converts the pulse signal reproducing the vortex into a digital vortex signal f _u and outputs the digital vortex signal f _u to the microcomputer 36. The microcomputer 36 performs a predetermined calculation and outputs it to the output end 37.

Further, the filter 33 is output to the amplitude / frequency conversion circuit 38, and the amplitude / frequency conversion circuit 38 converts the vortex signal obtained at the output end of the filter 33 into a frequency f _VD corresponding to the amplitude thereof, and a microcomputer. Output to 36.

The microcomputer 36 has a processor CPU, a memory MEM and the like, and executes various functions such as generation of a timing signal, control of output and calculation, as well as calculation processing of a flow rate signal.

[0038] The flow velocity v of the fluid to be measured, since the constant K is stored in the memory MEM, v = Kf microcomputer 36 as _u (6) can be a calculation using the same.

Further, the microcomputer 36 is supplied with the reference clock CL ₁ from the reference clock circuit 20 and operates on the basis of this reference clock CL ₁ .
The timing circuit 22 shown in FIG. 1 includes control signals CS ₁ and C ₁ .
By transmitting S ₂ and receiving the reception signal RS, the sound velocity C propagating in the measurement fluid is calculated to calculate an appropriate sampling position. This point will be described later in detail with reference to FIGS. 3 and 4.

Further, the microcomputer 36 uses the sound velocity C and the frequency f _VD corresponding to the amplitude of the vortex signal to perform noise discrimination based on the arithmetic procedure built in the memory MEM, and as a result, noise is present. If so, the output is cut, which will be described later in detail with reference to the flowchart shown in FIG.

First, calculation of sound velocity C and sampling signal S
The holding of _{P1 at} the optimum position will be described with reference to FIGS. The timing circuit 22 shown in FIG.
8, a counter 39, a gate generation circuit 40, etc., and a control signal CS ₁ for controlling the frequency division ratio of the frequency dividing circuit 38 and a control signal CS ₂ for controlling the sampling signal S _P1 from the microcomputer 36. Has been entered.

The reference clock CL ₁ is input from the reference clock circuit 20 to the frequency dividing circuit 38, and the control signal CS ₁
The timing signal TG ₁ (FIG. 4 (A)) for transmitting the burst wave, which is frequency-divided according to the frequency division ratio determined by, is transmitted to the drive circuit 21 to generate the drive signal DS ₂ (FIG. 4 (B)). )) Is sent to the ultrasonic transmitter 23.

The counter 39 uses the timing signal TG.
Reference clock CL _1, which is input in synchronization with the _first rising
Counting is started and the ultrasonic signal S _U4 (FIG. 4C) is received, the count value n is sent from the output end Q to the microcomputer 36 as a reception signal RS.

Assuming that the diameter of the measuring conduit 24 is D and the frequency of the reference clock CL ₁ is f ₀ , the processor CPU
Can calculate the sound velocity C using the arithmetic expression C = D / (n / f ₀ ) (7) built in the memory MEM.

Using the sound velocity C thus obtained, the processor CPU calculates the time when the sampling signal S _{P1 rises} according to the calculation procedure built in the memory MEM, and uses this as the preset set value PS. The control signal CS ₂ to be set is sent to the gate generation circuit 40. The preset set value PS is set so as to reach a predetermined wave number after receiving the sampling signal S _P1 .

The gate generation circuit 40 uses the timing signal TG.
Reference clock CL _1, which is input in synchronization with the _first rising
When the preset preset value PS is reached and the preset preset value PS is reached, the sampling signal S _P1 (FIG. 4 (D)) having the preset gate width is sent from the output terminal Q thereof.

Since the sound velocity C is measured and the position of the sampling signal S _P1 is set accurately in this way, even if the sound velocity changes greatly, the vortex signal may be missed due to the deviation of the gate position. There is no such thing.

Next, noise discrimination will be described with reference to the flowchart shown in FIG. First, step 1 will be described. Step 1 is a step which functions as a modulation coefficient calculation means for calculating the modulation coefficient m.

The ultrasonic signal sent from the ultrasonic transmitter 23 is phase-modulated by the Karman vortex and is received as the ultrasonic signal S _U3 by the amplifier 27 via the ultrasonic receiver 26, which is the sampling circuit 29. , Phase detection circuit 30,
It is demodulated by the sample hold circuit 32 and the filter 33.

In this case, the modulation index Φ indicating the degree of modulation
Is theoretically expressed as Φ = Dvmω / C ² with m as a modulation coefficient. Here, ω is the angular frequency of the ultrasonic signal.

When modified, the modulation coefficient m is represented by m = Φ / [Dvω / C ² ] (8).

Since the modulation index Φ is proportional to the frequency f _VD corresponding to the amplitude of the vortex signal, Φ = K _D f _VD (9) where the proportional constant is K _D.

Therefore, using equations (8) and (9),
The modulation coefficient m is m = K _D f _VD / [Dvω / C ² ] (10).

Here, the diameter D, the angular frequency ω, the proportional constant K
_D is preset in the memory MEM, the sound velocity C is calculated by the equation (7), and the flow velocity v is calculated by the equation (6). Therefore, the processor CPU can calculate the modulation coefficient m using these. . The numerator of the equation (10) is related to the phase shift because the vortex has a frequency f _VD corresponding to the amplitude of the vortex signal obtained by the modulation, and the denominator is related to the vortex frequency.

Then, the process proceeds to step 2. Step two
Is a step that functions as noise discrimination means. The modulation coefficient m is the allowable lower limit value NJ1 and the allowable upper limit value N for noise discrimination.
It is determined whether or not it is between J2.

Here, the allowable lower limit value NJ1 is an allowable lower limit value when the phase shift becomes relatively small with respect to the vortex frequency, and it is assumed that noise such as pulsation is mixed in. .

The allowable upper limit value NJ2 is an allowable upper limit value when the phase shift becomes relatively large with respect to the vortex frequency, and it is assumed that a large amount of bubbles are mixed in, for example.

The permissible lower limit value NJ1 and the permissible upper limit value NJ2 are stored in advance in the memory MEM, and the processor CPU uses these values to execute step 2
Make the judgment.

Steps 3 and 4 function as output permission means. The modulation coefficient m is the allowable lower limit value NJ1 and the allowable upper limit value NJ.
If it is between 2 and 2, the process proceeds to step 3 to permit the output, and if not, the process proceeds to step 4 to cut the output.

After executing these steps, the process proceeds to step 6 and then returns to step 1 (RTS),
Repeat these. The above calculation procedure is performed in advance in the memory MEM.
Stored in the CPU, and the processor CPU executes an operation by using this.

FIG. 6 is an explanatory diagram showing the relationship between the vortex signal region and the noise region when the horizontal axis represents the flow velocity v and the vertical axis represents the modulation coefficient m. As shown in FIG. 6, the allowable lower limit value NJ1 and the allowable upper limit value NJ2 are constant regardless of the flow velocity v, and the diameter D
Since it is not necessary to set a noise discrimination curve for each of them and it does not depend on the density ρ, noise discrimination becomes easy.

[0062]

As described above in detail with the embodiments, according to the invention described in claims 1 and 2, the microprocessor calculates the modulation coefficient in consideration of the aperture, the flow velocity, and the sound velocity. , This is used for noise discrimination, so there is no need to prepare multiple noise discrimination curves,
Therefore, there is an advantage that noise discrimination is easy and accurate.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating the operation of the embodiment shown in FIG.

FIG. 3 is a block diagram specifically illustrating a part of the embodiment shown in FIG.

FIG. 4 is a waveform diagram illustrating the operation of the configuration shown in FIG.

FIG. 5 is a flow chart illustrating a main part of the embodiment shown in FIG.

FIG. 6 is a characteristic diagram for explaining noise discrimination of the embodiment shown in FIG.

FIG. 7 is a block diagram showing a configuration of a conventional vortex flowmeter.

8 is a characteristic diagram illustrating characteristics of the vortex flowmeter shown in FIG.

[Explanation of symbols]

10 Piezoelectric element 11 Charge converter 14 Comparator 17 Schmitt trigger 18 gate circuit 19 Frequency / voltage converter 20 Reference clock circuit 21 Drive circuit 22 Timing circuit 23 Ultrasonic transmitter 24 measuring lines 25 Vortex generator 26 Ultrasonic receiver 28 pulse circuit 29 Sampling circuit 30 Phase detection circuit 31 Reference wave circuit 32 sample and hold circuit 34 Schmitt trigger 36 Microcomputer 38 frequency divider 39 counter 40 gate generation circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masami Wada 2-9-32 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Co., Ltd. (56) Reference JP-A-5-172599 (JP, A) 6-26814 (JP, Y2) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (2)

(57) [Claims] 1. An ultrasonic vortex flowmeter for calculating a flow rate of a measurement fluid flowing in a flow path using an ultrasonic signal modulated by a Karman vortex and outputting the vortex flow rate signal, wherein a phase shift of the ultrasonic signal is performed. Modulation coefficient calculating means for calculating a modulation coefficient obtained in relation to the ratio between the amount and the vortex frequency, and the allowable lower limit value and the vortex frequency when the phase shift amount becomes relatively small with respect to the vortex frequency. On the other hand, noise determining means for determining whether or not the modulation coefficient falls between the allowable upper limit value and the allowable upper limit value when the phase shift amount becomes relatively large, and the modulation coefficient is the allowable lower limit value and the allowable upper limit value. And an output permission unit that cuts the output when the vortex flow rate signal is output when the vortex flow rate signal is between the allowable lower limit value and the allowable upper limit value. Total. 2. The modulation coefficient m is f _VD which is a frequency corresponding to the amplitude of a vortex signal subjected to a phase shift, D is a diameter, v is a flow velocity,
The angular frequency of the ultrasound signal _{ω, mαf VD / [Dvω /} C 2] becomes ultrasonic flowmeter according to claim 1, wherein the calculating the relationship when the speed of sound with C.