JPH063384B2 - Ultrasonic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a propagation time difference of ultrasonic waves radiated in a forward direction and a reverse direction with respect to a flow of a fluid to be measured by a transducer provided in a conduit. The present invention relates to an ultrasonic flowmeter for measuring the flow rate of a fluid to be measured, and more particularly to an ultrasonic flowmeter improved to measure the flow rates of various fluids having different sonic speeds.

<Prior Art> Japanese Patent Application No. 59-18873 (Title of Invention: Ultrasonic Flowmeter) has been proposed as a conventional ultrasonic flowmeter of this type. The summary of the proposed contents is as follows. First, the speed of sound propagating in the fluid to be measured is calculated by a predetermined arithmetic expression based on a predetermined specific gravity of the fluid to be measured and the measured temperature of the fluid to be measured. Next, based on this calculated sound velocity, ultrasonic waves are incident on the pipe from the fluid to be measured based on Snell's law established between the transducer and the pipe and the fluid to be measured and the binding condition established between the transducer. The incident angle is calculated and the correction coefficient is calculated. Therefore, the flow rate is corrected for the flow rate measured from the propagation time difference using this correction coefficient.
In this way, the flow rates of fluids having different sonic speeds, such as various oils, are measured as accurately as possible.

<Problems to be Solved by the Invention> However, in such an ultrasonic flowmeter, if the specific gravity of the fluid to be measured is different, the estimated value of the sound velocity is different, and the sound velocity cannot be determined only by the temperature and the specific gravity. There is a problem that the correct flow rate cannot be obtained even if the correction is performed.

<Means for Solving Problems> In order to solve the above problems and to accurately measure the flow rate even with measured fluids having different sonic velocities, the present invention relates to the flow velocity direction of the measured fluid in a pipe and Is a flow rate calculation means for calculating the flow rate of the fluid to be measured using the time difference of the ultrasonic waves radiated through the shoe and the transducer fixed in the reverse direction and the temperature of the shoe. The sound velocity calculation means that calculates the sound velocity of the shoe and the pipe by a predetermined calculation formula, and the total propagation time of the ultrasonic propagation path estimated from this sound velocity, the estimated sound velocity of the fluid to be measured, and the installation conditions of the transducer. The time calculating means for calculating and the measured propagation time and the total propagation time obtained by the flow rate calculating means are calculated so that they match, and the refraction angle of the ultrasonic wave to the fluid to be measured and the fluid to be measured in the propagation path when they match. Calculate the propagation time of ultrasonic waves And a correction calculation means for correcting the flow rate using the refraction angle and the propagation time.

<Examples> Examples of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention.

The fluid to be measured 2 is caused to flow in the pipe line 1 in the direction indicated by the arrow, and the flow rate Q of the fluid to be measured 2 is measured. For this reason, the wave transmitters / receivers 3 and 4 are installed in the pipe line 1 so as to be obliquely opposed to the flow direction F. A trigger pulse T _p is applied to the drive circuit 6 from the synchronizing circuit 5 having a clock oscillator in one of the transmitters / receivers 3 and 4, and accordingly, for example, a peak value is present in its output.
A differential drive pulse D _p having a value of about 200 V is generated and applied via the changeover switch 7. Transducers 3, 4
On the other hand, the ultrasonic pulse received through the fluid to be measured 2 is received by the amplifier 8 through the changeover switch 7.

The ultrasonic pulse H output from the amplifier 8 is applied to one end of the input of the comparator 9, and the comparison voltage V _c is applied to the other end.
At the output end of the comparator 9, the zero-cross portion of the waveform exceeding the comparison voltage V _c of the ultrasonic pulse having a vibration wave is pulsed and output as an output pulse P.

The output pulse P of the comparator 9 is applied to the input end I ₁ of the arithmetic circuit 10, and the trigger pulse T _p from the synchronization circuit 5 is applied to the input end I _2.
Is applied at the same time as the start signal S is transmitted,
The arithmetic circuit 10 calculates these time differences and measures the propagation time in the propagation path of the ultrasonic pulse. Further, the measured time propagation similarly changeover switch 7 is switched by the switching signal S _w.

A temperature sensor 11 is fixed to the pipe wall of the pipe 1 to detect the temperature of the pipe wall or the shoe as a temperature signal t.

Reference numeral 12 denotes a microcomputer unit that receives signals from the arithmetic circuit 10 and the temperature sensor 11, processes the signals, and outputs the processed signals. An analog / digital converter (A / D converter) 13 converts the time signal from the arithmetic circuit 10 into a digital value. Reference numeral 14 is an A / D converter for converting the temperature signal t from the temperature sensor 11 into a digital value. Reference numeral 15 is a RAM (random access memory), 16 is a ROM (read only memory), and these addresses are designated from a CPU (processor) 17 via a bus 18 and a latch decoder 19. Each output data from the A / D converters 13 and 14 is stored in the RAM 15 via the data bus 20. R
A predetermined calculation program and initial data are stored in the OM 16, and the ROM 16 is controlled under the control of the CPU 17.
Is calculated according to the calculation procedure stored in
It is stored in AM15. Reference numeral 21 is a control bus, and the CPU 17 causes the A / D converters 13 and 14 and the RAM 1 to operate.
5, the timing signal the T _m to the synchronization circuit 5 to control the operation of the ROM 16, the switching circuit 7 outputs the switching signal S _w.

The final calculation result is converted into an analog signal through the digital / analog converter (D / A converter) 22 and the output terminal 2
3 is output.

Next, the signal processing in the microcomputer section shown in FIG. 1 will be described with reference to the flow chart shown in FIG.

First, in a step, the flow rate correction coefficient R _x is set in the RAM 12 from the ROM 16 as initial data. Next, in a step, the refraction angle θ of the ultrasonic wave to the fluid to be measured, the propagation time T during which the ultrasonic wave propagates in the fluid to be measured, the coefficient of a polynomial for calculating the speed of sound, and various constants such as the inner diameter of the pipe line. Are set in the ROM 16 to the RAM 15.

In step, switching signal from control bus 21
The switch 7 is switched to one by S _w, and the drive pulse D _p is emitted from the drive circuit 6 to the wave transmitter / receiver 4, for example, and the propagation time is changed by the timing signal T _m from the control bus 21. T ₁ is stored in the RAM 15 measured by the arithmetic circuit 10. Next, the changeover switch 7 is stored in the RAM15 is measured propagation time T ₂ in the same manner is switched to the other by switching signal S _w. Propagation time T ₁
And the propagation time difference ΔT between T ₂ and T ₂ are calculated by a calculation program built in the ROM 16 and stored in the RAM 15.

Since the propagation time difference ΔT is inversely proportional to the flow rate Q flowing in the pipe line 1, the flow rate Q is calculated in steps by the flow rate calculation formula stored in the ROM 16 using this value.

There is an error in this flow rate value due to temperature, etc., so it is necessary to correct it. However, since there is no abrupt change, it suffices to make a correction with a longer correction cycle T _c than the calculation of the flow rate. The determination of the correction cycle T _c for that purpose is executed in steps.

When the correction cycle T _c is exceeded, the process moves to step and the temperature signal t is read from the temperature sensor 11.

Next, in step S, the sound speed C _{1 of the} shoes 24 and 25 for fixing the transducers 3 and 4 to the conduit 1 and the sound speed C _{2 of the} conduit 1 are set to RO.
The calculation is performed according to the calculation program of the following quadratic equation regarding the temperature signal t stored in M16. In this case, shoe 2
The temperatures of the pipes 4, 25, the pipe 1 and the fluid to be measured 2 are considered to be almost the same.

C ₁ = A + Bt + Ct ² (1) C ₂ = A ′ + B′t + C′t ² (2) Here, A, B, C, A ′, B ′, and C ′ are preset in each step.

In the step, the total propagation time T _s of ultrasonic waves is calculated according to the model of the propagation path. Hereinafter, this calculation will be described. FIG. 3 is an enlarged view in which the vicinity of the pipe 1 is enlarged.

First, the propagation path of ultrasonic waves is obtained. The speed of sound of the shoe is C ₁ ,
Let C _{2 be} the speed of sound in the conduit ₁ , θ _{1 be} the incident angle of ultrasonic waves from the shoe 24 to the conduit ₁ , and θ _{2 be} the incident angle of ultrasonic waves from the conduit 1 to the fluid to be measured. Assuming that the estimated sound velocity of C is C ₃ and the incident angle of the ultrasonic wave from the fluid to be measured into the conduit 1 is θ ₃ , the sound velocity C ₁ and C ₂ calculated in the step are used to follow Snell's law. Thus, the incident angles θ ₁ and θ ₂ are calculated.

The horizontal distance between these transducers 3 and 4 is Is installed to satisfy _{Here, x 1/2, x 2} /
2, x ₃ are the distance from the center of the transducer 3 (4) to the outer wall of the conduit 1, the wall thickness of the conduit 1, and the inner diameter of the conduit 1, respectively.

As described above, the propagation path of ultrasonic waves can be determined by calculation, but the calculation program necessary for these calculations is ROM.
It is stored in 16 and has an estimated sound velocity C ₃ , incident angle θ ₃ , distance
x _{1 to} x ₃ etc. are preset in steps.

Next, the total propagation time T _s required for the ultrasonic wave to propagate along the thus determined propagation path is obtained.

The total propagation time T _s can be obtained based on a point source model assuming that the centers of the transducers 3 and 4 are point sources or a plane source model assuming that the transducers 3 and 4 are planar sources.

In the case of the point source model, ultrasonic waves propagate as spherical waves, and the distance L between the transducers 3 and 4 does not change even if the sound velocity C _i changes. For example, the propagation path of ultrasonic waves when each speed of sound changes due to temperature is as shown in FIG.
Does not change. The total propagation time T _{s in} this case is given by the following equation.

If the plane sound source model is assumed, the ultrasonic wave propagates as a plane wave, and the incident angle θ ₁ is constant even if the sound velocity C _i changes. For example, as shown in FIG. 4 (b), the distance L shifts to L'in the propagation path of ultrasonic waves when each sound velocity changes with temperature. The total propagation time T _{s in} this case is given by the following equation.

At this time, L'is calculated using the equation (4).

A calculation program corresponding to any of these models is stored in the ROM 16.

Then, the process proceeds to step. In the step, the propagation time T is obtained by taking the average value of the propagation times T ₁ and T ₂ of the measured ultrasonic waves input from the arithmetic circuit 10, and this and the total propagation time T obtained by the equation (5) or (6). _s is compared, the refraction angle θ ₃ is changed, and the propagation time T ₀ and the refraction angle θ ′ ₃ during which the ultrasonic wave propagates in the fluid to be measured where T = T _s are obtained by the successive approximation method.

In step, the correction coefficient k _x for the flow rate Q is calculated.
The flow velocity v of the fluid to be measured in the conduit 1 is expressed by the following equation, where k ⁻¹ is a correction factor for the flow velocity distribution and N is a constant.

Further, the flow velocity v when using the refraction angle θ and the propagation time T given as data in the step is Therefore, if we take the ratio of equations (7) and (8), Becomes That is, However, Becomes Since this correction coefficient k _x is a flow rate correction coefficient with respect to the initial value, it is corrected in real time by incorporating all factors such as specific gravity and temperature by multiplying this correction coefficient k _x when calculating the flow rate in steps. Is possible.

FIG. 5 is a characteristic diagram showing the results of examining the effect of this embodiment. (A) is the case without correction, (b) is the case with a point source model, and (c) is the case with a planar source model, both of which are shown as the error with respect to the flow velocity v ₀ of the calibration reference flow meter (pipe prober). is there. Compared to the uncorrected case, the corrected result using the model path gives a considerably improved result.

In the embodiment shown in FIG. 1, the temperature sensor 1 is installed in the conduit 1.
However, the present invention is not limited to this, and a temperature sensor may be separately provided. Further, when measuring the propagation time, the ΔT direct connection method has been described, but other means such as the sing-around method or the PLL method may be adopted.

<Effects of the Invention> As described above in detail with reference to the embodiments, according to the present invention, the model path is estimated from the actual measurement value, and the velocity of sound in the fluid to be measured is estimated using this to calculate the flow rate correction coefficient. Since the flow rate is corrected in this manner, the flow rates of various fluids having different sound speeds can be accurately measured in real time.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a flow chart showing the operation of the embodiment shown in FIG. 1, and FIG. 3 is an enlarged view enlarging the vicinity of the pipe in FIG. FIG. 4 is an explanatory diagram for explaining the sound source model, and FIG. 5 is a characteristic diagram for explaining the effect of the embodiment in FIG. 1 ... Pipe line, 3, 4 ... Transceiver, 7 ... Changeover switch, 9 ...
Comparator, 10 ... Arithmetic circuit, 11 ... Temperature sensor, 12 ...
… Microcomputer department.

Claims (1)

[Claims] 1. A flow velocity direction of a fluid to be measured in a pipe, and a propagation time difference of ultrasonic waves radiated through a shoe fixed to the pipe and a transducer in a direction opposite to the flow velocity. A flow rate calculating means for calculating the flow rate of the fluid to be measured, a sound velocity calculating means for calculating the sound velocity of the shoe and the pipe by a predetermined equation using the temperature of the shoe and the like, and estimating the sound velocity and the fluid to be measured. The time propagation means for computing the total propagation time of the propagation path of the ultrasonic wave estimated from the sound velocity and the installation condition of the transducer, and the actual propagation time obtained by the flow rate calculation means and the total propagation time are the same. Path calculation means for calculating the refraction angle of the ultrasonic wave to the fluid to be measured and the propagation time in which the ultrasonic wave propagates through the fluid to be measured in the propagation path when calculated and coincident, and the refraction angle Using the propagation time, etc. Ultrasonic flow meter, characterized by comprising a correction calculation means for correcting relative.