JPS6261893B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention measures the flow rate of the medium by detecting the time during which ultrasonic waves propagate through a medium to be measured in the forward and reverse directions relative to the flow.
The present invention relates to an ultrasonic flow rate measuring device capable of selectively selecting a large number of media to be measured and measuring the flow rate of each medium. As an example of a conventionally known ultrasonic flowmeter, a voltage-controlled type oscillator is used so that the time for counting N pulse signals of frequency f oscillated by a voltage-controlled oscillator matches the propagation time of the ultrasonic waves in the fluid. A closed loop is configured to control the oscillation frequency f of the oscillator, and in synchronization with the oscillation of one transducer, the output of a counter that counts N pulses of this frequency f is input to a time difference detection circuit, and the other is an ultrasonic receiver. There is a circuit in which a signal is also input to this time difference detection circuit and a time difference is output, and a closed loop is configured so that the time difference becomes zero. An example of such a conventional ultrasonic flowmeter is shown in the first example.
As shown in the figure. In the figure, a voltage controlled oscillation circuit 10
has two voltage controlled oscillators (hereinafter referred to as VCO) 13 and 15 whose oscillation frequency changes depending on the magnitude of the control voltage. VCO13
The oscillation output signal 21 (frequency f ₁ ) of the VCO 15 and the oscillation output signal 23 (frequency f ₂ ) of the VCO 15 are connected to the switch 25
The output signal 29 of the voltage controlled oscillator circuit 10 thus obtained is sent to the pulse generating circuit 27.
supply to. The pulse generating circuit 27 generates a pulse signal 31 in synchronization with the signal 29 and also generates a counting start signal 33. Based on this pulse signal 31, the transmitter circuit 35 generates a transducer drive signal 37. The two transducers 41 and 43 are connected to one another to convert an electrical signal into an acoustic signal (ultrasonic wave 45 or 47) in response to a transducer drive signal 37 that is alternately supplied by switching a switch 45. one side and the other acts as a receiver converting the acoustic signal into an electrical signal. An electrical signal obtained by receiving this acoustic signal is sent to a receiving circuit 55 as a received signal 53 via a changeover switch 51.
will be introduced in The reception circuit 55 supplies a reception detection signal 57 to the time difference detection circuit 59 in response to the reception signal 53. Further, the counter 61 activated by the counting start signal 33 counts the output signal 29 of the voltage controlled oscillation circuit 10. When the counting state reaches a preset value N, this counter 61 supplies a pulse output signal 63 to the time difference detection circuit 59, and is then reset. The time difference detection circuit 59 detects the time difference between both signals 57 and 63, and generates a control signal 65 with a voltage corresponding to the time difference. This control signal 65 is switched by a switch 67, and is applied to both VCOs 13 and 1 in the voltage controlled oscillator circuit 10.
5, its oscillation frequency
Control f ₁ or f ₂ . FIG. 2 shows the state in which both transducers are attached to the pipe line of the fluid to be measured, and also shows the propagation of ultrasonic waves. In the figure, the ultrasonic waves emitted from the upstream transducers 41, which are arranged opposite to each other, propagate to the fluid to be measured 75 through the plastic wedge 73 and the tube 71, which propagate the ultrasonic waves obliquely into the tube 71, and then back into the tube. 71 and another plastic wedge 77 to the downstream transducer 43. In this case, upstream transducer 4
The ultrasonic forward propagation time T ₁ from 1 to the downstream transducer 43 is given as T ₁ =D/cos θ/C _w +Vsin θ (1). Conversely, the ultrasonic reverse propagation time T ₂ from the downstream transducer 43 to the upstream transducer 41 is given as T ₂ =D/cos θ/C _w −Vsin θ (2). Here, D is the inner diameter of the tube 71,
C _w is the sound velocity in the fluid 75 when the fluid 75 is stationary, V is the flow velocity of the fluid 75, and θ is the incident angle at which the ultrasonic wave enters the fluid 75.
Note that both wedges 73 and 77 and the pipe 7 are shown here.
The time it takes the ultrasonic wave to propagate through the pipe thickness section 1 is ignored. Next, referring to FIGS. 1 and 2, the fluid 7
5. Flow rate measurement will be described. Note that this measurement principle is a well-known one that utilizes a phase lock loop, so it will be briefly explained. First, all the changeover switches 24, 45, 51 and 67 are connected to the contact point m.
Connect to the side for forward mode. In this case, the propagation time of the _ultrasonic wave 45 is
T ₁ is expressed by the above-mentioned equation (1). Also, the time T until the counting state of the counter 61 reaches N is N/
_f1 . So that this time T and the previous propagation time T ₁ have a predetermined relationship (in this case, they are equal),
It forms a phase lock loop that feedback controls the oscillation frequency f ₁ of the VCO 13. Therefore, once this system is stabilized, N/f ₁ =T ₁ , so the relationship f ₁ =N(C _w +Vsin θ)/D/cos θ (3) holds true. Further, all the changeover switches 25, 45, 51 and 67 are respectively switched to the contact n side to set the reverse direction mode. In this case as well, as mentioned above (2)
The phase lock loop system including the VCO 15 is stabilized so that the propagation time T ₂ of the ultrasonic wave 47 expressed by the formula and the time T until the counter 61 reaches the counting state N have a predetermined relationship (in this case, they are equal). do. Therefore, the oscillation frequency f ₂ of the VCO 15 is expressed as f ₂ =N(C _w −Vsin θ)/D/cos θ (4). Taking the difference Δf (=f ₁ - f ₂ ) between these two frequencies, Δf=2Nsinθ/D/cosθ・V=Nsi
It is given as n2θ/D·V(5). Therefore, if the angle of incidence θ is constant, the frequency difference Δf is given as a function only of the flow velocity V of the fluid 75, so if both signals 21 and 23 are counted and the difference Δf between these two frequencies is found, from that value, The flow velocity V of the fluid 75 can be calculated. Therefore, the flow rate of the fluid to be measured 75 can be measured. However, in such an ultrasonic flowmeter, the ultrasonic propagation time detection sections of the pair of transducers 41 and 43 and the other propagation time-frequency conversion sections are fixed in a one-to-one relationship. Therefore, various adjustments were required each time both transducers 41 and 43 were attached to the conduit 71 for the fluid to be measured 75. For example, it is necessary to change the internal settings due to differences in the diameter D of the pipes,
Span adjustment was required, and waveform balance adjustment was required by changing the detection unit. For these reasons, conventional ultrasonic flowmeters have not adopted a method of performing measurements by arbitrarily replacing the medium to be measured. Therefore, there has been a need to realize an ultrasonic flow rate measuring device that is capable of switching selection methods. SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic flow rate measuring device capable of switching and selecting the medium to be measured, in response to such demands. In the present invention, a plurality of transducer pairs;
means for selectively switching the plurality of transducer pairs to select one transducer pair;
A counter counts the oscillation output of the oscillator and the respective times during which the ultrasound propagates in the medium to be measured between the transducers of the selected transducer pair in the forward and reverse directions relative to the flow. means for controlling the two oscillation frequencies of the oscillator so that the time required for means for measuring the flow rate of the medium to be measured; means for switching and selecting the transducer pair and changing the set value of the counter; The above object is achieved by configuring the device to selectively measure the flow rate of the medium to be measured that is present between the transducers. The present invention will be explained in detail below based on the drawings. FIG. 3 is an embodiment of the present invention, in which the first
The same symbols as in the figure indicate the same circuits, etc. The difference from FIG. 1 is that there are multiple pairs of transducers T ₁ , T ₂ ,..., each attached to a separate pipe line for the fluid to be measured.
The purpose of the present invention is to switch and select T _o using changeover switches 301 and 303. Also shown is an intermediate arithmetic processing unit (hereinafter referred to as CPU) 310 that controls the entire device and performs arithmetic processing. Both VCO1
3 and 15 both oscillation output signals 21 and 23
is via both open/close switches 321 and 323.
Install it on CPU310. The operation in the above configuration will be explained. First of all,
Both switches 321 and 323 are opened by a first control signal 351 from CPU 310. Next, N
The setting signal 353 sets the set value N of the counter 61 to N ₁ , and the second control signal 355 connects both changeover switches 301 and 303 to contact a to select the transducer pair T _1. do. Thereafter, the third control signal 357 connects both changeover switches 45 and 51 to contact p, and the fourth control signal 359 connects both changeover switches 25 and 67 to contact m, respectively. In such a device state, CPU3
The pulse generating circuit 27 is energized by the energizing signal 361 from 10. Then, as explained with reference to FIG. 1, the forward ultrasonic propagation time T ₁₁ from the transducer 411 to the transducer 431
The oscillation frequency f ₁ of the VCO 13 is controlled so that the time when the counting state of the counter 61 that counts the oscillation output signal 21 of the VCO 13 reaches N ₁ becomes equal. Next, the third control signal 35 from the CPU 310
7 switches both switches 45 and 51 to the contact q side, and also outputs the fourth control signal 35.
9 switches both switches 25 and 67 to the contact n side. Then, as in the case of FIG. 1, the backward ultrasonic propagation time t ₂₁ from the transducer 431 to the transducer 411,
The oscillation frequency f ₂ of the VCO 15 is controlled so that the time required for the counting state of the counter 61 that counts the oscillation output signal 23 of the VCO 15 to reach N ₁ is equal to the time required. Here, the output signal 3 from the time difference detection circuit 59
41 is a signal indicating that both signals 57 and 63 in this circuit 59 match and are stable within a certain minute time range. Thereafter, the first control signal 351 closes both switches 321 and 323. CPU31
Both oscillation output signals 21 and 23 are counted by a counter in zero to obtain both oscillation frequencies f ₁ and f ₂ . From these two frequencies f ₁ and f ₂ , the frequency difference Δf is determined based on equation (5). Δf=f ₁ −f ₂ =N ₁ sin2θ ₁ /D ₁・V ₁ (6) Here, D ₁ is the inner diameter of the conduit in which the transducer pair T ₁ is installed, and θ ₁ is the ultrasonic wave at that time. , and V ₁ is the flow velocity of the fluid to be measured. At this time, the magnitude relationship between both frequencies f ₁ and f ₂ , that is, the sign (plus, minus) of the frequency difference Δf represents the flow direction of the fluid to be measured. That is, when the sign of the frequency difference Δf is positive, it represents a flow in the positive direction (flow in the direction of the arrow in FIG. 2), and when it is negative, it represents a flow in the opposite direction. Similarly, pair T ₂ of both transducers 412 and 432 or both transducers 41
To measure the flow rate of the fluid to be measured in each pipe line in which pairs T 3 and ₄₃₃ are installed,
The second control signal 355 is controlled by the CPU 310.
Both changeover switches 301 and 303 are switched to contact b or c, and the set value N of the counter 61 is reset to N ₂ or N ₃ using the N setting signal 353. Other than that, the same procedure may be followed. The general formula for the relationship between the frequency difference Δf and the flow velocity of the fluid to be measured is expressed as Δf=N _i sin2θ _i /D _i ·V _i (7). Therefore, the flow rate (flow rate) of any measured fluid is
When the calculation is performed by the CPU 310, the parameters N _i , θ _i and D _i in equation (7) may be changed each time. Note that the fluid to be measured may be selected arbitrarily in any order, but based on the control program,
Transducer pair T ₁ to _{T o} both switches 301
It is also possible to adopt a scanning type in which the parameters are sequentially switched by 303 and 303, various parameters are sequentially changed according to the switching, and the flow rate of each fluid to be measured is determined based on equation (7). Furthermore, the inner diameters D of the conduits in which the transducer pairs are installed may be different. By the way, normally when the transducer pair T _i is switched, the state of the device changes, so the magnitude of the so-called offset (resulting in a reading error) changes. Additionally, drift occurs due to environmental conditions such as temperature. Therefore, it is necessary to eliminate offsets including drift to eliminate flow rate measurement errors. As an example of such a means, an automatic zero adjustment method was introduced in the patent application "Ultrasonic Flowmeter" filed by the present applicant on the same date. In other words, the conversion frequency of the forward propagation time of the ultrasonic wave is determined not only by VCO13 but also by VCO1.
5 to obtain both such oscillation frequencies. Also, the conversion frequency of the backward propagation time of ultrasonic waves is
Instead of setting only the oscillation frequency of VCO15,
Also switch to VCO13 to set the oscillation frequency of both VCOs. The flow rate of each fluid to be measured is determined from the values of these four oscillation frequencies. The offset is then automatically canceled and there is no need to adjust it for each transducer pair. If the counter set value N is not changed even when the inner diameter D of the pipe changes, f ₁ and f ₂ determined based on equations (3) and (4) are as follows: As shown in the table below.

[Table] However, the counter setting value N, incident angle θ, and flow velocity V are completely the same. In addition, the pipe diameter D is 1D,
It is assumed that it changes from 2D to 4D. Then, in the above table, f ₁₁ =N(Cw+Vsinθ)/1D/cosθ _f12 =N(Cw+Vsinθ)/2D/cosθ=1/
2f ₁₁ f ₁₃ =N(Cw+Vsinθ)/4D/cosθ=1/
4f ₁₁ , that is, f ₁₁ =2f ₁₂ =4f ₁₃ . Therefore, if the set value N is not changed, the pipe diameter D will be doubled, 4 times, even though the flow velocity V is the same.
As the oscillation frequency _f1 changes by a factor of two, the oscillation frequency f1 also changes by a factor of two or four. The same applies to _f2 . This means that the oscillator must be able to vary its oscillation frequency significantly depending on the tube diameter D. However, manufacturing such an oscillator is difficult. Next, the counter setting value N is determined according to the inner diameter D of the pipe line.
A case (this embodiment) in which the value is changed will be described.
In this case, f ₁ and f ₂ determined based on equations (3) and (4) are as shown in the following table.

[Table] In other words, for cases 10, 20, and 30 where the counter setting value N is changed according to the pipe diameter D, f ₁₁₀ = 1N (Cw + Vsin θ)/1D/cos θ = N
(Cw+Vsinθ)/D/cosθ f ₁₂₀ =2N(Cw+Vsinθ)/2D/cosθ=f _1
10 f ₁₃₀ = 4N(Cw+Vsinθ)/4D/cosθ=f _1
10 , f ₁₁₀ = f ₁₂₀ = f ₁₃₀ . Therefore, when the flow velocity V is the same, if the counter setting value N is changed according to the pipe diameter D, the oscillation frequency f ₁ will not change even if the pipe diameter changes by a factor of two or four. The same applies to _f2 . In this way, when the counter set value N is changed as appropriate, the oscillation frequency can be selected without being influenced by the tube diameter, making it easy to manufacture the oscillator. As described in detail above, according to the present invention, by switching the set values of the transducer pair and the counter, it is possible to realize a flow rate measuring device that can measure the flow rate of a large number of target media with one converter. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional ultrasonic flowmeter, FIG. 2 is a diagram showing the installation state of the transducer pair in FIG. 1, and FIG. 3 is an example of an ultrasonic flow measurement device according to the present invention. FIG. 2 is a block diagram showing an embodiment. 13, 15... Voltage controlled oscillator, 35... Transmission circuit, 41, 43, 411, 412, 413, 43
1,432,433...transducer, 55...
Receiving circuit, 59... Time difference detection circuit, 61... Counter, 301, 303... Changeover switch.

Claims (1)

[Claims] 1. a plurality of transducer pairs each attached to a plurality of separate fluid pipes to be measured; means for selectively switching the plurality of transducer pairs to select one transducer pair; A counter counts the oscillation output of the oscillator and the respective times during which the ultrasonic wave propagates in the fluid under test in the forward and reverse directions with respect to the flow between the transducers of the selected transducer pair. means for controlling the two oscillation frequencies of the oscillator so that the times required for the ultrasonic waves to propagate in the forward and reverse directions are in a predetermined relationship; means for calculating the flow velocity of the fluid to be measured; and means for selectively switching the transducer pair and changing the set value of the counter according to the selected pipe line to be measured; An ultrasonic flow rate measurement device that selectively measures the flow rate of a plurality of fluids to be measured in a fluid pipeline.