JPS5917370B2 - ultrasonic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new type of ultrasonic flowmeter.

An object of this invention is to improve the accuracy, response speed, and temperature stability of an ultrasonic flowmeter.

Other objects of the present invention are to improve stability against loss of ultrasonic signals due to bubbles or foreign matter in the fluid, to ease requirements for installation dimensional accuracy, to reduce costs by simplifying the configuration, and to improve reliability. Ultrasonic flowmeters utilize the fact that the transmission time of ultrasonic waves in a fluid changes depending on the flow rate of the fluid.

Normally, two transmission paths for ultrasonic signals, one in the forward direction and the other in the opposite direction with respect to the flow direction, are provided in the piping through which the fluid passes, and the flow velocity of the fluid is determined by measuring the difference in transmission time. Measure. The fluid flow rate is proportional to this transmission time difference. This transmission time difference is minute, and is on the order of 1 ns, whereas the transmission time is normally 0.1 to 1 ms. Therefore, in order to accurately measure the flow rate, a time measurement accuracy on the order of 1 ns is required. Measuring this minute time difference is difficult with either analog or digital methods, so in many cases the transmission time is converted into a frequency and the frequency difference is measured. However, these schemes have the disadvantage of slow response times. An example of successful direct measurement of the propagation time difference is to transmit ultrasonic signals to two ultrasonic signal transmission paths at the same time, and measure the delay in the reception time of the signal going backwards based on the reception time of the signal going in the direction of the flow. There is a method to measure it analogously. Another problem with conventional ultrasonic flowmeters is that changes in transmission time due to temperature changes in the structures that make up the two forward and reverse ultrasonic transmission paths described above lead to flow velocity measurement errors. be.

Furthermore, the machining precision required to satisfy geometric uniformity of the two ultrasonic transmission paths is also one of the practical difficulties. As a solution to these problems, the ultrasound transmission path is unified, the ultrasound transmission direction is reversed every cycle, the transmission time in the forward direction and the reverse direction is measured, and the difference between them is calculated. There are several possible methods. In this way, the propagation times in the structure are canceled out when taking the difference between the forward and reverse propagation times, and temperature drifts are also eliminated. but,
In this method, the transmission times in both directions are measured separately and then the difference is calculated, which requires extremely high time measurement accuracy, which is difficult to achieve with analog methods. As mentioned above, the transmission time is 0
．． 1 to 1 ms, whereas the measurement accuracy of the difference in transmission time is required to be on the order of 1 ns, so the relative accuracy is required to be 1'5 to 10<-6 >.
This problem can be solved by using a digital system using a highly stable clock oscillator, but this poses the difficulty of requiring a high clock frequency on the order of 1 GHz. Several methods have been developed to convert the frequency into a frequency and measure it, but all of them have slow response speeds and problems with stability. Therefore, the method of eliminating errors caused by temperature changes by using a single ultrasonic transmission path has not been fully put into practical use.
Only a method in which the transmission direction is reversed every cycle has been put into practical use. The present invention aims to solve the above-mentioned difficulties in the alternating reversal method of a single ultrasonic signal transmission path, and to provide an ultrasonic flowmeter with good accuracy, response speed, and temperature stability.

In addition to the above, the ultrasonic flowmeter according to the method of this invention is stable against loss of ultrasonic signals due to bubbles or foreign objects in the fluid, has loose requirements for installation dimensional accuracy, and has a simple configuration. , improvements have also been made in terms of cost and reliability. The detailed contents of the present invention will be explained below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of an ultrasonic flowmeter according to the method of the present invention.

In the figure, 1 is a pipe through which the fluid to be measured flows, and 2 and 3 are ultrasonic receiving and transmitting elements (hereinafter simply referred to as appropriate) that are attached to the pipe 1 so as to face diagonally to the pipe 1 and receive and transmit ultrasonic waves. ), 4 is the master controller of the circuit system, 5 and 6 are ultrasonic receiving and transmitting elements 2,
3 is a pulse generator that excites the ultrasonic reception signal, 7 and 8 are amplifiers for the ultrasonic reception signal, 9 and 10 are pulse height selectors for the amplified ultrasonic reception signal, and 11 and 12 are controls for the pulse height selection devices 9 and 10. circuits, 13 and 14 are ramp signal generators, 15 and 16 are sample and hold circuits, 17 is a ramp signal generator, 18 is a control circuit for the ramp signal generator 17, 19 is a sample and hold circuit, 20 is a subtracter, 21, 22 is a low-pass filter, 23 is a squaring circuit, and 24 is a divider. Next, the operation of the embodiment shown in FIG. 1 will be explained using FIG. 2.
FIG. 2 is a time chart illustrating the operation of each part of the embodiment shown in FIG. The ultrasonic receiving and transmitting elements 2 and 3 are
Since they are installed diagonally with respect to the piping 1 and at positions facing each other, the ultrasonic signal Sg directed from the receiving/transmitting element 2 to the receiving/transmitting element 3 is the ultrasonic signal directed from the receiving/transmitting element 3 to the receiving/transmitting element 2. The transmission time is shorter than Sg, and this time difference is proportional to the fluid flow rate. On the other hand, the output signal MSTR of the master controller 4 is divided into % and the signals φA, φB (=
φA), which triggers the ultrasonic transmission pulse generators 5 and 6. The pulse generators 5, 6 are therefore triggered alternately every cycle of the signal MSTR. Furthermore, the signal MSTR
The generator that generates can be composed of an astable multivibrator. It can also be configured by combining a clock oscillator and a preset counter. However, in either case, it is necessary to be able to finely adjust each half period of ``1'' and ``0''. In the cycle in which the signal φA is triggered, the pulse generator 5 is triggered, and its output pulse excites the ultrasonic transceiver element 3 to transmit an ultrasonic signal Sg into the fluid.

This ultrasonic signal Sg reaches the ultrasonic receiving/transmitting element 2, and this receiving/transmitting element 2 generates a receiving signal. The received signal is amplified by an amplifier 7 and separated from noise by a pulse height selector 9. The pulse height selector 9 generates an output pulse SIG-A when the input signal exceeds a preset threshold voltage. The ultrasonic signal Sg emitted at the rising edge of the signal φA and the wave height selector 9 receive the ultrasonic signal Sg.
The correspondence relationship with the output pulse SIG-A emitted from the output pulse SIG-A is shown in FIG. 2 by a broken line arrow. Since ultrasonic signals often have a damped vibration waveform, the wave height selectors 9 and 10 used here have a function of stopping output for a certain period of time after generating an output signal so as not to respond to subsequent pulses. It is desirable to have

Furthermore, in order to prevent the pulse height selector 9 from responding to unnecessary noise pulses, the period during which it can respond to the input signal is limited.
This restriction is performed as follows. That is, the signal MS
TR triggers the signal φGT at the end of the half cycle when the output is "1". This signal φGT is generated during the minimum period including the expected arrival time of the ultrasound signal Sg. Further, the control circuit 11 generates a product (AND) of the signal φA and the signal φGT, and uses this as an enable signal SIG-ENA for the pulse height selector 9. Therefore, the pulse height selector 9 responds to the input signal only when the signal φGT is present and the ultrasonic wave receiving/oscillating element 3 is excited. Further, the ramp signal generator 13 is triggered by the rising edge of the signal φGT to generate a ramp signal, and is reset by the signal φRES. This signal φRES is triggered at the end of signal φGT. The rise of the ramp signal is interrupted for a predetermined period by receiving the output signal SIG-A from the pulse height selector 9 as a stop signal in the middle of the rise period. on the other hand,
This signal SIG-A also serves as a sample strobe signal to the sample and hold circuit 15, and samples the output signal of the ramp circuit 13 whose rise is interrupted, and waits until the next signal SIG-A is generated.
hold that output signal. Ramp signal generator 13
The reason for interrupting the rise of the output signal during the period of signal SIG-A is to facilitate sampling and improve sampling accuracy, but this may be omitted. The voltage of the signal sampled from the ramp signal, that is, the output voltage ΔTA from the sample-and-hold circuit 15, is proportional to the time between the rise time of the signal φGT and the generation time of the ultrasonic signal SIG-A. This time is calculated from the transmission time TA of the ultrasonic signal Sg from the transmitting/receiving element 2 to the transmitting/receiving element 3,
It is obtained by subtracting the "1" period TMSTR of TR.
+ In the next cycle of the signal MSTR, the signal φB triggers the pulse generator 6, and the ultrasonic transceiver element 2 is excited.

Thereafter, the amplifier 8, pulse height selector 10, and control circuit 1 are connected in the same way as the above-mentioned process for the cycle in which φA triggers.
2, ramp signal generator 14, sample hold circuit 16
is activated, and the output voltage ΔTB of the sample hold circuit 16
is proportional to the difference (TB-TMSR) between the generation time of the signal φGT and the generation time of the signal SIG-B. Here, the ramp signal generator 14 may be omitted and the ramp signal generator 13 may be used in common.

Subtractor 20 provides the difference (ΔTA−ΔTB) between the output voltages of sample and hold circuits 15 and 16 as an output.

Therefore, this output voltage is proportional to the difference in propagation time when the ultrasonic signal Sg travels forward and backward to the flow of the fluid, and is proportional to the flow rate of the fluid. Signal MST
Since the period R(7)1F' is included in common in the outputs of the sample and hold circuits 15 and 16, it is canceled out by subtraction and does not affect measurement accuracy. Therefore the signal MST
The generator of R can be constructed from a simple astable multivibrator. Signals SIG-A and SIG-B may be lost due to disturbances such as bubbles or foreign objects in the fluid, but in that case, the sample and hold circuit will hold the previous hold voltage as it is, so the output signal will not be disturbed. There isn't. The signal φGT is used as a noise countermeasure as described above, but in terms of time measurement, it serves to shorten the measurement range and improve the accuracy of time measurement. By setting the rise time of the signal φGT immediately before the signals SIG-A and SIH, the time measurement range can be shortened by about two orders of magnitude, and the measurement accuracy can also be lowered by that much.
Therefore, sufficient measurement accuracy can be obtained with a simple time measurement means using a ramp signal generator and a sample-and-hold circuit. The pass filter 22 smooths the output voltage of the subtracter 20,
This is intended to reduce agitation, but may be omitted in some cases. The ramp signal generator 17 is controlled by a control circuit 18, and is controlled by a period of 1 of the signal MSTR and a signal φG.
A ramp signal is generated over the period when T exists, and is reset by the signal φRES.

The sample hold circuit 19 samples the output signal of the ramp signal generator 17 at the time of the signal SIG-A or SIG-B, and samples the output signal of the ramp signal generator 17 at the time of the signal SIG-A or SIG-B for the next cycle.
The sampled value is held until the time of IG-B. The output voltage of the sample and hold circuit 19 is proportional to the transmission time of the ultrasonic signal Sg in the fluid, and the forward and reverse transmission times are alternately sampled and held every cycle of the signal MSTR. The low-pass filter 21 provides a time average value of the output voltage of the sample-and-hold circuit 19, but may be omitted in some cases. The output voltage of the low-pass filter 21 is the average value of the transmission time in the forward direction and the reverse direction, so it has little relation to the flow velocity, but it changes to follow the change in the sound speed due to the temperature change of the fluid, and the output voltage of the low-pass filter 22 It is used for temperature correction of the time difference signal. For temperature correction, divider 24 divides the output voltage of low-pass filter 22 by 2.
This is done by dividing by the output voltage of the multiplication circuit 23. This relationship will be explained below. Now, the diameter of the pipe 1 is D, the angle of the sound wave signal path with respect to the pipe axis is θ, the flow velocity of the fluid is V, and the outputs of the low-pass filter 22 and the square circuit 23 are 2 and V2, respectively.
3. Let TA and TB be the retrograde and antegrade propagation times, respectively, and C be the sound velocity in the fluid.

22 and V23 both depend on the speed of sound C and change with temperature, but by taking the ratio of the two, the temperature change can be eliminated.

Since the range of change in the input signal is narrow, the squaring circuit 23 may perform tangential approximation using a linear amplifier, and instead of sampling the output of the ramp signal generator, the period TA
, TB may be replaced.

Since TA2 and TB2 can be obtained by integrating the ramp signal, one (TA2s4+TB2) may be used as an approximation of equation (2).

Here, the explanation has been made by ignoring the transmission time required for the ultrasonic signal Sg to propagate through the structure of the ultrasonic transmission path, but the temperature correction amount can be corrected by the correction in 23 when taking this into consideration. It is. If the ultrasonic signals SIG-A and SIG-B are lost in the sample hold circuit 19 due to bubbles in the fluid, switching between TA and TB by sampling will be temporarily stopped. Since and TB are almost equal, the influence on the sample and hold circuit 19 is slight. Therefore, all three sample hold circuits 15, 16 and 19 are stable against defects in the ultrasonic signal, and stable outputs can be obtained against obstacles such as bubbles and foreign objects. The flow rate can be determined by multiplying the flow velocity value (or flow velocity equivalent value) thus obtained by a known quantity.

What is shown in FIG. 3 is another embodiment of the present invention, and in the same figure, the same reference numerals as in FIG. 1 indicate the same or corresponding parts as in FIG. .

In the example shown in FIG. 3, the lamp circuit 17 in FIG.
An adder 25 is used in place of the control circuit 18 and sample hold circuit 19.

Now, to explain the adder 25, this adder 25
The outputs from the sample and hold circuits 15 and 16 are inputted to the adder +25, and as described later, the signal MTSR is also inputted. It is configured to

Next, the operation of the device constructed as described above will be explained with reference to FIG.

Sample and hold circuits 15 and 16 from the receiving and transmitting elements 2 and 3
Up to this point, the operation is the same as that shown in FIG. 1, and the explanation of that part will be omitted. Based on the respective outputs ΔTA and ΔTB from the sample and hold circuits 15 and 16, the adder 25 calculates the average value of the forward and reverse transmission times of the ultrasonic signal.

Now, the forward and reverse transmission times are TB and TA, respectively, and the signal φ
When the period "1" of MSTR is TMSTR, the outputs .DELTA.TA and .DELTA.TB of the sample and hold circuits 15 and +16 are expressed by the following equations, respectively.

The input/output relationship of the adder 25 is expressed by the following equation.

TMSTR as an input of the adder 25 receives the signal φMS
A value obtained by multiplying the 6F period of TR by a time-voltage conversion factor is provided from a variable constant voltage source (not shown).

In FIG. 3, similar to FIG. 1, the low pass filter 21
gives the time average value of the output voltage of the adder 25, but may be omitted in some cases.

The output voltage of the low-pass filter 21 is the average value of the transmission time in the forward direction and the reverse direction, so it has little relation to the flow velocity, but it changes to follow the change in the sound speed due to the temperature change of the fluid, and the output voltage of the low-pass filter 22 It is used for temperature correction of the time difference signal. Temperature correction is performed by dividing the output voltage of the low-pass filter 22 by the output voltage of the square circuit 23 by the divider 24. This relationship is exactly the same as the example shown in FIG. 1, and the above-mentioned relational expressions (1) to (3) hold true.
That is, the output V22 of the low-pass filter 22 and the square circuit 2
The flow velocity V can be determined by calculating the ratio between the output voltage V23 of

In the embodiment shown in FIG. 3, the squaring circuit 23 may perform tangential approximation using a linear amplifier because the range of change in the input signal is narrow, as in the embodiment shown in FIG. ,
Furthermore, instead of sampling the output of the ramp signal generator, integration over the periods TA and TB may be used. Since TA2 and TB2 can be obtained by integrating the ramp signal, one (TA2+TB2) may be used as an approximation of equation (2). Although the explanation has been made here by ignoring the structure transmission time of the ultrasonic transmission path, the temperature correction amount can be modified by the modification 23 when taking this into consideration. In each of the above-mentioned embodiments, the flow velocity is evaluated by dividing the output V22 of the low-pass filter 22 and the output V2l of the low-pass filter 21. However, if the temperature change is small, the subtracter 2
Even if the flow velocity is evaluated using the output value of 0 or the output value V22 of the low-pass filter 22, sufficient measurement accuracy can be obtained. In place of the ultrasonic receiving and transmitting elements shown in the above-mentioned embodiments, an element may be used in which two independent elements are closely combined for reception and transmission.

Furthermore, although it is disadvantageous in terms of accuracy and circuit technology, it is also possible to replace the time measuring means consisting of a lamp circuit and a sample and hold circuit with a time measuring means consisting of a clock oscillator and a counter. Furthermore, using a plurality of ultrasonic flowmeters described herein, each ultrasonic signal transmission path is arranged on the same cutting plane of the fluid flow path, and the weighted average value of the output of each flowmeter is used. A method of reducing errors due to non-uniformity of flow velocity distribution within a flow path can also be applied. As is clear from the above explanation, the ultrasonic flowmeter according to the present invention has excellent accuracy, response speed, and temperature stability, is easy to install and construct, and is stable against obstacles such as bubbles and foreign objects. It is.

Furthermore, compared to conventional systems, the structure is simpler and the cost and reliability are improved.

[Brief explanation of the drawing]

FIG. 1 is a program diagram showing the configuration of an embodiment of an ultrasonic flowmeter according to the present invention, FIG. 2 is a time chart explaining the operation of each part of the above embodiment, and FIG. FIG. 4 is a program diagram showing the configuration of another embodiment of the ultrasonic flowmeter, and FIG. 4 is a time chart illustrating the operation of each part of the ultrasonic flowmeter shown in FIG. In the figure, 2 and 3 are ultrasonic receiving and transmitting elements, 4 is a master controller, 5 and 6 are pulse generators, 7 and 8 are wave height selectors, 13, 14, and 17 are lamp signal generators, and 15 and 16 are
, 19 is a sample hold circuit, 20 is a subtracter, 21,
22 is a low-pass filter, 23 is a squaring circuit, and 24 is a divider.

Claims (1)

[Scope of Claims] 1. First and second ultrasonic signal transmitting means that are arranged to face each other via a flow path through which a fluid to be measured flows and generate ultrasonic signals excited by an excitation means; first and second ultrasonic signal receiving means provided corresponding to the first and second ultrasonic signal transmitting means, receiving ultrasonic signals from them and outputting the received signals; First and second amplifiers provided corresponding to the second ultrasonic signal receiving means and amplifying the output signals from them; the output signal from the first amplifier is input and the value thereof is a first pulse height separator that generates an output in response to the excitation of the excitation means; a first ramp signal generating means that generates a ramp signal in response to the excitation of the excitation means; a first sample and hold means for sampling and holding a ramp signal from the first ramp signal generating means; a first time measuring means for emitting an output signal corresponding to the signal arrival time up to the time of reception by the second ultrasonic signal receiving means; an output signal from the second amplifier is inputted and the signal is measured according to the value; a second pulse height selector that generates an output; a second ramp signal generating means that generates a ramp signal in response to excitation of the excitation means; and a second pulse height selector that receives the output from the second pulse height selector; a second sample and hold means for sample-holding the ramp signal from the second ramp signal generation means; a second time measuring means for emitting an output signal corresponding to the signal arrival time up to the time when the ultrasonic signal receiving means receives the ultrasonic signal; and based on each output signal output from the first and second time measuring means. calculation means for performing a predetermined calculation and generating an output corresponding to the flow velocity of the fluid; and the first and second time measurement means each further measure the same predetermined time from the time when the ultrasonic signal is transmitted. an ultrasonic flow rate comprising means for generating said ramp signals from corresponding said first and second ramp signal generating means during a minimum period including a time at which said ultrasound signal is expected to arrive after said ultrasonic flow rate; Total. 2. The calculation means that generates an output corresponding to the flow velocity of the fluid is
Claims characterized by comprising: a subtracter for determining the difference between each output signal emitted from the first and second time measuring means; and a low-pass filter provided on the output side of the subtracter. The ultrasonic flowmeter according to item 1. 3. The calculation means that generates an output corresponding to the flow velocity of the fluid constitutes a subtraction section that performs subtraction based on each output signal emitted from the first and second time measurement means, and the first and second time measurement means. Based on the outputs from the first and second wave height selectors, calculate the average value of the ultrasonic signal arrival times from the first and second ultrasonic signal generating means to the corresponding first and second ultrasonic signal means. It is characterized by being comprised of an averaging section that calculates, a squaring section that squares the output from the averaging section, and a division section that divides the output from the subtraction section by the output from the squaring section. An ultrasonic flowmeter according to claim 1. 4 The averaging unit that calculates the average value of the arrival times of ultrasound signals from the first and second ultrasound signal generation means to the corresponding first and second ultrasound signal means a lamp signal generating means that is activated at the time when the transmitting means is excited by the excitation means and reset after a predetermined time has elapsed from the time of activation, and first and second wave heights that constitute the first and second time measuring means. 4. The ultrasonic flowmeter according to claim 3, further comprising sample and hold means for receiving the output from the sorter and sample and holding the ramp signal from the ramp signal generation means. 5. The calculation means that generates an output corresponding to the flow velocity of the fluid is
a subtraction section that performs subtraction based on each output signal emitted from the first and second time measurement means; an averaging unit that calculates the average value of the arrival times of ultrasonic signals from the first and second ultrasonic signal transmitting means to the corresponding first and second ultrasonic signal receiving units, and squares the output from this averaging unit; 2. The ultrasonic flowmeter according to claim 1, comprising: a squaring section; and a division section that divides the output from the subtraction section by the output from the squaring section. 6. The averaging section shall consist of an adder that adds each output signal from the first and second time measuring means and an additional signal of a predetermined value, and a low-pass filter provided on the output side of this adder. The ultrasonic flowmeter according to claim 5, characterized in that: 7. The first ultrasonic signal transmitting means and the first ultrasonic signal receiving means are integrally formed, and the second ultrasonic signal transmitting means and the second ultrasonic signal receiving means are integrally constituted. An ultrasonic flowmeter according to any one of claims 1 to 6, characterized in that the ultrasonic flowmeter is configured as follows. 8 The first corresponding to the first and second ultrasonic signal transmitting means
and second ultrasonic signal receiving means means that the ultrasonic signal transmission path from the first and second ultrasonic signal transmitting means to the corresponding first and second ultrasonic signal receiving means is fluid. The ultrasonic flowmeter according to any one of claims 1 to 7, characterized in that the ultrasonic flowmeter is arranged so as to be located on the same cutting plane of a flow path.