JPS61274221A - Supersonic flow rate meter - Google Patents

Abstract

PURPOSE:To enable high-accuracy flow rate measurement free from span-error, by setting a threshold value of level detection in a supersonic wave pulse shaping part received as signal prior to having influenced by multiple reflections in a pipe line. CONSTITUTION:In order to remove the influence of multiple reflections, in No.1 or No.2 wave of supersonic wave prior to arrival of the multiple reflected waves, the reference for detection of level is set. Propagating time T corresponding to each reference voltage li fed out from a D/A convertor 10 is measured and a threshold time table 23 is made in the specified area of the RAM22 backed up by a battery according to the ROM21 program. This threshold time table 23 is measured in repetition K times as frequently as each reference voltage li. In this case, as it is known from wave-shape observations of the supersonic wave pulses using several pipe lines 1, that the peak voltage of the No.2 wave of the supersonic wave pulse is higher by 20% and up than the peak voltage Vp of the supersonic wave pulse received, the upper limit value lH in the variable range of the standard voltage li is set at nearly 25% of the peak voltage Vp.

Description

[Detailed description of the invention] Industrial application field> The present invention relates to an ultrasonic flowmeter using a microconbeater, and in particular, it is possible to rationally determine the time point at which an ultrasonic pulse is received. Regarding ultrasonic flowmeters.

<Prior art> Ultrasonic flowmeters measure the flow rate using the time difference between when an ultrasonic pulse is sent to the fluid being measured and when it is received. It is necessary to decide accurately.

Various applications have been filed for this purpose, an example of which is Japanese Patent Application No. 59-142569 ``Ultrasonic Flowmeter''.
The main points will be explained using a diagram.

A fluid to be measured 2 is caused to flow through the pipe line 1 in the direction of arrow F, and a flow rate Q of the fluid to be measured 2 is measured. For this purpose, transducers 3 and 4 are installed in the conduit 1 so as to face each other diagonally with respect to the flow direction FilC. A trigger pulse Tp is applied to the drive circuit 6 from a synchronization circuit 5 having a black oscillator to either one of the transducers 3 and 4, and the output K is a differential wave having a peak value of, for example, about 200V. driving pulse D,
is applied via the changeover switch 7. Transducer/receiver 3, 4
On the other side, the ultrasonic pulses received through the fluid to be measured 2 are received by the amplifier 8 via the changeover switch 7 .

The ultrasonic pulse H at the output of the amplifier 8 is applied to one input end of the comparator 9, and the other end is connected to a digital/analog converter (
Hereinafter, it is abbreviated as D/A converter) From 10, the comparison voltage v0
is applied. At the output end of the comparator 9, the first zero-crossing portion of the waveform exceeding the comparison voltage vc among the vibration wave-like ultrasonic pulses is converted into a pulse and output as an output pulse P.

The pulse voltage of the output of the comparator 9 is applied to the input terminal 1 of the arithmetic circuit 11, and the start signal S, which is transmitted simultaneously with the sending of the trigger pulse T from the synchronization circuit 5, is applied to the input terminal 2. The arithmetic circuit 11 calculates these time differences, uses this result to calculate the flow rate, and outputs it to the output terminal 12.

The output pulse P of the comparator 9 is input to the counter 13. The counter 13 is inputted with a constant frequency of black and white from a black and white oscillator 14 . The counter 13 is clocked by the start signal S sent from the synchronization circuit 5.
It starts counting fo and stops counting when the first output pulse exceeds the comparison voltage vc of the comparator 9.

Random access memory (hereinafter referred to as R) in the control circuit 15
(abbreviated as AM) 16 is provided with an area forming a dark value time table 17. This threshold time table 17
A program for forming the counter 13 is written in advance in a memory (hereinafter referred to as ROM) 18, and according to this program, a microprocessor (hereinafter referred to as CPU) 19 reads the contents of the counter 13 and calculates this count. The value is processed and output to the D/A converter 10 via the bus 20.

Next, regarding the processing of the count value in the control circuit 15, the sixth
A more detailed explanation will be given based on the flowchart shown in the figure.

First, under the control of the CPU 19, the comparison voltage V of the comparator 9 is determined according to a predetermined program in the ROM 18. as D/
The reference voltage t1 is read out via the A converter 10 (steps and steps ①). Thereafter, the counter 13 is reset by the reset signal R, and the contents of the counter 3 are made zero (step 2). Next, the trigger pulse T from the synchronization circuit 5 causes the drive pulse D to be sent to the fluid to be measured 2 via the drive circuit 6, and at the same time the counter 13 receives the start signal S and starts counting the clock fQ. . On the other hand, the received ultrasonic pulse H is compared with the reference voltage t1 by the comparator 9 (step ■), and counting by the counter 3 ends when the output pulse P exceeding the reference voltage t1 is received (step ■).
).

Therefore, the count value nT of the counter 3 gives an approximate value of the propagation time T of the ultrasonic pulse H, and if (x) is a symbol representing the largest integer not exceeding X, then the following equation is obtained.

n = (fo T) (
1) Count value n of counter 3 for this reference voltage t1
T is stored in RAM 16 to form a threshold time table 17 (step ■).

The above steps from ■ to ■ are performed at a predetermined reference voltage (
tl, t2. ~ti, ~tN) (step ■), the threshold time table 17 is completed. The contents of the dark value time table 17 created in this way are average waveform information giving the envelope of the received ultrasonic pulse, as shown in FIG. In FIG. 7, the horizontal axis represents the propagation time T of the ultrasonic pulse, and the vertical axis represents the reference voltage ti. It shows. The propagation time T is measured as the count value nT of the counter 3. The threshold time table 17 includes each reference voltage (t1+L2'~
Since the approximate count value nT that gives the propagation time T corresponding to LI, ~tN) is stored, as shown in FIG. 7, the width of the reference voltage ti (threshold value The median value ti of the reference voltage tI that gives the maximum width R among the widths) and the corresponding count value nT are determined by the CPU 19 according to the procedure written in the ROM 18, and the RA
Store in M16 (step ■).

Next, this median value t is set as the comparison voltage vc of the comparator 10 via the D/A converter 10 (step ■)
.

Thereafter, flow rate measurement using the median value L'';' as a threshold is executed by the arithmetic circuit 11 (step ■).When the amplitude of the ultrasonic pulse changes greatly during flow rate measurement and the detection peak changes, f. The propagation time T at that time as the frequency of the ultrasonic pulse is IT −'rol)t/r
(2), so the following equation holds true.

1nT-nTl-f□/f≧0 (3) This pressure equation is calculated by the CPU 19 (Step 0), and its sign is determined in Step 0. Here, by setting f(y'f larger than 1, it is possible to judge the fluctuation of the detected peak. In addition, the more f(y'f is larger than 1 but closer to 1, the more severe the judgment can be made. In this case, the frequency f of the ultrasonic pulse is at most IM) (Z), and the clock fo may be several MH!, for example, a clock signal (4 to 6 MHz) of a microcopy/pi, etc. can be used.

As a result of the judgment in step O, if the left side of equation (3) is positive, it is judged that the detection peak of the ultrasonic pulse has changed significantly, and the calculation circuit 11 is commanded as W-O, and the calculation circuit 11 measures the flow rate. If the left side of equation (3) is negative, it is determined that there is no significant change in the detected peak and it is normal, and the arithmetic circuit 11 is commanded as w=i, and the flow rate measurement result in the arithmetic circuit 11 is rejected. is output (step O).

After that, the process moves to step 0, where it is determined whether a predetermined time has elapsed since the start of measurement, and if the predetermined time has not elapsed, the determined median value tl and the corresponding count value nT
It is assumed that there is no need to change the flow rate, and the flow rate measurement is repeated again by returning to step (3).

If the predetermined time has elapsed, the process returns to step (2) and executes the average head again to determine the median value Ll and the count value n7. In this way, it is determined whether the median value t1 and the count value n7 are appropriate values.

<Problems to be Solved by the Invention> However, such conventional ultrasonic flowmeters have the following problems.

FIG. 8 is an enlarged view of the vicinity of the vibrator attached to the conduit 1. A drive pulse D is applied to the vibrator 3a via a changeover switch 7 shown in FIG. By applying the drive pulse D to the vibrator 3a, the vibrator 3a resonates in its thickness direction, and the generated ultrasonic pulse has a waveform that vibrates as shown in FIG.

This ultrasonic pulse passes through the conduit 1 to the transducer 4 on the opposite side.
Let a vibrate and generate a voltage on it.

This voltage becomes an ultrasonic pulse with an envelope trailing backward due to resonance caused by the thickness of the pipe 1.

Here, it is assumed that the wall thickness of the conduit 1 is large.

The ultrasonic pulse a from the propagation path A shown in FIG. 8 and the ultrasonic pulse b reflected from the propagation path B arrive at the transducer 4a separated in time, so the propagation times Ta and Tb
are separated and there is no interference with each other (FIG. 10). Therefore, each waveform of the ultrasonic pulse is also sinusoidal and does not become a factor of error when measuring propagation time.

Note that the ultrasonic pulse C shown in Figure 810 is an ultrasonic pulse that reflected and followed another propagation path C not shown,
It is in a state separated from the ultrasonic pulses s and b.

On the other hand, when the wall thickness of the conduit 1 is small, the 11th
As shown in the figure, depending on the thickness of the wall, the ultrasonic pulse b%C is
The waveforms of the ultrasonic wave a become closer to each other, causing distortion in the waveform of the ultrasonic wave a. Therefore, the value of the zero-crossing point of the received waveform, which is the measuring point of the propagation time, fluctuates, resulting in a span error.

By the way, for example, the carrier frequency (1/
If you select IMH2K and use a pipe with a wall thickness of about 4.6 mm, which is a thin value for normally used pipes, then the time difference Δr (=Tb
-Ta) is approximately 1.7)Ig, so as shown in FIG. 12, the portions after the fourth peak of the ultrasonic pulse a are affected by multiple reflections.

Therefore, a commonly used pipe line is more or less affected by multiple reflections.

By the way, in the conventional ultrasonic flowmeter shown in FIGS. 5 and 6, the maximum width (threshold width) of the reference voltage t1 at which the count value nT is approximately constant is given as shown in FIG. The median value ti of the reference voltage tH is determined and used as i3.The propagation time difference is used as the threshold value for the profile γ. Depending on the waveform of the ultrasonic pulse, a dark value is set in the rear part of the waveform affected by multiple reflected waves, resulting in a span error.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a time measurement method for measuring the propagation time of an ultrasonic pulse from transmission of the ultrasonic pulse to reception via the fluid to be measured. means for setting a threshold value for changing the detection level of an ultrasonic pulse; table creation means for creating a dark value time table by measuring the propagation time corresponding to the detection level while changing the detection level; The first or second pulse having the minimum propagation time among the ultrasonic pulses whose propagation time is approximately constant.
a received wave selection means for selecting a received wave, a level determining means for determining a detection level of the selected received wave, and a flow rate of the fluid to be measured is measured using the detection level determined by the level determining means as a reference level. It is structured as follows.

<Example> Embodiments 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, and FIG. 2 is a flowchart explaining the operation of the embodiment shown in FIG. Incidentally, parts having the same functions as those in the prior art will be given the same reference number 4 and the explanation will be omitted as appropriate.

In the embodiment shown in FIG. 1, in order to eliminate the influence of multiple reflections, the standard for level detection is set on the first or second wave of the ultrasonic pulse before the arrival of multiple reflected waves.

In FIG. 1, the propagation time T corresponding to each reference voltage tiK sent out from the D/A converter 1o is measured in the same manner as shown in FIG.
The RAM 22 is battery-backed up as shown in steps ■ to ■ in FIG. 2 according to the program in step 1.
A dark value time table 23 is created in a predetermined area. This dark value time table 23 is repeatedly measured for each reference voltage ti. In this case, the peak voltage of the second wave of the ultrasonic pulse is determined by the peak voltage V of the received ultrasonic pulse from the results of waveform observation of the ultrasonic pulse using various types of pipes l.
Therefore, in the example shown in the m1 diagram, the upper limit of the variable range of reference voltage 1 (LH
is set to about 254 of the peak voltage V. Further, the lower limit value may be set to approximately the level of internal or external noise, but it may also be set to LL=O. As described above, the variable range of the reference voltage t1 is set to tL≦ti≦LH, the dark value time table 23 is created, and the process moves to step O.

In step O, the CPU 19 determines whether or not the above search operation has been completed, and if it has been completed, the process moves to the next step (2).

In step (2), it is determined whether or not the propagation time T is within a predetermined variation σ with respect to a change in the reference voltage ti among the data formed in the threshold time table 23. Judgment is made according to the judgment program 24, and propagation times T exceeding the variation σ are rejected.
Move to step OK.

In step O, the selection program 25 loaded in the RAM 22 searches for the one showing the minimum propagation time Tm1n among the propagation times within the variation σ. And the maximum reference voltage 'max' and the minimum reference voltage tnii'-n
, and the level difference Δv1('', 1oax −'m
1n) and ΔV2(='H-'max)'. - If the data shown at step 0%O is illustrated, it will be as shown in Figure 3. The propagation times corresponding to reference voltages below 'min are distributed over the σ value in the two measurements. The book with the smallest propagation time Tm1o among the σ values is T1
where T2 is the propagation time of the second wave corresponding to the next wave.

Steps @ and O constitute received wave selection means.

Step [stock] is the minimum propagation time T found in step O
ml. The reference voltage tfflax is compared with the upper limit LH, and it is determined whether tmax is equal to or smaller than LH.

When tmax < tH, proceed to step ■, and Δv
1 and Δv2 are compared. As a result, ΔVl )Δv2
If so, the process moves to step @ to set a threshold value for the first wave of the received ultrasonic pulse. If the condition of Δv1>Δv2 is not satisfied, the process moves to step O to set a threshold value for the second wave.

When tmaX='H, the propagation time can take either value 1 or T2, but in this case K is set to move to step @.

In step @, the calculation (tmi.+Lmaz)/2 is performed, and in step O, the calculation (LH'' tmax)/2 is performed, and the process moves to step (2).

The execution program from steps O to @ above is stored in RAM.
220 is stored in a predetermined area as a level determination program 26, and executed under the control of CPo 19.

RAM that stores this program 22. ROM
A control circuit 27 is composed of a 21° CPU 19, a path 20, and the like.

In steps ① to 0, the signal is processed in the same procedure as the steps shown in FIG.

By the signal processing as described above, the first wave or the second wave of the ultrasonic pulse, which is not affected by multiple reflected waves on the signal wave, is captured and the propagation time is measured, so that it is possible to perform a good flow rate measurement without causing a span error.

FIG. 4 is a waveform diagram for determining the level of another embodiment for detecting the first wave or the second wave of an ultrasonic pulse.

When the peak voltage of the first wave of the ultrasonic pulse is vl and the peak voltage of the second wave is v2, the respective propagation times are T1 and T
2, a predetermined margin Δv which is the difference in peak voltage
(= Vl -0, V2 - Vl,...), for example, a width of 0.2 volts is set, and the wave showing the smallest value of the propagation time T having a level greater than or equal to this margin Δma is, for example, In the example shown in FIG. 4, the second wave is obtained as Δv ) Vl and its intermediate value is set in the comparator 9 with T as the threshold.

A program for executing this is stored in the RAM 22.

This program is executed under the control of CPo 19.

<Effects of the Invention> As explained above in conjunction with the embodiments, according to the present invention, a dark value for level detection is added to the received ultrasonic pulse waveform portion before being affected by multiple reflections in the conduit. Since the settings are made in this way, highly accurate flow rate measurement is possible without the occurrence of span errors as in the conventional method.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a flowchart showing the operation of the embodiment shown in Fig. 1, and Fig. 3 is a dark value time. Figure 4 is a data distribution diagram showing the contents of the table; Figure 4 is a waveform diagram for determining the level of another embodiment for detecting the first wave or second wave of an ultrasonic pulse;
The figure is a block diagram showing the configuration of a conventional ultrasonic flowmeter.
The figure is a flow chart diagram explaining the operation of the ultrasonic flow meter shown in Figure 5, Figure 7 is a waveform diagram showing the relationship between propagation time and reference voltage of the ultrasonic flow meter shown in Figure 5, and Figure 8 is An enlarged view of the vicinity of the vibrator attached to the conduit, Fig. 9 is a waveform diagram showing the waveform of the ultrasonic pulse generated by the vibrator alone, and Fig. 10 is the reception when the conduit has a large wall thickness. Figure 11 is a waveform diagram of an ultrasonic pulse that shows the received wave when the wall thickness of the pipe is small, and Figure 12 is a waveform diagram of the ultrasound pulse that shows the received wave when the wall thickness of the pipe is small. FIG. 2 is an enlarged waveform diagram of the ultrasonic pulse shown in FIG. DESCRIPTION OF SYMBOLS 1... Pipe line, 3.4... Transmitter/receiver, 9...-Comparator, 1G... D/MU converter, 11... Arithmetic circuit, 13
...Counter, 14...Clock oscillator, 15.2
7... Control circuit, 16.22... RAM, 17
．． 23...Threshold time table, 18.21...80
M%19...CPU, 24...σ judgment program, 25...Selection program, 26...Level determination program, S...Start pulse, Tp...Trigger pulse, Dp...Drive pulse. Jli Figure 4 Figure 7 Figure B

Claims (1)

[Claims] time measuring means for measuring the propagation time of the ultrasonic pulse from transmission of the ultrasonic pulse to reception through the fluid to be measured; threshold setting means for changing the detection level of the ultrasonic pulse; and changing the detection level. table creation means for measuring the propagation time corresponding to the detection level and creating a threshold time table; a received wave selecting means for selecting the first or second received wave; a level determining means for determining the detection level of the selected received wave; An ultrasonic flowmeter characterized by measuring the flow rate of.