JPH053529B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an ultrasonic flowmeter using a microcomputer, and particularly to an ultrasonic flowmeter that can rationally determine the point at which an ultrasonic pulse is received. Regarding 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, one example of which is the patent application filed by the present applicant on June 29, 1980, entitled "Ultrasonic Flowmeter," as shown in Figure 1. Explain the main points.

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 F. Transducer/receiver 3,
An ultrasonic pulse B in the form of a vibration wave is sent from an ultrasonic oscillator 5 to either one of the oscilloscopes 4 and 4 via an amplifier 6 and a changeover switch 7. The ultrasonic pulse received by the other of the transducers 3 and 4 via the fluid to be measured 2 is received by the amplifier 8 via the changeover switch 7. The ultrasonic pulse H output from the amplifier 8 is applied to one input end of the comparator 9, and the comparison voltage V _c is applied to the other end from a digital/analog converter (hereinafter referred to as a D/A converter) 10. is being applied.
At the output end of the comparator 9, a portion of the waveform exceeding the comparison voltage V _c of the vibration wave-like ultrasonic pulse 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 output terminal _I1 of the arithmetic circuit 11, and the start signal S transmitted from the ultrasonic oscillator ₅ at the same time as the ultrasonic pulse B is applied to the input terminal I2. Ru. The calculation circuit 11 calculates the time difference between the output of the comparator 9 and the start signal S, uses this result to calculate the flow rate, and outputs the output terminal 1.
Output to 2.

On the other hand, the output pulse P of the comparator 9 is taken into the control circuit 14 via the high-speed counter 13. The control circuit 14 is a microprocessor (hereinafter referred to as a CPU).
15. Read-on memory (hereinafter referred to as
It is composed of a ROM (abbreviated as ROM) 16, a random access memory (hereinafter abbreviated as RAM) 17, and a bus 18 connecting these. A predetermined area is secured in the RAM 17 in which a probability table 19 to be described later is to be formed. Control circuit 14 from counter
A predetermined process is performed using the counted value taken in, and the result is provided as a comparison voltage V _c to the comparator 9 via the D/A converter 10 .

Next, the control circuit 14 will be explained in more detail. First, under the control of the CPU 15 and according to a predetermined program in the ROM 16, the reference voltage l ₁ is set as the comparison voltage V _c of the comparator 9 via the D/A converter 10.
After reading out, the ultrasonic pulse part which is larger than the reference voltage _l1 is compared with the ultrasonic pulse H of the output of the amplifier 8 and outputted from the comparator 9 as an output pulse P.
The output pulse P is counted by the counter 13.
It is stored in a predetermined area in the RAM 17. In this way, by repeating the reference voltages (l ₁ , l ₂ , ~ _li , ~ _lo ) predetermined in the ROM 16, the number of pulses exceeding each reference voltage l _i can be counted. When this procedure is repeated a predetermined number of times N, the output pulse P exceeding the reference voltage l _i each time
A probability table 19 is obtained that is displayed using the count values of .

Next, in this probability table 19, the count value
_Probability P(l _{i ,}
The distribution of N _i (constant) is determined as shown in FIG. 2, and the standard table 20 is created according to the program stored in the ROM 16.

Here, we set an appropriate probability criterion P ₀ (<1), and P
Find the reference count value NΓ _i (NΓ _{i =} 3 in the example in Figure 2) that gives the maximum width of the width Δl _i of the reference voltage l _i such that (l i , N _i (constant)) ≧ P ₀ , Furthermore, the median value lΓ _i (lΓ _i =l ₃ ° in the example of FIG. 2) of the reference voltage l _i corresponding to this is determined.

The median value lΓ _i obtained in this manner is set as the comparison voltage V _c of the comparator 9 via the D/A converter 10, and the flow rate is measured by the arithmetic circuit 11 using this as a reference.

Next, the output pulses P of the comparator 9 with the comparison voltage V _c set to the median value lΓ _i are counted by the counter 13 and taken into the control circuit 14 . Control circuit 14
Then, the count value N _i of counter 13 is the reference count value
A predetermined program in the ROM 16 is used to calculate whether or not it is equal to NΓ _i , and if N _i =NΓ _i , it is determined that a correct flow rate has been measured and an instruction W=1 is issued to the calculation circuit 11 to output the flow rate. , if N _i ≠ NΓ _i , it is determined that the measured flow rate is incorrect and an instruction W=0 is issued to reject the flow rate output.

Using the median value lΓ _i and the reference count value NΓ _i determined as above, the probability P (l _i , N _i ) becomes a constant value P ₀
Because the ultrasonic pulse H is larger _than ) Since only the reference count value NΓ _i of ultrasonic pulses exceeding ) is used, the time information of the ultrasonic pulses is not included and the waveform information is not accurate. For this reason, for example, in the case of an ultrasonic pulse waveform with a sharp rise as shown in FIG. 3, the following problem occurs. In the case of a waveform with a sharp rise like this, the peak X can almost certainly be detected by selecting l ^x _i in FIG. 3 as the reference voltage. However, the peak group Z that is later in time
Therefore, even if the peak X is detected, the number of peaks exceeding the reference voltage l ^x _i (the number of output pulses) is difficult to remain constant, and the maximum probability decreases. On the other hand, if the reference voltage is selected as l ^y _i , the probability is maximized because the number of peaks Y is counted each time and becomes a nearly constant value, and with this conventional reference voltage setting means, the peak Y is selected. . However, in this case, although there is a sharp peak X, it cannot be used for detection, and the optimum reference voltage cannot be selected.

<Object of the Invention> In view of the above-mentioned conventional technology, the present invention provides an ultrasonic flowmeter that can determine the detection level including time information of the waveform of the received ultrasonic pulse and perform stable flow measurement. The purpose is to

<Configuration of the present invention> The configuration of the present invention that achieves this object relates to an ultrasonic flowmeter, which measures the propagation time of an ultrasonic pulse from transmission of the ultrasonic pulse to reception via the fluid to be measured. a measuring means, a threshold setting means for changing the detection level of the ultrasonic pulse, a table creation means for measuring the propagation time corresponding to the detection level while changing the detection level and creating a threshold time table, Median value determining means for determining a median value of detection levels that provides a maximum width of detection levels at which the propagation time is approximately constant with respect to changes in level, and measuring the flow rate of a fluid to be measured using this median value as the detection level. It is characterized by:

<Example> Hereinafter, an example of the present invention will be described based on the drawings. Note that parts having the same functions as those in the prior art are given the same numbers, and redundant explanations will be omitted.

FIG. 4 is a block diagram showing an embodiment of the present invention. The output pulse P of the comparator 9 is input to the counter 21. A clock f ₀ of a constant frequency is inputted to the counter 21 from a clock oscillator 22 . The counter 21 starts counting the clock f ₀ by the start signal S sent from the ultrasonic oscillator 5 and stops counting by the first output pulse exceeding the comparison voltage V _c of the comparator 9. A RAM 24 in the control circuit 23 is provided with an area in which a threshold time table 25 is formed. A program for forming this threshold time table 25 is stored in the ROM 26.
According to this program, the CPU 15 reads the contents of the counter 21, processes this count value, and outputs it to the D/A converter 10 via the bus 18.

The above count value processing will be explained in more detail based on the flowchart shown in FIG.

First, under the control of the CPU 15, the comparison voltage of the comparator 9 is adjusted according to a predetermined program in the ROM 26.
The reference voltage _l1 is read out via the D/A converter 10 as _Vc (step). After this, the counter 21 is reset by the reset signal R, and the counter 21
The content of is set to zero (step). Next, the ultrasonic pulse B is sent from the ultrasonic oscillator 5 to the fluid to be measured 2, and at the same time the counter 21 receives the start signal S and starts counting the clock _f0 . on the other hand,
The received ultrasonic pulse H is compared with the reference voltage _l1 by the comparator 9 (step), and counting by the counter 21 ends when the output pulse P exceeding the reference voltage _l1 is received (step). Therefore, the count value _nT of the counter 21 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 _T = [f ₀ T] (1) Count value of counter 21 with respect to this reference voltage l _1
nT is stored in RAM 24 to form a threshold time table 25 (step).

The procedure from the above steps is performed using predetermined reference voltages (l ₁ , l ₂ , ~l ₁ , ~l _N ) and threshold time table 2
5 is completed. The contents of the threshold time table 25 created in this way are average waveform information giving the envelope of the received ultrasonic pulse, as shown in FIG. In Figure 6, the horizontal axis is the propagation time T of the ultrasonic pulse, and the vertical axis is the reference voltage l ₁ , where the dotted line waveform is the waveform of the ultrasonic pulse and the solid line is the reference voltage l _i
The propagation time T of the ultrasonic pulse is shown for . The propagation time T is measured as the count value _nT of the counter 21. Since the threshold time table 25 stores approximate count values _nT giving the propagation time T corresponding to each reference voltage (l ₁ , l ₂ , ~ _li , ~l _N ), as shown in FIG. From these, the maximum width R among the widths (threshold widths) of the reference voltage l _i where the count value n _T is almost constant.
According to the procedure written in the ROM, the median value lΓ _{i of} the reference voltage l _i that gives
It is obtained by the CPU 15 and stored in the RAM 24 (step).

Next, this median value lΓ _i is set as the comparison voltage V _c of the comparator 10 via the D/A converter 10 (step).

Thereafter, the arithmetic circuit 11 executes flow rate measurement using the median lΓ _i as a threshold (step). When measuring the flow rate, when the amplitude of the ultrasonic pulse changes greatly and the detection peak changes, the propagation time T at that time is |T-T ₀ |>1/f (2) where f is the frequency of the ultrasonic pulse. Therefore, the following formula holds true.

|n _T −n _T °|−f ₀ /f≧0 (3) The CPU 15 calculates this left equation (step), and determines whether it is positive or negative.
Here, by setting f ₀ /f larger than 1, the fluctuation of the detected peak can be determined. Note that the more severe the judgment can be made, the more f ₀ /f is set to an integer greater than 1 but closer to 1. Actually the frequency f of the ultrasonic pulse
is at most 1 MHz, and clock f ₀ may be several MHz,
For example, the microcomputer clock signal (4
~6MHz) can be used.

As a result of the judgment in step, 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 instructed to set W=0, and the flow rate measurement in the calculation circuit 11 is changed. The result is rejected (step), and 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 calculation circuit 11 is commanded to set W = 1, and the flow rate measurement result in the calculation circuit 11 is Output (step).

After this, the process moves to a step in which it is determined whether a predetermined time has elapsed since the start of measurement. If the predetermined time has not elapsed, it is necessary to change the determined median value lΓ _i and the corresponding count value n _T °. Assuming that there is no flow rate, the process returns to the step and the flow rate measurement is repeated again. If the predetermined time has elapsed, return to the step and execute the procedure to determine the median value lΓ _i and count value nΓ _T again. In this way, it is determined whether the median value lΓ _i and the count value nΓ _T are appropriate values.

FIG. 7 is a block diagram showing another embodiment of detection of received waves. This is an example in which received waves are detected at zero-crossing points. The output pulse P of the comparator 9 switches a switch 27 connected to the inverting input terminal of the comparator 9. Terminal 27a of switch 27 is connected to a common potential point. Terminal 27b is the D/A converter 10
connected to the output end of the The terminal 27c is connected to the inverting input terminal of the comparator 9, and the output pulse P
Terminal 27c is switched to terminal 27a or 27b. The operation of the above circuit will be explained using the waveform diagrams shown in FIGS. 8 and 9. In FIG. 8, the dotted line waveform is the waveform of the received ultrasonic pulse H, and the horizontal axis is time t. Comparison voltage V _c
As a result, the reference voltage _l1 from the D/A converter 10 is applied to terminal 2.
7b, and when the ultrasonic pulse H becomes higher than the reference voltage _l1 (at time _t1 ), the output of the comparator 9 switches the inverting switch 27 to the terminal 27a side and becomes zero potential. Next, at the time when the ultrasonic pulse H crosses zero (time _t2 ), the output of the comparator 9 is inverted and switched to the terminal 27b side, and the reference voltage _l1 is set as the comparison voltage _Vc . Furthermore, when the ultrasonic pulse H becomes larger than the reference voltage l ₁ i (at time t ₃ ), the switch 27 is switched to the terminal 27a side and becomes zero potential. By repeating the above operation, the comparison voltage
V _c becomes as shown in FIG. Although one reference voltage l ₁ has been described in FIG. 7, FIG. 9 shows this as a function of propagation time for each reference voltage l _i . As shown by the solid line in the figure, the propagation time T shows a stepwise change with respect to the reference voltage l _i due to the propagation time at the zero crossing point. This has the advantage that determining the median lΓ _i is easier. Note that the waveform shown by the dotted line is for the circuit shown in FIG.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, when determining the reception point of an ultrasonic pulse, the detection level is determined by including the time information of the waveform of the received ultrasonic pulse. Therefore, even if the received ultrasonic pulse has a waveform with poor vibration attenuation, the optimal detection level that makes detection errors least likely to occur can be automatically selected, making stable flow measurement possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a conventional ultrasonic flowmeter, Fig. 2 is a waveform diagram showing the probability distribution for the reference voltage when the count value is used as a parameter in Fig. 1, and Fig. 3 is an ultrasonic pulse FIG. 4 is a block diagram showing an embodiment of the present invention, FIG. 5 is a flowchart explaining the operation of the embodiment shown in FIG. 4, and FIG. FIG. 4 is a waveform diagram showing the relationship between propagation time and reference voltage in the embodiment shown in FIG. 7. FIG. 7 is a block diagram showing another embodiment of reception wave detection. FIG. 9 is a waveform diagram explaining the operation, and a characteristic diagram showing the relationship between the propagation time and the reference voltage of the embodiment shown in FIG. 7. DESCRIPTION OF SYMBOLS 1... Pipe line, 3, 4... Ultrasonic transducer, 5... Ultrasonic oscillator, 7... Changeover switch, 9... Comparator, 10
...D/A converter, 11... Arithmetic circuit, 15... CPU,
21...Counter, 22...Clock oscillator, 23...
Control circuit, 24...RAM, 25...Threshold time table, 26...ROM, 27...Switch, H...Ultrasonic pulse, S...Start signal, P...Output pulse = -

Claims (1)

[Claims] 1 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; Table creation means for creating a threshold time table by measuring the propagation time corresponding to the detection level while changing the detection level; An ultrasonic flowmeter comprising: a median value determining means for determining a median value of the detection levels that provides a maximum width; and a flow rate of the fluid to be measured is measured using the median value as the detection level.