JPH053530B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an ultrasonic flowmeter using a microcomputer, and in particular is capable of rationally determining the time point at which an ultrasonic pulse is received and the difference in propagation time. Regarding ultrasonic flowmeters.

<Prior art> Ultrasonic flowmeters measure the flow rate by using the time difference between the time when ultrasonic pulses are sent to the measured fluid and the time when they are received, so the detection level of ultrasonic pulses is optimized. It is necessary to accurately determine the propagation time difference by selecting a specific value.

Various applications have been filed for this purpose, among which a patent application was filed by the present applicant on July 10, 1980 for selecting the optimal detection level, and the name of the invention is "Ultrasonic Flowmeter". The main points will be explained using Figure 1.

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, the part of the waveform exceeding the comparison voltage _Vc of the vibration wave-like ultrasonic pulse is converted into a pulse and output as an output pulse P _L.

The pulse voltage of the output of the comparator 9 is applied to the input 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. The output pulse P _L of the comparator 9 is input to the counter 13. The counter 13 receives a constant frequency clock f ₀ from the clock oscillator 14.
is entered. The counter 13 is clocked by the start signal S sent from the ultrasonic oscillator 5.
It starts counting f ₀ and stops counting when the first output pulse exceeds the comparison voltage V _c of the comparator 9. A RAM 16 in the control circuit 15 is provided with an area in which a threshold time table 17 is formed. The program for forming this threshold time table 17 is
It is written in the ROM 18 in advance, and according to this program, the CPU 19 reads the contents of the counter 13, processes this count value, and transfers it to the bus 2.
0 to the D/A converter 10.

Next, the processing of the above count value will be explained. First, under the control of the CPU 19, the comparison voltage of the comparator 9 is adjusted according to a predetermined program in the ROM 18.
The reference voltage _l1 is read out via the D/A converter 10 as _Vc . After this, the counter 13 receives the reset signal R _s
The counter 13 is reset to zero. 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 13 receives the start signal S and starts counting the clock _f0 . On the other hand, the received ultrasonic pulse H is compared with a reference voltage _l1 by a comparator 9, and counting by the counter 13 ends when an output pulse P _L exceeding the reference voltage _l1 is received. Therefore, the count value n _T of the counter 13 gives an approximate value of the propagation time T _v 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 _v ] (1) Count value of counter 13 for this reference voltage l ₁
n _T is stored in RAM 16 to form a threshold time table 17.

On the premise that the waveform and propagation time _Tv of the ultrasonic pulse do not change during a short period of time, the above procedure is performed using predetermined reference voltages (l ₁ , l ₂ ,
~l ₁ , ~l _N ) to complete the threshold time table 17.

The contents of the threshold time table 17 created in this way are as shown in Figure 2, where the horizontal axis is the propagation time of the ultrasonic pulse and the vertical axis is the reference voltage l _i . This is average waveform information that gives an envelope. The propagation time T _v is measured as the count value n _T of the counter 13 . Threshold time table 17
Since the approximate count value n _T that gives the propagation time T _v corresponding to each reference voltage (l ₁ , l ₂ , ~l _i , l _N ) is stored in , as shown in Fig. 2, From count value n _T
The median value _{lΓ i} (degrees) of the reference voltage l _i that gives the maximum width R among the widths (threshold value width) of the reference voltage l _i where is almost constant
and the corresponding count value nΓ _T (degrees) are determined by the CPU 19 according to the procedure written in the ROM,
Store in RAM16.

Next, this median value lΓ _i (degrees) is converted to the D/A converter 10
is set as the comparison voltage V _c of the comparator 9 via the .

Thereafter, the arithmetic circuit 11 executes flow rate measurement using the median lΓ _i (degrees) as a threshold.

Next, as a conventional technology for determining the propagation time difference for flow rate calculation, Patent Application No. 58-70600 "Ultrasonic Flowmeter"
The main points will be explained using Figure 3.

Components having the same functions as those in FIG. 1 are designated by the same reference numerals, and redundant explanation will be omitted.

The synchronization circuit 21 receives the start signal S, is synchronized with the oscillation frequency f of the oscillator 22 controlled by the digital control signal W, and sends a synchronization signal A to the ultrasonic oscillator 5. At the same time, the oscillation frequency f is input to a counter 23 which is given a digital value control signal N and divides the frequency by a frequency division ratio _Nd . The output of the counter 23 is inputted to one end of the time difference detection circuit 24 as a frequency-divided signal _Sc . Therefore, the frequency division time T _s from sending out the synchronizing signal A until receiving it at the time difference detection circuit 24 is
T _s =N _d /f.

On the other hand, an ultrasonic pulse is sent out from the ultrasonic oscillator 5 in synchronization with the sending of the synchronization signal A, and is transmitted to the time difference detection circuit 2 via the amplifier 6, the changeover switch 7, the fluid to be measured 2, the changeover switch 7, and the amplifier 8.
4 is input to the other end. The propagation time of this ultrasound is
_Tv .

The time difference detection circuit 24 calculates the frequency division time T _s and the propagation time.
Compare T _v and output the magnitude as P _T. The comparison signal _PT is 1-bit information indicating only which one is faster.

The control circuit 25 includes a CPU 26, a ROM 27, and a RAM.
28 and a bus 29. The control circuit 25 takes in the comparison signal P _T and divides the frequency division time T _s
Correcting operations are performed under the control of the CPU 26 so that Tv corresponds to the propagation time _Tv . For this purpose, a control signal N to the counter 23 and a control signal W to the oscillator 22 are output from the control circuit 25. Oscillator 22
receives a digital value control signal W from the control circuit 25 and outputs an oscillation frequency in the form of f=f _c +kW. Here, f _c is the oscillation frequency when the control signal W is zero, and the frequency is changed in the vicinity of f _c by the control signal W (k is a constant). The division time T _s is N _d /
Since the frequency division ratio N _d of the counter 23 can be changed significantly by changing the frequency division ratio N d of the counter 23 using the control signal N, it can also be changed minutely by changing it in the vicinity of the oscillation frequency f _c using the control signal W. The propagation time is determined by changing this control signal N or W many times.
In order to bring the dividing time T _s close to T _v , known means such as successive approximation are used.

As described above, since the control circuit 25 can know the state where T _v =T _s , the propagation time T _v can be determined. If the propagation times when the changeover switch 7 is switched alternately and ultrasonic pulses are sent in the flow direction F and in the opposite direction are respectively T ₊ and T _- , the flow rate can be calculated using these differences, and the output circuit The flow rate Q is output from 30.

The conventional technique shown in FIG. 1 proposes the determination of the optimal detection level of ultrasonic pulses, and the conventional technique shown in FIG. 3 proposes the effective determination of the propagation time difference of ultrasonic pulses. A flowmeter must have both of these functions.

However, simply adding these two functions has the drawback of becoming redundant, lowering reliability, and increasing cost.

<Object of the Invention> In view of the above-mentioned prior art, the present invention provides an ultrasonic flowmeter that can set an optimal detection level of ultrasonic pulses, can reasonably calculate an effective time difference, and as a result can stably measure the flow rate. The purpose is to provide

<Configuration of the Invention> The configuration of the present invention that achieves this object relates to an ultrasonic flowmeter, in which an ultrasonic pulse transmitted and received by a fluid pulse to be measured is inputted to one side, and a comparison voltage is inputted to the other side. an oscillator that outputs a corresponding frequency that is controlled by a digital value, a preset counter that measures the frequency count from the sending of the ultrasonic pulse to its reception, and a preset counter that measures the corresponding count value while changing the comparison voltage. The first step is to calculate the median value of the comparison voltage that gives the maximum width of the comparison voltage at which the count value with respect to the change in the comparison voltage becomes almost constant.
Comparison between the calculation means and the time width obtained corresponding to the preset value by dividing the propagation time and frequency obtained from the count value of the preset counter when the median value is set as the comparison voltage by the preset counter. a second calculation means for changing the preset value and the digital value to match the time width to the propagation time;
It is characterized in that the flow rate is calculated using the calculation result by the second calculation means.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. In the following description, parts having functions corresponding to those shown in FIGS. 1 and 3 are given the same numbers, and redundant descriptions are omitted.

The oscillator 22 is given a control signal W of a digital value and outputs a corresponding oscillation frequency f. This output is input to the synchronization circuit 21 and the start signal S
In response to this, synchronization is established with the oscillation frequency f, and a synchronization signal A is given to the ultrasonic oscillator 5, which sends an ultrasonic pulse to the fluid 2 to be measured. The output terminal of the synchronizing circuit 21 is connected to the set terminal S of the flip-flop 31, and at the same time as the synchronizing signal A is sent out, the output terminal Q of the flip-flop 31 is set to the "H" level. Output end Q
Since one end of the input of the AND gate 32 is connected to the output end of the AND gate 32, the oscillation frequency f is outputted to the output end of the AND gate 32, which is connected to the output end of the oscillator 22. This output is input to a preset counter 33 with a preset value _Np , and the oscillation frequency f starts to be counted down, for example, from the sending of the synchronizing signal A.

On the other hand, the ultrasonic pulse H from the fluid to be measured 2 is input to one side of the comparator 9, and the other side is compared with the reference voltage _l1 given as the comparison voltage _Vc given from the D/A converter 10. , a pulse exceeding the reference voltage _l1 is output as an output pulse P _L. This output pulse P _L is applied to the reset terminal R of the flip-flop 31 to bring the level of its output terminal Q to the "L" level. Therefore, counting of the oscillation frequency f is stopped. Therefore, 1/f of the count value n _T p (=N _p -n) of the preset counter 33 gives an approximate value of the propagation time T _v of the ultrasonic pulse.
The value of 1/f of this count value _nT is stored in the CPU 3 in the threshold time table 17 of the RAM 35 in the control circuit 34.
6 is stored via the bus 38 according to a predetermined procedure of the ROM 37. The above procedure is repeated for various reference voltages (l ₁ , l ₂ to l _i , to l _N ) similarly to the ultrasonic flowmeter shown in FIG. 1 to complete the threshold time table 17. The procedure for determining the median value lΓ _i (degrees) using this threshold time table 17 is the same as that shown in FIG.

The median lΓ _i (degrees) determined in this way is D/
After setting the comparison voltage V _c via the A converter 10, the process moves on to measuring the propagation time of the ultrasonic pulse.

In response to the start signal S from the control circuit 34, the synchronization circuit 21 sends out the synchronization signal A, and at the same time sets the flip-flop 31. Therefore, the AND gate 32 opens and the preset counter 33 starts counting the oscillation frequency f. Assuming that the preset counter 33 counts down, after the propagation time T _v has elapsed since the synchronization signal A was sent out, an ultrasonic pulse is received, the flip-flop 31 is reset, the AND gate 32 is closed, and the operation of the preset counter 33 is stopped. Stop. At this time, preset counter 3
3, n _T = [fT _v ] pulses are sent, so the count value n is n = N _p −n _T (2).

Here, when N _p /f<T _v , the count value of the preset counter 33 is 0 before receiving the ultrasonic pulse.
When N _p /f>T _v , counting is stopped by reception of the ultrasonic pulse before the count value of the preset counter 33 reaches 0. Therefore, when the preset counter 33 stops counting, the magnitude of the propagation time _Tv and the frequency division time _Ts can be determined based on whether or not the counted value reaches the preset value _Np . The control circuit 34 controls the control signal W and the preset value N _p based on the judgment result of only the magnitude, so that N _p /f is the propagation time.
Take corrective action to match T _v . N _p /f=T _v
In this state, the propagation time T _v can be accurately determined from the values of N _p and f at this time.
For this corrective action, the control signal W and the preset value are
As an algorithm for changing N _p , the same method as shown in FIG. 3, such as the successive approximation method, can be used.

Thereafter, the flow rate is calculated in the same manner as shown in FIG.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, counters are used for setting the optimum detection level of ultrasonic pulses and determining the propagation time difference of ultrasonic pulses, as in the conventional case. By using one counter, it is possible to set the optimum detection level and determine the propagation time difference.

Therefore, it is possible to improve reliability and reduce costs by sharing hardware, and also to be able to measure the flow rate stably.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the first conventional ultrasonic flowmeter, Fig. 2 is a waveform diagram showing the relationship between propagation time and reference voltage of the ultrasonic flowmeter shown in Fig. 1, and Fig. 3 is a waveform diagram showing the relationship between propagation time and reference voltage of the ultrasonic flowmeter shown in Fig. FIG. 4 is a block diagram showing the configuration of a second conventional ultrasonic flowmeter, and FIG. 4 is a block diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Pipe line, 2... Fluid to be measured, 3, 4... Transducer/receiver, 5... Ultrasonic oscillator, 7... Selector switch, 9...
Comparator, 10...D/A converter, 11... Arithmetic circuit,
13... Counter, 14... Oscillator, 15, 25, 3
4...Control circuit, 16, 28, 35...RAM, 1
8, 27, 37...ROM, 19, 26, 36...
CPU, 22...oscillator, 23...counter, 31...
Flip-flop, 33...preset counter.

Claims (1)

[Claims] 1. A comparator into which the ultrasonic pulse sent to and received by the fluid to be measured is inputted to one side and a comparison voltage inputted to the other, an oscillator that outputs a corresponding frequency controlled by a digital value, and an oscillator that outputs the corresponding frequency by controlling a digital value. a preset counter that measures the count value of the frequency from transmission to reception; and a comparison device that measures the corresponding count value while changing the comparison voltage so that the count value remains approximately constant with respect to changes in the comparison voltage. a first calculation means for calculating the median value of the comparison voltage giving the maximum value of the voltage; and a first calculation means for calculating the median value of the comparison voltage giving the maximum value of the voltage; a second calculation means that changes the preset value and the digital value by comparing the time width obtained by dividing the frequency with the preset value by the preset counter to match the time width with the propagation time; An ultrasonic flowmeter characterized in that a flow rate is calculated using a calculation result by the second calculation means.