JPH053528B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an ultrasonic flow meter using a microcomputer, and particularly to an ultrasonic flow meter that can rationally determine the point at which an ultrasonic pulse is received. Regarding the meter.

<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.

Various applications have been filed for this purpose, one example being Japanese Patent Application No. 58-72490 ``Ultrasonic Measuring Device''.
is shown in Figure 1 and will be explained.

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. A predetermined process is performed using the count value taken into the control circuit 14 from the counter 13, and the result is provided as a comparison ultrasonic wave V _c to the comparator 9 via the D/A converter 10.

Next, the operation of the control circuit 14 will be explained using 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 16.
The reference voltage _l1 is read out via the D/A converter 10 as _Vc (step). Thereafter, the counter 13 is reset by the reset signal R, and the contents of the counter are set to zero (step). After setting the reference voltage _l1 as the comparison voltage _Vc , it is compared with the ultrasonic pulse H output from the amplifier 8, and the ultrasonic pulse portion larger than the reference voltage _l1 is output from the comparator 9 as the output pulse P.
Output as (step). FIG. 3 illustrates the above points. The horizontal axis is the time axis, and the vertical axis is the amplitude of the ultrasonic pulse H. The dotted line indicates the level of the reference voltage l _i . At the illustrated reference voltage _l1 , there is one output pulse P. This output pulse P is counted by the counter 13 (step) and stored in a predetermined area in the RAM 17 (step). Next, the reference voltage is changed to l ₂ (l ₁ >l ₂ ), and each step up to is executed. When repeating (step) only the reference voltages (l ₁ , l ₂ , ~ _li ~ _lo ) predetermined in the ROM 17 in this way, the first column (N=0) of the probability table 19 shown in FIG. ) The number of pulses exceeding each reference voltage l _i can be counted. By repeating the above procedure a predetermined number of times N (steps), a probability table 19 as shown in FIG. 4, for example, is obtained. The example in FIG. 4 is a case where the process is repeated 20 times. Total number of times N
The value obtained by dividing the count value in each column by (=20) is the probability P(l _i ,
N _i ). A probability table creation means is constructed by these steps. next,
Using this probability table 19, under the control of the CPU 15, the reference voltage l _n and count value N _n that give the maximum probability are determined according to the program in the ROM 16.
The data is stored in a predetermined area of the RAM 17 (step).

The reference voltage l _n determined in this way is set in the comparator 9 as the comparison voltage V _c via the D/A converter 10 (step). After this, the arithmetic circuit 11
calculates the flow rate using the time difference between the time of transmitting the start signal S and the time of receiving the output pulse for the reference voltage l _n (step).

Next, the count value N _i exceeding the reference voltage l _n is fetched from the counter 13 and stored in the ROM under the control of the CPU 15.
16, the count value N _n stored in a predetermined area of the RAM 17 is compared (step), and if the comparison result is N _i =N _n (step), the flow rate calculation result in the calculation circuit 11 is If it is assumed to be correct, an instruction to output the flow rate value is given to the calculation circuit 11 as the output enable signal W=1 (step), and if N _i ≠ N _n , the flow rate calculation result in the calculation circuit 11 is rejected as W=0 (step ). These steps,
, and constitute an output determination means.

After this, the process moves to step, where 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 reference voltage l _n and the corresponding count value N _n . 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 reference voltage l _n and count value N _n again. In this way, it is determined whether the reference voltage l _n and the count value N _n are appropriate values.

In addition, if the reference voltage l _i is 10 levels and the number of repetitions N is 20, the reference voltage l _n and the count value N _n
The time required to determine is approximately 200 ms, and considering that the flowmeter measurement time is on the order of seconds, it can be determined in a short amount of time.

However, regarding the above conventional technology, (a) When the amplitude of the ultrasonic pulse H is approximately constant,
There are cases where the value of probability P(l _i , N _i ) has many peaks, and the optimal l _n and N _n cannot be determined.

(b ₎ When the amplitude fluctuation of the ultrasonic pulse H does not vary much in each measurement, the probability P( _{l i} , N _i (constant) becomes 1 and the reference voltage
The optimal value l _n of l _i cannot be determined.

There are other problems.

<Object of the Invention> In view of the above-mentioned prior art, the present invention has been made to determine the optimal value of the reference voltage and the corresponding output pulse count value even when the amplitude of the ultrasonic pulse is almost constant or when there is little amplitude variation. The purpose of the present invention is to provide an ultrasonic flowmeter that can determine flow rates and measure flow rates with high accuracy.

<Configuration of the present invention> The configuration of the present invention that achieves this object includes a transducer that transmits and receives ultrasonic pulses that are alternately switched in the opposite direction to the flow direction of the fluid to be measured flowing through the pipe, and An amplifier that receives ultrasonic pulses from a transducer, a comparator that outputs an ultrasonic pulse that exceeds the comparison voltage by inputting the output of this amplifier to one side and inputting a comparison voltage to the other side, and this comparator. The ultrasonic flowmeter is equipped with an arithmetic circuit that calculates and outputs the flow rate of the fluid to be measured using the time difference between the time difference between the reception time of the output pulse and the time of transmission of the ultrasonic pulse. Probability table creation means that creates a probability table by sequentially outputting voltages, counting output pulses that exceed a reference voltage, and reading and writing the counted values for each reference voltage a predetermined number of times; a standard table creating means for creating a probability distribution for each reference voltage as a reference voltage; and a standard count value for determining a reference voltage width for a count value that gives a probability greater than a predetermined probability from this standard table, and a standard count value that gives the maximum reference voltage width from among the standard voltage widths. A reference value calculation means that calculates the median value of this maximum reference voltage width compares this reference count value with the count value of the output pulse corresponding to the comparison voltage set to the median value, and when it is equal to the reference count value, The present invention is characterized in that it includes an output determining means for outputting the flow rate from the arithmetic circuit.

<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. 6 is a block diagram showing essential parts of an embodiment of the present invention. In the RAM 21 in the control circuit 20, there is provided an area for forming a criterion table 22 in addition to the probability table 19. The program for forming this standard table 22 is stored in the ROM 23.
According to this program, the CPU 15 processes the count value read from the counter 13 and outputs it to the D/A converter 10 via the bus 18.

The above points will be explained in more detail based on the flowchart shown in FIG. In the flowchart of FIG. 2, steps 1 to 3 are the procedure for forming the probability table 19, and the probability table 19 created in this procedure is also used in this embodiment. First, in the probability table 19 created in this way, the distribution of the probability P (l _i , N _i (constant)) for each reference voltage l _i is determined with the count value N _i constant, and the distribution corresponds to FIG. Standard table 22
It is created according to the program stored in the ROM 23 (step). Figure 8 shows the count value N _i
The graph shows the relationship between the reference voltage l _i on the horizontal axis and the probability P(l _i , N _i ) on the vertical axis, using as a parameter. Here, we set an appropriate probability standard P ₀ (<1),
Find the reference count value N _{i Γ} (degrees) that gives the maximum width of the width Δl _i of the reference voltage l _i such that P(l i , N _i (constant))≧P ₀ (step). In the example in Figure 8, this
N _i Γ (degrees) = 3, corresponding to Δl _i =Δl ₃ . Next, P ₍ l _i ,
Median value l _i Γ (degrees) of the reference voltage l _i such that N _i Γ (degrees)) ≧ P ₀
Find (step). In the example of Figure 8, l _i Γ (degrees)
= l ₃ Corresponds to Γ (degrees). Steps constitute a reference value calculation means.

The median value l _i Γ (degrees) obtained in this way is set as the comparison voltage V _c of the comparator 9 via the D/A converter 10 (step), and the flow rate is measured in steps using this as a reference. Next, the output pulses P of the comparator 9 for the comparison voltage V _c corresponding to the median value l _i Γ (degrees) are counted by the counter 13 and sent to the control circuit 1
Incorporated into 4. In the control circuit 14, the counter 1
Calculate whether the count value N _i of 3 is equal to the reference count value N _i Γ (degrees) using a predetermined program in the ROM 23 (step), and if N _i =N _i Γ (degrees), the flow rate is correct. If N _i ≠ N _i Γ (degrees), it is determined that the measured flow rate is incorrect and the process moves to step (step). These steps, . . . constitute an output determination means.

Using the median value l _i Γ (degrees) determined as above and the standard count value N _i Γ (degrees), the probability P (l _i , N _i )
Since a value larger than a certain value (P ₀ ) is used, there is a high probability that the ultrasonic pulse H will be used effectively, and if the amplitude fluctuation of the ultrasonic pulse H increases, for example, the width of Δl ₃ will become narrower in Fig. 8. Even in this case, Δl ₃ Γ (degrees) has the widest width, and if the envelope of the ultrasonic pulse H changes, for example, the 8th
The curve in the figure moves along the horizontal axis, but even in this case
l _i Γ (degrees) is the median value, so it has the least influence;
The probability that the ultrasonic pulse H is used for flow rate measurement is maximized.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, even when the amplitude of the ultrasonic pulse is approximately constant or when the amplitude fluctuation is small, the reference voltage and the corresponding output pulse can be adjusted. Since the count value can be automatically determined under the most stable detection conditions, highly accurate flow rate measurement is possible.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional ultrasonic flowmeter, Figure 2 is a flowchart explaining the operation of the ultrasonic flowmeter in Figure 1, and Figure 3 shows the waveform of the ultrasonic pulse in Figure 1. Waveform diagram, Figure 4 is the 1st
Figure 5 is a probability distribution diagram showing an example of the contents of the probability table in Figure 1, Figure 5 is a waveform diagram showing the waveform when the fluctuation of the ultrasonic pulse in Figure 1 is small, Figure 6 is a summary of one embodiment of the present invention. Block diagram showing parts, No. 7
This figure is a flow chart explaining the operation of the embodiment shown in FIG. 6, and FIG. 8 is a probability distribution diagram showing the relationship between the count value in FIG. 6 and the probability with respect to the reference voltage as a parameter. DESCRIPTION OF SYMBOLS 1... Pipe line, 3, 4... Transducer/receiver, 5... Ultrasonic oscillator, 6, 8... Amplifier, 7... Selector switch, 9... Comparator, 10... D/A converter, 11... Arithmetic circuit, 1
3... Counter, 14, 20... Control circuit, 15...
CPU, 16...ROM, 17, 23...RAM, 19
...Probability table, 22...Criteria table.

Claims (1)

[Claims] 1: a transducer that transmits and receives ultrasonic pulses that are alternately switched in opposite directions with respect to the flow direction of the fluid to be measured flowing through the pipe; an amplifier that receives the ultrasonic pulses from the transducer; a comparator that outputs the ultrasonic pulse exceeding the comparison voltage by inputting the output of the amplifier to one side and inputting a comparison voltage to the other side; a time point at which the output pulse of the comparator is received and a time point at which the ultrasonic pulse is transmitted; and an arithmetic circuit that calculates and outputs the flow rate of the fluid to be measured using a time difference between Probability table creation means for creating a probability table by repeating the operation of counting the output pulses and reading out the count values for each reference voltage a predetermined number of times, and a criterion for creating a probability distribution for each reference voltage using the count values in the probability table as parameters. a table creation means; from the reference table, calculate a reference voltage width for the count value that gives a probability greater than a predetermined probability; and from this, calculate a median value between the reference count value that gives a maximum reference voltage width and the maximum reference voltage width; and a reference value calculation means that compares the reference count value with the count value of the output pulse corresponding to the comparison voltage set to the median value, and only when the count value is equal to the reference count value, the calculation circuit calculates the flow rate. An ultrasonic flowmeter characterized by comprising: output determination means for outputting.