JPS6113113A - Ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To measure flow rate at a high accuracy by a method wherein an ultrasonic pulse is transmitted to and received from a fluid of a pipeline and the received signal is compared with a comparison voltage to transmit an output pulse while the comparison voltage is decided optimally. CONSTITUTION:A pulse B is transmitted from an ultrasonic transmitter 5 and transmitted 3 to or received 4 from the flow of a fluid F of a pipeline 1 alternately varying the direction thereof by changing a selector switch 7. Then, the received signal H and a comparison voltage Vc from a D/A converter 10 are inputted into a comparator 9 and the part of the wavefrom surpassing the comparison voltage Vc is outputted as pulse output P. At this point, different reference voltages are outputted sequentially as comparison voltage Vc with a control circuit 14 to compute the size thereof with respect to the pulse output P thereby determining the optimum comparison voltage Vc. Then, the pulse output P is inputted into an arithmetic circuit 11 to determine flow rate from time difference between the pulse output P and the start pulse S of an ultrasonic pulse. Thus, the optimum comparison voltage can be determined with the control circuit though the amplitude of the ultrasonic pulse is almost constant thereby enabling highly accurate measurement of the flow rate.

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention relates to an ultrasonic flowmeter using a microcomputer, and in particular an ultrasonic flowmeter 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 measured fluid and when it is received. It is necessary to determine accurately.

Various applications have been filed for this purpose, and one example is Japanese Patent Application No. 58-72490 ``Ultrasonic Measuring Device''.
This is shown in the figure and explained below. .

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 6 and 4 are installed in the conduit 1 so as to face each other diagonally with respect to the flow direction F. An ultrasonic pulse B in the form of a vibration wave is sent from an ultrasonic oscillator 5 to one of the transducers 3 and 4 via an amplifier 6, a switching switch, and a chia. 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 of 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 abbreviated as D/A converter) from 10 to comparison voltage ■.

is applied. At the output end of the comparator 9, a portion of the waveform exceeding the comparison voltage vc among the vibration wave-like ultrasonic pulses is converted into a pulse and outputted as an output pulse P.

The pulse voltage of the output of the comparator 9 is applied to the input terminal 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.
is applied. The arithmetic 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 it to the output terminal 12.

On the other hand, the output pulse P of the comparator 9 is taken into the control circuit 14 via the high-speed counter 15. The control circuit 14 is composed of a microprocessor (hereinafter referred to as CPU) 15, a read-on memory (hereinafter referred to as ROM) 16, a random access memory (hereinafter referred to as RAM) 17, and a path 18 connecting these. has been done. RAM
17, a predetermined area is reserved 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 15, and the D/
It is given as a comparison voltage v0 of the comparator 9 via the 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 CPUj5, D/ is set as the comparison voltage v8 of the comparator 9 according to a predetermined program in the ROM+6.
The reference voltage L1 is read out via the A converter 10 (step ■). After that, the counter 13 is reset by the reset signal R, and the contents of the counter are reset to zero (step ■).
. After setting the reference voltage t1 as the comparison voltage vc, the reference voltage L1 is compared with the ultrasonic pulse H output from the amplifier 8.
The larger ultrasonic pulse portion is output from the comparator 9 as an output pulse P (step 2). FIG. 3 illustrates the above points. The horizontal axis is the time axis, and the vertical axis is the ultrasonic pulse H(7)m width. The dotted line is the reference voltage L1
It shows the level of At the reference voltage t1 shown in the figure, there are output pulses p (4+ pieces).
Counted by 3 (step (,!,)), RAM+7
(Step ■). Next, the reference voltage is changed to +2 (tl>+2), and steps ① to ① are executed. In this way, Rakashime RO
The reference voltage determined by M+7<1. ．． 12. ~Smell~L
n) times (step ■), each reference voltage 1. as shown in the first column (N=0) of the probability table 19 shown in FIG. It is possible to count the number of pulses exceeding . By repeating the above procedure a predetermined number of times N (steps, steps 2), a probability table 19 as shown in FIG. 4, for example, is obtained. The example in FIG. 4 is the case when it is repeated 20 times. Total number of times N (-20)
The value obtained by dividing the count value in each column by is the probability p(t,, N, )
give. The probability table creation means is constituted by these steps up to step ①.

Next, using this probability table 19, under the control of the CPU 15, the reference voltage tm and count value Nm that give the maximum probability are determined according to the program in the ROM+6, and the RAM 17
(step ■).

Reference voltage LmUD/A converter 1 determined in this way
0 via the comparison voltage vll! and set it in the comparator 9 (step ■). Thereafter, the flow rate is calculated using the time difference between the time point at which the arithmetic circuit 11 transmits the signal S and the time point at which the output pulse for the reference voltages Lr, l is received (step, phase).

Next, the count value N, which exceeds the reference voltage tm, is counted by the counter 13.
The count value N stored in a predetermined area of the RAM 17 according to a predetermined procedure in the ROM 16 under the control of the CPU 15 is taken in (Step 2), and the comparison result is N,
If '=Nm (step ■), the flow rate calculation result in the calculation circuit 11 is assumed to be correct, and an instruction to output the flow rate value is given to the calculation circuit 11 as the output enable signal W=1 (step (@
), N,'=Nm, set W=O and reject the flow rate calculation result in the calculation circuit 11 (step ■). (2), 0, and [phase] constitute an output determination means.

After this, the process moves to step O, where it is determined whether a predetermined time has elapsed since the start of measurement. If the predetermined time has not elapsed, there is no need to change the determined reference voltage tr11 and the corresponding count value Nm. As a result, the flow rate measurement is repeated again by returning to step O. If the predetermined time has elapsed, the process returns to step (2) and the procedure for determining the reference voltage tm and count value Nm is executed again. In this way, it is determined whether the reference voltage Lm and the count value Nm are appropriate values.

Note that the reference voltage L1 is 10 levels, and the number of repetitions is N.
Assuming 20 times, the reference voltage trIl and the count value N. The time required to determine is about 200 ma, and considering that the flow rate measurement time is on the order of seconds, it can be determined in a short time.

There are cases where the value of P(ti, Ni) has many peaks, and the optimal tm and Nm cannot be determined.

(b) When the amplitude fluctuation of the ultrasonic pulse H does not fluctuate in each measurement, the probability P(
t,, N, (constant)) 1, and the optimum value trn of the reference voltage t1 cannot be determined.

There are other problems.

<Object of the Invention> In view of the above-mentioned prior art, the present invention provides an optimization method for the reference voltage and the corresponding output pulse count value even when the amplitude of the ultrasonic pulse is approximately constant or when the amplitude does not fluctuate much. The purpose of the present invention is to provide an ultrasonic flow meter that can determine a value and measure a flow rate 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 This comparator includes an amplifier that receives ultrasonic pulses from a transducer, and a comparator that outputs ultrasonic pulses that exceed this comparison voltage by inputting the output of this amplifier to one side and inputting a comparison voltage to the other side. 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 repeating the operation of sequentially outputting voltages, counting output pulses that hold a reference voltage, and reading the counted values for each reference voltage a predetermined number of times; A standard table creation means for creating a probability distribution for a reference voltage; and a standard table creation means for calculating a reference voltage width for a count value that gives a probability greater than a predetermined probability from this standard table; A reference value calculation means that calculates the median value of the reference voltage width compares this reference count value with the count value of the output pulse corresponding to the comparison voltage trap set to the median value, and calculates only when it is equal to the reference count value. The present invention is characterized by comprising an output determination means for outputting the flow rate of the circuit.

<Example> Embodiments of the present invention will be described below with reference to 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 the main 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. A program for forming this standard table 22 is written in advance in the ROM 23, and 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. do.

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 ② are the steps for forming the probability table 19, and the probability table 19 created in this step is also used in this embodiment.

First, in the probability table 19 created in this way, the distribution of the probability P(t+, Nl (constant)) for each reference voltage t is determined with the count value N1 constant, and the standard table 22 corresponding to FIG. is created according to the program stored in the ROM 23 (step ■).

w, Figure 8 shows the horizontal axis po (〈
1)! 7, and P(t,, N, (constant))≧P
Reference voltage 1. width Δ1. The standard count value N that gives the maximum width? Find (step ■). This is the 8th
In the example in the figure, is it N? = 3, corresponding to Δphrase=Δt3. Next, the base i count value N? obtained in this way? For P(Ll
,N? ) The median value t of the reference voltage t, which is ζ0? Find (step [phase]). In the example of Figure 8, t? = actually corresponds. Ste.

Steps ■ and ■ constitute a reference value calculation means.

Step ◎ Set the median value tr obtained in this way as the comparison voltage vc of the comparator 9 via the D/A converter 10.
), the flow rate is measured in step O using this as a reference. Next, the output pulses P of the comparator 9 for the comparison voltage v0 corresponding to the median value t1 are counted by the counter 13 and taken into the control circuit 14. In the control circuit 14, the counter 13
Is the count value N1 the reference count value N? R
Step e), N, =N? If so, it is determined that the correct flow rate has been measured, and the process moves to step 0. If N, "qN?", it is determined that the measured flow rate is incorrect, and the process moves to step (2).

These steps O, ■, ■, and ■ constitute an output determination means.

Median value t? determined as above? and the standard count value N?
When using , the probability P(t, , N, ) becomes a constant value (P
o) Since a thicker one is used, there is a high probability that the ultrasonic pulse H will be used effectively.Also, if the amplitude fluctuation of the ultrasonic pulse H increases, the width of Δt3 becomes narrower in Fig. 8, but even in this case, the width of Δt3 has the widest width, and if the envelope of the ultrasonic pulse H changes further, the curve in FIG. 8 moves in the horizontal axis direction, but even in this case Z? Since is the median value, the influence of the change is small, and the probability that the ultrasonic pulse H is used for flow rate measurement is maximized.

◇Brightness Effect> As specifically explained above with the embodiments, according to the present invention, even when the amplitude of the ultrasonic pulse is almost 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 professional diagram of a conventional ultrasonic flowmeter, Figure 2 is a flowchart explaining the operation of the ultrasonic flowmeter in Figure 1, and Figure 5 is the waveform of the ultrasonic pulse in Figure 1. 4 is a probability distribution diagram showing an example of the contents of the probability table in FIG. 1, FIG. 5 is a waveform diagram showing the waveform when the fluctuation of the ultrasonic pulse is small in FIG. The figure is a block diagram showing the main parts of an embodiment of the present invention.
This figure is a flowchart 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... Switching switch, 9
...Comparator, 10...D/A converter, 11...Arithmetic circuit, 13...Counter, l, 20...Control circuit, 15...CPU, 16...ROM, +7,23
...RAM, 19 probability table, 22... criterion table. M3 Ward Figure 4 Figure 5 Eyebrow 6 Figure 1':) lj'
I':l //Z1 claw 7 figure step Hōnemero P()1. N? ≧Pot Hi Suru J! 1 (II @Central I direct 1? 1? conversion ticket 1" [shares] and otofu exchange +:, 7? to wealth in a fixed step (SJ flow meter rule [phase] red 8 figure

Claims (1)

[Claims] 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; and the amplifier. a comparator that outputs the ultrasonic pulse exceeding the comparison voltage by inputting the output of and an arithmetic circuit that calculates and outputs the flow rate of the fluid to be measured using a time difference of , wherein different predetermined reference voltages are sequentially outputted as the comparison voltage, and the output exceeds the reference voltage. Probability table creation means for creating a probability table by repeating the operation of counting pulses and reading out the count values for each reference voltage a predetermined number of times; and standard table creation for creating a probability distribution for each reference voltage using the count values in the probability table as parameters. means, and a standard for calculating a reference voltage width for the count value that gives a probability greater than a predetermined probability from the reference table, and calculating a reference count value that gives a maximum reference voltage width from among the reference voltage widths and a median value of the maximum reference voltage width. A value calculation means compares the reference count value with the count value of the output pulse corresponding to the comparison voltage set to the median value, and outputs the flow rate from the calculation circuit only when the count value is equal to the reference count value. An ultrasonic flowmeter characterized by comprising: output determination means for determining an output.