JPH10142019A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultrasonic flowmeter in which an adjusting operation can be simplified by a method wherein ultarsonic waves are transmitted and received continuously a plurality of numbers of times while a reference voltage level used to detect received waves is changed sequentially in the forward direction and the reverse direction and a reference voltage level at a time when a change in the arrival time is large is decided as an optimum value. SOLUTION: A control part performes an oardinay measurement at intervals of about two seconds, and it optimizes an amplification degree and a reference voltage level at intervals of about one minute in the intervals. That is to say, a transmission-reception changeover signal is set to the forward direction, an amplification-degree selection signal is set to a minimum amplification degreg, a reference-voltage-level selection signal is set to a minimum level, and a measurement ON-OFF signal is set to the ON-side. When a received-wave detection signal is interrupt-input, a counter reads out a measured arrival time value so as to be compared with a previously read-out value. When their difference e is large, by how many steps the reference voltage level is raised since the value is changed largely before is investigated. When the reference voltage level is raised by four steps or higher, it is judged that a third wave is detected, a reference voltage level in the number of levels between a previous reference voltage level and the reference voltage level is used as an optimum reference voltage level, and an amplification degree at this time is used as an optimum amplification degree.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of an ultrasonic flowmeter.

[0002]

2. Description of the Related Art In FIG. 11, if the sound velocity in a stationary fluid is C and the flow velocity of a fluid is V, if the propagation direction of the sound wave coincides with the direction along the flow (hereinafter referred to as forward direction), The propagation speed is C + V, and is C-V in the direction opposite to the flow (hereinafter referred to as the reverse direction).

A pair of transducers 1 and 2 are arranged at a distance L from each other upstream and downstream of a flow tube 3, and when one transducer 1 transmits ultrasonic waves in the forward direction, Is the arrival time required for the ultrasonic wave to reach the transmitter / receiver 2, and the arrival time required for the ultrasonic wave to reach the transmitter / receiver 1 when the ultrasonic wave is transmitted from the transmitter / receiver 2 in the reverse direction is t. ', T = L / (C + V) (1) t' = L / (C−V) (2)

The arrival times t, of the ultrasonic waves in the forward and reverse directions,
t ′ is measured, and the flow velocity V is calculated from the measured t ′.
The flow rate and the integrated flow rate (fluid volume) were calculated. Flow velocity V
Was determined from the above equations (1) and (2) as, for example, V = L {(1 / t)-(1 / t ')} / 2 (3).

To measure the arrival times t, t ', etc., FIG.
As shown in FIG. 2, the time t from the transmission drive signal P for exciting the transmitter / receiver on the transmitting side to the arrival of the received wave at the transmitter / receiver on the receiving side may be directly measured. Can not.

[0006] Because the received wave is very small, it is first amplified. FIG. 12 shows a reception waveform after amplification. At the time when “A” arrives, the amplitude gradually increases thereafter to reach the maximum amplitude, and then gradually decreases. However, since the leading "a" of the amplified received wave, which is the arrival point of the received wave, is hidden by noise, it is impossible to detect it.

Therefore, as a method of knowing the arrival time of a received wave, a threshold value V _TH sufficiently larger than noise is first determined as a reference voltage level for reception, and the amplified wave which first reaches this level crosses the zero level through a zero crossing. It detects points and detects received waves.

The threshold value V _TH is set so as to detect a zero cross point of some specific wave of the received wave.
The actual arrival times t and t 'are, for example, described in terms of the arrival time t in forward measurement. The actual arrival times t and t' are experimentally obtained in advance from the measurement time t + τ from the transmitted wave drive signal P to the zero cross point "c" in FIG. It was obtained by subtracting the time τ that had been set.

In FIG. 12, the third wave of the received wave has reached the threshold value V _TH at the point “b”, the third wave detects a zero cross point “c” passing through the zero level, and the received wave is detected. Detected.

The measurement accuracy of the forward arrival time t and the reverse arrival time t 'is determined by the resolution of the reference clock used when measuring these arrival times.
The accuracy of the flow rate, flow rate, integrated flow rate, and the like calculated based on t 'is also determined by the resolution of the reference clock.

Therefore, as a method of improving the accuracy of the flow velocity, the flow rate, the integrated flow rate, and the like using the reference clocks having the same resolution, a simple procedure from transmission (transmission) to reception is used to measure the arrival times t and t '. Rather than measuring the arrival time of one,
By repeating the next transmission in the same direction at the same time as the reception, a plurality of (n) times, the arrival times t and t 'are respectively continued a plurality (n) times, and the first (first) transmission is performed. From the time until the last (n-th) reception nt
+ Nτ and nt '+ nτ are collectively measured, and nτ, which is obtained and stored in advance by experiments or the like, is subtracted to obtain nt or n
Ultrasonic flow meters adapted to determine t 'are well known.

In this case, even if the resolution of the reference clock is the same, the measurement accuracy of the arrival time is improved by n times, so that the accuracy of the flow velocity, the flow rate, the integrated flow rate, etc. is also improved by n times. Therefore, for example, if n is set to 100, the accuracy is improved 100 times.

However, the magnitude of the received wave varies depending on the difference in the pressure of the gas to be measured or the individual characteristics of the ultrasonic transducers constituting the transducers 1 and 2. As a result, the zero-cross point of the preceding first wave or the succeeding fifth wave may be erroneously detected instead of the intended specific wave (for example, the third wave as shown in FIG. 12).

In this case, the arrival time is incorrect for one period of the ultrasonic wave. Therefore, if this erroneous measured value is used as it is, an erroneous flow velocity or flow rate will naturally be introduced, which causes a large error. Becomes

In particular, in order to improve the measurement accuracy of the arrival time, transmission / reception in the same direction is repeated a plurality of times (n) continuously, and the times nt and nt 'which are a plurality of (n) times the arrival times t and t' are collectively obtained. In the ultrasonic flowmeter of the above-described method, all of the plurality of (n) reception wave detections must capture a specific target wave.

Therefore, a so-called AG for controlling the gain of the amplifier so that the maximum amplitude of the amplified received wave is always constant.
There is an ultrasonic flowmeter employing C (Automatic Gain Control).

[0017]

The prior art employing the AGC requires a peak value hold circuit and the like.
Since the scale of the analog electronic circuit is increased, there is a problem that the cost of the flow meter increases or the current consumption increases. Moreover, when a small-diameter flow path is used, a phenomenon in which the waveform near the peak of the received wave is likely to be disturbed due to the influence of the reflected wave from the pipeline, so even if the magnitude of the peak is set to a constant value, the target is aimed. Since the waves do not have the same magnitude, they are not suitable for small ultrasonic flowmeters and have a problem that it is difficult to realize them.

In the prior art that does not employ AGC, if the level of the received wave differs depending on the local conditions where the flow meter is installed, particularly, the pressure of the fluid, it becomes susceptible to noise,
As described above, a stable measurement cannot be performed because a specific target wave cannot be detected.

Therefore, when the flowmeter is installed, it is necessary to adjust the threshold value _VTH and the gain of the amplifier to optimum values in accordance with the local conditions, and there is a problem that the installation cost increases. .

That is, it is necessary to adjust the threshold value V _TH and the gain of the amplifier so that a specific wave that is aimed at can always be caught. In an actual operation, an oscilloscope must adjust while comparing an incoming wave with a threshold value V _TH so that it is possible to know which wave (how many waves) is being captured, and the adjustment operation is troublesome.

Furthermore, not only is it necessary to provide an adjusting terminal, but also it is necessary to take measures to devise the electronic circuit of the flow meter so that the oscilloscope is not adversely affected even if the oscilloscope is connected. There is also a problem that the cost is increased.

Accordingly, an object of the present invention is to provide an ultrasonic flowmeter which can solve the above-mentioned various problems by automatically optimizing the threshold value _VTH and the gain of the amplifier.

[0023]

In order to achieve the above object, the invention according to claim 1 is directed to at least one pair of ultrasonic transducers (1) acting on both the transmitting side and the receiving side.
(2) is an ultrasonic flow meter that transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream in the fluid flow, and obtains the flow velocity and the flow rate from the arrival time in each direction. The transmitter / receiver (1) transmits the signal, and the received wave detector (4), which inputs the signal of the receiver / receiver (2), detects the received wave.
Is transmitted, and this is repeated a fixed number of times (n times). The time from the first transmission to the reception of the fixed number of times (n times), that is, n times of the arrival time, is collectively measured. The flow rate and the flow rate are obtained, and the reception wave detection unit (4) is composed of an amplification unit and a comparison unit, and a signal from the transmission side transducer (1 or 2) is:
It is first amplified and then compared with the reference voltage level, and the point where the wave exceeding the reference voltage level first passes through the zero level is the point where the received wave is detected, The reference voltage level can be changed in several steps, apart from the usual measurement for determining the flow rate, periodically or irregularly in the forward direction,
In each of the opposite directions, while changing the reference voltage level stepwise at every transmission or reception or every several transmissions and receptions, the transmission and reception of ultrasonic waves repeated continuously plural times as in the normal measurement So that the change in the arrival time of each transmission / reception can be monitored, and for some reference voltage levels, when it can be determined that the change in the arrival time is large with respect to the change of one stage, these reference voltages Than the voltage level
An ultrasonic flowmeter characterized in that an optimum reference voltage level is determined for each of the forward direction and the reverse direction, and that level is used in normal measurement.

The time from the transmission pulse corresponding to the transmission drive signal of each transmission and reception to the detection of the zero cross point of the reception wave is, for example, t1, t for successive n transmissions and receptions.
Assuming that 2, the total time required for n successive transmissions and receptions is approximately nt + nτ, and the change in the flow velocity during this period can be regarded as almost zero. Therefore, as long as the reference voltage level as the threshold value reliably captures the targeted specific wave, t
Are almost the same, and the difference between two adjacent values is almost zero.

However, according to the first aspect of the present invention, the reference voltage level V _TH is changed stepwise, so that the captured wave changes, and accordingly, the time from the transmission timing to the detection of the zero cross level of the received wave, in other words, the arrival time Can change greatly.

This will be described with reference to FIG. This is an example in which a reference voltage level V _TH as a threshold value is increased stepwise from the minimum value for each transmission and reception. t1 captures the first wave. t2 also captures the first wave. Therefore, t2 is t1
And the value is almost the same, and the difference between them is small. However, the reference voltage level V _TH at the next third reception is above the peak of the first wave, and the wave to be captured changes to the third wave. Therefore, t3 is larger than t2 by about one wavelength and changes greatly. Since t4 is the reception that also captures the third wave, t4
There is almost no difference from 3.

That is, when there is a large change in the arrival time,
It can be recognized that there is a peak of the received wave between the reference voltage level of the reception and the reference voltage level of the immediately preceding reception.
This is illustrated in FIG. It is assumed that the reception waveform is as shown in the drawing (after amplification), and the reference voltage level V _TH increases in order from 1 in each reception. In this case, t3, t11, t2
3 greatly changes. This indicates that there are peaks near the reference voltage level at those times.

Therefore, when detecting the third wave (wave having the second peak on the positive side), V _TH3 and t
An approximate average value of V _TH11 at the time of 11 measurement is determined as an optimum reference voltage level, and a correct zero cross point is detected in the subsequent transmission and reception.

In this manner, even if the magnitude of the received wave changes due to a change in pressure or the like, an optimum reference voltage level can be set.
No difficult adjustments are needed. According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, when the reference voltage levels when the change in the arrival time of each transmission / reception is large are arranged in ascending order, the reference voltage level is a certain multiple of the smaller reference voltage level. The reference voltage level is detected, and an average value of the reference voltage level and the one less reference voltage level is determined as the optimum reference voltage level.

In general, the received wave is the first wave from the top,
The peak gradually increases as the second wave, the third wave, the fourth wave, the fifth wave, the sixth wave, and the seventh wave. It is known that the degree of increase in the peak voltage is large at the beginning and gradually decreases.

That is, comparing the magnitudes of the peaks, on the positive first wave side, the third wave / first wave is maximum, and the fifth wave / third wave and the seventh wave / third wave are gradually smaller. Become. On the negative second wave side, the fourth wave / second wave is at most the sixth wave / fourth
Wave, the eighth wave / sixth wave.

It has been confirmed by experiments and the like that the above ratio hardly changes even when the overall amplitude changes due to pressure or the like. Therefore, if only the magnitude of each peak is known, it is possible to detect the number of the wave of the peak from the ratio with respect to the immediately preceding peak.

In particular, the third wave / first wave and the fourth wave / second wave are sufficiently large compared to other ratios, so that they can be easily distinguished. Therefore, when the zero-cross point of the third wave or the fourth wave is detected as the receiving point, the third wave or the fourth wave can be reliably detected according to the second aspect of the present invention.

Referring to FIG. Suppose V _TH1 is 200mV
Hereinafter, it is assumed that V _TH2 is increased by 100 mV such as 300 mV. In this case, t3, t11, t23
, The arrival time greatly changes, but the reference voltage levels at that time are 400 mV, 1200 mV, and 240 mV, respectively.
0 mV.

Therefore, when looking at the ratio, the third wave / the first wave
= 3, fifth wave / third wave = 2. Magnification of cutting (ratio
Rate) is set to 2.5, the peak detected at t11
It can be determined that the wave having the peak is the third wave. In that case,
However, the peak of the first wave is near t3,
The optimal reference voltage level for capturing the wave is (V_TH3+
V _TH1) / 2.

It should be _noted that the peak of the first wave is V _TH1 or more,
Also, if the peak of the third wave is not smaller than the prepared maximum reference voltage level, that is, V _{TH24 of} FIG.
No wave ratio can be detected.

According to a third aspect of the present invention, in the ultrasonic flowmeter according to the second aspect, the amplification degree of the amplifying section of the reception wave detecting section can be changed by several steps, and is a constant multiple of the one smaller reference voltage level. If there is no reference voltage level, the amplification is changed in order, and transmission and reception for determining the reference voltage level are performed for each amplification. If there is a reference voltage level that satisfies the above condition, the amplification is performed. Is determined as the optimum amplification degree, and is used for ordinary measurement.

The present invention is for optimizing the degree of amplification of the preceding amplification unit so that the peak of the first wave and the peak of the third wave fall between the minimum value and the maximum value of the prepared reference voltage level. Then, by increasing the amplification from the minimum, for example, while performing the above-mentioned transmission and reception one by one, it is possible to determine the optimum amplification for the prepared reference voltage level range.

According to a fourth aspect of the present invention, in the ultrasonic flowmeter of the third aspect, the reference voltage level is provided in a plurality of stages in an exponential function of voltage.

In the second aspect of the present invention, whether the third wave / first wave or the like has a certain value or more is determined by first calculating a ratio and comparing the ratio with the certain value. However, division by a microcomputer or the like is troublesome. Therefore, the invention of claim 4 enables the determination as to whether or not the above condition is satisfied without performing the cumbersome operation of division.

Assuming that the reference voltage level V ' _TH is exponentially calculated from the bottom, 200 mV, 251 mV, 316 mV, 39
8mV, 500mV, 629mV, 791mV, 994
mV, 1250 mV, it is decided to increase by about 1.26 times.
Double the voltage.

[0042] Figure 2 for the same received waveform as that with the reference voltage level V _'TH is FIG. The arrival time greatly changes at t3 and t8. The reference voltage levels at these two points are V ' _TH3 and V' _TH8 . V ' _TH8 is 5 of V' _TH3
It is on the stage. Since there are 2.5 times in four stages, it is possible to determine that the ratio is 2.5 times or more without troublesome division.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. [Embodiment 1] In Embodiment 1 of FIG. 4, so-called normal measurement is performed at intervals of 2 seconds, and transmission and reception for optimizing the amplification factor and the reference voltage level are performed once a minute using the interval. I have. The configuration is as follows.

1). A pair of ultrasonic transducers 1 and 2 that transmit and receive ultrasonic waves in the same direction or in the flow of the fluid
And 2). A received wave detector 4 which is connected to the transmitter / receiver 2 on the receiving side and outputs a received wave detection signal when detecting a received wave; 3). Each time the measurement ON / OFF signal changes from the OFF side to the ON side, the transmitter / receiver 1 or 2 on the transmission side is driven, and thereafter, each time a reception wave detection signal is input, the n-th reception wave detection signal is input. The transmitter driver 5 stops driving when the measurement ON / OFF signal is turned off or when the measurement ON / OFF signal is turned off, 4). The reception wave detection signal from the reception wave detection unit 4 is input, and each time the measurement ON / OFF signal is turned on, the counting is started from zero, and the nth reception wave detection signal is detected by detecting the nth reception wave detection signal. A first counter 6 for outputting a detection signal; 5). N-th measurement ON / OFF signal
Second counter 7 for measuring time until reception wave detection signal
And 6). The transmission and reception are switched at a certain timing, and the measurement ON / OFF signal is changed from OFF side to ON side each time,
An ultrasonic flow meter having a control unit 8 for reading a measurement value (count value) of a second counter 7 upon receiving an n-th received wave detection signal and calculating a flow velocity, a flow rate, and the like, 7). A third counter 9 for measuring and outputting the time from the measurement ON / OFF signal being turned ON to the first reception wave detection signal and thereafter the time from the reception wave detection signal to the next reception wave detection signal. 8). The reception wave detection unit 4 includes an amplification unit and a comparison unit. The signal from the transmission / reception transmitter / receiver 1 or 2 is first amplified by the amplification unit and then compared with the reference voltage level by the comparison unit. The point where the wave that first exceeds the reference voltage level passes through the next zero level is set as the point at which the received wave is detected. One is selected by the amplification degree selection signal from the control unit 8. Also, one of eight reference voltage levels prepared by a reference voltage level selection signal from the control unit 8 is selected and used. Eight of the reference voltage levels are set on the positive (plus) side, and 200 mV, 251 mV, 316 mV,
398mV, 500mV, 629mV, 791mV, 9
It is determined to be 94 mV and increase by about 1.26 times.

9). The control unit 8 is constituted by a microcomputer and performs the above-described movement for the so-called normal measurement at intervals of two seconds. An operation for level optimization is performed. That is, 10). The transmission / reception switching signal is set to the forward direction, 11). The amplification degree selection signal is selected as the minimum amplification degree, and 12). The reference voltage level selection signal is selected as the minimum level, and 13). Then, the measurement ON / OFF signal is turned ON. This movement is shown in FIG. 5 as the optimization start.

14). The received wave detection signal is input as an external interrupt. This interrupt processing is shown in FIG. 15). When the received wave detection signal is input as an interrupt, the arrival time measured by the third counter 9 is read. If the difference is large (more than a certain value) compared to the previous reading, it is checked how many steps the reference voltage level has risen since the previous large change, and if it is larger than 4 steps , It is determined that the third wave has been detected. Then, the reference level having a level number intermediate to the previous reference voltage level is set as the optimum reference level, and the amplification at that time is set as the optimum amplification.

16). In addition, the reference voltage level is increased by one stage for each input of the reception wave detection signal, and when the condition is not satisfied even in the eighth reception wave detection signal input which is reception at the maximum reference voltage level. Assuming that the amplification degree is not suitable, the amplification degree is increased by one stage and the optimization operation is started again.

17). When the optimum level is determined in the forward direction, the measurement ON / OFF signal is turned off at that time, and then the transmission / reception switching signal is set in the reverse direction to minimize the amplification and restart the optimization.

18). If the difference between the level numbers exceeds 4, it means that the voltage exceeds 2.5 times, and the level determined as optimal will surely catch the third wave. 19). In this way, the optimum reference voltage level and amplification level are automatically determined for each direction, and normal measurements are performed using them. And accurate measurement is possible.

20). In the present embodiment, the reference voltage level is set on the positive side, but it can be set on the negative (minus) side, and it is similarly possible to configure so as to capture the fourth wave. 21). Further, in this embodiment, the reference level is increased in ascending order for each transmission / reception. However, the reference level can be reduced in ascending order.

22). Further, in this embodiment, the change of the arrival time is checked every time the reception wave detection signal is input. However, the arrival time can be stored only and the measurement can be checked after the measurement at all the reference voltage levels is completed.

23). Further, transmission and reception are performed a plurality of times at the same level. That is, it is also possible to change the level by one step every time a certain number of transmissions / receptions are performed.
According to this method, even when the received wave has noise, of the arrival times of a plurality of transmissions / receptions of the same reference voltage level, the arrival time of a large group of the arrival times at the reference voltage level is determined. Optimization not affected by noise can be realized.

FIG. 7 shows a specific example of the electric circuit of the third counter 9, which includes an OR gate 10 and a resettable counter 11.
A reference clock generator 12 for inputting a reference clock to a clock input CK of the counter 11 and a latch circuit 13 for temporarily storing a time count value of the counter 11 and outputting the time count value to the control unit 7 are connected as shown in the figure. ing. The reception wave detection signal is input to the latch input of the latch circuit 13, and the time count value of the counter 13 is first latched and stored.
The timing is determined so that the received wave detection signal via the R gate 10 resets the time count value of the counter 11 to zero.

Although the reference clock generator 12 is specially provided in FIG. 7, a reference clock generator built in the second counter 7 in FIG. 1 is used, and the reference clock of the counter 11 in FIG. You may make it input into the clock input CK.

FIG. 8 shows the measurement ON / OF in the above embodiment.
In the timing diagram of the F signal and the reception wave detection signal, n reception wave detection signals are sequentially set to 1,
, M-1, m, m + 1,..., N-1, n. T is a time value (count value) measured by the second counter 7.

FIG. 9 shows a specific example of an electric circuit of the amplifying unit of the received wave detecting unit 4 in the above embodiment. The operational amplifier 14 has eight feedback resistors R20 to R via an analog switch 15.
27 is connected, and an analog switch 15 is supplied by the amplification degree selection signals S10, S11, S12 from the control unit 8.
By selecting one of the switches and turning it on,
Select the degree of amplification of the amplifier. V _in is on the receiving side transducer 2
Or via the resistor R ₁ in the received signal from the first operational amplifier 1
4 inverting input.

The resistance values of the feedback resistors are determined by the relationship of R20 <R21 <... <R27, and the amplification factors are mutually determined as follows: (R20 / R1) <(R21 / R1) <.
R1).

FIG. 10 shows a specific example of the electric circuit of the comparison unit of the reception wave detection unit 4 in the above embodiment. The output _V.sub.out from the comparison unit shown in FIG. The inverting input has the reference voltage level V
_TH is entered.

S20, S21 and S22 are reference voltage level selection signals from the control section 8, and when any one of the analog switches 17 is selected and turned on, any one of the eight resistors R40 to R47 is selected. The comparator 1 divides a constant reference voltage 18 by one of them and the resistor R3.
A reference voltage level V _TH for inputting the inverted input of 6 is created.

The relationship among the resistance values of the eight resistors R40 to R47 is as follows: R40 <R41 <R42 <... <R47, and the reference voltage level from the control unit is used to select the analog switch 17 with a selection signal. Thus, the reference voltage level can be selected.

In this embodiment, the optimization is performed every minute. However, when an abnormality is detected in the normal measurement,
The optimization can be performed immediately. In addition, transmission and reception are performed continuously, and since the flow rate is short, the flow velocity hardly changes during that time, and there is almost no difference particularly in continuous transmission and reception. Therefore, it is possible to transmit and receive the optimization even when the gas is flowing and the flow velocity is changing.

[0062]

According to the present invention, as described above, the reference voltage level (V _TH ) and the amplification degree are automatically adjusted even if the magnitude of the received wave changes due to a change in fluid pressure or the like. Since the optimum value is determined and determined, troublesome adjustment work is not required.

Then, accurate measurement is always obtained. Further, since a circuit such as a peak value hold is not used, a low-cost and low-power-consumption ultrasonic flowmeter can be realized.

Even in the case of a small aperture, stable measurement accuracy can be maintained without being adversely affected by reflected waves. Furthermore, even if the size of the received wave decreases over time due to deterioration of the transmitter / receiver due to aging, the reference voltage level and the amplification degree are automatically optimized in accordance with the deterioration, so that the stability is maintained over a long period of time. Performance is obtained and the reliability of the flow meter is improved.

[Brief description of the drawings]

FIG. 1 is a timing chart illustrating an operation of detecting a zero cross point of a received wave according to the present invention.

FIG. 2 is a diagram illustrating a detection operation by changing a reference voltage level for detecting a zero cross point of a received wave according to the present invention.

FIG. 3 is a diagram for explaining a detection operation by changing a reference level.

FIG. 4 is a block diagram of an embodiment of the present invention.

FIG. 5 is a flowchart of the embodiment of FIG.

FIG. 6 is also a flowchart.

FIG. 7 is a diagram of a specific electric circuit of a second counter in the embodiment of FIG.

FIG. 8 is a timing chart for explaining the operation of the second counter of FIG. 4;

FIG. 9 is a diagram showing a specific example of an electric circuit of an amplification unit used in the received wave detection circuit in the embodiment of FIG.

FIG. 10 is a diagram showing a specific example of an electric circuit of a comparison unit used in the received wave detection circuit in the embodiment of FIG.

FIG. 11 is a schematic diagram illustrating the principle of an ultrasonic flowmeter.

FIG. 12 is a diagram showing electric signal waveforms for explaining the operation of the reception wave detection unit of the ultrasonic flowmeter.

[Explanation of symbols]

1, 2 Ultrasonic transducer 3 _Flow tube 4 Received wave detector V _TH , V ' _TH , V _{TH1 to} V _TH24 , V' _{TH1 to} V ' _TH9
Reference voltage level

Claims (4)

[Claims] At least one pair of ultrasonic transducers that work on both a transmitting side and a receiving side are provided to transmit and receive ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. An ultrasonic flowmeter that obtains the flow velocity and the flow rate from the arrival time of the ultrasonic wave, firstly transmits the transmitter / receiver on the transmission side, and when the reception wave detection unit that inputs the signal of the reception side transducer detects the reception wave, At the same time, make the transmitting / receiving transmitter transmit again,
This is repeated a certain number of times (n times), and the time from the first transmission to the reception of the certain number of times (the n-th time), that is, n times of the arrival time, is collectively measured, and the flow velocity and the flow rate are obtained from the result. The reception wave detection unit is configured by an amplification unit and a comparison unit, a signal from the transmission side transducer is first amplified, and then compared with a reference voltage level, The point where the wave exceeding the reference voltage level passes through the next zero level is set as the point where the received wave is detected, and the reference voltage level can be changed in several stages. In addition to the normal measurement for determining the flow velocity, the reference voltage level is gradually or irregularly set in the forward and reverse directions in steps, for each transmission / reception or several times. While changing each time As in the case of normal measurement, the transmission and reception of ultrasonic waves are repeated a plurality of times continuously, so that the change of the arrival time of each transmission and reception can be monitored. For a certain reference voltage level, the change of one stage When it can be determined that the change in the arrival time is large, the optimum reference voltage level is determined for each of the forward and reverse directions from those reference voltage levels, and the level is used in normal measurement. Characteristic ultrasonic flow meter. 2. When the reference voltage levels when the change in arrival time of each transmission / reception is large are arranged in ascending order, a reference voltage level that is a fixed multiple of a reference voltage level that is smaller by one is detected, and the reference voltage is detected. 2. The ultrasonic flowmeter according to claim 1, wherein a substantially average value of a level and said one smaller reference voltage level is determined as an optimum reference voltage level. 3. The amplification degree of the amplification section of the reception wave detection section is configured to be able to be changed in several steps, and when there is no reference voltage level that is equal to or more than a certain multiple of the reference voltage level smaller by one, the amplification degree is changed. The transmission and reception for changing the reference voltage level in order are performed for each amplification degree, and if there is a reference voltage level that satisfies the above condition, the amplification degree is determined as the optimum amplification degree and used for normal measurement. The ultrasonic flowmeter according to claim 2, wherein 4. The ultrasonic flowmeter according to claim 3, wherein a plurality of reference voltage levels are prepared in an exponential function of voltage.