JPH10197302A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform measurement with accuracy in response to the distribution of flow velocity in a flow pipe and to prevent the consumption of current and the increase of cost. SOLUTION: The reaching time of ultrasonic waves in forward and reverse directions is measured by a pair of transducers 1A and 2A to calculate flow velocity VA. The reaching time in forward and reverse directions is measured by another pair of transducers 1B and 2B to calculate flow velocity VB. Measurement by the pairs of the transducers is performed not simultaneously but at different times. In an electronic part 5, a switching device 4 is operated by a controller 10 constituted by a microcomputer to selectively use each pair of the transducers. Operation is performed at a control part. The rate of flow and integrated rate of flow are obtained from the flow velocity VA and VB and displayed. A flow pipe 3 has a circular cross section, the pair of the transducers 1A and 2A are arranged on the center axis of the flow pipe 3, and the other pair of transducer 1B and 2B are displaced from the center by r/2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an ultrasonic flowmeter.

[0002]

2. Description of the Related Art In FIG.
Assuming that the velocity of the fluid flow is V, if the propagation direction of the sound wave coincides with the direction along the flow (hereinafter referred to as the forward direction), the propagation velocity becomes (C + V), and the direction opposite to the flow (hereinafter the reverse direction) (CV).

When 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 an ultrasonic pulse is transmitted from one transducer 1 in a forward direction, The propagation time required for the ultrasonic pulse to reach the other transducer 2 is t ₁ , and when the ultrasonic pulse is transmitted from the transducer 2 in the opposite direction, the ultrasonic pulse reaches the transducer 1. Assuming that the required propagation time is t ₂ , t ₁ = L / (C + V) t ₂ = L / (C−V)

In a conventional ultrasonic flow meter, each propagation time (hereinafter also referred to as arrival time) t ₁ and t ₂ of an ultrasonic pulse is measured, a flow velocity V is calculated from this, and a flow rate and an integrated flow rate (fluid volume) are calculated. ) Was calculated.

For example, from the arrival times t ₁ and t ₂ , there is a relation of (1 / t ₁ ) − (1 / t ₂ ) = 2 V / L. V = (L / 2) {(1 / t ₁ ) − (1 / t ₂ )}.

A correction coefficient taking into account the flow tube cross-sectional area and the flow velocity distribution in the flow tube cross section is stored in advance, the flow rate is obtained by multiplying the correction coefficient by the flow velocity V, and the flow rate is integrated and integrated. The flow rate (that is, the volume of the fluid) was calculated. The flow distribution is determined in advance.

The arrival time is known by measuring the time from when the transmitting / receiving transducer on the transmitting side is pulse-driven until the ultrasonic pulse reaches the transmitting / receiving transducer on the receiving side. As a way of knowing the reception wave arrival point, first determine the threshold V _TH as the reference voltage level of the received, first the level of the threshold V _TH of the received amplified signal on the receiving side transducer wave This is done by detecting the zero cross point where the reached wave passes through the zero level.

[0008] The threshold value V _TH is set so as to detect the zero cross point of some specific wave of the received wave.
In FIG. 5, the third wave of the received wave reaches the level of the threshold value V _TH at the point “b”, and the third wave detects the zero cross point “c” passing through the zero level, and the time when the received wave is detected And

The head of the received wave is at the point "a",
At points “a” and “c”, the time period of the ultrasonic wave is 1.5 times.
Since there is a double shift, the arrival time is measured based on the arrival time “C” of the reception wave.

Vp is the peak value of the received wave. As another conventional technique, an ultrasonic beam is emitted in a diagonal direction to a flow in a fluid flow, a linear average flow velocity on the ultrasonic beam is measured, and the average flow velocity is converted into an average flow velocity in a flow tube cross section. The flow rate was calculated by multiplying the flow rate by the flow tube cross-sectional area, and the integrated flow rate was further integrated to calculate the integrated flow rate (fluid volume).

[0011]

The former of the above prior arts has a problem that the correction coefficient cannot be expressed in a simple form because the flow velocity distribution is different if the flow velocity is different under various conditions such as the position and location in the flow path. However, there is a problem that it causes a measurement error.

In this case, a plurality of sets of transducers are arranged, and the total flow rate is determined from the flow velocity obtained for each set. However, this method is disadvantageous in terms of cost because the number of transducers and the number of electronic parts for driving and receiving the transducers are required. Furthermore, in the latter case of the prior art, since a pair of ultrasonic transducers is used, only the flow velocity on a straight line connecting the transducers can be known, and the whole is estimated based on the value. The flow rate has been determined. Accordingly, there is a problem that a measurement error occurs when the flow is deviated.

Accordingly, an object of the present invention is to provide an ultrasonic flowmeter which can solve these problems by utilizing a plurality of pairs of transducers and a single electronic unit.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, there is provided an ultrasonic transducer which works on both a transmitting side and a receiving side on an upstream side and a downstream side, and a flow of a fluid is provided. Is provided with at least two pairs that transmit and receive ultrasonic waves from upstream to downstream, and from downstream to upstream, and obtain the total flow rate from the arrival time between each pair, One electronic part is provided for at least two pairs of transducers, and the electronic part drives the transmitter / receiver on the transmitting side, receives a signal from the transducer on the receiving side, and detects the arrival time. The received wave detecting unit constituting the electronic unit is constituted by an amplifying unit and a comparing unit, and a signal from the transmitting / receiving transducer is first amplified and then compared with a reference voltage level. First, when the reference voltage level is exceeded The point at which the wave next passes through the zero level is set as the point at which the received wave is detected, and the amplification degree of the amplifying unit and the reference voltage level of the comparing unit are set to the transmitter / receiver connected each time. The level is set to an optimum level for measurement, and a switch selects one pair of the at least two pairs of transducers so that the pair can be connected to the electronic unit. This is an ultrasonic flowmeter characterized by transmitting and receiving ultrasonic waves while selecting a vessel, and obtaining the total flow rate from the results of all pairs.

According to the present invention, since the flow rate of the entire pipe is obtained from the flow rates detected by the plurality of pairs of transducers, measurement errors due to fluctuations in the flow rate distribution can be reduced. Also, even if the level of the received wave differs due to individual differences between the transducers, the amplification degree of the amplifier of the received wave detector and the reference voltage level of the comparator are
By setting the optimum value for the connected transducer every time, one electronic unit can handle all transducers.

Therefore, since a complicated peak value hold circuit and an automatic gain control circuit are not used, low cost and low current consumption are required. According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, the electronic unit first causes a pair of connected transducers to transmit a transducer on a transmission side,
When the received wave detector that inputs the signal of the transmitter / receiver detects the received wave, the transmitter / receiver of the transmitter is transmitted again at the same time, and this is repeated a fixed number (n) times. It is characterized in that the time from transmission to the reception of a fixed (n) number of times, that is, n times of the arrival time is collectively measured, and the flow rate is obtained from the result.

According to the present invention, the accuracy of measuring the arrival time can be increased without increasing the resolution of the clock for counting the arrival time, and as a result, the accuracy of the flow meter can be improved without increasing the current consumption.

According to a third aspect of the present invention, in the ultrasonic flowmeter of the first or second aspect, at least two pairs of transducers are provided so that the ultrasonic waves transmitted and received by each pair propagate through paths having different flow velocities. It is characterized by being arranged.

According to the present invention, by arranging the pairs of the transducers so that the ultrasonic waves propagate along the paths having different flow velocities, the pattern of the flow velocity distribution can be detected. And the like can be distinguished, and the overall flow rate can be derived with higher accuracy.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. As shown in FIG.
Out of the B2 pairs (hereinafter referred to as two sets) of the transducers, set A is arranged on the central axis of the flow tube 3 having a circular cross section, and set B is arranged at a radius of r / 2 in the radial direction from the central axis. I have.

Reference numerals 1A and 2A denote transmitters and receivers forming group A.
1B and 2B are the transducers that make up the B group. r is the radius of the flow tube 3. The two sets of transducers 1A, 2A, 1B, 2
In order to prevent the flow velocity from being deviated by arranging B, B sets of transducers 1B and 2 are set with respect to the central axis of the flow tube.
A dummy 1 'having the same shape as the transducer at a position symmetrical to B,
2 'was arranged.

Two sets (two pairs) of transducers 1A, 2A and 1
One of the sets B and 2B is connected to the electronic section 5 via the switch 4. The selection is made by operating the switch 4 with a set selection signal from the electronic unit 5.

The electronic unit 5 is connected to a transmitter / receiver (for example, 2B) on the receiving side of a set (pair) of transmitters / receivers (for example, 1B and 2B) connected, and detects a received wave. Received wave detector 6 for outputting a detection signal, measurement ON / OF
Each time the F signal changes from OFF to ON,
The transmitter / receiver (e.g., 1B) on the transmitting side of the pair is driven, and thereafter driven every time a received wave detection signal is input.
When a received wave detection signal is input or the measurement ON / OFF signal is turned to the OFF side, the transmitter driving unit 7 that stops driving, and a received wave detection signal from the received wave detection unit 6 are input,
A first counter 8 which starts counting from zero every time the measurement ON / OFF signal is turned ON, detects the nth received wave detection signal and outputs the nth received wave detection signal,
A second counter 9 for measuring the time from when the OFF signal is turned ON to the nth received wave detection signal, and when measuring, the measurement ON / OFF signal is changed from the OFF side to the ON side to detect the nth received wave detection signal The control unit 10 has a control unit 10 that reads the measured value (count value) of the second counter 9 when receiving the signal, and calculates the flow velocity, flow rate, and the like. configured, a signal from the transmitting transducer is then is first amplified by the amplifying section, beyond they become as will be compared with the reference voltage level V _TH comparison unit, the first reference voltage level V _TH waves The next point that passes through the zero level is the point where the received wave is detected,
Eight levels of amplification of the amplifying unit are prepared, and one of them is selected by an amplifying degree selection signal from the control unit 10. The reference voltage level V _{TH is} also selected from eight prepared by the reference voltage level selection signal of the control unit 10 and used.

The switching between the forward direction and the reverse direction of the measurement is performed by operating the switching unit 11 with a transmission / reception switching signal from the control unit 10. The state shown in FIG. 1B shows a state at the time of forward measurement by the set B of transducers.

The control unit 10 is constituted by a microcomputer, and is programmed to perform continuous measurements in the same direction by two sets of transducers while changing directions at intervals of 2 seconds.

That is, first, the transmission / reception switching signal is measured in the forward direction in which the upstream transmitter / receiver transmits and the downstream transmitter / receiver receives, and the set selection signal is set as Group A. After the measurement is completed, the group selection signal is subsequently measured as group B. Thus, a set of measurements in the forward direction is made, and then a similar set of measurements in which the transmission / reception switching signal is reversed is alternately performed at 2-second intervals.

In each measurement, the amplification degree selection signal and the reference voltage level are set so that the amplification degree and the reference voltage level V _{TH which} are stored in advance and are optimal for each measurement (reception) are set by the reception wave detector 6. The microcomputer constituting the control unit 10 outputs the selection signal.

The control unit 10 measures the arrival time before and after every two seconds (count value of the second counter 9).
Then, the value of the flow velocity V _A on the central axis by the set A of transducers and the value of the flow velocity V _{B at} a distance r / 2 in the radial direction from the central axis by the set B of transducers are calculated.

The calculation of the flow velocity uses the time reciprocal difference method. From the example, V _B / V _A correction coefficient at the time of laminar flow it is determined that the laminar flow when below a certain value alpha, for example using a K _1, the flow rate Q and the flow rate V _A by Group A, Q = Calculate as K ₁ · V _A.

When V _B / V _A is larger than the fixed value α, it is determined that the flow is turbulent, and the correction coefficient K ₂ at the time of the turbulence and the flow velocity V _A of the set A of the transducers are used. Calculate as K ₂ · _VA .

Further, in this embodiment, the flow rate is integrated using the flow rate, and the integrated flow rate (volume of the fluid) is displayed. FIG. 2 is a specific example of an electronic circuit of an amplification unit used for the reception wave detection unit 6. Eight feedback resistors R 20 to R 27 are connected to an operational amplifier 15 via an analog switch 16, and an amplification degree selection from the control unit 14 is performed. Signals S10 and S1
At 1, S12, any one of the analog switches 16 is selected and turned on, thereby selecting the amplification degree of the amplifier.

V _in is a received wave signal from the transmitter / receiver (for example, 2B) on the receiving side, and is input to the inverting input of the operational amplifier 15 via the resistor R1. The resistance value of the feedback resistor is determined by the relationship of R20 <R21 <... <R27, and the amplification factors are mutually expressed as (R20 / R1) <(R21 / R1) <.
R1).

FIG. 3 is a specific example of a part of the electronic circuit of the comparison unit of the reception wave detection unit 10. The output _Vout from the amplification unit of FIG. The reference voltage level V _TH is input to the inverting input.

S20, S21 and S22 are reference voltage level selection signals from the control unit 14, and when one of the analog switches 18 is selected and turned on, the eight resistors R40 to R47 are turned on. A constant reference voltage 19 is divided by one of them and the resistor R3 to generate a reference voltage level V _TH to be input to the inverting input of the comparator 17.

The relationship between the resistance values of the eight resistors R40 to R47 is as follows: R40 <R41 <R42 <... <R47, and the analog switch 17 is selected by the reference voltage level selection signal from the control unit 14. To determine the reference voltage level V _TH .

[0036]

Since the ultrasonic flowmeter of the present invention is constructed as described above, it is possible to realize an ultrasonic flowmeter with good measurement accuracy and low current consumption at low cost.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing an arrangement of a transducer in an embodiment of the present invention, and FIG. 1B is a block diagram.

FIG. 2 is a specific example of an electronic circuit of an amplification unit used in the embodiment of FIG.

FIG. 3 is a specific example of a part of an electronic circuit of a comparison unit used in the embodiment of FIG. 1;

FIG. 4 is a schematic diagram illustrating the principle of an ultrasonic flowmeter.

FIG. 5 is a diagram showing electric signal waveforms for explaining an operation of a reception wave detection unit of the ultrasonic flowmeter.

[Explanation of symbols]

 1 ', 2' Dummy 1A A set of upstream transducers 2A A set of downstream transducers 1B B set of upstream transducers 2B B set of downstream transducers 3 Flow tube 4 Switcher 5 Electronics Unit 6 Received wave detector 7 Transmitter driver 9 Counter to measure arrival time

Continuation of the front page (72) Inventor ▲ Tomi ▲ Akio Tada 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi Inside Osaka Gas Co., Ltd. (72) Inventor Tokuyuki Nabeshima 1-chome 2-70, Atsuta-ku, Nagoya-shi, Aichi Prefecture No. within Aichi Watch Electric Co., Ltd. (72) Inventor Yutaka Tanaka Inside Aichi Watch Electric Co., Ltd. 2-70, Millennial, Atsuta-ku, Nagoya-shi, Aichi

Claims (3)

[Claims] 1. An ultrasonic transmitter / receiver that works on both a transmitting side and a receiving side is provided on an upstream side and a downstream side, and transmits and receives ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. At least two pairs of such pairs are provided, and the total flow rate is obtained from the arrival time between each pair. One electronic unit is provided for the at least two pairs of transducers, and The unit drives the transmitter / receiver on the transmission side, receives the reception signal from the transmitter / receiver on the reception side, detects the arrival time, and obtains the flow rate, The reception wave detection unit constituting the electronic unit, The signal from the transmitter / receiver is composed of an amplifier and a comparator.The signal from the transmitter / receiver is first amplified and then compared with the reference voltage level. The point that passes the level is the point where the received wave is detected The amplification degree of the amplifying unit and the reference voltage level of the comparing unit are set and measured at an optimum level for the connected transducer every time, and the switching unit One pair of the two transducers is selected so that it can be connected to the electronic unit. The ultrasonic wave is transmitted and received while sequentially selecting one pair of the transducers. An ultrasonic flowmeter for determining a flow rate. 2. The electronic part transmits a transmitting-side transducer to a pair of connected transducers, and a receiving-wave detecting part that inputs a signal of the transmitting-side transducer receives a receiving wave. Is detected, and at the same time, the transmitter and receiver on the transmitting side are transmitted again,
This is repeated a certain number of times (n), and the time from the first transmission to the reception of the certain number (n) times, that is, n times of the arrival time is collectively measured, and the flow rate is obtained from the result. The ultrasonic flowmeter according to claim 1. 3. The ultrasonic flowmeter according to claim 1, wherein at least two pairs of transducers are arranged so that ultrasonic waves transmitted and received by each pair propagate through paths having different flow velocities.