JP4615531B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter provided with space detection means for detecting a space in a fluid.

  Conventionally, in a time-difference type ultrasonic flowmeter with a small inner diameter of a flow path tube body, the flow tube body is positioned at opposite positions on both sides of a straight pipe portion of a U-shaped flow path tube body 1 as shown in FIG. Sonic transducers 2 and 3 are installed. The ultrasonic beam B is transmitted and received alternately between the ultrasonic transducers 2 and 3 to propagate the ultrasonic beam B from the upstream side to the downstream side, and the ultrasonic beam from the downstream side to the upstream side. From the time difference caused by the propagation of B, the flow velocity and flow rate of the fluid flowing in the tube 1 are obtained.

  For example, Patent Documents 1 to 3 are known as ultrasonic flowmeters provided with means for detecting bubbles mixed in the fluid. However, these patent documents are directed to minute bubbles mixed in the fluid, and even if such bubbles may cause measurement errors, flow measurement is not disabled. In addition, the bubble information is obtained from the reception signal of the ultrasonic beam for flow measurement without providing a dedicated bubble detector for that purpose.

  However, in the conventional ultrasonic flowmeter, when the inner diameter of the tube body 1 is a small diameter such as several millimeters, for example, a space that is large enough to cause air bubbles attached to the tube wall to sometimes peel off and block the tube body 1. A may pass through the tube 1 together with the fluid. If such a space A exists in the propagation path of the ultrasonic beam B, the ultrasonic beam B cannot be propagated between the ultrasonic transducers 2 and 3 and the flow rate measurement becomes impossible.

  Specifically, when the space A reaches the position of the inlet S1 of the straight pipe portion of the tube 1 at time t1, the ultrasonic beam B is not propagated, so that the flow rate measurement becomes impossible. Until the time t2 when the space A moves to the outlet S2 of the straight pipe portion, the propagation of the ultrasonic beam B is blocked by the space A and cannot be measured. When the space A passes the position S2, the ultrasonic wave is again transmitted. The beam B can propagate and measurement can be resumed. Therefore, the flow rate is interpolated using the data when it is normally propagated in the time when the measurement is impossible due to the space A.

  In other words, in the conventional ultrasonic flowmeter, a technique for unavoidably averaging the instantaneous flow rate values immediately before and after the measurement value when the measurement value cannot be obtained due to the impossibility of propagation of the ultrasonic beam is employed.

  FIG. 10 is a graph showing the instantaneous flow rate value in this case. Times t1 to t2 during which the space A passes between S1 and S2 are times when the ultrasonic beam B has not been propagated, and during these times t1 and t2, interpolation is performed based on the previous flow rate value.

  For example, when a space A of 5 ml exists in a fluid flowing at a flow rate of 100 ml / min, if interpolation is performed when measurement is impossible using data when an ultrasonic beam is normally propagated, 1 minute The flow rate flowing is calculated as 100 ml / min. However, in practice, the flow rate that flows in 1 minute is 95 ml, which is 100 ml minus 5 ml of space A, and an error of 5 ml occurs.

  In order to accurately determine the flow rate, it is necessary to estimate the size of the space A, but it is difficult to determine the size of the space A with these times t1 to t2. This is because the shape and size of the space A is not constant. For example, a plurality of spaces A as shown in FIG. 11 may be mixed, or a space A ′ having a large length may flow as shown in FIG. is there. In these cases, just because the ultrasonic beam B is not propagated at the times t1 to t2, it is impossible to estimate the size of the space and subtract the amount to obtain the flow rate.

  As described above, in the conventional ultrasonic flowmeter, if the space exists in the fluid, the size of the space and the like cannot be detected to accurately measure the instantaneous flow rate and the integrated flow rate.

JP 2001-281032 A JP 2005-181268 A JP 2006-337313 A

  An object of the present invention is to provide an ultrasonic flowmeter capable of solving the above-described problems, detecting the size of a space, and reducing measurement errors when a space exists in a fluid. is there.

In order to achieve the above object, an ultrasonic flowmeter according to the present invention is provided with a pair of ultrasonic transducers on the upstream side and the downstream side in the fluid flow direction of a flow path tube body, and these ultrasonic transducers The ultrasonic beam is alternately transmitted and received by a vessel, and the flow rate value is measured based on the propagation time difference generated in the ultrasonic beam propagating through the fluid by the flow velocity of the fluid flowing through the flow path tube. An ultrasonic flowmeter in which space detecting means for detecting a space passing through the body together with the fluid is installed in the tube body between the pair of ultrasonic transducers , wherein the ultrasonic beam is transmitted by the ultrasonic transducers. In the first measurement mode when the space is not detected by the space detecting means, the flow rate value is measured based on the obtained ultrasonic beam to obtain the measured flow rate value, and the ultrasonic transducer is used to measure the flow rate value. Detecting a sound beam and said In the second measurement mode when the space is detected by the interval detection means, the size of the space is detected based on the output of the space detection means and the size of the space obtained in advance, and obtained based on the ultrasonic beam. A measured flow rate value is obtained by subtracting the size of the detected space from the obtained flow rate value, and a third case where no ultrasonic beam is detected by the ultrasonic transducer and no space is detected by the space detection means. In the measurement mode, the last flow rate value measured in the first measurement mode is set as the measurement flow rate value, and when the ultrasonic beam is not detected by the ultrasonic transducer and the space is not detected by the space detection means. In the fourth measurement mode, the measured flow rate value is set to zero.

  According to the ultrasonic flowmeter of the present invention, even when a space exists in the fluid, the flow rate can be accurately measured by detecting the size of the space.

  The present invention will be described in detail based on the embodiment shown in FIGS.

  FIG. 1 shows a configuration diagram of an ultrasonic flowmeter according to the first embodiment. A flow path tube 11 has a U-shape, and is opposed to an outer wall on the upstream side and a downstream side across an intermediate straight pipe portion. A pair of ultrasonic transducers 12a and 12b is attached to the position. A space detection means comprising a light emitter 13a and a light receiver 13b for detecting a space existing in the fluid at a position facing the tube axis of the straight pipe portion which is a light transmission tube of the flow path tube 11. Is attached. The ultrasonic transducers 12a and 12b, the light emitter 13a, and the light receiver 13b are connected to the calculation control means 14, and the output of the calculation control means 14 is connected to the display means 15.

  When measuring the flow rate, the ultrasonic transducers 12a and 12b alternately transmit and receive the ultrasonic beam B, and the time until the ultrasonic beam B reaches the downstream side from the upstream side. The calculation control means 14 measures the propagation time difference due to the flow velocity of the time to reach the upstream side. Based on this propagation time difference, the calculation control means 14 calculates a flow rate value by a known method and displays it on the display means 15.

  For example, an infrared LED made of GaAlAs, GaAs, or the like is used for the light emitter 13a that is a signal transmitter of the space detection means. A photodiode, a phototransistor, a photo IC, or the like is used for the light receiver 13b that is a signal receiver. When the light receiver 13b detects light, a current proportional to the amount of light is obtained. When the light emitted from the light emitter 13a enters the flow path tube body 11 formed of a light transmission tube, crosses the fluid, and reaches the light receiver 13b, the light quantity is transmitted through the fluid and attenuated by the fluid. Since the amount of light when transmitted through the space is different, the presence of the space can be detected.

  That is, the time during which the presence of the space is detected by the space detection means is the time during which the space passes through the light transmission path of the space detection means, and the calculation control means 14 has a magnitude corresponding to this time corresponding to the space. Is subtracted from the flow rate value to calculate an accurate flow rate value, and the display means 15 displays an accurate flow rate value or further an alarm.

  FIG. 2 is an explanatory diagram when the space A exists in the fluid, and FIG. 3 shows an instantaneous flow rate value, presence / absence of space detection, and integrated flow rate value when the space A moves. When the space A reaches the position indicated by S1, the ultrasonic beam B is not propagated and cannot be measured.

The flow rate is interpolated by the immediately preceding flow rate value from the time t1 at which the space A reaches the space detection means at the position S1. When time ta is reached, space A is detected by the space detection means, and the flow rate value at that time is set to zero. In this way, the flow rate when the space A is detected is set to 0, so that the flow rate is accurately integrated.

  The space A is not detected by the space detector during the period from the time tb when the space A has passed the detection range of the space detector to the time t2 immediately before the ultrasonic transducer 12b. Beam B is not propagated. Similarly to the times t1 to ta, the time tb to t2 during this time is interpolated using the flow rate value before the space A reaches the position S1 or the flow rate value after passing through the position S2.

  However, this interpolation method is effective in the case where there is a space A in which the size of the space A is almost the same as the inner diameter of the tube body 11, but when the size of the space A is small, for example, a bubble. The ultrasonic beam B may be propagated even if the space A exists.

In this case, the relationship between the size of the space detected by the space detection means in the experiment and the transmission intensity and reception intensity of the space detection means at that time is obtained in advance and stored in the storage device and calculated by the calculation control means 14. do it.

  That is, when the space A is detected by the space detection means despite the normal propagation of the ultrasonic beam B, the size of the space is obtained from the received intensity of the space detection means by the storage device. By subtracting the distance, an accurate flow rate value can be calculated.

  FIG. 4 shows the space detecting means of the second embodiment. The light emitter 13a and the light receiver 13b are arranged on the same side of the tube body 11, and the light from the light emitter 13a is reflected by the inner wall of the tube body 11 to receive the light receiver 13b. To be back. In this case, the reflection surface in the tube 11 may be a reflection mirror or the like, or may be incident on the reflection surface at an angle such that the light beam is totally reflected.

  The space detection means by photoelectric conversion of the first and second embodiments is effective for a slurry liquid having a low light transmittance of fluid. However, when the fluid is water having a high light transmittance, the difference in the amount of light when the space A is mixed and when the space A is not mixed is small. Therefore, as shown in FIG. 1 or FIG. Since it is difficult to detect with the required method, the refraction of light can be considered.

  For example, in Example 3 shown in FIG. 5, when there is no space, the light from the light emitter 13a is prevented from reaching the light receiver 13b due to the optical refractive index of the fluid. It is configured to go straight and reach the light receiver 13b. On the contrary, it is possible to obtain a configuration in which the amount of light is obtained when a space exists and light cannot reach when the space does not exist.

  As a result, a large difference occurs in the amount of received light when the space exists and when it does not exist, so that space detection is performed reliably.

  FIG. 6 shows the configuration of the fourth embodiment, in which the light emitter 13a and the light receiver 13b are arranged on the same side of the tube body 11, and light from the light emitter 13a passes through the tube when there is a space due to the light refractive index of the fluid. The configuration is such that the light is reflected within the body 11 and returned to the light receiver 13b, and the detection of the space is the same as in the case of FIG.

  FIG. 7 shows the arrangement of the light emitters 13a and the light receivers 13b as viewed from the cross-sectional direction of the tube body 11 of the fifth embodiment, and the configuration that produces the same effect as the previous embodiment depending on the installation position on the outer periphery of the tube body 11. It is said that.

  That is, the light emitter 13a and the light receiver 13b are arranged at the same position in the tube axis direction around the tube body 11, and detect the space using the light refractive index of the fluid. Even in this case, the reflection method can be used as shown in FIG.

  FIG. 8 is an operation flowchart in each embodiment. It is detected whether the ultrasonic beam B propagates between the ultrasonic transducers 12a and 12b (step S1).

  When the ultrasonic beam B is propagating, the presence of the space is detected by the space detecting means (step S2). If no space is detected, flow measurement by the ultrasonic beam B is continued (step S3). When the space is detected in step S2, bubbles that are large enough to propagate the ultrasonic beam B are present. The size of the bubbles is estimated by the space detection means using the interpolation method described above, and an experimental value is obtained. From this, the amount of bubbles mixed is calculated and the flow rate is corrected (step S4).

  If the propagation of the ultrasonic beam B is not detected in step S1, the presence of space is detected by the space detection means (step S5). When the space is not detected, the position is unknown in the path of the ultrasonic beam, but there is a space, and the last flow rate value at which the measurement was normally performed is used as the flow rate value (step S6). When a space is detected in step S5, the fluid does not flow by the size of the space, so the flow value during that time is set to 0 (step S7).

  In addition, when light is used for the space detection unit as in the above-described embodiment, it is also preferable to modulate the signal light to distinguish it from disturbance light as a noise countermeasure.

  In addition to transmitting and receiving light as a space detection means, a piezoelectric element such as lead zirconate titanate is used as a signal transmitter / receiver, and an ultrasonic beam is transmitted across the tube 11 or a tube The space can also be detected by reflecting on the inner wall of 11. In this case, the tube 11 need not be a light transmission tube.

  In addition, this invention is applicable also to the pipes for flow paths other than the U-shaped pipe like an Example.

It is a block diagram of an Example. It is explanatory drawing in case space exists in the fluid. It is explanatory drawing of the instantaneous flow value when space moves, space detection, and an integrated flow value. It is a block diagram of the space detection means of Example 2. It is a block diagram of the space detection means of Example 3. It is a block diagram of the space detection means of Example 4. It is a block diagram of the modification of the space detection means of Example 5. It is an operation | movement flowchart figure. It is a block diagram of the conventional ultrasonic flowmeter. It is a graph of the conventional instantaneous flow rate value. It is explanatory drawing when a some space is mixed in a tubular body. It is explanatory drawing when a space with a long length exists in a tubular body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Pipe body for flow paths 12a, 12b Ultrasonic transmitter / receiver 13a Light emitter 13b Light receiver 14 Operation control means 15 Display means

Claims (8)

A pair of ultrasonic transducers are attached to the upstream and downstream sides of the fluid flow direction of the flow path tube body, and the ultrasonic flow is alternately transmitted and received by these ultrasonic transducers. A pair of space detecting means for measuring a flow rate value based on a propagation time difference generated in an ultrasonic beam propagating in the fluid according to a flow velocity of the fluid flowing in the tube, and detecting a space passing through the tube together with the fluid; An ultrasonic flowmeter installed in the tube between the ultrasonic transducers of
In a first measurement mode in which an ultrasonic beam is detected by the ultrasonic transducer and a space is not detected by the space detector, a flow rate value is measured by measuring a flow rate value based on the obtained ultrasonic beam. age,
In the second measurement mode when the ultrasonic beam is detected by the ultrasonic transducer and the space is detected by the space detection means, the output of the space detection means and the size of the space obtained in advance are used. By detecting the size of the space and subtracting the detected size of the space from the flow rate value obtained based on the ultrasonic beam,
In a third measurement mode in which no ultrasonic beam is detected by the ultrasonic transducer and no space is detected by the space detection means, the last flow value measured in the first measurement mode is a measured flow value. age,
And in the fourth measurement mode when detecting no space by and the space detecting means detects no ultrasonic beam by the ultrasonic transducer, ultrasonic flowmeter, characterized in that the measured flow rate value is zero.   The space detection means is composed of a signal transmitter and a signal receiver, and the signal transmitter and the signal receiver are installed on the outer wall of the flow path tube body facing each other across the flow path tube body. The ultrasonic flowmeter according to claim 1, wherein a signal transmitted from the signal transmitter passes through the tube and is received by the signal receiver.   The space detection means includes a signal transmitter and a signal receiver, and the signal transmitter and the signal receiver are installed on the same side of the outer wall of the flow path tube body, and a signal transmitted from the signal transmitter is received. 2. The ultrasonic flowmeter according to claim 1, wherein the signal is received by the signal receiver at a position that passes through the tube and is reflected by an inner wall of the tube and returns.   The flow passage tube is a light transmission tube, the signal transmitter is a light emitter, the signal receiver is a light receiver, and the presence of space is detected by photoelectrically converting the amount of light received by the light receiver. The ultrasonic flowmeter according to claim 2 or 3, wherein   The light emitter and the light emitter so that light emitted from the light emitter is received by the light receiver when there is no space in the fluid and is not received when there is space in the fluid, depending on the refractive index of the fluid. The ultrasonic flowmeter according to claim 4, wherein the light receiver is installed.   The light emitter and the light emitter so that light emitted from the light emitter is received by the light receiver when there is a space in the fluid, and is not received when there is no space in the fluid, depending on the refractive index of the fluid. The ultrasonic flowmeter according to claim 4, wherein the light receiver is installed.   The ultrasonic flowmeter according to any one of claims 4 to 6, wherein light emitted from the light emitter is modulated.   The ultrasonic flowmeter according to claim 2 or 3, wherein the signal transmitter and the signal receiver are ultrasonic transducers.

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