JP2011058883A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter automatically starting measurement in accordance with occurrence of a drift flow, determining the speed at the fastest part and determining the flow rate with errors reduced to a minimum. <P>SOLUTION: The ultrasonic flowmeter includes a sensor part 1 for measuring the flow velocity at multiple parts while moving in the circumferential direction of a pipe 6; and a converter 2 for specifying a part with the fastest flow velocity based on the measurement results obtained by the sensor part 1 and moving the sensor part 1 to the fastest part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter that measures a flow rate in a pipe using ultrasonic propagation time.

  2. Description of the Related Art An ultrasonic flow meter is known as one of devices for measuring the flow rate of a liquid or gas flowing in a pipe in a water and sewage system or a plant. The ultrasonic flowmeter includes at least one sensor installed on each of the upstream side and the downstream side of the pipe surface. Ultrasonic waves are transmitted and received between these sensors, and the flow rate of the liquid flowing in the pipe is obtained from the difference between the time required for propagation of the ultrasonic wave in the upstream direction and the time required for propagation in the downstream direction. The flow rate is calculated based on the flow rate.

  In a pipe, the flow velocity is not always uniform. For example, when there is a bend upstream of the pipe, a flow state called a drift current is formed, in which a portion with a large flow velocity and a small portion are formed in a cross section perpendicular to the pipe axis. Occurs. If a flow rate is calculated based on a portion where the flow velocity is large or small with an ultrasonic flowmeter and a flow rate is calculated based on the measured flow rate, an error occurs between the flow rate and the actual flow rate.

  Conventionally, a flow meter that can cope with drift even when a sufficient straight pipe length cannot be secured has been developed. In Patent Document 1, a pair of audible acoustic transducers are disposed at upstream and downstream sides of a gas pipe in opposite directions with respect to the tube axis and spaced from each other along the tube axis. There is described a sonic gas flow rate measuring device which is arranged in a relationship and is movable in the circumferential direction on the outer periphery of a gas pipe while maintaining a relative positional relationship. This gas flow rate measuring device collects flow velocity data from a large number of measurement lines, and tries to obtain an accurate flow rate measurement value in which the influence of the deviation of the flow velocity distribution is canceled. Patent Document 2 describes an ultrasonic flowmeter that attempts to reduce variation in measured values due to drift by installing a plurality of sensors in a pipe and enabling measurement between a plurality of sensor pairs. ing.

  The drift may be caused not only by the bending of the pipe but also by a change in the pipe control unit such as a pump or a valve located upstream or downstream of the measurement site. In this case, it is expected that the state of drift changes depending on the operation state of the pipe control unit. Therefore, in order to measure an accurate flow rate, it is necessary to measure the speed each time a change occurs in the pipe control unit.

JP 2002-139357 A JP 2005-164571 A

  The present invention provides an ultrasonic flowmeter that can automatically start measurement in response to the occurrence of drift, can easily determine the speed of the fastest part, and can determine the flow rate with minimal errors. There is.

  According to the present invention, while moving in the circumferential direction of the pipe, the sensor unit that measures the flow velocity at a plurality of sites, the fastest part of the flow velocity is specified based on the measurement result by the sensor unit, and the sensor unit is An ultrasonic flow meter having a transducer that is moved to the fastest part is provided.

  According to the ultrasonic flowmeter of the present invention, measurement can be automatically started in response to the occurrence of drift, the speed of the fastest part can be easily determined, and the flow rate with minimal errors can be determined. .

The schematic diagram which shows an example of the ultrasonic flowmeter which concerns on this invention. The block diagram of the converter of the ultrasonic flowmeter concerning the present invention. The graph which shows the relationship between a movement angle and a flow velocity. The piping sectional view showing the flow velocity distribution in the piping. Sectional drawing which shows the relationship between piping and a sensor part seen from piping side surface direction.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram showing an ultrasonic flowmeter according to an embodiment of the present invention. The ultrasonic flowmeter includes a pair of sensor units 1A and 1B and a transducer 2. The sensor units 1A and 1B and the converter 2 are connected by a cable 3. Each of the sensor units 1A and 1B is movably supported on two rails 4 installed along the outer periphery of the pipe 6. The converter 2 includes a cable take-up reel 5, and a part of the cable 3 is taken up.

  The paired sensor units 1A and 1B are installed at symmetrical positions around the tube axis of the pipe 6 with a space between the upstream side and the downstream side in the tube axis direction. Each sensor unit 1A, 1B has an ultrasonic transmission / reception unit. The sensor units 1A and 1B can be moved in the circumferential direction on the rail 4 by a driving device (not shown). The paired individual sensor portions 1A and 1B move synchronously and maintain a symmetrical positional relationship about the tube axis.

  The converter 2 obtains the data detected by the sensor units 1A and 1B, calculates the acquired data, outputs a signal for moving the sensor units 1A and 1B based on the calculation results, and the like. Responsible for overall control of the meter.

  FIG. 2 is a block diagram showing the converter 2. As shown in FIG. 2, the converter 2 includes an A / D converter 201 that converts data from the sensor units 1A and 1B, a memory 202 that stores data converted by the A / D converter 201, and the like. A rotation angle control circuit 204 is provided that outputs a rotational motion signal to the driving devices of the sensor units 1A and 1B based on signals from the CPU 203 and the CPU 203 that calculate the data. Optionally, a display unit 205 for displaying the measurement results, a monitoring control device 206 for detecting the operation status of the piping control unit for piping such as pumps and valves, and an interface for inputting measurement conditions, etc. Other elements can be provided.

  Next, measurement using the ultrasonic flowmeter of the present invention will be described with reference to FIG. The measurement is started when the monitoring control unit 206 detects a change in the operation status of the piping control unit such as a pump or a valve located upstream or downstream of the sensor units 1A and 1B. The change in the operation status means, for example, the start or stop of the pump operation or the fluctuation in the rotation speed, or the opening / closing of the valve or the change in the opening degree.

  Receiving the measurement start signal, the CPU 203 outputs a signal to the rotation angle control circuit 204 that causes the sensor units 1A and 1B to move by a certain angle and measures the flow velocity every time the movement of the certain angle is finished. The constant angle at this time is 180 ° / n (n is an arbitrary integer), and n is preset in consideration of accuracy and measurement time. When n is set to a larger value, the sensor units 1A and 1B move by a smaller angle, so that the number of flow rate lines can be increased.

  Information on the flow velocity detected by the sensor units 1A and 1B in the range of 0 to 180 ° is transmitted to the A / D converter 201 as an analog signal. The A / D converter 201 that has received the information on the flow velocity performs A / D conversion on the signal and then transmits the signal to the memory 202. The memory 202 accumulates a plurality of measurement results corresponding to n.

  After completing a series of measurements, the CPU 203 obtains the relationship between the movement angle and the flow velocity as shown in FIG. 3 based on the measurement results stored in the memory 202. FIG. 3 shows the results when n = 6. FIG. 4 schematically shows the flow velocity distribution in the pipe 6, where regions having the same flow velocity are expressed by the same concentration, and the concentration is higher as the flow velocity is higher. For example, when the flow velocity is uniform in the pipe 6 as shown in FIG. 4a, the same flow velocity value can be obtained regardless of the angle, as shown in FIG. 3a. It has a horizontal straight line. On the other hand, FIG. 4B schematically shows a flow velocity distribution when the inside of the pipe 6 has a drift. In FIG. 4b, the region with the highest flow velocity is offset from the tube axis and is biased towards the periphery of the tube. In this case, the relationship between the movement angle and the flow velocity is, for example, as shown in FIG. As shown in this figure, the flow velocity created on the basis of the actual measurement value in the case of drifting changes stepwise according to the movement angle. When the flow velocity change due to the actually measured value is approximated to a curved flow velocity change, it is as shown in FIG. The flow velocity change as shown in FIG. 3 is displayed on the display unit 205 as appropriate. The operator can also adjust n based on the displayed flow velocity distribution diagram.

  Next, the CPU 203 determines an angle at which the maximum flow velocity is obtained based on the measurement result, and transmits information on the angle to the rotation angle control circuit 204. Based on this information, the rotation angle control circuit 204 moves the sensor units 1A and 1B to target angles and performs measurement at the positions. As long as the operation status of the piping control unit does not change again, it is not necessary to move the sensor units 1A and 1B. The sensor units 1 </ b> A and 1 </ b> B measure the flow velocity at the position, and transmit the measurement result to the memory 202 via the A / D converter 201. The CPU 203 displays the measurement result on the display unit 205.

  When the operation status of the pipe control unit changes again, the series of measurements described above is resumed, but in this case, the moving direction is reversed from the previous measurement. In this way, it is possible to prevent the cable 3 from being tangled with the rotational movement of the sensor units 1A and 1B.

  In addition to the maximum flow velocity value, the flow rate is also calculated based on the flow velocity distribution diagram. The CPU 203 calculates an average flow velocity based on a series of results measured a plurality of times according to n. By multiplying this average flow rate by the cross-sectional area of the pipe, a flow rate that flows through the pipe in a certain time is obtained. This calculated flow rate is also displayed on the display unit 205.

  Next, details of the calculation of the flow velocity and the flow rate will be described.

  FIG. 5 is a cross-sectional view showing the relationship between the pipe 6 and the sensor units 1A and 1B as seen from the side surface direction with respect to the pipe axis. In FIG. 5, the sensor unit 1A is located on the upstream side of the pipe 6, and the sensor unit 1B is located on the downstream side. Here, the diameter of the pipe 6 is D. Since the sensor units 1A and 1B rotate in the circumferential direction of the pipe 6 while maintaining their relative positions, the distance between the sensor units 1A and 1B, that is, the length L of the survey line 7 is constant, and the survey line 7 And the acute angle φ formed by the pipe 6 is also constant. Further, the velocity of the ultrasonic wave traveling along the measuring line 7 is C, and the velocity of the flow 9 to be measured is V.

First, ultrasonic waves are transmitted and received between the sensor units 1A and 1B, and a time Tab required for propagation from 1A to 1B and a time Tba required for propagation from 1B to 1A are measured. Here, the propagation from 1A to 1B proceeds while being pushed by the flow 9, whereas the propagation from 1B to 1A proceeds due to the resistance of the flow 9. As a result, the propagation speed of the ultrasonic wave changes. Considering this point, Tab and Tba are represented by the following equations (i) and (ii), respectively.

From the above equations (i) and (ii), the following equation (iii) is obtained when V is obtained while erasing C.

  From equation (iii), since L and φ are constant values, it can be understood that the velocity of the flow 9 is obtained based on the time required for the ultrasonic wave to travel between the sensor units 1A and 1B.

  The flow rate is obtained by obtaining an average flow velocity from the flow velocity V measured a plurality of times based on the value of n and multiplying it by the cross-sectional area.

  With the ultrasonic flowmeter of the present invention, even when a drift occurs in the pipe, the flow velocity of the fastest part can be easily determined, and the flow rate can be accurately determined. In response to changes in the status of piping control units such as pumps and valves, measurement is automatically started and the flow rate and flow rate of the fastest part can be grasped.

  The ultrasonic flowmeter of the present invention can measure, for example, water and sewage piping, chemical plant piping, food plant piping, and the like. The substance flowing inside the pipe can be water, a liquid such as a solution, or a gas such as a fuel gas. If a certain degree of uniformity is maintained, it can be applied to a pipe through which a liquid containing solids flows. The applicable pipe material is not particularly limited, such as metal or polymer.

  DESCRIPTION OF SYMBOLS 1A, 1B ... Sensor part, 2 ... Converter, 3 ... Cable, 4 ... Rail, 5 ... Cable take-up reel, 6 ... Pipe, 7 ... Measuring line, 9 ... Flow, 201 ... A / D converter, 202 ... Memory , 203 ... CPU, 204 ... rotation angle control circuit, 205 ... display unit, 206 ... monitoring control device.

Claims (6)

While moving in the circumferential direction of the pipe, a sensor unit that measures the flow velocity at multiple sites,
The ultrasonic flowmeter which has the converter which specifies the fastest part of the flow velocity based on the measurement result by the said sensor part, and moves the said sensor part to the fastest part.   The ultrasonic flowmeter according to claim 1, wherein the converter starts measurement by the sensor unit in response to a change in an operation state of a pipe control unit installed in the pipe.   The ultrasonic flowmeter according to claim 1, wherein the sensor unit measures a flow velocity while moving in a circumferential direction by 180 ° / n (n is an integer).   The ultrasonic flowmeter according to claim 1, wherein the sensor unit includes a driving device and moves on a rail installed in a circumferential direction of the pipe.   The ultrasonic flowmeter according to claim 1, wherein the converter includes a take-up reel of a cable connecting the sensor unit and the changer. A pair of sensor units that are supported movably along the outer periphery of the pipe so as to be symmetric with respect to the pipe axis center on the upstream side and the downstream side along the pipe axis direction of the pipe,
A drive unit that moves the pair of sensor units synchronously along the outer periphery of the pipe while maintaining symmetry with respect to the tube axis center;
The position where the fastest part of the flow velocity is obtained is determined by moving the pair of sensor parts in the circumferential direction by a certain angle along the outer periphery of the pipe to detect the flow speed of the fluid in the pipe. The ultrasonic flowmeter which has a converter which moves the pair of sensor parts to the position where the fastest part of the flow velocity is obtained by the drive part.

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