JP4368616B2 - Flowmeter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow meter such as an ultrasonic flow meter.
[0002]
[Prior art]
Conventionally, as a flow measurement device that measures the flow rate of a fluid such as gas (for example, city gas, propane gas) or liquid (for example, water), for example, an ultrasonic flowmeter that measures a flow velocity using ultrasonic waves is known. Yes. In general, a “propagation time difference method” is used as a measurement principle at that time. This is provided with a pair of ultrasonic transmission / reception units on the upper and lower sides of the fluid flow direction of the flow path, and alternately switching the transmission / reception of ultrasonic signals, and the ultrasonic transmission unit (transmission-side transducer) on the upper side in the flow direction From the time Tj until reaching the ultrasonic receiving unit (reception side transducer) on the lower side in the flow direction (hereinafter referred to as forward arrival time) Tj, and from the ultrasonic transmission unit (transmission side transducer) on the lower side in the flow direction From the time difference (arrival time difference) ΔT = Tg−Tj to the time (hereinafter referred to as reverse direction arrival time) Tg until reaching the ultrasonic wave receiving unit (reception side transducer) on the upper side in the flow direction This is a method for obtaining the average flow velocity and flow rate.
[0003]
Theoretically, when the flow rate Q = 0 (average flow velocity v = 0), the arrival time difference ΔT = 0, but in reality ΔT is not equal to 0 due to a manufacturing error or the like (also called an offset; For example, see FIG. This deviation amount (offset amount) can be measured at the time of shipment from the factory as a value unique to each ultrasonic flowmeter (ultrasonic sensor), and the origin is corrected (zero point correction) in the form of an initial value or a calibration curve. The offset amount may vary due to changes over time. However, once installed in a gas meter or the like, the use of gas cannot be stopped in principle for a certain period of time, so it is difficult to measure and correct the offset amount again. Therefore, Patent Document 1 discloses a technique that enables the origin correction even when the flow rate is not completely zero by using a pressure sensor.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-249038
[Problems to be solved by the invention]
However, in the technique described in Patent Document 1,
(1) Since a pressure sensor for detecting the absolute pressure of the fluid is provided, high accuracy is required. Therefore, it is necessary to further increase the resolution (sensitivity and amplification factor) when confirming whether or not it is equal to the occlusion pressure.
(2) Since the current offset amount is unknown and the flow rate is measured using an ultrasonic sensor that needs to be corrected from now on, the measurement data is used as a criterion for determining whether or not the flow rate in the measurement channel can be regarded as zero. The reliability of measurement data and judgment results is poor.
[0006]
Accordingly, an object of the present invention is to provide a flow meter that can accurately determine the presence or absence of a flow rate and can easily obtain an origin correction value by detecting a pressure difference between fluids on the inlet side and the outlet side. It is in.
[0007]
[Means for Solving the Problems and Effects of the Invention]
As flowmeter as the prerequisite in order to solve the above problems,
An inlet and an outlet opening on the outer surface for introducing and delivering a fluid for flow measurement, respectively;
A pressure loss portion formed between the inlet and the outlet and including a flow path for allowing the fluid to pass through;
When the pressure difference of the fluid between the inlet side and the outlet side sandwiching the pressure loss portion is equal to or less than a predetermined value, there is no or substantially no flow rate of the fluid flowing through the flow path. A flow rate presence / absence judging means for outputting a signal,
Can be provided.
[0008]
In addition, as a prerequisite flow meter to solve the above problems,
An inlet and an outlet opening on the outer surface for introducing and delivering a fluid for flow measurement, respectively;
A pressure loss portion formed between the inlet and the outlet and including a flow path for allowing the fluid to pass through;
A pressure detection pipe provided with a pressure sensor for detecting the pressure difference of the fluid between the inlet side and the outlet side sandwiching the pressure loss part;
When the pressure sensor detects a pressure difference equal to or less than a predetermined value, there is no flow rate of the fluid flowing through the flow path, or a flow rate presence / absence determining means for outputting a signal indicating that there is substantially no flow rate;
Can be provided.
[0009]
According to these flow meters, the pressure loss caused by the flow of the fluid is detected as the pressure difference (differential pressure) of the fluid between the inlet side and the outlet side. It is easy to detect the expansion (amplification) of the differential pressure by the pressure loss portion that generates the differential pressure. As described above, since the resolution at the time of detecting the differential pressure can be easily increased, the determination accuracy of the flow rate can be maintained at a high level, and the origin correction value (offset amount) can be obtained accurately and easily. Moreover, since it is possible to determine whether or not the flow meter origin can be corrected only by detecting the differential pressure between the inlet side and the outlet side, a complicated determination process such as determining whether or not the flow meter needs to be corrected is not required. The reliability with respect to the obtained origin correction value becomes high.
[0010]
In such a flow meter, when a pressure detection tube is used for differential pressure detection, a pressure sensor having a detection body such as a diaphragm or bellows can be used as a discrimination switch, and a highly accurate detection unit is incorporated in a compact manner. be able to.
[0011]
Furthermore, in order to solve the above problems, the flowmeter according to the present invention is:
An inlet and an outlet opening on the outer surface for introducing and delivering a fluid for flow measurement, respectively;
A pressure loss part including a flow path formed between the inlet and the outlet and provided with a flow rate measuring means for measuring the flow rate while passing the fluid; and
When the pressure difference of the fluid between the inlet side and the outlet side sandwiching the pressure loss portion is equal to or less than a predetermined value, there is no or substantially no flow rate of the fluid flowing through the flow path. A flow rate presence / absence judging means for outputting a signal,
Origin correction value storage means for storing the origin correction value measured by the flow rate measuring means based on the output signal without flow rate from the flow rate presence / absence judging means;
A pressure loss amplifying means for amplifying and detecting the pressure difference of the fluid between the inlet side and the outlet side sandwiched between the pressure loss parts, provided in the pressure loss part;
Equipped with a,
The pressure loss amplifying means is a variable throttle mechanism capable of changing the flow passage cross-sectional area stepwise or continuously, and as the valve element disposed opposite the valve seat moves in the direction of closing the flow passage. It has a shut-off valve whose flow path cross-sectional area becomes small stepwise or continuously, and adjusts the throttle amount by moving the valve body of the shut-off valve in the flow path closing direction so that the pressure difference becomes a predetermined value or less. In addition, by controlling the pressure loss to achieve an approximate no flow state,
At this time, the origin correction value storage means stores the measurement value measured by the flow rate measurement means based on the output signal without flow rate from the flow rate presence / absence discrimination means as an origin correction value .
[0012]
According to this flow meter, the above-described highly accurate and reliable origin correction value can be acquired regularly or irregularly and used while being updated as an initial value or a calibration curve for flow rate measurement. As a result, it is possible to maintain and manage the accuracy of the determination of the presence or absence of the flow rate and the origin correction value and thus the flow rate measurement at a high level. For example, in an ultrasonic household gas meter, when the origin correction according to the present invention is performed at a frequency of once / year or more, the discrimination accuracy for a minute flow rate of less than 1 liter / hour is easily maintained for more than 10 years legally. It becomes possible to manage.
[0013]
And in the flow meter as described above, if pressure loss amplifying means is provided in the pressure loss part, and the pressure difference of the fluid between the inlet side and the outlet side sandwiching the pressure loss part is amplified and detected, The accuracy of determining the presence or absence of the flow rate is further improved, and a more accurate origin correction value can be obtained.
At that time, when adopting a variable throttle mechanism that can change the channel cross-sectional area step by step or continuously as the pressure loss amplification means, the pressure loss is controlled with high accuracy by adjusting the throttle amount, and the approximate no flow state Can be realized. Accordingly, it is possible to obtain the origin correction value while maintaining the function as a normal flow meter or ensuring the return to the normal flow state immediately when the use of the fluid is started. As such a variable throttle mechanism, a motor control type shut-off valve can be exemplified.
And in the shut-off valve used as the variable throttle mechanism, the structure in which the cross-sectional area of the flow path becomes smaller stepwise or continuously as the valve element disposed opposite the valve seat moves in the direction of closing the flow path. If it is adopted, the expansion rate (amplification factor) of the pressure loss can be increased, so that the presence or absence of the flow rate can be determined with higher accuracy.
[0014]
By the way, in the case of an ultrasonic flow meter, if an ultrasonic sensor for flow measurement is installed and the pressure loss part is set so as to include a measurement flow path having a small cross-sectional area from other parts for flow measurement By increasing the flow velocity and pressure loss in the measurement channel, it is possible to improve both the flow rate measurement accuracy during normal measurement and the flow rate presence / absence discrimination accuracy during origin correction.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. Fig.1 (a) shows front sectional drawing of the ultrasonic flowmeter used for a general residential gas meter etc. as one Example of a flowmeter. The ultrasonic flowmeter 100 includes a main body unit 110, an intermediate flow path forming unit 120, and a shutoff valve 130.
[0016]
As shown in FIG. 1A, the main body unit 110 has a rectangular parallelepiped shape as a whole, and an upper surface thereof has an inlet 112 connected to the upstream gas pipe and a flow connected to the downstream gas pipe. Each outlet 113 is open. In addition, a main body flow path 114 (pressure loss portion; flow path) for allowing a gas (fluid) to pass between the inflow port 112 and the outflow port 113 is formed therein. A main body channel cut-out portion 115 is formed in the lower part of the main unit 110 from the back side to the near side in FIG. 1A, and the intermediate channel formation unit 120 is fitted into the main body channel cut-out portion 115. ing.
[0017]
The intermediate flow path forming unit 120 has an intermediate portion connected to the main body flow path 114 when fitted to the main body flow path cutting portion 115 of the main body unit 110 from a direction (fitting direction) orthogonal to the gas flow direction. A flow path 121 (pressure loss portion; flow path) is formed through. The intermediate flow path 121 includes an inlet side connection flow path 121b (pressure loss portion) and an outlet side connection flow path 121c (pressure loss portion) that are smoothly continuous with the main body flow path 114, and both connection flow paths 121b and 121c at both ends. And a straight intermediate flow path 121a (pressure loss portion) disposed along the lower surface of the main unit 110 in a form substantially orthogonal to the main flow path 114. In addition, a pair of ultrasonic transmission / reception units 2 and 3 of an ultrasonic sensor are detachably attached to the intermediate flow path forming unit 120 in order to measure the flow rate of gas passing through the straight intermediate flow path 121a. Yes. The axial cross-sectional area of the straight intermediate flow path 121a is made smaller (throttle) than the axial cross-sectional area of the main body flow path 114, the pressure loss of the gas flowing through this portion is increased, and the linear intermediate flow path 121a flows. The flow rate of gas (flow velocity) measured by the ultrasonic sensor (ultrasonic transmission / reception units 2 and 3) is increased by increasing the gas flow velocity.
[0018]
Thus, between the inflow port 112 and the outflow port 113, the pressure loss part comprised by each flow path 114,121 etc. for allowing gas to pass through is formed. In order to detect a gas pressure difference between the inlet 112 side and the outlet 113 side sandwiching such a pressure loss part, a pressure sensor 118 is provided in the middle part, and the inlet 112 side and the outlet 113 side are provided. A pressure detection pipe 119 is provided in which the distal ends of the communication pipes 116 and 117 extending from the main body channels 114 and 114 are connected to the pressure sensor 118.
[0019]
An explanatory diagram in the case of using a capacitance type pressure sensor as an example of the pressure sensor 118 is shown in FIG. This pressure sensor functions as a switch that turns on and off because the capacitance between the fixed electrodes 118b and 118b changes due to the movement of the diaphragm 118a as the central movable electrode. Therefore, when the gas pressure difference between the inlet 112 and the outlet 113 introduced through the communication pipes 116 and 117 is equal to or smaller than a predetermined value, the gas is turned on (or turned off), and the channels 114 and 121 are turned on. It is detected that there is no or substantially no flow rate of the flowing gas.
[0020]
Returning to FIG. 1A, the main body flow path 114 between the inlet 112 and the intermediate flow path 121 has a shutoff valve 130 (pressure loss amplifying means; variable throttle mechanism for blocking the gas flow in the main body flow path 114. ) Is provided. As shown in FIG. 4, the shut-off valve 130 converts the rotational motion of an electric motor 131 (variable throttle mechanism) such as a stepping motor capable of rotating forward and reverse to a reciprocating linear motion by a valve body moving means (not shown), The valve body 132 (variable throttle mechanism) can be moved close to or separated from the valve seat 133 (variable throttle mechanism) against an elastic member 134 (variable throttle mechanism) such as a coil spring to stop or release the gas flow. Further, the shutoff valve 130 constitutes a variable throttle mechanism capable of changing the cross-sectional area of the channel stepwise or continuously, and the pressure of the gas at the inlet 112 side and the outlet 113 side sandwiching the pressure loss portion by the throttle. It also functions as pressure loss amplification means for amplifying the difference.
[0021]
Specifically, as shown in FIG. 4, the shut-off valve 130 has a flow path as the valve element 132 disposed to face the valve seat 133 moves in a direction to close the main body flow path 114 (flow path). The cross-sectional area is configured to decrease stepwise. The valve body 132 has a plurality of (for example, three) flat plate-like valve portions 137, 138, and 139 arranged in the moving direction to the valve seat 133. Except for the valve portion 139 farthest from the valve seat 133, each valve portion 137, 138 is formed with through holes 137 a, 138 a in the thickness direction in the center, and these through holes 137 a, 138 a are formed in the valve seat 133. (The outlet side; the lower side of the main body channel 114) is formed with a larger diameter.
[0022]
Further, the valve body 132 is provided with a sequential closing mechanism 140 for reversibly moving the valve portions 137, 138, 139 as in the following (1) to (3).
(1) From the fully open position (see FIG. 4 (b)) where the valve portions 137, 138, 139 are arranged at a predetermined interval,
(2) After the valve portion 135 on the side close to the valve seat 133 is sequentially moved to the valve seat 133 side,
{Circle around (3)} All valve portions 137, 138, 139 overlap in the plate thickness direction (moving direction) and reach the fully closed position where they contact and close the valve seat 133 (see FIG. 4C).
[0023]
Details of the sequential closing mechanism 140 are shown in FIG. One or a plurality of (for example, two) recesses 137b, 138b, 139b are formed on the end surfaces of the valve portions 137, 138, 139, respectively. Concave portions 137b and 138b formed in adjacent valve portions 137 and 138 on the side close to the valve seat 133 are arranged so as to face each other, and the compression coil spring 141 (elastic member) straddles the opposed concave portions 137b and 138b. ) Is inserted and inserted. Similarly, a compression coil spring 142 (a resilient member) is inserted and interposed across the recesses 138b and 139b formed in the valve portions 138 and 139 adjacent to the valve seat 133 on the far side. Since the spring constant of the compression coil spring 142 farther from the valve seat 133 is larger (the elastic force of the elastic member is large), it is pressed by the elastic force of the elastic member 134 or the driving force of the electric motor 131. Occasionally, the valve portion sequentially closes and moves from the valve portion on the side close to the valve seat 133 (exit side; lower side of the main body flow path 114).
[0024]
Therefore, by setting and adjusting the spring constants of the compression coil springs 141 and 142 (the elastic force of the elastic members), the valve portions 137, 138, and 139 are adjusted according to the number of steps of the stepping motor 131 (electric motor). It is possible to realize a state in which there is no or substantially no flow of gas flowing through the main body flow path 114 by sequentially closing. Further, since the enlargement factor (amplification factor) of the pressure loss can be increased in this way, the presence / absence of the flow rate by the pressure sensor 118 can be determined with high accuracy. Reference numeral 143 denotes a support shaft that is inserted through the shaft holes 137c, 138c, and 139c formed in the valve portions 137, 138, and 139. The support shaft 143 is supplementarily used to smoothly operate the closing mechanism 140 sequentially. Is provided.
[0025]
The shut-off valve of FIG. 4 can also have a simplified structure as in the modification shown in FIG. In the shut-off valve 130 ′ of FIG. 5, one or a plurality of stepped steps 132 a and 133 a (for example, three steps each) are formed in the valve body 132 ′ and the valve seat 133 ′ in the axial direction. As a result, the flow passage cross-sectional area is continuously reduced as the valve element 132 ′ disposed opposite to the valve seat 133 ′ moves in a direction to close the main body flow passage 114 (flow passage). Has been. That is, the gap 135 formed between them has a step shape along these steps 132a and 133a, and the confinement effect (labyrinth effect) in the gap 135 is increased, and the expansion factor (amplification factor) of the pressure loss is increased. Therefore, the presence / absence of the flow rate by the pressure sensor 118 can be determined with high accuracy. The gap 135 is formed so as to be closer to the valve seat 133 (exit side; lower side of the main body flow path 114).
[0026]
FIG. 2 shows a basic configuration of the measurement unit of such an ultrasonic flowmeter 100.
A flow rate measuring gas (fluid) flows along the flow direction axis O in the illustrated flow direction (average flow velocity v) in the linear intermediate flow path 121a for flow rate measurement of the ultrasonic flow meter 100. . A pair of ultrasonic transmission / reception units 2 and 3 (flow rate measuring means; ultrasonic sensors) are attached to the wall 10 of the flow path 121a. In FIG. 2, the ultrasonic transmission / reception unit 2 (transmission / reception transducer 21 (first transducer)) on the upper side in the fluid flow direction and the ultrasonic transmission / reception unit 3 (transmission / reception transducer 31 (second oscillation) on the lower side in the fluid flow direction are shown. )) Is configured in a transmissive Z-arrangement facing each other across the flow path 121a.
[0027]
In the measurement channel 121a, the flow direction axis O is linear between at least the pair of ultrasonic transmission / reception units 2 and 3, and the shape and cross-sectional area of the axial cross section are the same in the flow direction. When the measurement target is gas, the axial cross-sectional shape of the measurement channel 121a only needs to form a space closed by the wall 10, and may be any one of a circular shape, an elliptical shape, a square shape, a rectangular shape, and the like. May be adopted.
[0028]
The ultrasonic transmission / reception unit 2 includes a transmission / reception vibrator 21 (first vibrator) that is fixed to the wall 10 of the flow path 121a and includes a piezoelectric element, a vibration plate, an electrode plate, and the like. On the other hand, the ultrasonic transmission / reception unit 3 is fixed to the wall 10 on the lower side in the flow direction than the ultrasonic transmission / reception unit 2 (first vibrator 21), and includes a transmission / reception vibrator composed of a piezoelectric element, a diaphragm, an electrode plate, and the like. 31 (second vibrator). Further, the pair of ultrasonic transmission / reception units 2 and 3 includes a transmission unit 22 including a driving voltage circuit for oscillating the first transducer 21 or the second transducer 31, and the first transducer 21 or Receiving means 32 including a voltage detection circuit for detecting the voltage generated by the second vibrator 31 and the like. Thereby, the first vibrator 21 transmits the ultrasonic wave toward the lower side of the fluid flow direction (the ultrasonic transmission / reception unit 3 side) and receives the ultrasonic wave transmitted by the second vibrator 31. On the other hand, the second vibrator 31 transmits ultrasonic waves toward the upper side in the fluid flow direction (the ultrasonic transmission / reception unit 2 side) and receives the ultrasonic waves transmitted by the first vibrator 21.
[0029]
In FIG. 2, the average flow velocity of the gas is v, the speed of sound propagating in the gas is c, and the angle between the ultrasonic traveling direction (measurement line M) and the gas flow direction (flow direction axis O) is θ (hereinafter referred to as a measurement line). If the propagation distance of the ultrasonic wave is L, the forward arrival time Tj and the reverse arrival time Tg are respectively expressed as follows.
Tj = L / (c + v · cos θ) (1)
Tg = L / (cv · cos θ) (2)
The following expression is obtained from the expressions (1) and (2).
v = K (L / 2 cos θ) (Tg−Tj) / (Tg · Tj) (3)
Q = v · A (4)
However, K is a correction coefficient, A is a cross-sectional area of the flow path 1, and Q is a gas flow rate.
Therefore, the average gas flow velocity v and the flow rate Q are obtained from the measurement of the forward arrival time Tj and the reverse arrival time Tg (arrival time difference ΔT). In this way, by eliminating the sound velocity c depending on the gas temperature, the contained component, etc. from the equation (3), the measured value (arrival time Tj, Tg; arrival time difference ΔT) and a constant value (propagation distance L, line angle) θ) and the flow velocity v can be obtained.
[0030]
Therefore, as shown in FIG. 2, the ultrasonic flowmeter 100 includes a measurement control unit 4 and a switching unit 7 as a measurement unit in addition to the pressure sensor 118 and the shutoff valve 130 described above. The switching unit 7 includes a reception signal switching unit 71 that switches a signal to be processed by the receiving unit 32, and a transmission switching unit 72 that switches between the transducers 21 and 31 to be transmitted.
[0031]
The measurement control unit 4 includes a CPU 41, a RAM 42, a ROM 43, an input / output interface 44, and the like, and is configured by a microcomputer connected so as to be able to transmit and receive via a bus 45. The ROM 43 has a program storage area 43a and a data storage area 43b. The program storage area 43a stores an offset execution program, which will be described later. An origin correction value is stored in the data storage area 43b and has a function of an origin correction value storage means. The CPU 41 has a function as a flow rate presence / absence discriminating unit as will be described later. The pressure difference detected by the pressure sensor 118 and the ultrasonic reception signal received by the receiving unit 32 are input to the measurement control unit 4 via the input / output interface 44. On the other hand, a command from the CPU 41 is output to the switching means 7 via the input / output interface 44, and is also output to the electric motor 131 that drives the shutoff valve 130 via the motor driver 136. Furthermore, the data storage area 43b is preferably an EPROM so that an origin correction value can be written each time the origin is corrected.
[0032]
Next, the operation of the measurement unit of the ultrasonic flowmeter 100, specifically, the contents of the offset execution program will be described with reference to the flowchart of FIG.
First, it is checked whether a predetermined correction time (for example, once / year) has come (S1). If the correction time has arrived (YES in S1), the measurement control unit 4 next checks whether the current time is a gas non-use time zone among the life patterns already learned (S2). If it is a gas non-use time zone (YES in S2), it is checked whether the flow rate value measured by the ultrasonic sensor (ultrasonic transmitting / receiving units 2 and 3) is close to 0 (S3). When the flow rate value is close to 0 (YES in S3), it is determined that no gas is used, and the electric motor 131 is driven in S4 to slightly turn off the shutoff valve 130 (for example, several steps of the motor 131 or the valve portion 137). , 138, 139). At this time, the gas pressure difference between the inlet 112 side and the outlet 113 side is detected by the pressure detection pipe 119 (pressure sensor 118) (S5).
[0033]
If the pressure difference is equal to or less than the set threshold value (YES in S6), it is determined that there is no or substantially no flow rate of gas flowing through the flow path 121a, and an ultrasonic sensor (ultrasonic transmission / reception) is determined. (S2), and the arrival time difference ΔT is detected from the above equation (3) (S8). Further, the obtained arrival time difference ΔT is stored in the data storage area 43b as an origin correction value (S9). Thereafter, the electric motor 131 is driven to return the shut-off valve 130 to full open (S10), and the process returns. If the pressure difference detected in S5 exceeds the set threshold (NO in S6), the operations of S4 (shutoff valve 130 closed) and S5 (pressure detection pipe 119 pressure difference detection) are repeated. If NO in S1, S2, and S3, the process returns. If the shut-off valve 130 is allowed to be fully closed, a more accurate origin correction value can be obtained by fully closing the shut-off valve 130 before S7 (ultrasonic sensor transmission / reception) (S100). . Further, in order to enable origin correction with higher reliability, the offset execution program may be executed a plurality of times to obtain an average value of the origin correction values acquired each time.
[0034]
Further, when a pressure difference is detected by the pressure detection pipe 119 (pressure sensor 118) during the operation of the offset execution program shown in FIG. 3, it is determined that gas use has started, and the execution of the program is stopped immediately, and the shut-off valve If 130 is returned to full open, normal gas use can be prevented. Furthermore, when the correction time has arrived (YES in S1) and the gas is being used (NO in S3), an alarm indicating “cannot be corrected” may be issued. This is effective for cases where operations are continued for 24 hours in a chemical factory.
[0035]
In the embodiment, only the case where the ultrasonic transmission / reception units 2 and 3 (transmission / reception transducers 21 and 31) are arranged in the transmission type Z array has been described. Applicable. The present invention can also be applied to other flow meters such as a fluidic flow meter in addition to the ultrasonic flow meter.
[Brief description of the drawings]
FIG. 1 is a front sectional view of an ultrasonic flow meter as an embodiment of a flow meter according to the present invention, and an explanatory view of a pressure sensor.
FIG. 2 is an explanatory diagram showing a basic configuration of a measurement unit of the ultrasonic flowmeter of FIG.
FIG. 3 is a flowchart showing the operation of a measurement unit.
FIG. 4 is an explanatory diagram of a shutoff valve.
FIG. 5 is an explanatory view showing a modified example of the shut-off valve of FIG. 4;
[Explanation of symbols]
2,3 Ultrasonic transmitter / receiver (flow rate measuring means; ultrasonic sensor)
4 Measurement control unit 41 CPU (flow rate presence / absence determining means)
43 ROM (origin correction value storage means)
100 Ultrasonic flow meter (flow meter)
114 Body flow path (pressure loss part)
121 Intermediate channel (pressure loss part)
118 Pressure sensor 119 Pressure detection pipe 130 Shut-off valve (variable throttle mechanism; pressure loss amplification means)

Claims (2)

An inlet and an outlet opening on the outer surface for introducing and delivering a fluid for flow measurement, respectively;
A pressure loss part including a flow path formed between the inlet and the outlet and provided with a flow rate measuring means for measuring the flow rate while passing the fluid; and
When the pressure difference of the fluid between the inlet side and the outlet side sandwiching the pressure loss portion is equal to or less than a predetermined value, there is no or substantially no flow rate of the fluid flowing through the flow path. A flow rate presence / absence judging means for outputting a signal,
Origin correction value storage means for storing the origin correction value measured by the flow rate measuring means based on the output signal without flow rate from the flow rate presence / absence judging means;
A pressure loss amplifying means for amplifying and detecting the pressure difference of the fluid between the inlet side and the outlet side sandwiched between the pressure loss parts, provided in the pressure loss part;
Equipped with a,
The pressure loss amplifying means is a variable throttle mechanism capable of changing the flow passage cross-sectional area stepwise or continuously, and as the valve element disposed opposite the valve seat moves in the direction of closing the flow passage. It has a shut-off valve whose flow path cross-sectional area becomes small stepwise or continuously, and adjusts the throttle amount by moving the valve body of the shut-off valve in the flow path closing direction so that the pressure difference becomes a predetermined value or less. In addition, by controlling the pressure loss to achieve an approximate no flow state,
At this time, the origin correction value storage means stores the measurement value measured by the flow rate measurement means based on the output signal without the flow rate from the flow rate presence / absence discrimination means as an origin correction value . 2. The flow meter according to claim 1, wherein the pressure loss unit includes a measurement flow path in which an ultrasonic sensor for flow rate measurement is installed and a cross-sectional area is made smaller than other portions for flow rate measurement.

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