JP2002250649A - Gas meter and its calibrating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas meter capable of simply measuring both a large gas flow and a small gas flow in a short time. SOLUTION: This gas meter 1 is equipped with a gas flow measurement part 3, provided on a main gas passage 2 and a small gas flow measurement part 5 provided on a sub-gas passage 4, having a diameter smaller than that of the gas passage 2 and connected in parallel with the gas passage 2; the mater 1 is equipped with a shut-off mechanism 6 capable of shutting off a gas flow in the main gas passage 2; when the gas flow in the main gas passage 2 is shut off by the mechanism 6, the differential pressure across the sub-gas passage 4 is measured by a differential pressure gauge 7 provided in the small flow part 5, and a gas flow in the sub-gas passage 4 is derived therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a gas meter integrally configured to measure a large flow rate and a small flow rate, and a method of calibrating the gas meter.

[0002]

2. Description of the Related Art Conventionally, a method for measuring both a large flow rate and a small flow rate in a gas meter has been proposed. Among them, it is difficult to ensure measurement accuracy in small flow rate measurement.For example, when a fluid meter is used as a gas meter, a valve provided in a gas flow path upstream of the fluid meter is opened after being shut off for a certain period of time. By doing so, a method of improving measurement accuracy by flowing a mass gas flow into a fluidic meter has been performed.
Alternatively, when using an ultrasonic flow meter as a gas meter, it is difficult to derive an accurate gas flow value because the gas flow rate is low when the gas flow rate is small, but the measurement of the gas flow rate is repeatedly performed, A method of obtaining a reliable flow velocity value by integrating the measured values has been performed.

[0003]

However, when a high-accuracy small flow rate measurement is to be performed using the conventional method, there is a problem that the measurement requires a long time of about several tens of minutes. Even when a small flow rate measurement is performed using a fluidic meter or an ultrasonic flow meter, the time for storing a certain amount of gas and the integration time for measurement are required as described above. Furthermore, the need to perform flow measurement for a long period of time means that power consumption will increase, and if the gas meter is running on a battery, its consumption will be faster. Problems arise.

Further, since a large number of valve mechanisms and gas consuming devices are connected to the gas flow path, there is a problem that pressure fluctuations occur inside the gas pipe. There is a need for a gas meter that can avoid such a problem of pressure fluctuation.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas meter that can easily measure both a large flow rate and a small flow rate of a gas in a short time. It is in.

[0006]

A first feature of a gas meter according to the present invention for solving the above-mentioned problems is provided in a main gas passage as described in claim 1 of the claims. A gas meter comprising: a gas flow measuring unit provided; and a small flow measuring unit provided in a sub-gas flow passage having a smaller diameter than the main gas flow passage connected in parallel with the main gas flow passage. And a shutoff mechanism capable of shutting off gas flow in the main gas flow path, and when the shutoff mechanism interrupts gas flow in the main gas flow path, the differential pressure gauge provided in the small flow rate measurement unit causes the auxiliary flow rate to be reduced. The point is to derive the gas flow rate in the sub gas flow path by measuring the differential pressure at both ends of the gas flow path.

[0007] A second feature of the gas meter according to the present invention for solving the above-mentioned problem is that, in addition to the first feature, as described in claim 2 of the claims section, the gas meter has a difference. The point is that the gas flow rate in the auxiliary gas flow path is derived from the result of the differential pressure measurement after the time variation of the pressure is stabilized within a certain range.

[0008] A third feature of the gas meter according to the present invention for solving the above-mentioned problem is that, in addition to the first feature, the gas meter according to the third aspect of the present invention is characterized in that: When the pressure fluctuates with time, the result is that the results of the differential pressure measurement are integrated and averaged.

[0009] A fourth feature of the gas meter according to the present invention for solving the above-mentioned problem is, in addition to the third feature, as described in claim 4 of the claims. When the pressure fluctuates in a predetermined cycle, the result of the differential pressure measurement is integrated in synchronization with the cycle and averaged.

A fifth feature of the gas meter according to the present invention for solving the above-mentioned problems is as described in any one of the first to fourth features, as described in claim 5 of the claims. In addition to the above, an alarm means for issuing an alarm when the temporal variation of the differential pressure is equal to or more than a predetermined value is further provided.

According to a sixth aspect of the gas meter according to the present invention for solving the above-mentioned problems, in addition to the first aspect, the gas meter according to the present invention further comprises a difference meter. 294Pa pressure from 127Pa (13mmH ₂ O)
(30 mmH ₂ O) is that the main gas flow path is opened when the value is equal to or more than a predetermined value.

According to a seventh aspect of the gas meter according to the present invention for solving the above-mentioned problems, as described in claim 7 of the claims, any one of the first to sixth aspects is provided. In addition to the above, when the gas flow rate in the main gas passage is equal to or less than a predetermined value, the main gas passage is shut off.

An eighth feature of the gas meter according to the present invention for solving the above-mentioned problems is as described in any one of the first to seventh features, as described in claim 8 of the claims. In addition to the above, the upstream side and / or the downstream side of the small flow rate measuring section or both of the auxiliary gas flow paths are constituted by a pressure fluctuation reducing section for reducing pressure fluctuation of gas.

According to a ninth aspect of the gas meter according to the present invention for solving the above-mentioned problems, in addition to the eighth aspect, in addition to the above-mentioned eighth aspect, the gas pressure is further improved. The point is that the fluctuation alleviating portion includes at least one capillary tube.

According to a tenth feature of the gas meter according to the present invention for solving the above-mentioned problems, as described in claim 10 of the claims, in addition to any one of the ninth features described above. The diameter of one of said capillaries is 2 mm or less;
The point is that the total cross-sectional area is 3.5 mm ² or less.

According to an eleventh feature of the gas meter according to the present invention for solving the above-mentioned problems, in addition to the tenth feature, the gas meter according to the present invention has the following features. The pressure fluctuation reducing section includes a plurality of capillaries,
The diameter of one of the capillaries is 0.5 mm or more and 1 mm or less, and the total cross-sectional area of the plurality of capillaries is 1 mm ² or less.

According to a twelfth feature of the gas meter according to the present invention for solving the above-described problems, in addition to the tenth feature, the gas meter according to the present invention has the following features. The pressure fluctuation reducing section includes a plurality of capillaries,
The diameter of one of the capillaries is 0.05 mm or more and 0.5 mm
And the total cross-sectional area of the plurality of capillaries is 1 m
m ² or less.

A first characteristic configuration of the calibration method according to the present invention for solving the above-mentioned problem is as described in claim 13 of the claims. A calibration method for calibrating a differential pressure gauge provided in a gas meter according to the above, wherein the main gas flow path is open, and the difference in the sub gas flow path when the gas flow rate in the main gas flow path is substantially zero. The point is to calibrate the pressure to zero.

A second characteristic configuration of the calibration method according to the present invention for solving the above-mentioned problems is as described in claim 14 of the claims. A calibration method for calibrating a differential pressure gauge provided in the gas meter according to the above, wherein the main gas flow path is open, the sub-gas when the gas flow rate in the main gas flow path is stable at a predetermined value The point is that the differential pressure in the flow path is calibrated using the gas flow value in the main gas flow path.

The operation and effect will be described below. According to the first characteristic configuration of the gas meter according to the present invention, the flow rate of the gas flowing in the main gas flow path is measured by the gas flow rate measurement unit provided in the main gas flow path, and the gas flow in the main gas flow path is measured. When a shutoff mechanism capable of shutting off shuts off gas flow in the main gas passage, a small gas passage provided in a sub gas passage smaller in diameter than the main gas passage connected in parallel with the gas flow measurement unit is provided. The differential pressure at both ends of the sub gas flow path is measured by the small flow rate measurement section by the differential pressure gauge provided in the flow rate measurement section, and the gas flow rate in the sub gas flow path can be derived. As a result, the large gas flow measurement by the gas flow measurement unit and the small gas flow measurement by the small flow measurement unit can be performed integrally.

Alternatively, from the viewpoint of gas leak detection as one of the small flow rate measurements, when the main gas flow path is shut off by the shut-off mechanism, the gas may be located downstream or upstream of the gas flow rate measurement unit. If not used, the differential pressure value measured by the differential pressure gauge should be zero, but when a small amount of gas is flowing due to gas leakage upstream or downstream of the shutoff mechanism, etc. Causes a pressure difference between the upstream side and the downstream side of the shutoff mechanism. By measuring the differential pressure with a differential pressure gauge, the presence or absence of gas leakage can be detected, and the flow rate of the leaked gas can be known. In addition, by looking at the sign of the differential pressure, it is possible to know which of the gas flow paths on the upstream side or the downstream side of the shutoff mechanism has leaked gas.

According to the second characteristic configuration of the gas meter according to the present invention, when the differential pressure measured in the small flow rate measuring unit fluctuates with time, the flow rate is derived from the result of the differential pressure measurement. Instead, wait until the differential pressure stabilizes, and derive the gas flow rate from the result of the differential pressure measurement after the temporal fluctuation of the differential pressure stabilizes within a certain range, so that the derived flow rate value is a reliable value. Can be

According to the third feature of the gas meter according to the present invention, when the differential pressure measured in the small flow rate measuring unit fluctuates with time, the results of the differential pressure measurement are integrated and averaged. Thus, it is possible to reduce the error of the gas flow rate value due to the temporal variation of the differential pressure value.

According to the fourth characteristic configuration of the gas meter according to the present invention, when the differential pressure measured in the small flow rate measuring unit fluctuates in a predetermined cycle, the result of the differential pressure measurement is synchronized with the above cycle. By integrating and averaging, it is possible to reduce the error of the gas flow rate value due to the temporal variation of the differential pressure.

According to the fifth characteristic configuration of the gas meter according to the present invention, the alarm means is provided to the measurer when the temporal variation of the differential pressure measured in the small flow rate measuring section is equal to or more than a predetermined value. By issuing the alarm, it is possible to warn the possibility that the flow rate is derived from the differential pressure including an error due to temporal fluctuation.

According to the sixth characteristic configuration of the gas meter according to the present invention, the differential pressure measured by the small flow rate measuring section is 12
From _{7Pa (13mmH 2 O) 294Pa (} 30mmH 2
When the gas flow rate is equal to or more than the predetermined value set during O), the main gas flow measurement unit is opened, so that the gas flows to the main gas flow measurement unit and the gas does not flow to the small flow measurement unit. The gas flow measurement can be switched from the small flow measurement unit to the gas flow measurement unit. In other words, when the differential pressure is large, it is determined that the gas flow rate is large, and an accurate gas flow rate value can be obtained by using a flow rate measurement unit (gas flow rate measurement unit) suitable for measuring the actual gas flow rate. Can be.

According to the seventh characteristic configuration of the gas meter according to the present invention, when the gas flow rate measured by the gas flow rate measuring section is equal to or less than a predetermined value, the main gas flow path is shut off,
By flowing the gas through the sub gas flow path, the measurement of the gas flow rate can be switched from the gas flow rate measurement unit to the small flow rate measurement unit. As a result, a flow measurement unit (small flow measurement unit) suitable for measuring the actual gas flow can be used, and an accurate gas flow can be obtained.

According to the eighth characteristic configuration of the gas meter according to the present invention, the pressure fluctuation can be prevented from being included in the gas flow present in the auxiliary gas flow path by providing the pressure fluctuation reducing portion. As a result, it is possible to prevent an error from occurring in the gas flow value measured by the small flow measurement unit.

According to the ninth characteristic configuration of the gas meter according to the present invention, even if the gas flow passing through the capillary includes pressure fluctuations, the capillary tube as the pressure fluctuation relieving section can reduce the pressure inside the capillary. Pressure fluctuations are mitigated by frictional resistance between the wall surface and the gas flow, so that the gas flow that passes through the capillary tube and reaches the small flow rate measurement unit can be free from pressure fluctuations. As a result, the reliability of the gas flow value obtained by the measurement can be improved.

According to a tenth characteristic configuration of the gas meter according to the present invention, the diameter of one capillary is 2 mm or less, and the total cross-sectional area of one or a plurality of capillaries is 3.5 mm ^2.
By being configured as follows, even if the gas flow passing through the capillary as the pressure fluctuation reducing portion includes pressure fluctuations such as pulsation, the pressure fluctuations are effectively mitigated. be able to.

According to the eleventh characteristic configuration of the gas meter according to the present invention, the diameter of one capillary is not less than 0.5 mm and not more than 1 m.
m or less, and the total cross-sectional area by a plurality of capillaries is 1 mm
^By being configured to be ² or less, even when the gas flow passing through the capillary is even smaller, pressure fluctuations contained in the gas flow can be effectively mitigated.

According to a twelfth characteristic configuration of the gas meter according to the present invention, the diameter of one capillary is not less than 0.05 and not more than 0.5.
mm, and the total cross-sectional area of a plurality of capillaries is 1 m
By being configured to be not more than m ² , even if the gas flow passing through the capillary is even smaller, pressure fluctuations contained in the gas flow can be effectively mitigated.

According to the first characteristic configuration of the calibration method according to the present invention, when the gas flow rate in the main gas flow path is substantially zero, the measurement can be performed even when the differential pressure measurement is performed using the small flow rate measurement unit. Since the differential pressure to be performed should be zero, the zero point of the small flow rate measuring unit can be calibrated using the actual differential pressure measurement value. Therefore, by calibrating the zero point of the small flow rate measurement unit,
The reliability of the subsequent differential pressure measurement, that is, gas flow measurement can be improved.

According to the second characteristic configuration of the calibration method according to the present invention, when the gas flow rate in the main gas flow path is stable at a predetermined value, the differential pressure measurement is performed using the small flow rate measurement unit. And calibrate the measurement value of the small flow measurement unit by calibrating the gas flow value derived from the result of the differential pressure measurement based on the stable gas flow value measured by the gas flow measurement unit. Therefore, the reliability of the subsequent differential pressure measurement, that is, the measurement of the gas flow rate can be improved.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a gas meter according to the present invention will be described with reference to FIG. The gas meter 1 is provided in a gas flow measuring unit 3 provided in a main gas flow path 2 and in a sub gas flow path 4 smaller in diameter than the main gas flow path 2 connected in parallel with the main gas flow path 2. And a small flow rate measuring unit 5. Further, the main gas flow path 2 is provided with a shutoff mechanism 6 capable of shutting off the gas flow in the main gas flow path 2. Flows into the auxiliary gas flow path 4, and the gas flow rate in the auxiliary gas flow path 4 can be derived by measuring the differential pressure at both ends of the auxiliary gas flow path 4 by the differential pressure gauge 7 provided in the small flow rate measuring unit 5. It is configured to be able to.

When detecting gas leakage in the main gas flow path 2, if the leaked gas flow rate is very small, it is difficult to perform accurate measurement in the gas flow rate measuring section 3,
By shutting off the main gas flow path 2 using the shut-off mechanism 6 and using the small flow rate measurement unit 5 installed in the sub gas flow path 4, accurate gas flow rate measurement or gas leak detection can be performed.

In FIG. 1, an ultrasonic flow meter is used as the gas flow measuring unit 3, and the signal processing device 9 includes an ultrasonic vibrator 8a installed on the upstream side and an ultrasonic vibrator 8a installed on the downstream side. The transmission and reception of the ultrasonic wave is performed between the transducer 8b, the difference in the propagation time of the ultrasonic wave from the upstream side to the downstream side, and the difference from the downstream side to the upstream side is obtained,
The gas flow value in the main gas flow path 2 is derived from the cross-sectional area of the main gas flow path.

Further, the differential pressure at both ends of the auxiliary gas flow path 4 is measured using the differential pressure gauge 7 in the small flow rate measuring section 5 and the signal processing device 9 processes the result of the differential pressure measurement.
The gas flow rate flowing through the sub gas flow path 4 is derived. The length of the sub gas passage 4 is L.

When the auxiliary gas flow path 4 is a circular pipe, the radius of the circular pipe: R, the length of the auxiliary gas flow path: L, the viscosity of the fluid: η, and the measured differential pressure value: ΔP are used. , Flow rate: Q is generally expressed by the following equation (1).

[0040]

## EQU1 ## Q = πR ⁴ × ΔP / 8Lη

In this embodiment, the diameter (2R) of the auxiliary gas passage 4 is set to 0.8 mm. In this case, if the gas flow rate is about 60 liters or less per hour, a reliable gas flow rate value can be obtained using the differential pressure gauge 7.

Whether the gas flow rate is measured by the gas flow rate measuring section 3 (for large flow rate) or the small flow rate measuring section 5 (for small flow rate) will be described below. When the shutoff mechanism 6 is opened under the control of the signal processing device 9 and the gas is flowing through the main gas flow path 2, the gas flow rate measurement unit 3 measures the gas flow rate. When the measured gas flow rate is a small flow rate that is equal to or less than a predetermined value, the signal processing device 9 shuts off the main gas flow path 2 by using the shut-off mechanism 6 and sends the gas to the sub gas flow path. Then, control is performed such that the gas flows into the small flow rate measuring unit 4, and the flow is switched to the gas flow rate measurement by the small flow rate measuring unit 5. This is because if the gas flow value is small, the gas flow measurement unit 3 may not be able to perform accurate gas flow measurement.
Therefore, the above-mentioned predetermined value is a value of the lower limit of measurement of the gas flow measuring unit 3.

When the shut-off mechanism 6 is shut off by the control of the signal processing device 9, the gas does not flow through the main gas flow path 2 and the gas flows through the sub-gas flow path 4. The differential pressure at both ends of the sub gas flow path 4 is measured by the differential pressure gauge 7, and a gas flow value flowing through the sub gas flow path 4 is obtained. still,
The measured differential pressure is 127 Pa (13 mmH ₂ O) to 2
When the pressure is equal to or more than a predetermined value set between 94 Pa (30 mmH ₂ O), the main gas flow path 2 is opened using the shut-off mechanism 6, and control is performed such that gas flows through the main gas flow path 2. Then, the mode is switched to the gas flow rate measurement by the gas flow rate measuring unit 3.
This means that when the differential pressure is large, the gas flow rate is large, and by flowing such a large flow rate through the small-diameter sub-gas flow path 4, the pressure loss increases, and accurate gas flow rate measurement cannot be performed. Because.

Various valve mechanisms are often installed on the upstream side of the gas meter 1, and the pressure fluctuation of the gas flow due to the opening and closing operations of these valve mechanisms may reach the gas meter 1. Further, various gas consuming devices are often installed downstream of the gas meter 1, and pulsations generated by the operation timing of these devices may reach the gas meter 1. As described above, when the gas flow rate is small, the differential pressure at both ends of the sub gas flow path 4 is measured by the differential pressure gauge 7 provided in the small flow rate measurement unit 5 of the sub gas flow path 4, and the gas flow rate is derived. Therefore, if the gas flow includes a pressure fluctuation, the result of the differential pressure measurement is likely to include an error, and as a result, the derived gas flow rate value is also likely to include an error. Therefore, an apparatus and a method for obtaining a highly reliable gas flow value will be described below.

When the signal processing device 9 determines that the result of the differential pressure measurement by the differential pressure gauge 7 fluctuates with time due to the above-described pressure fluctuation, the signal processing device 9 does not derive the gas flow rate value. Then, the monitoring of the differential pressure value is continued. And when it can be considered that the differential pressure value has converged to a certain value,
A gas flow rate is derived from the differential pressure value. As described above, by monitoring the differential pressure value and deriving the gas flow value using the differential pressure at the time when the pressure fluctuation is not included, highly accurate gas flow measurement is performed.

If the result of the differential pressure measurement by the differential pressure gauge 7 fluctuates with time due to the above-described pressure fluctuation, and the fluctuation range exceeds a predetermined range, a signal processing device for processing the differential pressure result Numeral 9 samples the differential pressure result at predetermined intervals, stores the result in the storage device 10, and performs signal processing such as taking an average thereof. By performing this averaging process, the temporal variation of the differential pressure included in the differential pressure result is smoothed, and a highly accurate differential pressure measurement result can be obtained. As a result, a highly accurate gas flow rate value can be obtained. Can be obtained. Here, the sampling may be performed at regular intervals, at random intervals, or at intervals in accordance with a predetermined rule.

If the temporal fluctuation of the result of the differential pressure measurement is a periodic fluctuation, and the period is known or the period can be obtained, the sampling interval of the differential pressure result is set to the period. (Half cycle), and performs signal processing to take the average. By performing this averaging process, it is possible to obtain the result of the differential pressure measurement excluding the temporal pressure fluctuation. This is because when sampling is performed in a half cycle of the cycle of the pressure fluctuation, the amplitude of the waveform of the pressure fluctuation component is the same, and the differential pressure value when the sign is positive and negative is sampled. Because. As a result, the amplitude of the pressure fluctuation component is canceled by the averaging process, and a highly accurate differential pressure value, that is, a gas flow value can be obtained.

Further, when the differential pressure value fluctuates with time, an alarm is issued using the alarm means 11 connected to the signal processing device 9, so that the differential pressure value includes temporal fluctuation. To the outside. As the alarm means 11, various means such as a voice type and an optical type in which light blinks can be used. Also,
The installation place may be provided in the gas meter 1, or may be installed on the security company side of the gas meter 1 in a remote place by using communication means such as a telephone line.

Next, a method of calibrating the zero point and the differential pressure value of the differential pressure gauge 7 will be described with reference to FIGS. 2 (a) and 2 (b). As shown in FIG. 2A, when the main gas flow path 2 is open and the gas flow rate in the main gas flow path 2 measured by the gas flow rate measuring unit 3 is almost zero (step 20), shut off. Even if the main gas flow path 2 is shut off using the mechanism 6, no gas flows in the sub gas flow path 4,
The differential pressure value (step 22) measured by the small flow rate measuring unit 5 (differential pressure gauge 7) can be regarded as zero. Here, when the differential pressure value by the differential pressure gauge 7 is not zero, it means that the measurement by the differential pressure gauge 7 is erroneous, and the differential pressure gauge 7 needs to be calibrated. Therefore, the pointer value of the differential pressure gauge 7 when the gas flow rate in the main gas flow path 2 is almost zero is calibrated to zero (step 24). Thereby, the zero point calibration of the differential pressure gauge 7 is performed.

As shown in FIG. 2B, the main gas flow path 2 is open, and the gas flow rate in the main gas flow path 2 measured by the gas flow rate measuring unit 3 is stable at a predetermined value. When the main gas flow path 2 is shut off using the shut-off mechanism 6 (step 32) (step 32), the gas flow flows into the sub gas flow path 4, so that the differential pressure value measured by the differential pressure gauge 7 The gas flow rate can be derived (step 3
4). Here, the calibration of the differential pressure gauge 7 is performed by making the obtained differential pressure value equal to the differential pressure value converted from the gas flow rate value measured by the gas flow rate measuring unit 3 using the above-described formula 1. (Step 36). As a result, accurate differential pressure measurement, that is, gas flow measurement can be performed. Further, if the pressure loss generated in the sub gas flow path 4 where the differential pressure measurement is performed is taken into consideration, more accurate calibration can be performed. The calibration of the differential pressure value described here is desirably performed after the above-described zero point calibration is performed. These calibrations are performed artificially by calibration means normally provided in the differential pressure gauge 7.

Next, as a method for avoiding a measurement error due to pressure fluctuation, a case where a pressure fluctuation mitigation section 12 is provided in the upstream side and / or downstream side of the small flow rate measuring section 5 or in both of the sub-gas flow paths 4 is shown. 3 will be described. Although FIG. 3 shows a case where the pressure fluctuation alleviating part 12 is provided in both the sub-gas flow path 4 on the upstream side and the downstream side of the small flow rate measuring part 5, it may be provided in only one of them. .

As shown in FIG. 3, on both sides of the auxiliary gas flow path 4, capillaries as pressure fluctuation relieving portions 12 are arranged with the space portion 13 interposed therebetween. Therefore, even if the gas flow in the main gas flow path 2 includes a pressure fluctuation, the pressure fluctuation is absorbed by the interaction between the inner wall of the capillary and the gas flow, and the gas flow reaching the space 13 has the pressure fluctuation. Because it does not include
A reliable measurement of the differential pressure value, ie a measurement of the gas flow, can be performed.

As illustrated in FIGS. 4A and 4B, the capillary as the pressure fluctuation relieving section 12 is composed of one or a plurality of capillaries. FIG. 4A illustrates a case where the pressure fluctuation relieving unit 12 is configured by a single capillary having a diameter of 2R. The size of the capillary may be any size as long as the target pressure fluctuation can be reduced. However, the diameter of one capillary is 2 mm or less, and the cross-sectional area (gas Is preferable to be 3.5 mm ² or less. If multiple capillaries are formed,
Each may be a capillary of different dimensions,
The cross-sectional shape may be polygonal instead of circular.

More preferably, as shown in FIG. 4B, the pressure fluctuation relieving section 12 includes a plurality of capillaries, and one of the capillaries has a diameter (2r) of 0.5 mm or more and 1 m.
m or less, and the total cross-sectional area by a plurality of capillaries is 1 mm
² or less. By providing such a pressure fluctuation reducing section 12, the pressure fluctuation reducing section 12 capable of effectively absorbing the pressure fluctuation is configured. Still more preferably, one diameter (2r) of the capillary is 0.05 mm or more and 0.5 m or more.
m and the total cross-sectional area of a plurality of capillaries is 1 mm
² or less. By providing such a pressure fluctuation reduction section 12, the pressure fluctuation reduction section 12 that can more effectively absorb small pressure fluctuations such as pulsation is configured.

As a specific example, when the pressure fluctuation relieving section 12 including 40 circular capillaries having a diameter of 0.1 mm is provided on the upstream side and the downstream side of the sub gas flow path 4, the pressure fluctuation relieving section 12 is provided. Although the pressure measured by the differential pressure gauge 7 also becomes small due to the pressure loss caused by the pressure loss, the diameter of the auxiliary gas flow path 4 may be made smaller than that in the case where the pressure fluctuation reducing section 12 is not provided. In the above embodiment, the case where the diameter of the sub gas flow path 4 is set to 0.8 mm and the gas flow rate of about 60 liters or less per hour is measured, but the diameter of the sub gas flow path 4 is reduced, When the thickness is 0.6 mm, a reliable gas flow value can be obtained for measuring a gas flow rate of about 40 liters or less per hour. It should be noted that the pressure loss generated in the pressure fluctuation mitigation unit 12 and the auxiliary gas flow path 4 can be a design item in advance, and the pressure loss can be adjusted by adjusting the length of each pipe or flow path (the longer the pressure, Loss is increased).

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a gas meter.

FIG. 2 is a diagram illustrating a method of calibrating a differential pressure gauge.

FIG. 3 is a configuration diagram of a gas meter provided with a pressure fluctuation reducing section.

FIGS. 4A and 4B are diagrams illustrating an example of a pressure fluctuation reducing section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas meter 2 Main gas flow path 3 Gas flow rate measurement part 4 Sub gas flow path 5 Small flow rate measurement part 6 Shut-off mechanism 7 Differential pressure gauge 8a Ultrasonic transducer 8b Ultrasonic transducer 9 Signal processing device 10 Storage device 11 Alarm means 12 Pressure Fluctuation mitigation part 13 Space part

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Claims (14)

[Claims] 1. A gas flow rate measuring unit provided in a main gas flow path, and a small flow rate provided in a sub gas flow path smaller in diameter than the main gas flow path connected in parallel with the main gas flow path. A gas meter comprising a measuring unit, comprising: a shutoff mechanism capable of shutting off gas flow in the main gas flow path, wherein when the gas flow in the main gas flow path is shut off by the shutoff mechanism, the small flow rate A gas meter, wherein a gas flow rate in the sub-gas flow path is derived by measuring a differential pressure at both ends of the sub-gas flow path by a differential pressure gauge provided in a measuring unit. 2. The gas flow rate in the sub-gas flow path is derived from a result of the differential pressure measurement after the temporal variation of the differential pressure is stabilized within a certain range.
The gas meter according to 1. 3. The gas meter according to claim 1, wherein when the differential pressure fluctuates with time, the results of the differential pressure measurement are integrated and averaged. 4. When the differential pressure fluctuates in a predetermined cycle,
The gas meter according to claim 3, wherein a result of the differential pressure measurement is integrated in synchronization with the cycle and averaged. 5. The gas meter according to claim 1, further comprising an alarm unit that issues an alarm when the temporal variation of the differential pressure is equal to or greater than a predetermined value. 6. The gas meter according to claim 1, wherein the main gas passage is opened when the differential pressure is equal to or more than a predetermined value set between 127 Pa and 294 Pa. 7. The gas meter according to claim 1, wherein the main gas passage is shut off when a gas flow rate in the main gas passage is equal to or less than a predetermined value. 8. The method according to claim 1, wherein the auxiliary gas flow path on the upstream side and / or the downstream side of the small flow rate measuring unit is constituted by a pressure fluctuation reducing unit configured to reduce a gas pressure fluctuation. The gas meter according to any one of claims 1 to 7. 9. The gas meter according to claim 8, wherein the pressure fluctuation reducing section includes at least one capillary. 10. The gas meter according to claim 9, wherein one of the capillaries has a diameter of 2 mm or less, and a total cross-sectional area of one or a plurality of the capillaries is 3.5 mm ² or less. 11. The pressure fluctuation reducing section includes a plurality of capillaries, one of the capillaries has a diameter of 0.5 mm or more and 1 mm or less, and a total sectional area of the plurality of capillaries is 1 mm ² or less. The gas meter according to claim 10, wherein: 12. The pressure fluctuation reducing section comprises a plurality of capillaries, one of the capillaries has a diameter of 0.05 mm or more and less than 0.5 mm, and a total cross-sectional area of the plurality of capillaries is 1 mm ² or less. 2. The method according to claim 1, wherein
The gas meter according to 0. 13. A calibration method for calibrating a differential pressure gauge included in a gas meter according to any one of claims 1 to 12, wherein the main gas flow path is open, and A calibration method comprising: calibrating a differential pressure in the sub gas flow path to zero when a gas flow rate is substantially zero. 14. A calibration method for calibrating a differential pressure gauge included in a gas meter according to any one of claims 1 to 12, wherein the main gas flow path is open, and A calibration method comprising: calibrating a differential pressure in the sub-gas flow path using the gas flow value in the main gas flow path when the gas flow rate is stable at a predetermined value.