Diaphragm gas meter and its magnetic gas flow detection mechanism replacement method

Abstract

To provide a membrane gas meter that includes a magnetic gas flow rate detection mechanism whose cost is reduced by using existing components, which is easily manufacturable, and whose measurement accuracy is improved.SOLUTION: In a magnetic gas flow rate detection mechanism 40 of a membrane gas meter 1, the rotation of a vertical revolving shaft 11 is significantly slowed down via a worm gear and transmitted to a horizontal worm shaft 20 which is disposed orthogonally to the vertical revolving shaft, and the rotation of the horizontal worm shaft 20 is speeded up via a gear box and transmitted to a magnet 43 of the magnetic gas flow rate detection mechanism 40. Since the magnet 43 only requires the speed increase ratio of the gear box to be set so that the magnet 43 rotates at a speed where necessary measurement accuracy is obtained, there is no need to increase the number of magnetic sensors to raise measurement accuracy. Thus, a membrane gas meter equipped with a high-accuracy magnetic gas flow rate detection mechanism 40 in which a magnet and a magnetic sensor face from the front-back direction of the meter can be manufactured at low cost.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a diaphragm gas meter equipped with a magnetic gas flow detection mechanism. More specifically, the present invention relates to a diaphragm gas meter configured to allow an existing magnetic gas flow detection mechanism, which has a magnet and a magnetic sensor facing each other from above and below the meter, to be easily replaced with a high-precision detection mechanism, which has a magnet and a magnetic sensor facing each other from the front and rear of the meter, and a method for replacing the magnetic gas flow detection mechanism. [Background technology]

[0002] A diaphragm gas meter is equipped with a crank mechanism for opening and closing an on-off valve of a metering chamber in conjunction with the reciprocating motion of a metering membrane that separates the gas flow metering chamber. As shown in FIG. 4, the crank mechanism 100 of the diaphragm gas meter includes a vertical rotation shaft 102 rotatably supported about a central axis 101 extending in the up-down direction of the meter, a crank shaft 103 that revolves at a constant radius about the central axis 101 as the vertical rotation shaft 102 rotates, and a pair of crank arms (a large elbow and a small elbow) that swing in conjunction with the reciprocating motion of the metering membrane. The swinging motion of the crank arms is converted into the rotational motion of the vertical rotation shaft 102. The rotation of the vertical rotation shaft 102 is converted, via a link mechanism (not shown), into the opening and closing motion of an on-off valve that is linked to the reciprocating motion of the metering membrane.

[0003] A magnetic sensor is generally used as the gas flow detection mechanism in membrane-type gas meters of this configuration. In such magnetic gas flow detection mechanisms, a magnet 106 for detecting the gas flow rate is attached to a magnet mounting portion 105 provided on a crank arm 104 (small elbow) that oscillates in conjunction with the reciprocating motion of the metering membrane. A reed switch (not shown) is disposed as a magnetic sensor above the meter relative to the position through which the magnet 106 passes as the crank arm 104 oscillates. During one rotation of the crank mechanism 100, the magnet 106 passes through the detection area of ​​the reed switch once, outputting a detection signal with one pulse per cycle, and the gas flow rate is measured based on this detection signal.

[0004] In such a magnetic gas flow detection mechanism, the pulse output interval of the detection signal is wide, and the detection accuracy may be insufficient. Also, depending on the installation location of the membrane gas meter, it may be necessary to arrange the magnet and magnetic sensor facing each other in the front and rear directions of the meter instead of facing each other in the top and bottom directions of the meter at the top of the meter to avoid the influence of magnetism from peripheral devices, etc.

[0005] Patent Document 1 proposes a method for improving the gas flow measurement accuracy of a magnetic gas flow detection mechanism in an existing diaphragm-type gas meter, as well as a method for changing the mounting positions of a magnet and a magnetic sensor. Patent Document 1 employs a method for replacing the existing crank mechanism with a crank mechanism consisting of a single-piece plastic molded part with a magnet attached. In the replaced magnetic gas flow detection mechanism, a gas flow detection magnet is positioned on the vertical rotation axis of the crank mechanism, and the rotating magnetic field of the magnet rotating around the rotation centerline of the vertical rotation axis is detected using a magnetic sensor such as an MR sensor. This provides a detection signal with eight pulses per rotation, improving measurement accuracy. Furthermore, even when changing a magnetic gas flow detection mechanism from one in which the magnet and magnetic sensor face each other from the top and bottom of the meter to one in which the magnet and magnetic sensor face each other from the front and back of the meter, all parts, including the crank mechanism, are replaced. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6436642 Summary of the Invention [Problem to be solved by the invention]

[0007] In this way, the method disclosed in Patent Document 1 improves detection accuracy by replacing the entire crank mechanism of an existing diaphragm gas meter with a crank mechanism that is an integrally molded plastic product equipped with a magnet. That is, the entire set of crank mechanism 100 components, including vertical rotating shaft 102, crank shaft 103, and crank arm 104 equipped with magnet 106, which constitute crank mechanism 100 shown in FIG. 4, is replaced with a new crank mechanism. Because the entire set of components must be replaced in this way, the replacement cost is high and the replacement work is not easy.

[0008] Furthermore, if the magnet and magnetic sensor facing each other from the top and bottom of the meter are changed to facing each other from the front and back of the meter, the rotation of the vertical rotating shaft of the crank mechanism is transmitted via a worm gear to a horizontal worm shaft arranged perpendicular to the meter, and the rotating magnetic field of the magnet attached coaxially to the tip of this horizontal worm shaft is detected by the MR sensor. In this case, the worm gear that transmits rotation between the perpendicular shafts has a large reduction ratio, so the rotation of the vertical rotating shaft linked to the metering membrane is significantly reduced before being transmitted to the magnet. Since the magnet's rotation speed is reduced, the detection pulse accuracy of the MR sensor is reduced. In order to improve detection accuracy, multiple MR sensors and magnets must be installed, which is costly.

[0009] The object of the present invention is to propose a membrane type gas meter that can be changed to a magnetic gas flow detection mechanism with high detection accuracy in which a magnet and a magnetic sensor face each other from the front and rear of the meter, simply by replacing the minimum number of parts required in the crank mechanism of an existing membrane type gas meter, and a method for replacing the magnetic gas flow detection mechanism in a membrane type gas meter. [Means for solving the problem]

[0010] The membrane type gas meter of the present invention comprises: a crank arm that converts the reciprocating motion of a metering membrane that separates the gas metering chamber into a rotational motion of a vertical rotation shaft centered on a vertical axis extending in the up-down direction of the meter; a link that converts the rotation of the vertical rotary shaft into an opening and closing motion that opens and closes the on-off valve in the measuring chamber; a worm gear that converts the rotation of the vertical rotation shaft into rotational motion of a horizontal worm shaft about a horizontal axis extending in the front-to-rear direction of the meter; a magnetic gas flow rate detection mechanism including a magnet that rotates in synchronization with the rotation of the horizontal worm shaft and a magnetic sensor that detects the rotating magnetic field of the magnet; It is equipped with:

[0011] The magnet of the magnetic gas flow detection mechanism is located on the front side of the meter relative to the horizontal worm shaft, and the magnetic sensor faces the magnet from the front side of the meter. A transmission gear shaft extending in the fore-and-aft direction of the meter is coaxially disposed on the side of the horizontal worm shaft in front of the meter. The tip end of the horizontal worm shaft in front of the meter is mechanically engaged with the rear end of the transmission gear shaft in rear of the meter so that the transmission gear shaft rotates in the same direction at the same speed in synchronization with the rotation of the horizontal worm shaft in one direction. A speed-increasing gear train is disposed between the transmission gear shaft and the magnet, and transmits the rotation of the transmission gear shaft to the magnet after increasing its speed. In the magnetic gas flow rate detection mechanism of this configuration, the rotating magnetic field of the magnet, which rotates at an increased speed in synchronization with the rotation of the horizontal worm shaft, is detected by the magnetic sensor.

[0012] In the magnetic gas flow detection mechanism of the diaphragm gas meter of the present invention, the rotation of the vertical rotation shaft is significantly reduced via a worm gear and transmitted to a horizontal worm shaft arranged perpendicular to the vertical rotation shaft. The rotation of the horizontal worm shaft is accelerated via a speed-up gear train and transmitted to the magnet. The speed-up ratio of the speed-up gear train can be set so that the magnet rotates at a speed that provides the required measurement accuracy. Therefore, there is no need to increase the number of magnets and magnetic sensors to improve measurement accuracy. A diaphragm gas meter equipped with a highly accurate magnetic gas flow detection mechanism in which the magnet and magnetic sensor face each other from the front and rear of the meter can be manufactured at low cost.

[0013] Furthermore, when replacing a magnetic gas flow detection mechanism in which a magnet and a magnetic sensor, which are built into an existing diaphragm gas meter, face each other from above and below the meter with a magnetic gas flow detection mechanism in which a magnet and a magnetic sensor face each other from the front and rear of the meter, with higher measurement accuracy, only the magnet can be removed from the existing crank mechanism, and the rest of the mechanism can be used as is. The rotation, which is significantly slowed down by the worm gear, is accelerated and transmitted to the magnet via a speed-up gear train. The magnet can be rotated at a speed that achieves the required detection pulse accuracy. Therefore, a magnetic gas flow detection mechanism in which a magnet and a magnetic sensor, which are built into an existing diaphragm gas meter, face each other from above and below the meter with a magnetic gas flow detection mechanism in which a magnet and a magnetic sensor face each other from the front and rear of the meter, can be easily replaced with a magnetic gas flow detection mechanism in which a magnet and a magnetic sensor face each other from the front and rear with higher measurement accuracy, without incurring any additional cost. [Brief explanation of the drawings]

[0014] [Figure 1] 1A is a schematic front view of a membrane gas meter to which the present invention is applied, and FIG. 1B is a schematic longitudinal sectional view thereof. [Figure 2] FIG. 2 is an explanatory diagram showing a crank mechanism and a magnetic gas flow detection mechanism arranged above a measuring chamber of a membrane gas meter. [Figure 3] (A) is a front view showing the crank mechanism and the main parts of the magnetic gas flow detection mechanism, (B) is a left side view thereof, (C) is a right side view thereof, (D) is a plan view thereof, and (E) is a bottom view thereof. [Figure 4] FIG. 1 is a perspective view showing a crank mechanism and a magnetic gas flow rate detection mechanism of a typical diaphragm gas meter. DETAILED DESCRIPTION OF THE INVENTION

[0015] A membrane gas meter according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1(A) is a front view of the membrane gas meter, and Fig. 1(B) is a schematic vertical cross-sectional view taken along line AA'. Fig. 2 is an explanatory diagram showing the crank mechanism and magnetic gas flow detection mechanism arranged above the measuring chamber of the membrane gas meter. The basic structure of the membrane gas meter 1 is the same as that of a conventional one, and only the parts related to the present invention will be described below.

[0016] The meter case 2 of the diaphragm gas meter 1 is composed of an upper case 3 and a lower case 4. Inside the lower case 4, gas flow metering chambers 5F and 5R are located at the front and rear. The interiors of the front and rear metering chambers 5F and 5R are divided into front and rear sections by metering membranes 6F and 6R, respectively. Front and rear blade shafts 7F and 7R extend vertically on the front and rear of the left end of the meter and rotate due to the reciprocating motion of the front and rear metering membranes 6F and 6R. The upper ends of the front and rear blade shafts 7F and 7R extend into the upper case 3. Inside the upper case 3, there is a crank mechanism 10 that converts the rotation of the front and rear blade shafts 7F and 7R into rotational motion of a vertical rotation shaft 11 that extends vertically on the meter, and a link mechanism 9 that converts the rotational motion of the vertical rotation shaft 11 into opening and closing motion of the on-off valves 8F and 8R of the front and rear metering chambers 5F and 5R.

[0017] In the crank mechanism 10, the rotational motion of the blade shafts 7F, 7R is converted into the rotational motion of a vertical rotation shaft 11 via a pair of crank arms 12A, 12B (large elbows) and a pair of crank arms 13A, 13B (small elbows). The rotation of the vertical rotation shaft 11 is connected to the on-off valves 8F, 8R of the front and rear metering chambers 5F, 5R via front and rear links 9F, 9R that make up the link mechanism 9. The on-off valves 8F, 8R open and close alternately in conjunction with the reciprocating motion of the metering membranes 6F, 6R.

[0018] 3A is a front view showing the crank mechanism 10 and the main parts of the magnetic gas flow detection mechanism 40, (B) is a left side view thereof, (C) is a right side view thereof, (D) is a plan view thereof, and (E) is a bottom view thereof.

[0019] Referring also to FIG. 3, the vertical rotation shaft 11 of the crank mechanism 10 is supported rotatably around its vertical center axis 11a. Specifically, a crank base 14 (see FIG. 1(B)) attached to the upper end of the lower case 4 is disposed above the front and rear measuring chambers 5F, 5R. The vertical rotation shaft 11 is rotatably supported on the crank base 14 in a vertical position extending in the up-down direction of the meter. A lower crank plate 15 is horizontally fixed to the upper end of the vertical rotation shaft 11. A first crank shaft 16 is vertically attached to a portion of the lower crank plate 15 horizontally spaced a predetermined distance from the vertical rotation shaft 11. As shown in FIG. 2, one end of each of the front and rear links 9F, 9R is swingably connected to the first crank shaft 16. The other ends of the links 9F, 9R are connected to the sides of the on-off valves 8F, 8R of the front and rear measuring chambers 5F, 5R.

[0020] An upper crank plate 17 is fixed horizontally to the upper end of the first crank shaft 16. A second crank shaft 18 is fixed vertically to a portion of the upper crank plate 17 that is horizontally spaced a predetermined distance from the central axis 11a and spaced a predetermined angle, for example, approximately 90°, around the central axis 11a relative to the first crank shaft 16. As shown in FIG. 1, one ends of crank arms 13A, 13B (small elbow brackets) are horizontally connected to the second crank shaft 18.

[0021] Here, one crank arm 13B has a cup-shaped magnet mounting portion 19 that opens above the meter attached to a longitudinal position thereof as shown in Fig. 2. The gas flow rate detection magnet attached to magnet mounting portion 19 has been removed from magnet mounting portion 19.

[0022] Next, a horizontal worm shaft 20 extending in the fore-and-aft direction of the meter is disposed to the side of the vertical rotation shaft 11 of the crank mechanism 10. Rotation of the vertical rotation shaft 11 is transmitted to the horizontal worm shaft 20 via a worm gear 30. The worm gear 30 is composed of a cylindrical worm 31 and a cylindrical worm wheel 32, with the worm 31 formed coaxially on or attached to the vertical rotation shaft 11, and the worm wheel 32 formed coaxially on or attached to the horizontal worm shaft 20. A shaft tip 21 on the meter front side of the horizontal worm shaft 20 has a truncated cone shape tapering toward the front of the meter, and extends while bending at an angle of less than 90° in a direction away from the axis 20a of the horizontal worm shaft 20.

[0023] (Magnetic gas flow detection mechanism) A magnetic gas flow detection mechanism 40 is disposed at a position on the horizontal worm shaft 20 in front of the meter to detect the gas flow rate by utilizing the rotation of the horizontal worm shaft 20. As shown in Fig. 1(B) , the magnetic gas flow detection mechanism 40 of this example includes a transmission gear shaft 41 to which the rotation of the horizontal worm shaft 20 is transmitted, a gear box 42 (speed-up gear train) that speeds up the rotation of the transmission gear shaft 41, a disk-shaped magnet 43 to which the speed-up rotation output from the gear box 42 is transmitted, and a magnetic sensor 44 that detects the rotating magnetic field of the magnet 43. The magnetic gas flow detection mechanism 40 also includes a circuit board 45 on which a drive control circuit for the magnetic sensor 44, a signal processing circuit, etc. are mounted.

[0024] As can be seen from Figures 2 and 3, the transmission gear shaft 41 is arranged coaxially with the horizontal worm shaft 20 at a position on the front side of the meter. The rear end of the transmission gear shaft 41 on the rear side of the meter forms a bent shaft portion 41b that bends and extends in a direction away from its central axis 41a. In this example, the bent shaft portion 41b bends at a substantially right angle and engages with the shaft tip portion 21 of the horizontal worm shaft 20 from the side opposite to the rotation direction. As a result, when the horizontal worm shaft 20 rotates, the shaft tip portion 21 pushes the bent shaft portion 41b in the same direction, and the transmission gear shaft 41 rotates in the same direction as the horizontal worm shaft 20 at the same speed.

[0025] The transmission gear shaft 41 is the rotation input shaft of the gear box 42, and the rotation of the transmission gear shaft 41 is accelerated via the speed-increasing gear train of the gear box 42. In this example, the speed-increasing gear train of the gear box 42 is made up of an input side transmission gear 42a attached coaxially to the transmission gear shaft 41, a transmission compound gear 42b whose small gear meshes with the input side transmission gear 42a, and an output side transmission gear 42c whose large gear meshes with the transmission compound gear 42b. The output side transmission gear 42c is attached coaxially to the output shaft 42d.

[0026] A disk-shaped magnet 43 is attached coaxially to the output shaft 42d of the gearbox 42. The magnet 43 is a magnet that is magnetized with two poles in the circumferential direction. A magnetic sensor 44 faces the magnet 43 from the front side of the meter, sandwiching an internal partition plate 3a formed on or attached to the upper case 3. The magnetic sensor 44 is, for example, an MR sensor, and detects the rotating magnetic field of the magnet 43.

[0027] (Replacing the magnetic gas flow detection mechanism of a membrane gas meter) The membrane gas meter 1 of this example is obtained by replacing the magnetic gas flow rate detection mechanism of an existing membrane gas meter with the magnetic gas flow rate detection mechanism 40 having the above-described configuration.

[0028] An existing membrane gas meter, for example, similar to the membrane gas meter 1 of this example, is equipped with a crank arm that converts the reciprocating motion of the metering membrane that separates the gas metering chamber into rotational motion of a vertical rotation shaft centered on a vertical axis extending in the up-down direction of the meter, a link that converts the rotation of the vertical rotation shaft into opening and closing motion that opens and closes the on-off valve in the metering chamber, and a worm gear that converts the rotation of the vertical rotation shaft into rotational motion of a horizontal worm shaft that extends in the front-to-back direction of the meter, and the tip of the horizontal worm shaft bends and extends toward the front of the meter.

[0029] The magnetic gas flow detection mechanism of an existing membrane-type gas meter may incorporate a detection mechanism including a magnet facing upwards of the meter and a magnetic sensor facing the magnet from above the meter. In this case, as explained with reference to Fig. 4, a magnet 106 for detecting the gas flow rate is attached to a magnet mounting portion 105 attached to a crank arm 104 that swings in response to the reciprocating motion of the metering membrane. A reed switch is disposed as a magnetic sensor 107 on the upper side of the meter relative to the position through which the magnet 106 passes as the crank arm 104 swings. During one rotation of the crank mechanism 100, the magnet 106 passes through the detection area of ​​the magnetic sensor 107 once, and a detection signal with one pulse per cycle is output, and the gas flow rate is measured based on this detection signal.

[0030] In replacing the magnetic gas flow detection mechanism of an existing membrane type gas meter with the magnetic gas flow detection mechanism 40 of this example, first, the magnet (magnet 106 in FIG. 4) and the magnetic sensor (magnetic sensor 107 in FIG. 4) that face each other from above and below the meter are removed from the existing membrane type gas meter. This state is the same as that of the membrane type gas meter 1 before the magnetic gas flow detection mechanism 40 is installed.

[0031] Thereafter, the gear box 42 to which the transmission gear shaft 41, which is a component of the magnetic gas flow detection mechanism 40 of this example, is attached is attached to the partition plate 3a formed in the upper case 3. The transmission gear shaft 41 is positioned on the meter front side with respect to the horizontal worm shaft 20, and the bent shaft portion 41b at the rear end of the shaft is engaged with the shaft tip portion 21 of the horizontal worm shaft 20 from the rotational direction side, so that the rotation of the horizontal worm shaft 20 can be transmitted to the transmission gear shaft 41.

[0032] In addition, a circuit board 45 on which a magnetic sensor 44 is mounted is attached to the front surface of the meter on the internal partition plate 3a of the upper case 3, and the magnetic sensor 44 is positioned so as to face the magnet 43 from the front side of the meter, making it possible to detect the rotating magnetic field of the magnet 43.

[0033] In this way, the crank mechanism and horizontal worm shaft of an existing diaphragm-type gas meter can be used as is to replace the magnetic gas flow detection mechanism in which a magnet and a magnetic sensor are arranged to face each other from above and below the meter with a magnetic gas flow detection mechanism in which a magnet and a magnetic sensor are arranged to face each other from the front and rear at the front side of the meter. Compared to replacing the crank mechanism components as well, the replacement of the detection mechanism can be done easily and inexpensively.

[0034] Furthermore, in the replaced detection mechanism, the rotation of the horizontal worm shaft 20 is accelerated via the gearbox 42 and transmitted to the magnet 43. The rotation of the horizontal worm shaft 20, which is significantly decelerated by the worm gear 30, can be accelerated and transmitted to the magnet 43. The magnet 43 can be rotated at a speed that achieves the required measurement accuracy. There is no need to increase the number of magnets 43 and magnetic sensors 44 to improve measurement accuracy, and the improvement in measurement accuracy can be achieved without increasing costs. [Explanation of symbols]

[0035] 1. Diaphragm gas meter 2 Meter case 3 Upper case 3a Partition 4 Lower case 5F, 5R Measuring room 6F, 6R Measuring membrane 7F, 7R wing shaft 8F, 8R shut-off valve 9 Link mechanism 9F, 9R Link 10 Crank mechanism 11 Vertical rotation axis 11a Vertical center axis 12A, 12B crank arms 13A, 13B crank arms 14 Crank stand 15 Lower crank plate 16 First crankshaft 17 Upper crank plate 18 Second crankshaft 19 Magnet mounting part 20 horizontal worm shaft 20 Transmission gear shaft 20a axis 21 Shaft tip 30 worm gear 31 Warm 32 worm wheel 40 Magnetic gas flow detection mechanism 41 Transmission gear shaft 41a Center axis 41b Shaft 42 Gearbox 42a Input side transmission gear 42b Compound transmission gear 42c Output transmission gear 42d Output shaft 43 Magnet 44 Magnetic Sensor 45 Circuit Board 100 crank mechanism 101 Center axis 102 Vertical rotation axis 103 Crankshaft 104 crank arm 105 Magnet mounting part 106 Magnet 107 Magnetic Sensor

Claims

1. A method for replacing a magnetic gas flow detection mechanism of a diaphragm gas meter, comprising the steps of: The membrane gas meter is a crank arm that converts the reciprocating motion of a measuring membrane that separates a gas flow measuring chamber into a rotational motion of a vertical rotation shaft centered on a vertical axis extending in the up-down direction of the meter; a link that converts the rotation of the vertical rotation shaft into an opening / closing motion that opens and closes the opening / closing valve of the measuring chamber; a worm gear that converts the rotation of the vertical rotation shaft into rotational motion of a horizontal worm shaft about a horizontal axis extending in the front-to-rear direction of the meter; It is equipped with a shaft tip portion of the horizontal worm shaft extends toward the front of the meter, bending at an angle of less than 90° in a direction away from the horizontal axis, The first magnetic detection mechanism, which is the magnetic gas flow detection mechanism before replacement, a first magnet attached to the crank arm; a first magnetic sensor that faces the first magnet from above the meter at a position where the first magnet passes as the crank arm swings; It has The second magnetic detection mechanism, which is the magnetic gas flow detection mechanism after replacement, is A second magnet; a second magnetic sensor for detecting a rotating magnetic field of the second magnet; a transmission gear shaft for inputting the rotation of the horizontal worm shaft; a speed-increasing gear train for increasing the rotation of the transmission gear shaft and transmitting the increased rotation to the second magnet; one shaft end of the transmission gear shaft is a bent shaft end that extends in a direction away from the central axis of the transmission gear shaft, The replacement of the first magnetic detection mechanism with the second magnetic detection mechanism is performed by: removing the first magnet and the first magnetic sensor; The second magnet is disposed on the front side of the meter with respect to the horizontal worm shaft, instead of the first magnet. Instead of the first magnetic sensor, the second magnetic sensor is disposed at a position facing the second magnet from the front side of the meter, so that the rotating magnetic field of the second magnet can be detected. The transmission gear shaft is coaxially disposed on the meter front side of the horizontal worm shaft so that the bent shaft end of the transmission gear shaft is positioned within the rotation locus of the shaft tip portion of the horizontal worm shaft, thereby enabling the rotation of the horizontal worm shaft to be transmitted to the transmission gear shaft, a speed-increasing gear train disposed between the transmission gear shaft and the second magnet, so that the rotation of the transmission gear shaft can be increased and transmitted to the second magnet.

2. A membrane gas meter obtained by replacing a magnetic gas flow detection mechanism by the replacement method described in claim 1, a crank arm that converts the reciprocating motion of a measuring membrane that separates a gas flow measuring chamber into a rotational motion of a vertical rotation shaft centered on a vertical axis extending in the up-down direction of the meter; a link that converts the rotation of the vertical rotation shaft into an opening and closing motion that opens and closes the opening and closing valve of the measuring chamber; a worm gear that converts the rotation of the vertical rotation shaft into rotational motion of a horizontal worm shaft about a horizontal axis extending in the front-to-rear direction of the meter; a magnetic gas flow rate detection mechanism including a magnet that rotates in synchronization with the rotation of the horizontal worm shaft and a magnetic sensor that detects the rotating magnetic field of the magnet; It is equipped with The magnet is located on the front side of the meter with respect to the horizontal worm shaft, The magnetic sensor faces the magnet from the front side of the meter, A transmission gear shaft extending in the front-rear direction of the meter is coaxially disposed on the front side of the meter with respect to the horizontal worm shaft, a shaft rear end portion of the transmission gear shaft on the meter rear side is mechanically engaged with a shaft tip portion of the horizontal worm shaft on the meter front side so that the transmission gear shaft rotates in the same direction and at the same speed as the horizontal worm shaft, a speed-increasing gear train is disposed between the transmission gear shaft and the magnet, which increases the rotation speed of the transmission gear shaft and transmits the increased rotation speed to the magnet; The rotating magnetic field of the magnet, which rotates at an increased speed in synchronization with the rotation of the horizontal worm shaft, is detected by the magnetic sensor. The shaft tip portion of the horizontal worm shaft extends toward the front of the meter while being bent at an angle of less than 90° in a direction away from the horizontal axis, the rear end of the transmission gear shaft is bent in a direction away from the horizontal axis and engages with the front end of the shaft from the side in the rotation direction of the horizontal worm shaft, A diaphragm gas meter characterized in that a cup-shaped magnet mounting portion that opens above the meter is attached to the crank arm.

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