JPH08159836A - Gas meter - Google Patents

Abstract

PURPOSE: To provide a gas meter which close a shutoff valve quickly and accurately judging the difference of gas kind when a gas of a different composition from the composition at a normal time flows in. CONSTITUTION: In the gas meter which contains a pressure sensor, a vibration sensor, and the like, and to which a shutoff valve 7 is set, a gas kind discriminating sensor 6 is provided in a gas path 5 on the upstream side from the shutoff valve 7, and the shutoff valve 7 is operated in accordance with a sensor output outputted from the gas kind discriminating sensor 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas meter, and more particularly to a gas meter having a gas sensor having a gas type discriminating function.

[0002]

2. Description of the Related Art A gas type discrimination sensor is based on the following principle. That is, when a constant current is passed through a heater wire installed in a gas atmosphere, Joule heat is generated from the heater wire, and this heat propagates to the gas around the heater wire and the solid in contact with the heater wire.

When the temperature, pressure, gas type and flow rate of the atmosphere are not changed, the amount of heat propagated is constant and the temperature of the heater wire is also kept constant.

If there is no gas flow, the state of heat propagation from the heater wire depends on the temperature and pressure of the gas atmosphere around the heater wire,
And it is determined by the thermal conductivity of the gas.

Furthermore, if the temperature and pressure of the gas atmosphere are constant, the thermal conductivity of the gas determines the state of heat transfer from the heater wire. In other words, the thermal conductivity of the gas can be known by measuring the temperature of the heater wire, and the type of gas can be specified. This is because the thermal conductivity of gas differs depending on the type of gas.

To measure the temperature change of the heater wire, the resistance value change of the heater wire may be measured, and a known method such as a constant current method, a constant voltage method, or a constant temperature method can be used.

Even if there is a gas flow, it is possible to obtain an almost accurate thermal conductivity of gas by detecting the gas flow rate and correcting the separately detected temperature of the heater wire with the detected gas flow rate. In this way, the gas species existing around the sensor can be identified.

A gas type discriminating sensor based on the above principle is disclosed, for example, in the specification and drawings of Japanese Patent Application Laid-Open No. 4-301555 and Japanese Patent Application No. 6-139916 by the present applicant (both of which are currently unpublished). There is.

On the other hand, a conventional gas meter for measuring the flow rate of gas is combined with a pressure sensor, a vibration sensor, a shutoff valve, etc. in addition to the flow meter.

The flow meter measures the flow rate of the supplied gas,
The pressure sensor measures the pressure in the conduit, and the vibration sensor detects an earthquake. Then, the shutoff valve is actuated by a signal output from at least one of the flow meter and each sensor at the time of abnormality, and serves to stop the supply of gas.

For example, when the pressure inside the pipe decreases due to gas leakage due to corrosion of the pipe, a signal is output from the pressure sensor,
Furthermore, in the event of a large earthquake, a signal is output from the vibration sensor, and the shutoff valve operates to stop the gas supply.

[0012]

However, in the conventional gas meter, even if a gas having a composition different from the composition in the normal state flows in, the composition abnormality of the gas cannot be detected unless the pressure is the same as in the normal state. For example, when the atmosphere is mixed into the conduit from a damaged portion due to a disaster, there is a risk of defective ignition or abnormal combustion in the gas combustion device depending on the degree of mixing of the atmosphere into the methane gas. Conventional gas meters are not equipped with the function of preventing the possibility of such accidents and damage to combustion equipment.

Therefore, at present, for the purpose of ensuring safety, an employee visits each home in the area after the construction and confirms that the supplied gas has a normal composition, and then opens the gas meter plug. It is open, at the cost of much effort and time to ensure safety.

The present invention has been made in view of the above-mentioned circumstances in the prior art, and an object of the present invention is to change the kind of gas when a gas having a composition different from that in the normal state flows. It is to provide a gas meter configured to quickly and accurately determine a difference and close a shutoff valve.

[0015]

To achieve the above object, according to one aspect of the present invention, in a gas meter provided with a shutoff valve, a gas type discrimination sensor is provided in a gas passage upstream of the shutoff valve. And a shutoff valve is operated according to a sensor output output from the gas type determination sensor.

The gas type discriminating sensor described in the above aspect is preferably a micro gas sensor, and more preferably a micro gas sensor having a windbreak structure.

[0017]

When a gas having an abnormal composition flows in, the sensor output of the gas type discrimination sensor immediately becomes an abnormal value. At the same time the change in the sensor output is quickly judged by the judgment circuit,
The shutoff valve drive circuit is energized to automatically close the shutoff valve of the gas meter. As a result, the supply of gas having an abnormal composition is stopped, and accidents and damage to the equipment due to poor ignition or abnormal combustion in the gas combustion equipment are prevented.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in more detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view showing an embodiment of the gas meter of the present invention. Gas inlet 1 of gas meter
Is connected to one end of a gas supply pipe 3 whose other end is connected to a main branch pipe (not shown) buried underground, while one end of a gas delivery pipe 4 is connected to the gas outlet 2. There is.

The gas inlet 1 and the gas outlet 2 are connected via a gas passage 5 formed in the housing of the gas meter, and along this gas passage 5 a gas type discrimination sensor 6 and a shutoff valve 7 are provided. A pressure sensor, a flow meter, etc. (not shown) are provided. The arrangement of the components other than the gas type discriminating sensor 6 in the gas meter is already well known, and therefore a description thereof will be omitted here. The gas type discriminating sensor 6 itself and the relationship between the gas type discriminating sensor 6 and the shutoff valve 7 will be described below. To do.

The gas type discrimination sensor 6 immediately discriminates the composition abnormality of the gas when the gas of the abnormal composition is supplied, and controls the shut-off valve 7 so that the gas of the abnormal composition does not flow to the downstream side of the shut-off valve 7. Since it is for outputting the sensor output for the closing operation, it is installed at a proper position in the gas passage 5 between the gas inlet 1 and the shutoff valve 7.

FIG. 2 shows a microflow sensor as an example of the gas type discrimination sensor 6. This microflow sensor has a heater wire 9 formed on the surface of a silicon substrate 8 having a side of about 3 mm by using a semiconductor fine processing technique. The pad portions 9a and 9b at both ends of the heater wire 9 are connected to a constant current source and a processing circuit, which are not shown, and are adapted to discriminate the gas type by the action described later.

The microflow sensor shown in FIG. 2 is provided with a windproof hood 20 having a ventilation hole so that the heater wire 9 is not directly affected by the gas flow. Further, in order to achieve a heat insulating effect between the heater wire 9 and the silicon substrate 8, the substrate 8 of the heater wire portion has a diaphragm structure,
A cavity is formed below it.

FIG. 3 is a block diagram showing a structural example of a processing circuit 10 connected between the gas type discrimination sensor 6 and the shutoff valve 7. The processing circuit 10 includes a sensor output circuit 11, a determination circuit 12, And a shutoff valve drive circuit 13.

Sensor output circuit 1 when the constant temperature method is used
An example of the main part of No. 1 is shown in FIG. The sensor output circuit 11 includes a bridge circuit 15 having four resistors R1 to R4 connected to a power source E via a transistor 14.
Is provided.

The sensor output circuit 11 is a bridge circuit 15
Of the four resistors R1 to R4 constituting the above, only R1 generates heat as the heater wire 9 of the gas type discrimination sensor 6, and as is clear from FIG. 4, the resistor R1 always maintains a constant heat generation temperature. It has such a circuit configuration. As for the temperature resistance coefficient, R1 and R2 have the same temperature resistance coefficient, and R3 and R4 have the same temperature resistance coefficient, and R1 × R3.
= R2 × R4 is always satisfied.
Furthermore, the only resistors exposed to the gas are R1 and R2.

The output of the bridge circuit in the sensor output circuit 11 is input to the operational amplifier 16 as an operation input, and the output V from the operational amplifier 16 is sent to the judgment circuit 12 as a sensor output.

Next, the operation of the sensor output circuit 11 will be described with reference to the graph of FIG. FIG. 5 is a graph showing the relationship between the thermal conductivity of gas and the sensor output of the gas type discrimination sensor 6.

As shown in FIG. 5, the sensor output at the thermal conductivity K ₀ of city gas having a normal composition is the reference output V _0.
Then, since the thermal conductivity K _air is lower than K ₀ ,
The sensor output V _{air for air} also has a value smaller than V ₀ . Therefore, the sensor output of the city gas diluted with air and diluted becomes naturally smaller than V ₀ .

Assuming that the thermal conductivity of a gas having a threshold amount of aerated air which is a limit for causing ignition failure or abnormal combustion is K _th and the sensor output at that time is a threshold output V _th , the sensor output V from the operational amplifier 16 is given. When V ≦ V _th , the determination circuit 12 determines that the composition of the gas is abnormal, and excites the shutoff valve drive circuit 13 to close the shutoff valve 7.

As described above, according to the gas meter of the present invention, the supply of the gas having the abnormal composition to the gas combustion equipment is stopped, and the damage to the combustion equipment and the accident related to the gas are prevented.

The above description is merely illustrative of the preferred embodiments of the present invention and the scope of the present invention is not limited thereto. Many more variations and modifications of the present invention will readily suggest themselves to those skilled in the art without departing from the scope of the invention.

[0033]

According to the gas meter of the present invention, when a gas having an abnormal composition different from the normal composition flows in, the composition abnormality of the gas is quickly and accurately determined, and the shutoff valve is closed. The supply of the gas having the composition abnormality to the gas combustion equipment or the like is automatically stopped. As a result, accidents due to poor ignition or abnormal combustion in the gas combustion device, damage to the device, and the like can be prevented in advance.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of a gas meter of the present invention.

FIG. 2 is a schematic exploded perspective view showing an example of a gas type discrimination sensor used in an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a processing circuit for an embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of a sensor output circuit in the processing circuit shown in FIG.

FIG. 5 is a graph showing the sensor output of a gas type determination sensor with respect to the thermal conductivity of gas.

[Explanation of symbols]

1 Gas Inlet 2 Gas Outlet 3 Gas Supply Pipe 4 Gas Delivery Pipe 5 Gas Passage 6 Gas Type Discrimination Sensor 7 Shutoff Valve 8 Silicon Substrate 9 Heater Wire 9a, 9b Pad 10 Processing Circuit 11 Sensor Output Circuit 12 Judgment Circuit 13 Shutoff Valve drive circuit 14 Transistor 15 Bridge circuit 16 Operational amplifier 20 Windbreak hood R1 Heating resistor R2, R3, R4 Resistor K ₀ , K _th , K _air Thermal conductivity V Sensor output V ₀ Reference output V _th Threshold output V _{air For} air Sensor output

Claims (3)

[Claims] 1. In a gas meter provided with a shutoff valve, a gas type discrimination sensor is provided in a gas passage upstream of the shutoff valve, and the shutoff valve is operated in accordance with a sensor output outputted from the gas type discrimination sensor. A gas meter characterized by being configured as described above. 2. The gas meter according to claim 1, wherein the gas type discrimination sensor is a micro gas sensor. 3. The gas meter according to claim 2, wherein the micro gas sensor has a windbreak structure.