JP2001165730A - Gas meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas meter capable of effectively making the completion of air purging known and capable of efficiently performing air purging work. SOLUTION: A gas meter consists of a propagation time measuring means A for measuring the signal propagation time in a gas flow channel, a flow rate operation means 17 for calculating a flow rate on the basis of the propagation time data from the propagation time measuring means A to integrate the calculated flow rate, a proparation time memory means 18 for preliminarily storing the signal propagation time of gas and a judge means 19 comparing the propagation time data from the propagation time measuring means A with the propagation time value from the propagation time memory means 18 to judge whether the propagation time data coincides with the propagation time value and an alarm sound means 21 emitting an alarm sound when it is judged that the propagation time data coincides with the propagation time value by the judge means 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas meter for measuring a flow rate of a gas flowing through a gas flow path using, for example, an ultrasonic wave.

[0002]

2. Description of the Related Art A conventional gas meter of this type is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-32823, and has a configuration shown in FIG.

[0003] In FIG. 4, the gas meter includes a pipeline 1, a first ultrasonic probe 2, a second ultrasonic probe 3, a switch 4, a receiving circuit 5, a transmitting circuit 6, a propagation time difference circuit 7, a flow rate calculating circuit 8, Consists of

[0004] The switch 4 switches the direction of propagation of the ultrasonic wave in the pipeline 1. For example, the first ultrasonic probe 2 is energized by a transmission wave from the transmission circuit 6, and the ultrasonic wave propagating in the direction opposite to the gas flow in the pipeline 1 (in the direction of the arrow) is received by the second ultrasonic probe 3. The signal is again passed through the switch 4 and the receiving circuit 5
To obtain the received wave. The propagation time difference circuit 7 measures the ultrasonic propagation time in the reverse direction based on the received wave. Next, by switching the switch 4, the second ultrasonic probe 3 is energized by the transmission wave from the transmission circuit 6, and the ultrasonic wave that has propagated in the forward direction of the gas flow in the pipeline 1 (in the direction of the arrow) is
The wave is received by the first ultrasonic probe 2 and is again applied to the receiving circuit 5 via the switch 4 to obtain a received wave. Propagation time difference circuit 7
Measures the ultrasonic propagation time in the forward direction based on the received wave. The propagation time difference circuit 7 calculates the difference between the backward ultrasonic wave propagation time and the forward ultrasonic wave propagation time. Flow rate calculation circuit 8
Calculates the flow rate based on the propagation time difference obtained by the propagation time difference circuit 7.

Similarly, there is a flow meter using an ultrasonic wave disclosed in Japanese Patent Application Laid-Open No. Hei 10-318811, which has a configuration shown in FIG. In FIG. 5, the flow meter comprises a flow velocity measuring means 9, a propagation time difference measuring means 1
6, a flow rate calculating means 17, a propagation time storing means 18, a determining means 19 and a display means 20.

The flow velocity measuring means 9 comprises a first flow velocity detecting means 1
0, second flow rate detecting means 11, first receiving means 12, second receiving means 13, first transmitting means 14, and second transmitting means 15.

The first flow velocity detecting means 10 is connected to the second ultrasonic probe 3 provided on the upstream side of the pipeline 1 or provided directly on the upstream side of the pipeline 1 and outputs an ultrasonic signal. Or a first receiving means 1 which is constituted by an element capable of receiving.
2 and the first transmission means 14 are connected.

The second flow rate detecting means 11 is connected to the first ultrasonic probe 2 provided on the downstream side of the pipeline 1 or provided directly on the downstream side of the pipeline 1 and outputs an ultrasonic signal. Or a second receiving unit 1
Third and second transmission means 15 are connected.

First receiving means 12 and second receiving means 13
Are connected to the propagation time difference measuring means 16. The flow rate calculating means 17 calculates the flow rate of the gas flowing in the pipeline 1 based on the propagation time difference calculated by the propagation time difference measuring means 16.

The propagation time storage means 18 stores in advance the propagation time of the ultrasonic signal in the medium, for example, the propagation time of the component state of the LP gas, especially the propagation time when air or the like is mixed.

The determination means 19 determines the mixing of another medium, for example, the LP gas in the medium, based on the propagation time in the medium to be measured from the propagation time storage means 18 and the first receiving means 12 and the second receiving means 13. It is determined whether or not air is mixed.

The display means 20 displays a warning if the determination means 19 determines that another medium is mixed.

Next, the operation of the above configuration will be described. Pipe line 1
Inside, the flow velocity detecting means 9 is attached such that the first flow velocity detecting means 10 and the second flow velocity detecting means 11 face each other. First, the first receiving means 12 connected to the first flow rate detecting means 10 receives a signal emitted from the second transmitting means 15 via the second flow rate means. The propagation time of the signal from the start of transmission to the reception is determined by the propagation time difference measuring means 16. Next, the second receiving means 13 connected to the second flow rate detecting means 11 receives the signal emitted from the first transmitting means 14 via the first flow rate detecting means 10. Similarly, the propagation time of a signal from the start of transmission to the reception is measured by a propagation time difference measuring means 1.
Find in 6.

Normally, when there is no flow rate, the propagation time difference is zero. The propagation time of the signal sent from the second flow velocity detecting means 11 on the downstream side to the first flow velocity detecting means 10 on the upstream side increases as the flow rate of the measurement medium, for example, gas or the like, increases. Conversely, the first flow velocity detecting means 1 on the upstream side
The signal propagation time from 0 to the second flow velocity detecting means 11 becomes shorter. That is, the magnitude of the flow value is proportional to the signal propagation time difference.

When the ultrasonic signals are received from the opposed flow velocity detecting means 10 and 11, the propagation time difference measuring means 16 calculates the propagation time difference, and the flow rate calculating means 17 calculates the flow rate based on the calculated propagation time difference.

On the other hand, the propagation time storage means 18 stores the propagation time in a liquid such as water or machine oil, the propagation time in a gas such as LP gas or city gas, and further stores the propagation time in air such as LP gas or city gas. The propagation time when a different medium is mixed is stored in advance. The propagation time according to the mixing ratio of air and gas, and the propagation time at 100% air are also stored.

Therefore, the judging means 19 calculates the propagation time values in various media stored in the propagation time storage means 18,
The propagation time value obtained by the first receiving means 12 and the propagation time value obtained by the second receiving means 13 are compared and determined, and when the storage time value and the reception time are different, another different medium such as LP gas or city is included in the measurement medium. It detects that air or the like is mixed in the gas or the like. As a result, when the determination unit 19 determines that the mixture has occurred, the display unit 20 displays a warning.

In particular, when a flow meter is installed as a gas meter, a large amount of air remains in the pipeline 1. At the beginning of use, if the gas appliance is used with air remaining, a dangerous state of abnormal combustion or emission of unburned gas resulting from the unignited state of the gas appliance will occur. The air mixed in the LP gas or the city gas can be detected based on the difference in the propagation time value, and can be notified to the user or a gas meter installation company, thereby improving safety and quickly installing the flow meter as the gas meter. In this way, by detecting the mixture of the different medium and issuing a warning, the gas distributor or the gas user is notified, so that an abnormal state in using the gas appliance can be quickly determined.

[0019]

When a gas pipe is newly installed or a gas meter is replaced, the air existing in the pipe or the gas meter is supplied to the supply gas (LP gas, city gas, etc.) before the gas is used. ), It is necessary to perform an air purge operation. Therefore, it is necessary to repeat the operation of igniting the combustor until the completion of the air purge. At this time, it is convenient if the completion of the air purge can be surely known.

However, the gas meter as shown in the configuration example of FIG. 4 usually merely integrates the flow rate of the flowing gas without discriminating the gas type, and does not disclose a method of knowing the completion of the air purge. .

On the other hand, when a different medium is mixed in the gas when a gas meter is installed, for example, LP
A method of determining when air is mixed in gas, city gas, or the like using, for example, an ultrasonic flow meter is disclosed in Japanese Patent Application Laid-Open No. H10-318811, that is, the configuration example in FIG. . Therefore, the completion of the air purge can be determined using the ultrasonic gas meter, and the completion of the air purge can be displayed as a warning. Since the completion of the air purge can be objectively determined, it is effective in the sense that the disappearance caused by the erroneous determination of the operator can be prevented.

However, in the gas meter as shown in the configuration example of FIG. As described above, it is necessary to repeat the operation of igniting the combustor until the air purge is completed.However, since the gas meter and the combustor are usually installed at a certain distance from each other, the combustion by one worker alone is I can't check the display of the gas meter at a remote place while Ignition work is done. Therefore, the display means 2 of the gas meter
There is a problem that it is difficult to actually confirm the completion of the air purge even if a warning display of the completion of the air purge is displayed at 0.

Further, Japanese Patent Application Laid-Open No. 11-51727 discloses a gas meter provided with a gas type discriminating means and capable of measuring the flow rate of another type of gas. No way to know is disclosed.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to effectively notify the completion of air purging.
An object of the present invention is to provide a gas meter capable of improving the efficiency of an air purge operation.

[0025]

SUMMARY OF THE INVENTION In view of the above object, a gas meter according to the first aspect of the present invention has a propagation time for measuring a signal propagation time in a gas flow path as shown in a basic configuration diagram of FIG. Measuring means A, a flow rate calculating means 17 for calculating a flow rate based on the propagation time data from the propagation time measuring means A and integrating the obtained flow rate, and a propagation time storing means for storing the signal propagation time of the gas in advance And comparing the propagation time data from the propagation time measurement means A with the propagation time value from the propagation time storage means 18 to determine whether or not the propagation time data matches the propagation time value. Means 19 and an audible alarm means 21 for issuing an audible alarm when the determination means 19 determines that the propagation time data matches the propagation time value.

In the first aspect, the propagation time measuring means A measures the signal propagation time in the gas flow path.
The flow rate calculating means 17 calculates the flow rate based on the propagation time data from the propagation time measuring means A, and integrates the calculated flow rates. The propagation time storage means 18 stores the signal propagation time of the gas in advance. The determination unit 19 compares the propagation time data from the propagation time measurement unit A with the propagation time value from the propagation time storage unit 18 to determine whether the propagation time data matches the propagation time value. The warning sound unit 21 emits a warning sound when the determination unit 19 determines that the propagation time data matches the propagation time value.

According to a second aspect of the present invention, in the gas meter of the first aspect, the alarm sound means 21 emits an alarm sound after a predetermined delay time from the time point of the determination by the determination means 19. .

According to the second aspect of the present invention, the alarm sound means 21 emits an alarm sound after a predetermined delay time from the time point of the judgment by the judgment means 19.

According to a third aspect of the present invention, in the gas meter according to the first or second aspect, the propagation time measuring means A is provided upstream of the gas flow path and outputs or receives an ultrasonic signal. 1 flow velocity detecting means 10, a second flow velocity detecting means 11 provided on the downstream side of the gas flow path for outputting or receiving an ultrasonic signal, and the first flow velocity detecting means 1
0, a first receiving means 12 for receiving an ultrasonic signal emitted from the second flow velocity detecting means,
A second receiving means 13 connected to the flow velocity detecting means 11 for receiving an ultrasonic signal emitted from the first flow velocity detecting means, and a first receiving means 13 for supplying an ultrasonic signal to the first flow velocity detecting means 10 , A second transmitting unit 15 for supplying an ultrasonic signal to the second flow velocity detecting unit 11, a propagation time of the ultrasonic signal received by the first receiving unit 12, and the second And a propagation time difference measuring means for calculating a propagation time difference from the propagation time of the ultrasonic signal received by the receiving means.

According to the third aspect of the present invention, the propagation time measuring means A includes a first flow velocity detecting means 10, a second flow velocity detecting means 11, a first receiving means 12, and a second receiving means. 13, first transmitting means 14, and second transmitting means 15
And a propagation time difference measuring means 16. The first flow velocity detecting means 10 is provided on the upstream side of the gas flow path, and outputs or receives an ultrasonic signal. The second flow velocity detecting means 11
It is provided downstream of the gas flow path and outputs or receives an ultrasonic signal. The first receiving means 12 is connected to the first flow velocity detecting means 10 and receives an ultrasonic signal emitted from the second flow velocity detecting means. The second receiving means 13 is connected to the second flow velocity detecting means 11 and receives an ultrasonic signal emitted from the first flow velocity detecting means. First transmission means 14
Supplies an ultrasonic signal to the first flow velocity detecting means 10.
The second transmitting means 15 supplies an ultrasonic signal to the second flow velocity detecting means 11. The propagation time difference measuring means 16 calculates a propagation time difference between the propagation time of the ultrasonic signal received by the first receiving means 12 and the propagation time of the ultrasonic signal received by the second receiving means 13.

According to a fourth aspect of the present invention, in the gas meter according to any one of the first to third aspects, the propagation time storage means 18 stores the signal propagation time of the LP gas or the city gas in advance. It is characterized by having.

In the fourth aspect of the invention, the propagation time storage means 18 stores the signal propagation time of the LP gas or the city gas in advance.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the gas meter according to the present invention. In FIG. 2, the gas meter comprises a propagation time measuring means A, a flow rate calculating means 17, a propagation time storing means 18, a determining means 19, a display means 20, and an alarm sound means 21.

The propagation time measuring means A comprises a flow velocity measuring means 9 and a propagation time difference measuring means 16.

The flow velocity measuring means 9 comprises a first flow velocity detecting means 1
0, second flow rate detecting means 11, first receiving means 12, second receiving means 13, first transmitting means 14, and second transmitting means 15.

The first flow velocity detecting means 10 is connected to the second ultrasonic probe 3 provided on the upstream side of the pipeline 1 or directly provided on the upstream side of the pipeline 1 and outputs an ultrasonic signal. Or a first receiving means 1 which is constituted by an element capable of receiving.
2 and the first transmission means 14 are connected.

The second flow rate detecting means 11 is connected to the first ultrasonic probe 2 provided on the downstream side of the pipe 1 or provided directly on the downstream side of the pipe 1 and outputs an ultrasonic signal. Or a second receiving unit 1
Third and second transmission means 15 are connected.

First receiving means 12 and second receiving means 13
Are connected to the propagation time difference measuring means 16. The flow rate calculating means 17 calculates the flow rate of the gas flowing in the pipeline 1 based on the propagation time difference calculated by the propagation time difference measuring means 16.

The propagation time storage means 18 stores in advance the propagation time of the ultrasonic signal in the gas, for example, the propagation time values of the LP gas and the city gas.

The determination means 19 compares the propagation time value from the propagation time storage means 18 with the propagation time data of the ultrasonic signals received by the first receiving means 12 and the second receiving means 13, and Is equal to or not equal to the propagation time value.

The display means 20 displays a warning if the determination means 19 determines that the propagation time data matches the propagation time value.

If the determination means 19 determines that the propagation time data matches the propagation time value,
Emit a warning sound.

Next, the operation of the above configuration will be described. Here, as an example, it is assumed that after the installation of the gas meter, the combustor is ignited for an air purging operation, whereby the gas meter starts operating. First, the first receiving means 12 connected to the first flow rate detecting means 10 receives a signal emitted from the second transmitting means 15 via the second flow rate detecting means 11. Signal propagation time t from start of transmission to reception
1 is obtained by the propagation time difference measuring means 16.

Here, the distance between the first flow velocity detecting means 10 and the second flow velocity detecting means 11 facing each other in the pipeline 1 is represented by L.
, The sound velocity is C, the gas flow velocity is V, and the ultrasonic wave propagation direction (that is, the line connecting the first flow velocity detection means 10 and the second flow velocity detection means 11) and the central axis of the pipe 1 are Assuming that the angle is θ, the propagation time t1 is obtained by the following equation. t1 = L / (C−Vcos θ) (1)

Next, the second receiving means 13 connected to the second flow rate detecting means 11 receives the signal emitted from the first transmitting means 14 via the first flow rate detecting means 10.
Similarly, a propagation time difference t2 of the signal from the start of transmission to the reception is determined by the propagation time difference measuring means 16 based on the following equation. t2 = L / (C + Vcos θ) (2)

Next, the propagation time difference measuring means 16 calculates the propagation time difference between the propagation times t1 and t2 based on the above equations (1) and (2), and calculates the flow rate calculating means 17 based on the obtained propagation time difference. To calculate the flow velocity, and then calculate the flow rate. That is, from the above equations (1) and (2),
The flow velocity V is as follows: V = L / 2 cos θ (1 / t2-1 / t1) (3)

Therefore, assuming that the sectional area of the pipe 1 is S, the flow rate Q is as follows: Q = SV (4), and the instantaneous flow rate is obtained. Next, the flow rate calculating means 17 integrates the determined instantaneous flow rates to determine an integrated flow rate.

On the other hand, the propagation time storage means 18 stores the propagation times of the ultrasonic signals in the LP gas and the city gas in advance.

Therefore, the judging means 19 determines the propagation time value stored on the basis of the propagation time value stored in the propagation time storage means 18 and the ultrasonic signals received by the first receiving means 12 and the second receiving means 14. The time data is compared to determine whether the propagation time data matches the propagation time value.

For example, when the gas to be used is LP gas, the judgment means 19 determines the propagation time value (for example, T) of the LP gas stored in the propagation time storage means 18.
Is compared with the propagation time data t actually measured by the first receiving means 12 and the second receiving means 14 to determine whether or not the propagation time data matches the propagation time value (T = t). I do.

If it is determined that the propagation time data t does not coincide with the propagation time value T, it is considered that air is still mixed in the LP gas in the gas meter, and the gas meter continues to operate, and the air purge is performed. Work continues.

On the other hand, if it is determined that the propagation time data t matches the propagation time value T, it is considered that the air present in the gas meter has been completely replaced with the LP gas and the air purge has been completed. The determination means 19 is a display means 2
Control 0 to display a warning that air purge is complete,
The alarm sound means 21 is driven to emit an alarm sound indicating the completion of the air purge.

Therefore, when the determination means 19 determines that the propagation time data t coincides with the propagation time value T during an air purge operation or the like when the gas meter is installed,
That is, when it is determined that the air purge is completed, it can be confirmed by the alarm sound that the air purge has been completely completed even near the combustor at a distance from the gas meter,
The efficiency of the air purge operation can be improved.

After the air purge operation is completed, the gas meter
When the reset button (not shown) is pressed, the initial state is restored, and the shut-off means 22 releases the shut-off to open the gas flow path and prepare for normal gas use.

Next, the above operation will be described with reference to the flowchart shown in FIG. First, in step S1, the propagation time data t of the LP gas is measured based on the ultrasonic signals received by the first receiving means 12 and the second receiving means 13. Next, in step S2, the determination unit 19 compares the LP gas propagation time value T stored in the propagation time storage unit 18 with the above-described propagation time data t, and the propagation time data matches the propagation time value. It is determined whether (T = t).

If not T = t, the process returns to step S1 and T
If = t, the process proceeds to steps S3, S4, S5.

In step S3, the judging means 19 controls the display 20 to display a warning indicating that the air purge has been completed.

In step S4, the judging means 19 drives the alarm sound means 21 to emit an alarm sound indicating the completion of the air purge.

On the other hand, when the gas used is city gas,
The judging means 19 calculates the city gas propagation time value (for example, T ′) stored in the propagation time storage means 18,
The propagation time data t actually measured by the first receiving means 12 and the second receiving means 13 are compared with each other to determine whether or not the propagation time data matches the propagation time value (T '= t). .

If it is determined that the propagation time data t does not coincide with the propagation time value T, it is considered that air is still mixed with the city gas in the gas meter, and the gas meter continues to operate, and the air purge is continued. Work continues.

On the other hand, if it is determined that the propagation time data t matches the propagation time value T, it is considered that the air present in the gas meter has been completely replaced with the city gas and the air purge has been completed. The determination means 19 is a display means 2
Control 0 to display a warning that air purge is complete,
The alarm sound means 21 is driven to emit an alarm sound indicating the completion of the air purge.

Therefore, in the air purging operation at the time of installation of the gas meter, etc., when the judging means 19 judges that the propagation time data t matches the propagation time value T ', that is, when it is judged that the air purge is completed. The warning sound can surely confirm that the air purge has been completed even in the vicinity of the combustor at a distance from the gas meter, and can improve the efficiency of the air purge operation.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications and applications are possible.

For example, the warning sound means 21 can be a sound such as a continuous sound or an intermittent sound, or a voice message such as "air purge end" as the warning sound.

Further, the alarm sound means 21 may be built in the gas meter, or may be a gas leak alarm device installed in the combustor room linked to the gas meter.

Further, after the completion of the air purge, a delay time may be set in consideration of the length of the pipe from the gas meter to the combustor until the start of emission of the alarm sound by the alarm sound means 21.

[0067]

According to the first aspect of the present invention, the completion of the air purge can be effectively notified by an alarm sound, and the efficiency of the air purge operation can be improved.

According to the second aspect of the present invention, the notification of the completion of the air purge can be delayed in consideration of the length of the pipe from the gas meter to the combustor.

According to the third aspect of the present invention, the propagation time data to be compared with the stored propagation time value can be obtained based on the ultrasonic signals propagating in the gas flow path in the forward and backward directions.

According to the fourth aspect of the present invention, the efficiency of the air purging operation when using LP gas or city gas can be improved.

[Brief description of the drawings]

FIG. 1 shows a basic configuration diagram of a gas meter according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a gas meter according to the present invention.

FIG. 3 is a flowchart illustrating the operation of the gas meter.

FIG. 4 shows a configuration example of a conventional ultrasonic gas meter.

FIG. 5 shows another configuration example of a conventional ultrasonic gas meter.

[Explanation of symbols]

 A Propagation time measurement means 17 Flow rate calculation means 18 Propagation time storage means 19 Judgment means 21 Alarm sound means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Isao Masuda 23 Minami-Kashima, Futamata-cho, Tenryu-shi, Shizuoka Inside Yazaki Keiki Co., Ltd. (72) Inventor Akihiro Harada 23, Minami-Kashima, Futamata-cho, Tenryu-shi, Shizuoka Inside Yazaki Keiki Ltd. (72) Inventor Yuji Sugimoto 23 Minamikashima, Futama-machi, Tenryu-shi, Shizuoka Prefecture Inside Yazaki Keiki Co., Ltd. (72) Inventor Norio Shinmura 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Ichitaka Asano 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture, Japan Matsushita Electric Industrial Co., Ltd. F-term (reference) in Matsushita Electric Industrial Co., Ltd. 2F030 CA03 CC13 CE02 CE04 CE32 CF11 2F035 DA14

Claims (4)

[Claims] 1. A propagation time measuring means for measuring a signal propagation time in a gas flow path, a flow rate calculating means for calculating a flow rate based on the propagation time data from the propagation time measuring means, and integrating the obtained flow rate. A propagation time storage means for storing in advance the signal propagation time of the gas; and comparing the propagation time data from the propagation time measurement means with the propagation time value from the propagation time storage means, and Determining means for determining whether or not the transmission time value matches the time value; and an alarm sound means for generating an alarm sound when the determination means determines that the propagation time data matches the propagation time value. And a gas meter. 2. The gas meter according to claim 1, wherein the alarm sound means emits an alarm sound after a predetermined delay time from the time point of the determination by the determination means. 3. The propagation time measuring means is provided on an upstream side of a gas flow path, a first flow velocity detecting means for outputting or receiving an ultrasonic signal, and provided on a downstream side of a gas flow path, A second flow rate detecting means for outputting or receiving a signal; a first receiving means connected to the first flow rate detecting means for receiving an ultrasonic signal emitted from the second flow rate detecting means; Second receiving means connected to the second flow rate detecting means for receiving an ultrasonic signal emitted from the first flow rate detecting means, and a first transmission for supplying an ultrasonic signal to the first flow rate detecting means. Means, a second transmitting means for supplying an ultrasonic signal to the second flow velocity detecting means, a propagation time of the ultrasonic signal received by the first receiving means, and an ultrasonic signal received by the second receiving means. Propagation to find the difference between the propagation time of the sound signal and the propagation time Gas meter according to claim 1 or 2, wherein the consisting of between difference measurement means. 4. The gas meter according to claim 1, wherein the propagation time storage means stores the signal propagation time of the LP gas or the city gas in advance.