| 摘要 |
PROBLEM TO BE SOLVED: To obtain a gas safety device by which a very small gas leak can be detected. SOLUTION: In this gas safety device, the propagation time T1 of ultrasonic waves up to a downstream-side ultrasonic sensor 1 from an upstream-side ultrasonic sensor, and the propagation time T2 of ultrasonic waves up to the upstream-side ultrasonic sensor from the downstream-side ultrasonic sensor 1, are recorded when a minimum flow rate in one day is measured. At a time when the minimum flow rate in one day does not become 0 (L/H), the change amount of the proparation time T1 is designated asα1, and the change amount of the propagation time T2 is designated asα2. When the flow rate of a gas exists, the absolute value of theα1 and the absolute value of theα2 are equal,α1>0, andα2<0. By using this, whether the gas is leaked or whether an error is due to the change with the passage of time of the ultrasonic sensors or not can be discriminated.
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