Patent ID: 8620601

Claim:
A gas cutoff apparatus for cutting off supply of gas when an abnormality occurs, comprising: a flow rate detecting unit for measuring a flow rate using an ultrasonic signal; an amplification degree adjusting unit for adjusting a signal amplification degree for the ultrasonic signal depending on an amplitude of the ultrasonic signal; a flow rate computing unit for computing an instantaneous flow rate value from the flow rate measured by the flow rate detecting unit; an amplification degree determining unit for determining the signal amplification degree adjusted by the amplification degree adjusting unit; a time measuring unit for starting timing when the instantaneous flow rate value computed by the flow rate computing unit is a predetermined flow rate or less and the signal amplification degree determined by the amplification degree determining unit is a predetermined value or more; a measurement condition setting unit for changing a measurement condition of the flow rate detecting unit based on the flow rate obtained by the flow rate computing unit, wherein the measurement condition is selected from a plurality of different stepwise measurement conditions for measuring the flow rate; a measurement ratio computing unit for obtaining a ratio of a number of times measured on one or more of the different stepwise measurement conditions with respect to a number of times measured on all of the plurality of different stepwise measurement conditions during predetermined time timed by the time measuring unit; an average flow rate computing unit for obtaining an average flow rate from the instantaneous flow rate obtained by the flow rate computing unit; an abnormality determining unit for determining the presence or absence of the abnormality from the obtained average flow rate or determining that the abnormality occurs in the flow rate detecting unit when the ratio obtained by the measurement ratio computing unit is a predetermined ratio or more; and a cutoff unit for cutting off the supply of the gas when the abnormality determining unit determines that the abnormality occurs.