GAS SHUT-OFF DEVICE

PROBLEM TO BE SOLVED: To prevent erroneous shut-off by monitoring abnormal measurement in ultrasonic flow rate measurement.SOLUTION: A gas shut-off device comprises: flow rate detection means 1 for measuring flow rates; means for calculating instantaneous flow rates or an average flow rate; abnormal measurement determination means 13 for monitoring whether or not there is abnormality in the flow rate detection means 1 and determining that there is abnormal measurement when abnormality is detected; timer means 15 for counting a predetermined time; use state storage means 16 for storing a use state within a predetermined time period on the basis of the average flow rate; appropriate use condition change means 17 for changing appropriate use conditions according to contents of the use state storage means 16; period time counting means 18 for starting operations of the abnormal measurement determination means 13 after a predetermined time period is counted; abnormality determination means 19 for determining whether or not there is abnormality on the basis of the calculated average flow rate and resetting appropriate conditions by the appropriate use condition change means 17; forced relearning means 22 for restarting the timer means 15 and the period time counting means 18 and for retarding abnormal measurement determination; and shut-off means 20 for shutting off supply of gas when it is determined that there is abnormality by the abnormality determination means 19.