Patent ID: 8245582

Claim:
A method of measuring a gas flow velocity using an ultrasonic gas flow meter ( 10 ), wherein said ultrasonic gas flow meter ( 10 ) includes a horizontal piping ( 12 ) through which gas ( 14 ) can flow in a flow direction (A) and which has a central axis ( 36 ), at least one pair of measurement paths ( 30 ) of equal length spaced apart, extending parallel to one another in separate horizontal planes and inclined to said flow direction (A), wherein each horizontal plane of a pair of measurement paths ( 30 ) is vertically offset by an equal predefined distance from said central axis ( 36 ), wherein an ultrasonic transducer ( 16 , 18 ) is arranged at each end of said measurement path ( 30 ) and each ultrasonic transducer ( 16 , 18 ) is adapted to selectively act as an ultrasonic transmitter ( 22 ) and an ultrasonic receiver ( 24 ), the method comprising the steps of measuring a flow velocity of said gas ( 14 ) in a measurement path ( 30 ) arranged in an upper region of said piping ( 12 ), measuring a flow velocity of said gas ( 14 ) in a measurement path ( 14 ) arranged in a lower region of said piping ( 12 ) and using the results of these two measurements to predict if a liquid ( 24 ) is present in said piping ( 12 ) during said measurement, wherein said measurement of the respective flow velocities is repeated at a predetermined frequency and for a predetermined time period, to form a mean flow velocity and a statistical spread for each measurement path ( 30 ), wherein said statistical spread is correlated to a turbulence present in said measurement path ( 30 ), wherein a turbulence ratio is formed by dividing a sum of said turbulences measured for each measurement path ( 30 ) arranged in said lower region by a sum of said turbulences measured for each measurement path ( 30 ) arranged in said upper region, and wherein a velocity ratio is formed by dividing a sum of said mean flow velocities measured for each measurement path ( 30 ) arranged in said upper region by a sum of said mean flow velocities measured for each measurement path ( 30 ) arranged in said lower region, and wherein a liquid factor (S 2 ; S 4 ; S 6 ) is calculated by multiplying said velocity ratio by said turbulence ratio.