Ultrasonic Flow Meter

A method for determining an absolute transit time of an ultrasonic signal in an ultrasonic flow meter having a flow path for a fluid to be measured, a first ultrasonic transducer having a first characteristic quantity and a second ultrasonic transducer having a second characteristic quantity, said method comprising the steps of repeatedly:

• measuring the first characteristic quantity of the first ultrasonic transducer;
• measuring the second characteristic quantity of the second ultrasonic transducer;
• determining a simulation model of the flow meter based on the measured first characteristic quantity and the measured second characteristic quantity;
• and
• calculating the absolute transit time of an ultrasonic signal in the flow path using the simulation model in the calculation of the absolute transit time;
• the method further including reducing a phase error in the calculated absolute transit time by the steps of:
• determining a relation between the first characteristic quantity and the second characteristic quantity;
• estimating a phase error value indicative of the phase error from the determined relation between the first characteristic quantity and the second characteristic quantity;
• and
• correcting, based on the estimated phase error value, a difference between absolute transit times measured by the ultrasonic flow meter.

A method for determining a time delay of an ultrasonic signal in an ultrasonic flow meter having a flow path for a fluid to be measured, a first ultrasonic transducer and a second ultrasonic transducer, said method comprising the steps of repeatedly:

• characterizing the first and second ultrasonic transducers by determining characteristic quantities, such as an angular frequency wD and a damping coefficient a of dampened oscillations of the transducers;
• using the determined characteristic quantities of the transducers for finding an equivalence model of the transducers and establishing a numerical simulation model of the transducers and one of
• an electronic circuit of a signal generator,
• a receiver circuit of the flow meter, and
• an electronic circuit of a signal generator and a receiver circuit of the flow meter;
• simulating the flow meter system by entering an input signal function or a sampled version of a physical transmission signal reaching the first transducer into the numerical simulation model, thereby obtaining a simulation model response corresponding to an output signal from the receiver circuit as it would be according to the model, if there was no time delay in a transmission of an ultrasonic signal between the two transducers,
• recording a physical flow meter response actually received by the receiver circuit, and
• calculating an absolute transit time by determining a time delay of the physical flow meter response as compared to the simulation model response;
• the method further including reducing a phase error in the calculated absolute transit time by the steps of:
• determining a relation between the first characteristic quantity and the second characteristic quantity;
• estimating a phase error value indicative of said phase error from the determined relation between the first characteristic quantity and the second characteristic quantity;
• and
• correcting, based on the estimated phase error value, a difference between absolute transit times measured by the ultrasonic flow meter.

An ultrasonic flow meter comprising a flow path for a fluid;

• a first ultrasonic transducer having a first characteristic quantity;
• a second ultrasonic transducer having a second characteristic quantity;
• a measuring arrangement for repeatedly measuring the first characteristic quantity and the second characteristic quantity;
• a transmission time measuring arrangement for repeatedly measuring transmission times between the two ultrasonic transducers
• a phase error reduction arrangement arranged to repeatedly determine a relation between the measured first characteristic quantity and the measured second characteristic quantity, estimate a phase error value indicative of a phase error from the determined relation between the first characteristic quantity and the second characteristic quantity and correcting, based on the estimated phase error value, a difference between the measured transmission times between the two ultrasonic transducers;
• and
• a signal processing unit for repeatedly providing an output indicative of the flow rate in the flow path from the corrected difference between the measured transmission times.

A method of reducing a phase error of a flow rate measurement in an ultrasonic flow meter having a flow path for a fluid to be measured, a first ultrasonic transducer having a characteristic quantity and a second ultrasonic transducer having a second characteristic quantity, said method comprising the steps of repeatedly:

• measuring the first characteristic quantity of the first ultrasonic transducer;
• measuring the second characteristic quantity of the second ultrasonic transducer;
• determining a relation between the first characteristic quantity and the second characteristic quantity;
• estimating a phase error value indicative of the phase error from the determined relation between the first characteristic quantity and the second characteristic quantity;
• correcting, based on the estimated phase error value, transmission times measured by the ultrasonic flow meter;
• and
• providing an output indicative of the flow rate of the fluid in the flow path with reduced phase error from the corrected transmission times.