Ultrasonic flow meter compensating for a measurement drift due to ageing transducers by adjusting the measurement trip based on a compensation trip time

A method of measuring a speed of a fluid, the method being performed by an ultrasonic fluid meter having a duct, two transducers, two reflector mirrors positioned between the two transducers, and processor means, the measurement method comprising measurement stages, each comprising measurement steps, during which:

• one of the two transducers emits an ultrasound measurement signal;
• the other one of the two transducers receives the ultrasound measurement signal after it has traveled along a measurement path;
• the processor means evaluate the speed of the fluid as a function of a measured time of flight taken by the ultrasound measurement signal to travel along the measurement path;
• the measurement method further comprising compensation stages, each comprising compensation steps, during which:
• one of the two transducers emits an ultrasound compensation signal;
• the one of the two transducers receives the ultrasound compensation signal after it has traveled along a compensation path during which it is reflected by one of the two reflector mirrors;
• the processor means compensate any measurement drift of the one of the two transducer by adjusting the measured time of flight as a function of a compensation time of flight taken by the ultrasound compensation signal to travel along the compensation path,
• wherein each of the two transducers and the two reflector mirror is annular in shape and fits closely to an inside wall of the duct.