An ultrasonic flow meter is a type of a flow meter that measures the velocity of a fluid with ultrasound enabling it to calculate the volume flow. Using ultrasonic transducers, which convert a signal in one form of energy to another form of energy, the flow meter can measure the average velocity along the path of an emitted beam of an ultrasound, by averaging the difference in measured transit time between the pulses of ultrasound propagating into and against the direction of the flow or by measuring the frequency shift from the theory of the Doppler effect, which works the same way as a moving car with a siren.