The Time Delta S is a fixed ultrasonic flow meter based on the transit time measurement method for measuring flow rates of relatively clean homogeneous liquids utilizing clamp-on sensors. Thanks to microprocessor based electronics, the flow meter can be easily configured from the front keyboard to particular applications. The Time Delta S is ideally suited for liquid flow measurement for pipe diameters from 0.50 to 235 inches. Systems are composed of a converter and sensor set. Applications include flow measurement of any fluid through which an ultrasonic signal may be transmitted, including those of unknown sound velocities. The flow meter is a compact and lightweight instrument incorporating the latest electronics and high speed digital signal processing technologies (32 bit MPU), resulting in high performance and easy operation.