A measuring system, embodied as a clamp-on, ultrasonic, flow measuring device, comprises a tube, or a pipe, having a lumen surrounded by a tube, or pipe, wall, which tube or pipe is adapted to guide a volume portion of the fluid in its lumen; an ultrasonic transducer mounted on the tube, or pipe, on an outside of the tube, or pipe, wall facing away from the lumen, and acoustically coupled via the tube, or pipe, wall to fluid guided in the lumen, and adapted to convert a time varying electrical voltage into ultrasonic waves propagating through the tube, or pipe, wall and further through fluid guided in the lumen; an ultrasonic transducer mounted on the tube, or pipe, separated from the ultrasonic transducer on the outside of the tube, or pipe, wall, and acoustically coupled via the tube, or pipe, wall to fluid guided in the lumen, and adapted to receive ultrasonic waves propagating through fluid guided in the lumen, and further through the tube, or pipe, wall and to transduce such into an electrical voltage varying as a function of time; as well as an operating- and measuring electronics adapted to generate, a driver signal for the ultrasonic transducer. The driver signal has a time variable, electrical voltage, for effecting a received signal, of the ultrasonic transducer likewise having an electrical voltage, uB,II, varying as a function of time, in such a manner that both the driver signal, as well as also the received signal, each contain a plurality of spectral signal components, equally as well, in each case, a dominating spectral signal component having a maximum power spectral density, and that a frequency, of the dominating signal component of the driver signal, deviates by a magnitude of no more than |±100 kHz| from a frequency of the dominating signal component of the received signal, and/or by no more than 10% of the frequency of the dominating signal component of the received signal, from such frequency. Furthermore, the operating- and measuring electronics is adapted to produce by means of the received signal, at least one measured value for the at least one parameter.