This thesis deals with the analysis of the reliability and metrological stability of the FlowTracker2 ultrasonic meter under laboratory conditions. The work directly follows on from previous research carried out as part of the author's bachelor's thesis and expands on it with long-term monitoring of metrological characteristics and a completely new experiment focused on the influence of the concentration of reflective particles on measurement accuracy. The theoretical part of the thesis provides an overview of current methods for measuring point velocities and flows in open profiles. It includes a review of global knowledge on the influence of environmental reflectivity on acoustic signal quality, particularly with regard to the SNR parameter. The practical part was carried out on a laboratory test track. The first phase of the experiment focused on the statistical evaluation of the intermediate precision and stability of the measuring device over time, which made it possible to assess its metrological development over a period of 28 months. The second phase focused on simulating the effect of the concentration of reflective particles in water on measurement accuracy. The results of the work should contribute to a deeper understanding of the influence of the time factor on the metrological properties of the ultrasonic measuring device and to an understanding of the importance of monitoring the conditions under which the measurement is performed.