A system for detecting the presence of bubbles in a solution includes an ultrasonic receiver, receiving a pair of signals having different frequencies after passage through the solution, and a computing unit. The computing unit computes a signal value for each of the signals, the signal value representing a defined signal property, compares the signal values for the signals with each other and/or each with a predefined reference value, and computes a deviation of the signal values from each other and/or between the signal values and the predefined reference value. The computing unit generates a bubble confirmation signal that confirms the presence of bubbles in the solution if the deviation is greater than a predefined threshold value.