The invention relates to a device (100) having multiple capacitively working channels, wherein the device (100) comprises a advancable sensor (3.1, 3.2) and a fluid container per channel. The device (100) also comprises a generator (G) for providing a periodic input signal (s,in(t)). In addition, the device (100) comprises one compensation circuit (CT.1, CT.2) per channel, which can be supplied with the periodic input signal (Sin(t)) and which is designed to provide an input signal (Sin1(t), Sin2(t)) at a first output (A.1, A.2) for applying to the sensor (3.1, 3.2) of the channel, wherein the compensation circuit (CT.1, CT.2) comprises a further output (6.1, 6.2) which is designed to provide a signal (s1(t), s2(t)) that can be evaluated to detect a phase boundary.