In a mixing tank for cream, quark and yogurt, the empty indication is verifi ed by means of a point level switch. Until now, a conductive rod probe was used along with evaluation electronics installed in an external switch cabinet. However, this probe erroneously output a “medium present” signal (full indication) when residual medium in the tank foamed up during cleaning of the tank. This caused the mono pump to switch on, which ran dry after a short period because of the absence of medium in the tank. As a result, the system switched into a malfunctioning state, interrupting the cleaning cycle and requiring a manual restart.