Abstract: The state of operability of a circuit having at least one group of condition responsive monitoring switches, the switches having first terminals connected to an input signal source and output terminals connected to an evaluation unit, is monitored by periodically interrupting the connection between at least one of the condition responsive switches of each group and the evaluation unit. The evaluation unit compares the change in potential at the output terminal of the one switch, resulting from the interruption, with the potential at the output terminal of another switch.

Abstract: In order to make it possible to empty in particular, large containers with a crew of just one person, an emptying device with a tilting/lifting device 1 and a control unit 4 is described to which a trigger switch 2 is connected which is actuated by the container to be emptied as it approaches the lifting/tilting device and which triggers the raising phase of the lifting/tilting process automatically. When a preset raised level of the lifting/tilting device is reached the control unit interrupts the raising phase. In addition, a first manual actuator 8 to trigger the automatic emptying process, which actuator has an effect upon the control unit 4 only after the interruption of the lifting process, is connected to the control unit. The control unit 4 contains a programmable device 5 into which the preset raised level can be inputted.