Abstract: A control circuit for controlling the voltage supply to selected ones of a plurality of output terminals to which controllable devices are connected to is described. The control circuit comprises manually operable function switches which are connected to an integrated circuit providing output logic signals to feed an interlock circuit to select the operation of one or more of a plurality of high voltage electronic switching devices. An interface circuit is connected between the switching devices and the interlock circuit to trigger the operation of selected switching devices to connect a high voltage supply to associated ones of the output terminals. The interface circuit also prevents feedback voltage surges from the one or more switching devices to protect electronic circuits in the control circuit.

Abstract: In the measurement of the permeability of a filter medium a cake of the medium is formed in a holder by supplying an excess of the medium, as a suspension under pressure, to the holder, the pressure being relieved and the excess portion being removed to leave an undried cake of medium when the excess portion has dried to a given level as sensed by a pair of electrodes. Two further electrodes are used to determine the time for a given volume of liquid to pass through the cake for measuring its permeability.