Abstract: A transistorized power switching circuit for controlling the conductive state of a Darlington transistor. The circuit, driven by a single signal driver, operates to switch the Darlington transistor from a conducting state to a nonconducting state as well as from a nonconducting state to a conducting state. The circuit minimizes the number of components in the circuit that introduce time delays in switching the Darlington transistor. To further enhance switching the Darlington transistor from a conducting state to a nonconducting state, a reverse bias is employed to sweep the charge back out through the base of the Darlington transistor rather than permitting the charge to pass through the Darlington transistor then to the load. The reverse bias is maintained on the Darlington transistor for the duration of the off time regardless of the duration of the off period.

Abstract: In a tumbling hammer type rapper (10), a feedback signal is provided via limit switch (30) and cam (28) mounted on rapper shaft (14) to control the rotation of rapper shaft (14) through one revolution. Rapper shaft (14) rotation is monitored to ensure that rapper shaft (14) completes one revolution, returning to the initial position, within a normal predetermined time period. If rapper shaft (14) fails to rotate from the initial position or fails to complete one revolution within the normal predetermined time period, an alarm is energized.

Abstract: An automatic voltage control system controls the firing angle of a solid state switch (20), in turn the voltage applied to the primary winding (12) of a step-up transformer (10), in turn the voltage applied to the grid (38) and in turn the electric field intensity between grid elements (38) in an electrostatic separation process. Two voltage control signals are generated in the control system. The first voltage control signal is a protective control signal generated to maximize the voltage applied to the primary winding under normal operating conditions and to reduce the voltage to zero for a short time period following abnormal operating conditions then to reapply voltage to the primary winding (12) again. The second voltage control signal is a periodic signal of adjustable rate and frequency that functions as a variable upper limit to the magnitude of the first control signal.