Abstract: Video signal control circuitry for use in a video display system in which a variation in a brightness level of a video display signal causes a corresponding variation in a beam current signal, wherein such video signal control circuitry maintains a controllable video display signal brightness level at a substantially constant average value notwithstanding a variation in the incoming video signal brightness level.

Abstract: A powered controlled acceleration suspension work platform hoist system for raising and lowering a work platform at a predetermined acceleration. The system incorporates several hoists attached to the work platform and in electrical communication with the motor control system. The motor control system is attached to the work platform and is in electrical communication with a constant frequency input power source and the hoist motors. The motor control system controls the acceleration of the work platform as it is raised and lowered by controlling the hoist motors. The controlled acceleration hoist system also includes a platform control system attached to the work platform that is in electrical communication with the motor control system and the hoist motors. Acceleration control is achieved by converting the constant frequency input power to a variable frequency power supply. This may be accomplished through the use of a variable frequency drive(s).

Abstract: A self-erecting suspension platform system having a work platform suspended between a sinistral modular mast and a dextral modular mast by a hoisting system. The modular masts are composed of at least two mast units stacked vertically and attached to one another. Each mast unit has a multifunction rail including a plurality of safety engagement devices and a stabilizer guide device, a unit interconnection device, and a unit assembly guide. The work platform has at least two mast stabilizers that cooperate with the stabilizer guide devices to prevent undesired swaying of the suspended work platform. The work platform has a plurality of platform mast engagers cooperating with at least one of the mast safety engagement devices to releasably lock the platform to the modular mast. The hoisting system includes multiple carriages, hoists, and mast cables. Each carriage receives the associated mast so that the carriage may be conveniently slid up and down the mast.

Abstract: A portable screen with a raising and levelling system for raising a frame of the system containing a vibrating screen away from ground on which the system is positioned and for levelling the frame and vibrating screen for improved operation. A wheel assembly rigidly fixed relative to the frame extends from the frame at a first end wall where a first raising and levelling assembly is provided. At an opposite end wall of the frame, a second raising and levelling system is provided. First and second shedding roofs are respectively positioned over the wheel assembly and first and second hydraulic raising and levelling assemblies. With the portable screen having a raising and levelling system as disclosed, the system may be operated on sloping ground and/or ground having undulations and other protrubances.