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For those of you interested in some technical details, here is additional
information. When the semaphore signal is in the red/stop position, the slot arm mechanism is in the down position and no voltage is present on the control signal or on the motor or coils. When the control voltage is applied (by the control relays), a voltage is applied to the solenoid slot coil and motor causing the motor to start operating. As the motor turns, the chain operates and moves rollers attached. As a roller moves around, it catches the slot fork mechanism, raising the slot arm and moving the mechanism to green/clear. As the arm nears the upper position, it is latched by the solenoid and opens a set of switch contacts. This removes power from the motor and pull-in winding of the solenoid slot coil but leaves power to the low current holding coil. This low current is enough to keep the solenoid energized and hold the slot arm in the upper locked position. The slot arm mechanism is now in the "up" position with the signal in the green/clear position and a control voltage continuously applied to the signal. When it is desired to return the slot arm to the "down" position indicating red/stop, the control voltage is removed. This allows the solenoid slot coil armature to fall away from the coil and unlock the linkage that holds the slot mechanism in the latch. Gravity then causes the slot arm mechanism to fall, which returns the signal via the operating rods to the red/stop position. The descent speed of the mechanism is controlled via linkage to a piston in the buffer cylinder (upper right in photos). The buffer cylinder has an adjustable screw, which allows the air to escape at a prescribed rate varying the descent of the mechanism. ********************************************************************** |