Vinten Radamec SP-2000 Pedestal - Manual (Page 100)

SP-2000/X-Y Maintenance And Repair
4-34 User Manual
The Targeting System
The targeting system in the pedestal consists primarily of the Dolly Board and
the three sensors. If the controller is operating normally, the cables are ok and
the target itself is clean, a failure to target is likely to be caused by a problem in
the sensors (cleaning or calibration) or the Dolly Board.
Lowering The Sensors
In normal operation, the Dolly Board supplies +24V to the three chassis
mounted solenoids. Targeting is initiated by an active low signal from the Dolly
Board to energize the solenoids and drop the sensors.
Each solenoid operates an arm to lower the respective sensor assembly onto the
target. The arm is counterbalanced so that the arm lower smoothly when the
solenoid is energized and will retract under the force of gravity.
The Sensor Assembly
Each sensor assembly contains three optosensors that generate red and infrared
light and detect the light reflected off the target. The three sensors provide for
redundancy in case of dirt or marks on the target. Each sensor assembly is con-
nected by a cable to the Dolly Board that provides sensor power and detects the
sensor output. The sensor assemblies are somewhat difficult to access, so their
operation is best verified from measurements made on the Dolly Board.
If the sensors are kept clean (as described earlier in this chapter) and the targets
themselves are also kept clean and free from damage such as delamination, there
should be no need for electrical readjustments of the sensor voltage offsets.
The Dolly Board
The Dolly Board performs several functions including local control and target-
ing. When the pedestal is controlled by the MCB controller, the Dolly Board
interprets the local control joystick output and generates the serial data signals
to control the pedestal. The Dolly Board also controls the targeting operation.
U15 and Q22 activate the solenoids which lower the three sensors to read the
target. U19, U20, U21 and U16 interpret the signals from the three optosensors
on each sensor assembly. The three signals from each sensor block are voted to
reduce errors caused by floor dirt. The threshold values on the sensors are
tracked electronically to allow for the slow accumulation of film on the optosen-
sor windows.
The Dolly Board is controlled by microprocessor U9, with ROM (U3), RAM
(U2), and peripheral devices. Basic operation of the microprocessor may be
confirmed by looking for signal activity at pins 26, 27, and 28. The RS-422 data
path section of U15, U27, U28 and associated circuitry manages the rerouting of
data when control is transferred from remote to local. The analog section
including U24, U25 and U17 buffers and measures signals from the joystick on
the MCB controller.