d. Position Sensing. The SFD uses a combination of a Hall effect and three
opto-electronic (opto-interrupter) sensors in the chassis. Additionally, the power-assist
handle uses opto-interrupters (two each) at each end. The chassis-mounted sensors
are used for internal interlocking, while the handle-mounted sensors are used to control
external power assists for spot-film device vertical and tower horizontal motion. Since
both types of sensor, which can be considered functionally equivalent to switches,
involve no contact with moving parts, reliability is greatly enhanced over miniature
snap-action switches. Consequently, failures are extremely rare and, when the
functions are understood, quickly diagnosed.
e. Adjustment of Chassis Sensors. Figure 1-3 below shows the locations of
the chassis-mounted sensors, their functions, and the connection points on the interface
Figure 1-3. Chassis sensor locations.