Design of the Optical Module
DSX™ System Service Manual 10-5
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STEPPER MOTOR DRIVE SYSTEM – The stepper motor drive system consists of
two UDN 2916 bipolar stepper motor controllers (Allegro Microsystems). The stepper
motor drivers maintain a constant current through the motor windings using a pulse
width modulation technique. The current to the motors can be reduced, under software
control, when the motors are stationary. This reduces the heating in both the driver
chips and the motors, which reduces the load on the 12V-power supply.
The system acts in Master/Slave Mode with respect to the personal computer. When the
system is powered up, the following tests are performed:
FILTER MOTOR TEST OPTION – This option is responsible for verifying the
functionality of the filter motor and the filter wheel home sensor. This will be
accomplished by rotating the filter wheel at least one complete rotation and checking
the filter wheel index position.
BACKGROUND LIGHT LEVEL TEST OPTION – This option is responsible for
verifying the light tight soundness of the AM Module and the accuracy of the plate
carrier dark read position. This will be accomplished by turning the lamp off,
verifying that all 12 photodiodes read between 520,000 < counts < 525,000, turning
the lamp on, moving the plate carrier into the dark read position and verifying that all
12 photodiodes read between 520,000 < counts < 525,000.
LAMP VOLTAGE TEST OPTION – This option is responsible for verifying the
functionality of the lamp. It is accomplished by turning the lamp on and reading the
voltage drop across the lamp.
LAMP MARGIN TEST OPTION – This option is responsible for verifying that the
system will perform under degraded power conditions. This is accomplished by
moving to the filter 1 position and adjusting the lamp duty cycle to maximum and
ensuring the minimum channel reads above 200,000 counts.
LAMP CALIBRATION TEST OPTION – This option is responsible for calibrating
the lamp duty cycle at each installed filter wavelength. This is accomplished by
assigning all lamp duty cycles an arbitrary number moving to each installed filter
position and adjusting the lamp duty cycle until the minimum channel reads 170,000
counts above the dark reading and the maximum channel reads less than 275,000
counts above the dark reading.
EEPROM TEST OPTION – This option is responsible for verifying the
functionality of the EEPROM. This is accomplished by reading the entire EEPROM
and comparing the data to the EEPROM mirror values.
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