5 : T h e o r y o f O p e r a t i o n
CHRISTIE INC. -
CHRISTIE INC. - 35/70 Service/PM Manual
July, 1997
T h e R e e l i n g S y s t e m C i r c u i t r y
The major components of the upper reeling circuit are the upper reel motor and brake, the tacho-roller, and the upper
torque arm with its optical potentiometer. The major electronic components are the Supply PWM Amplifier (2285) and
the Supply Reel Control circuitry on the Main Electronics Board. (See Figure 5.8.)
M
U25A
U40
T
E
2285
Signal
PWM
AMP
U32
Film
Tachometer
Optical Sensor
11
SUMMING
AMP
29
26
Current Limiting
27
U39
28
COMP
Direction
CV Tachometer
To CPU
U34
COMP
ABS VAL
AMP
U25B/U26
Sawtooth
COMP
Figure 5.8: Upper Reel Motor Control Circuit
The reel motor control is accomplished by comparing the speed of a film-driven Tacho-roller with the voltage from the
constant-velocity tachometer using summing amplifier U25A. In addition, the upper torque arm position, sensed by an
optical pot, feeds into the summing amplifier. As the voltage becomes more negative, more torque is applied in the take-
up direction. The circuit is biased in such a manner that the input signal from the optical pot will be zero volts when the
torque arm is at normal position, independent of speed.
The output of U25A goes to an absolute value circuit, formed by U25B and U26, where it is converted to a PWM signal
by U40. U40 compares the analog voltage to the output of the sawtooth generator, as is done by U42 for the shutter.
U25A also goes to a comparator, U39, which determines the polarity of U25A and outputs a direction signal to the upper
torque power amplifier. The current limiting signal from the power amplifier turn on the photocoupler, U41, which limits
the voltage sent to the pulse width modulator, U40.
The Optical Sensor is also monitored by the CPU using comparator U34. Transistor Q9 turns off the drive to the reel
motor in the Platter mode of operation.
The lower torque circuit is similar to the upper. The major components of the lower reeling circuit are the lower reel
motor and brake, the tacho-roller, and the lower torque arm with its optical potentiometer. The major electronic
components are the PWM Amplifier and the Reel Control circuitry on the Main Electronics Board. (See Figure 5.9.)
