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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.)
11
To CPU
CV Tachometer
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.)
CHRISTIE INC. - 35/70 Service/PM Manual
CHRISTIE INC. -
July, 1997
U34
Optical Sensor
COMP
U32
SUMMING
AMP
AMP
Figure 5.8: Upper Reel Motor Control Circuit
5 : T h e o r y o f O p e r a t i o n
Tachometer
ABS VAL
AMP
Current Limiting
U25A
U25B/U26
29
26
Sawtooth
U39
COMP
E
T
U40
PWM
Signal
2285
27
COMP
Direction
28
Film
M
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