Electrical System with TX and TT Card
PS
S5.0
5000
F-code
Section
C-code
Version no
T-code
001
OE35
© BT Products
137
Service Manual
1997-10-23
4. Control Features
4.1. Oscillator
The oscillator section of the card has two adjustable features
and one fixed feature. With the accelerator potentiometer at
maximum ohms, the creep speed can be adjusted by the
handset unit. Top speed is fixed by card and is obtained with
the accelerator potentiometer at minimum ohms. The % ON
time has a range of approximately 5 to 95 percent. The center
operating condition of the oscillator is at 50 percent ON time
with a nominal 1.8 milliseconds ON time and 1.8 millisecond
OFF time. This corresponds to a maximum operating
frequency of about 300 hertz. At creep the ON time will
decrease to approximately 0.8 milliseconds while OFF time
will become in the order of 20 milliseconds. At full SCR
operation, this condition will be reversed (short OFF time,
long ON time). This variation of ON and OFF time of the
oscillator produces the optimum frequencies through the SCR
range. The frequency curve of the oscillator is shown above.
The rate at which the oscillator may increase its percent ON
time is limited by “Controlled Acceleration”. The minimum
time required to go from creep speed to 80-85% on time point
may be varied by function 3, adjustable from approximately
0.1 seconds to 22.0 seconds.
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