Revision C 170 Series Monitor 5-39
2000947-004
Theory of Operation: FECG/IUP Board Theory of Operation
ground on the non-floating side of the barrier. It is then sensed by the system
microprocessor.
The IUP enable ties resistor R97 to the floating ground when the IUP transducer
cable is attached. This causes approximately 4.5 mA to flow in the LED of opto-
coupler U17. The current transfer function of the coupler is 19% typically which
causes 860 µA to flow in the photo-transistor of U17 in turn causing R104 to be
pulled to ground on the non-floating side of the barrier. It is then sensed by the
system microprocessor. The tocotransducer enable ties resistor R100 to the floating
ground when the IUP transducer cable is attached. This causes approximately 4.5
mA to flow in the LED of opto-coupler U17. The current transfer function of the
coupler is 19% typically which causes 860 µA to flow in the photo-transistor of
U17in turn causing R105 to be pulled to ground on the non-floating side of the
barrier. It is then sensed by the system microprocessor.
For a Model 174 only, the ultrasound enable ties resistor R109 to the RL when the
ultrasound cable is attached. This causes approximately 4.5 mA to flow in the LED
of opto-coupler U17. The current transfer function of the coupler is 19% typically
which causes 860 µA to flow in the photo-transistor of U17 in turn causing P16 (pin
6) to be pulled to ground on the non-floating side of the barrier. It is then sensed by
the system microprocessor. In summary, the US1 enable isolated one channel of US
from the Main Board along with a mode enable from the FECG/IUP Board.
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