Fresenius Medical Care 4008 E Technical Manual page 317

Clamp control
The clamp magnet can be controlled via transistor T13. This method is used for turn-off in case of
all blood alarms and for single needle control. If an H level is applied to the CLAMP-CTRL signal
at pin 8 of plug X351, the output voltage at pin 7 of OP IC 19, which is connected as integrator,
drops linearly. Should this voltage fall below the reference voltage at pin 3 of IC 19, the output pin
1 turns to H level and controls T13 via T7. This delayed opening of the clamp magnet is
coordinated with the starting delay of the blood pump and requisite for a trouble-free single
needle operation. If the CLAMP-CTRL signal turns to L level, the integrator is rapidly recharged
again via DI12 and R86, and the venous line clamp is actually closing without delay.
Pulse generation
Timer IC 11 is connected as astable multivibrator. It generates a symmetrical square-wave
frequency of approx. 2.8 kHz, which is divided by the binary divider IC 10. 90 Hz are available at
pin 3 for energizing the infrared emitter of the optical detector. The unbalanced square-wave
voltage for energizing the ultrasonic transmitter (90 ms L level, 0.2 ms H level) is generated via
the flip-flop IC 9.
Visual section
The infrared emitter of the optical detector is energized by pin 3 of IC 10 at a frequency of 90 Hz
via transistors T10 and T11. The phototransistor on the opposite side of the optical sensor
absorbs the modulated light and controls IC 14, which is connected as current-voltage converter,
at pin 6. A square-wave voltage, whose amplitude is proportional to the transparency of the
medium in the optical sensor, is applied to pin 7 of IC 14. This voltage reaches pin 3 of comparator
IC 14 via voltage divider R65 and R66. If the positive half waves exceed the reference level at pin
2 of IC 14, a square-wave voltage is delivered by output pin 1; otherwise, the output is provided
with L potential. Via pin 5 of plug X351, the square-wave voltage is delivered to the monitor,
where it is used to generate a logic level.
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Fresenius Medical Care 4008 4/09.03 (TM)