P.c.b. Lp 634 Output Board; Description - Fresenius Medical Care 4008 E Technical Manual

8.14

P.C.B. LP 634 Output board

8.14.1

Description

Address decoding (circuit diagram 1/9)
The binary code applied to the address inputs is decoded via IC 14. It energizes the respective
latches via the enable line 1-11 and 14 and the D-A converter (IC 53) via pin 13.
Eight output voltages within a range from 0 to 5 V are delivered by the D-A converter. Out1 and
Out 5 are amplified to a factor of 2 via OP27 and OP36 respectively. The 5-V reference voltage for
the D-A converter is delivered by IC 27, pin 1.
Degassing pump control (circuit diagram 2/9)
Via the ST-EP control line at IC 8, which is used to compensate mass distortions, the rated
voltage for the degassing pump is directed to the control input of the PWM module IC 50, pin 2.
Via voltage dividers R100 and R97, the output voltage for the degassing pump is directed to the
input of amplifier IC 50, pin 1, where it is compared with the rated voltage. The resultant signal
controls the duration for starting the power transistor T4.
The output current is measured at the variable 0.1-ohm multiplier R110, resulting in a maximum
current of 2 A.
Flow pump control and end position recognition (circuit diagram 3/9)
Speed control:
The dialysate flow is adjusted by means of a speed-controlled gear pump.
Via the ST-FP control line at IC 8, which is used to compensate mass distortions, the rated
voltage for the flow pump is directed to the control input of the PWM module IC 38, pin 2.
Via voltage dividers R68 and R67, the output voltage for the flow pump is directed to the input of
amplifier IC 38, pin 1, where it is compared with the rated voltage. The resultant signal controls
the duration for starting the power transistor T1.
The output current is measured at the variable 0.1-ohm multiplier R70, resulting in a maximum
current of 2 A.
End position recognition:
As soon as the balancing chamber is filled on the drain side, the dialysate flow is stopped. This
leads to an increase in pressure which, in turn, causes a current increase in the motor of the gear
pump and is measured at R70.
The motor current is amplified via OP32, pins 6 and 7, and is filtered by collector frequencies by
means of C31, C44, and C32.
The motor current is differentiated via C51, R42, and OP32. This differentiated current pulse is
shaped into a square-wave signal by Schmitt trigger OP32.
The signal, which is depending upon the current increase, is available at the output of the
differentiating network C38 and R33.
Fresenius Medical Care 4008 4/09.03 (TM)
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