Fresenius Medical Care 4008 E Technical Manual page 365

Analog and digital outputs (circuit diagram 5/6)
The analog outputs are required for detuning the sensors during the test generation. The digital-
to-analog converter IC11 (AD7226) is provided with four analog outputs. During the test,
channels C and D are switched onto the sensor lines via analog switches (IC 20, CD40066). The
analog switches are activated via level converters (IC 32, 4505). During hemodialysis, channel C
is additionally used to adjust the working point of the high-resolution dialysate pressure amplifier
(IC 3, LM324N). Channels A and B of the D-A converter simultaneously serve to generate the
calibration voltages for the temperature display and the dialysate pressure (TMP display).
The 10-V reference voltage is deducted from the temperature-stabilized zener diode IC 28
(ZN458B). IC 3/OP-2 operates as non-inverting amplifier and generates the +10-V reference
voltage for the D-A converter IC11.
Since it might become necessary to activate various peripheral equipment (control signals,
actors, etc.), P.C.B. LP 632 is provided with TTL level outputs IC 24 / 74HC541/74HC574 and IC
30 / 74HC574 as well as with level converters (IC 33, 4504), which generate the 12-V signals. The
IC 29 (UCN2803) with Darlington output stage (max. 600 mA) is used to control actuators (e.g.
solenoid valves V43).
In addition, 8 status LEDs are available, which are switched by the microcontroller via IC 21
(74HC574).
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Fresenius Medical Care 4008 4/09.03 (TM)