Fresenius Medical Care 4008 4/09.03 (TM) 8-35
8.9 P.C.B. LP 624 Control board (BP)
8.9.1 Description
● General information
This printed circuit board comprises both the control and the power part.
Plug connections on P.C.B. LP 624:
– X186, connection to the position sensor
– X188, connection to the stepper motor
– X189, connection to P.C.B. LP 748
– X190, connection to the lid switch
– X192, connection to the pressure transducer
– X348, connection to the dialysis monitor
Hex switches on P.C.B. LP 624:
0 Arterial blood pump
1 Single needle blood pump
2 – A Without function
B Adjustment of BP stop alarm (15 or 30 sec)
C Without function
D Inquiry of time meter (display x 100 = number of hours)
E Test operation (for the manufacturer only)
F Calibration of pressure transducer
● Voltage generation
Both the +24-V and the +12-V voltage supply are made available to the blood pump by the
monitor. From the +24-V voltage, the +5-V supply voltage is generated on the module by the
switching regulator IC 20, in order to minimize the dissipated power.
● Stepper motor activation
For noise reduction purposes, the stepper motor is operated in the microstep mode. Resolution
amounts to 60 microsteps per step. The RISC processor alternately transmits an 8-bit dataword
to pins 3 and 5 of the two D-A converters of IC 7. At the output of the converters, two sine-wave
voltages are available, which are phase-shifted by 90 degrees. Together with the current
direction signals, these voltages are supplied to the stepper motor controller IC 2. Together with
the two SM drivers IC 1/IC 22 and the current sensor resistors R58/R59, IC 2, as feedback, forms
a closed control loop, which impresses two sine-wave currents (phase-shifted by 90 degrees) in
the two windings of the SM.
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