Mindray Passport 5-Lead, Руководство по обслуживанию

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Block Diagrams Theory of Operation
2 - 62 0070-00-0420 Passport 5-Lead, 5L, LT, XG Service Manual
The dump valve is controlled by the DVEN signal. This signal drives MOSFET Q1, which
switches the valve coil voltage. This is a normally vented valve, meaning that air flow occurs
from the manifold to the atmosphere while blocking the pump when the coil is de-energized.
This corresponds to a logic low on the DVEN signal. Should an overpressure condition occur,
the valve defaults to the vented state. The DVEN signal is gated in U3 to protect against a
single fault failure which would cause the dump valve to remain in the energized (non-vented)
state. In order for the dump valve to be energized, two dump valve enable signals must
agree. One signal is generated by the microprocessor on the companion control board, and
the other from microcontroller U1 on the pneumatics board.
The overpressure circuitry identifies two separate patient types; adult and neonatal. The
neonatal mode is inferred from the existing conditions during pump-up. If the motor is running
and a valve is open, then the neonatal mode is identified and NEO is set low by U1. The
over pressure comparator in U6 compares the output of the overpressure transducer with the
output of a voltage divider. If the pressure transducer voltage is higher than the output of the
voltage divider, OPS is brought low. A single overpressure trip point can be exactly
calibrated by adjusting potentiometer R1, presumably the neonatal point. This reduces any
error caused by resistor tolerances and inexact transducer readings. NEO is compared to a
threshold by a second comparator in U6, and if low, resisterR15 is shunted across resistor
R25. This reduces the effective resistance in the grounded resistor in the voltage divider,
causing a lower overpressure trip point in the neonatal mode.
FIGURE 2-27 Linear Bleed Block Diagram