Mindray Passport 5-Lead, Service Manual

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Passport 5-Lead, 5L, LT, XG Service Manual 0070-00-0420 2 - 61
Theory of Operation Block Diagrams
Pneumatic and Miscellaneous Control
The five MSB’s of I/O port 1 of the 80C196 are used to control the air valves. All the valves
are of the normally open type. In case of loss of power, the valves will open VALVE0 is the
dump valve, which lets air out of the cuff when the measurement is complete. VALVE1,
VALVE2, VALVE3, and an optional VALVE4 controls valves that have different orifice
openings. They are used to control the bleed rate of the pressure in the cuff during a
measurement. The valve control signals are buffered by U15, an ULN2003. U21D
implements an optional linear valve driver that is driven by channel A of U9, the AD7226
quad DAC. It is currently not used.
The pump is controlled by a pulse width modulated output from bit 1 of the high speed out
put section of the 80C196 (U5 pin 29). In adult mode, the pump runs at full speed; in
neonate mode, the pump is pulse width modulated to moderate the pump speed. The pump
signal is active high and the high speed outputs reset to a zero state. On power-up, the pump
is turned off.
An overpressure switch will close when the pressure in the cuff is 375 mmHg +/-5%. This will
set the latch implemented by U17A and U17B which cause the OVPR signal to go high. This,
in turn, will force VALVE 0 to open and the pump to stop. This condition can only be reset by
resetting the entire module. This is done by power-cycling the unit.
Pneumatic and Miscellaneous Control - Linear Bleed
The pneumatics board consists of two valves, and EMI filter and connector for a chassis
mounted pump, an overpressure transducer and detection scheme, and control logic to
operate the linear bleed system. The pump is used to inflate the cuff at the beginning of each
measurement cycle. Inflation pressure is regulated by software monitoring a pressure
transducer located on the companion control board. In the event of a runaway condition of
the pump, the patient size sensitive overpressure circuitry will completely open the linear
valve and close the dump valve, fully venting the cuff while at the same time blocking the
pump from further inflating the manifold. At the onset of the actual measurement phase, the
bleed valve (V2) opens to provide a gradual reduction of the cuff pressure. This is a so-called
proportional solenoid valve. Rather than providing only “on-off” control, it can be opened to
a variable degree, in proportion to the current flowing in the valve coil. Note that this valve is
a normally closed type; coil current must be supplied to cause the valve to open. A servo
control loop maintains the pressure bleed down rate at a nominal 6 mmHg per second,
regardless of the cuff pressure or system volume. During the measurement phase, the
pressure signal acquired by the transducer on the control board is processed to extract the
oscillometric blood pressure data. At the conclusion of the measurement phase, the dump
valve (V1) is opened, in addition to the bleed valve, to rapidly exhaust the residual cuff
pressure.
The pump control is provided by the MOTOR signal, generated on the companion control
board and routed to the pneumatic board through connector J30. Power to the motor is
supplied by means of a decoupling network L2/C12 from the host’s +12 volt bus. A common
mode coil, L1, provides further attenuation of the motor brush noise.