Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual
10070389 Rev. A
2-49
• The
PEEP drive circuit
sends a pulse-width modulated signal to control the output of the
PEEP pump.
• The
thermistor/interface circuit
includes an onboard thermistor that senses internal
ventilator compartment temperature. It provides supporting circuitry for it and these
additional offboard thermistors: exhalation (2 inputs), inspiration, and air flow (2 inputs).
• The
safety valve circuit
de-energizes the safety valve solenoid if the cylinder or exhalation
(patient) pressure exceeds 115 cmH
2
O, which opens the safety valve to atmosphere. This
circuit provides redundancy for the software. (The safety valve is opened under software
control at 92 cmH
2
O cylinder pressure and in other circumstances.)
• The
fan circuit
detects an open circuit to the main fan or a stalled fan condition. The fan
must always be on when the unit is ventilating.
• The
heater circuit
controls the exhalation heaters. The heaters’ temperature is maintained
at approximately 50 °C. A thermistor in contact with one of the heaters provides feedback
used to control the heater’s temperature. The second thermistor serves as a backup
monitor.
• The
tachometer circuit
measures the piston velocity.
•
LEDs
on the PCB permit monitoring of these lines:
– Local voltages (+5V ON, +15V ON, and -15V ON) (constant LEDs)
– Exhalation heater (MANIFOLD HEAT ON) (flashing LED with varying duty cycle)
– Flow sensor pressure transducer heater (for temperature compensation) (TRANS HEAT
ON) (flashing LED with varying duty cycle)
• The
voltage monitor test connector (J2) can be used to check these local voltages: +1.2 V,
+5 V, UI-5V, +15 V, -15 V, and +24 V.
Summary of Contents for Puritan Bennett 700 Series
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