Covidien Puritan Bennett 700 Series, Service Manual

Page: 107 / 439

Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual 10070389 Rev. A 2-51
2.3.5 Backup alarm driver
The backup alarm driver circuit, located on the backup alarm driver PCBA contains the
electronics that activate the 700 ventilator backup alarm (Figure 2-24 and Figure 2-37) The
backup alarm circuit provides for 120 seconds of alarm sound in the event of a failure of the
+24V Bus or the +5V Vcc of the breath delivery supply. The backup alarm is independent of
software control during a power loss condition and has its own power source to enable it to
annunciate its alarm. The backup alarm monitors it’s own output and declares a fault to the
BD controller if a fault condition is detected. Also under breath delivery control, the backup
alarm is sounded if a failure of the main alarm is detected. (See note below for fault
conditions that activate the backup alarm). The main alarm is audibly tested during SST and
EST, where the operator must confirm the operation of the alarm or SST will fail removing
the ventilator from service. The backup alarm circuit itself has built in redundancy as the
circuit is replicated twice on the backup alarm driver PCBA.
NOTE:
Fault conditions that activate backup alarm:
• 24V supply line failure
• 5V supply line failure
• main alarm failure
• if the processor enables the back-up alarm either actively or as a result of a processor or
logic circuit error that releases the back-up alarm inhibit signal
2.3.6 Controller PCB
The controller PCB has two sections: the breath delivery (BD) and the user interface (UI)
sections. (See Figure 2-37 for controller PCB installed in ventilator and Figure 2-38 for
controller PCB.) These sections are physically separate, each residing on one half of the PCB.
Each section contains its own microprocessor and external memory. The BD section controls
the electronic and pneumatic components that ventilate the patient. The
UI section reads and
interprets information from the operator via the keypad, knob and displays; it also monitors
the BD. Both sections communicate continuously with each other.
The BD section includes these circuits, which perform the indicated functions:
• The CPU section includes a Motorola 68HC16 microcontroller , which operates at 16 MHz.
(The microcontroller chip contains a microprocessor, clock, internal watchdog, memory, an
I/O interface, and A/D converter.) Two EPROMs (Figure 2-39) totaling up to 512 KB contain
the software for the BD section. These plug into the PCB and must be retained with the
ventilator when a replacement controller PCB is installed. 64 KB of RAM is used for
ongoing calculations and data storage.
• The motor controller circuit is a special-purpose chipset that monitors the position of the
motor shaft and controls the motor drive circuitry on the BBU PCB.
• I/O registers allow monitoring and control of solenoids, optoswitches, and audible
alarms.
• The ventilator inoperative circuit invokes the safety valve open (SVO) condition and
generates audible/visual alarms in the event of a catastrophic failure.
• The external watchdog circuit monitors for safe CPU operation.
• The optoswitch circuit provides interfacing for the optoswitches.