Theory of operation
2-66
10070389 Rev. A
Puritan Bennett™ 700 Series Ventilator System Service Manual
2.6.1 Piston initialization
During POST, the piston is initialized to determine its position; it is important the ventilator
know the piston’s position before breath delivery begins. (See Figure 2-55). To initialize the
piston, the ventilator drives the piston forward until the flag on the rack intercepts the end
optoswitch. Then the piston is retracted until the flag intercepts the home optoswitch. Based
on the number of quadrature counts (“quad counts”) tallied by the motor controller circuit,
the magnitude of the cylinder’s stroke is determined. Now the piston is ready to deliver
breaths.
The actual number of encoder counts between optoswitches is stored in NVRAM. The number
counted during POST is compared with this number. If the counts measured during POST are
within limits, POST passes; otherwise, POST fails.
Figure 2-55. Piston initialization
7-00166
Piston is driven forward until rack
flag intercepts end optoswitch
Piston is retracted until rack flag
intercepts home optoswitch
Piston moves forward a short
distance to be safely within
piston’s ventilating range
Rack
flag
Rack
flag
Rack
flag
Operating
range
Home
optoswitch
End
optoswitch
Home
optoswitch
End
optoswitch
Home
optoswitch
End
optoswitch
Summary of Contents for Puritan Bennett 700 Series
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