Puritan Bennett 840 Service Manual

Theory of operation 2
Puritan Bennett 800 Series Ventilator System Service Manual 2-91
On the 9.4-inch GUI, the touch frame communicates with the GUI CPU PCB via a Carroll-
Touch proprietary interface and operates from +5V and +12V supplies. Two sides of the touch
frame PCB (Figure 2-70) have rows of infrared (IR) LEDs, while their opposite sides have
corresponding rows of phototransistors. Whenever the ventilator is on, the IR touch scanner
interface on the GUI CPU PCB sequentially pulses the LEDs, creating an invisible grid of IR
light beams just in front of the display surface. The phototransistors sense these light beams.
When the screen is touched, the light beams from certain LEDs are obstructed and do not
reach their corresponding phototransistors. The interface constantly monitors the presence,
or in this case the absence, of the IR light beams received by the phototransistors and can
thus determine the X- and Y-coordinates of the touch activation.
On both the 10.4-inch and 9.4-inch GUIs, the touch frame is attached to the face of the
display, where it is concealed behind an IR-transparent bezel (a type of enclosure that is
opaque to the eye, but that allows IR light to pass through).
2.4.8.3 Keyboard assembly with knob
A membrane keyboard assembly (Figure 2-71) is attached to the GUI CPU PCB. A software
debounce routine protects against unintended multiple keystrokes.
The multiposition knob assembly, which is part of the keyboard assembly, permits ventilator
setting selections or changes. Knob encoder/decoder circuitry on the GUI CPU PCB
determines the direction and position of the shaft based on encoder outputs.

Puritan Bennett 840 Specifications

General

Type	Ventilator
Flow Rate	Up to 180 L/min
Power Requirements	100-240 VAC, 50/60 Hz
Display	Color LCD Touchscreen
Category	Critical Care
Manufacturer	Medtronic
Model	840
Operating Modes	Assist/Control, SIMV, Spontaneous, BiLevel
FiO2 Range	21 to 100%
PEEP/CPAP Range	0-45 cmH2O
Alarms	High/Low Pressure, High/Low Volume, Apnea, High Respiratory Rate
Power Source	AC Power
Data Connectivity	RS-232
Compliance	ISO 80601-2-12