Mechanical Ventilation Switch; Audio Alarm; Manifold Pressures; Front Panel Assembly - Datex-Ohmeda 7900 Service Manual

2/Theory of Operation

Mechanical Ventilation Switch

This switch is electronically debounced and it inputs to a hardware latch which tog-
gles between set and reset states with each depression of the switch. The output
of this latch directly drives the ventilation state LED on the front panel as well as
controlling the drive signal to the flow valve independent of the processor. The
latch is reset by the power-up (hard) reset signal, an IRQ7 Interrupt, a processor
control signal, or a switch depression. The state of this latch as well as the direct
switch signal is input to the 68340 processor for monitoring purposes.

Audio Alarm

The audio alarm meets the requirements of the ISO standard 9703-2, "Anesthesia
and Respiratory Alarm Signals: Part 2, Auditory Alarm Signals".
The circuit consists of a Yamaha YM2413 Sound Generator and a National Semi-
conductor LM4860M audio amplifier. The sound generator interfaces directly to
the CPU and the audio amplifier drives an 8 ohm speaker.

Manifold Pressures

A Setra pressure sensor (model 210 PCBM) monitors manifold pressure. It is lo-
cated in the oxygen isolation barrier between the electronics and pneumatics
chambers.
The signal conditioned pressure transducer outputs are:
Manifold pressure:

Front Panel Assembly

The front panel assembly has a 480 by 240 pixels EL panel that displays measured
and user adjustable parameters. The user can change parameters with touch
switches on the membrane or a rotary encoder with a switch. LED's are incorpo-
rated in the membrane switch to indicate alarms, mechanical ventilation On/ Stand-
by and Mains power.
1503-0151-000
-20 to 120 ± 1.5 cmH
cmH
2
-20 to 120 ± 5% cmH
30 cmH
3/27/97
O, less than 30
2
O;
O, greater than
2
O
2
2-23