Datex-Ohmeda Aestiva 7900 SmartVent, Service Manual

Page: 43 / 181

2/Theory of Operation
1503-0151-000 3/27/97 2-25
O2 Concentration Measurement
The Oxygen sensor generates a linear output voltage that depends upon the con-
centration being measured. It produces an output of 57
±
- 14 mV dc at 100% con-
centration, therefore its output is amplified by a factor of 52 to make it compatible
with the current transmitter. This produces a maximum output of 2.50 volts.
The 0 to 20 mA current signals are sent to the Ventilator where a voltage drop is
produced across 200 ohm resistors, for a 0 to 4.00 volt signal to be measured by
the A/D converter.
Switch Connections
The SIB is used as a connection point for the various switches that indicate the
state of the machine. These include the O
2
flush, the Power On switch, the DCGO
switch fitted to French SE anesthesia machine, and the O
2
pressure switch mount-
ed on the SIB.