Teledyne 3300PA - Low cost percent oxygen analyzer - Manual (Page 16)

2-6
2 Operational Theory Model 3300 PA
Teledyne Analytical Instruments
In the presence of oxygen the cell generates a current. This current flows
through an internal thermistor compensation network.
The output of the sensor is converted to voltage in the millivolt range. This
output is fed to a voltage amplifier. The internal thermistor network provides
temperature compensation of the sensor output. The resistance of the network
changes with temperature, compensating for the changes of the microfuel cell
output to temperature.
The output from the sensor amplifier is sent to an analog to digital converter
(ADC), and the resulting digital concentration signal is sent to the
microcontroller.
The digital concentration signal along with input from the front panel buttons
(KEYBOARD) is processed by the microcontroller, and appropriate output
signals are directed to the display and alarm relays. The same digital information
is also sent to a 12-bit digital to analog converter (DAC) that produces the 0-10
V dc analog concentration signal and the 0-10 V dc analog range ID output. A
current to voltage converter (E–I CONV) produces the 4-20 mA dc analog
concentration signal.