Teledyne 3300TB - Low cost trace oxygen analyzer - Manual (Page 16)

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2 Operational Theory Model 3300 TB
Teledyne Analytical Instruments
In the presence of oxygen the cell generates a current. The sensor has an
internal thermistor compensation network.
The output of the sensor is converted to voltage millivolt range. This output
is fed to a voltage amplifier. The internal thermistor network provides tempera-
ture 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 temperature compensation 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
voltage current converter (E–I CONV) produces the 4-20 mA dc analog
concentration signal.