Teledyne 3000TA-XLEU - Trace oxygen analyzer - Manual (Page 33)

Trace Oxygen Analyzer Operational Theory
Teledyne Analytical Instruments 17
In the presence of oxygen the cell generates a current. A current to
voltage amplifier converts this current to a voltage, which is amplified in
the second stage amplifier.
The second stage amplifier also supplies temperature compensation
for the oxygen sensor output. This amplifier circuit incorporates a
thermistor, which is physically located in the cell block. The thermistor
is a temperature dependent resistor that changes the gain of the amplifier
in proportion to the temperature changes in the block. This change is
inversely proportional to the change in the cell output. The result is a
signal that is temperature independent within a specified tolerance. The
output from the second stage amplifier is sent to an 18 bit analog to
digital converter controlled by the microprocessor.
The digital concentration signal along with input from the control
panel is processed by the microprocessor, and appropriate control
signals are directed to the display, alarms and communications port. The
same digital information is also sent to a 12 bit digital to analog
converter that produces the 4-20 mA DC and the 0-1 V DC analog
concentration signal outputs, and the analog range ID outputs.
Signals from the power supply are also monitored, and through the
microprocessor, the system failure alarm is activated if a malfunction is
detected.