2-10
2 Operational Theory Model 3000TA-XL-EU
Teledyne Analytical Instruments
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 inde-
pendent 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.