Teledyne BDS-3960 Operating Instructions Manual page 27

Oxygen Analyzer Operational Theory
as the signal is passed to a second channel of the analog to digital
converter.
The raw counts of the analog to digital converter for both the
oxygen sensor amplifier and temperature amplifier are sent to the PPC
via RS232 interface once every second along with a status byte. The
PPC performs processing on this data to calculate oxygen concentration,
temperature, as well as decisions regarding the condition of the alarm
contacts, range, amplifier gain, solenoid control, and the analog output
required. After processing, the PPC sends a message back to I/O board,
via RS232, with commands for all the I/O functions. The 8051
microprocessor in the I/O board evaluates this data and the appropriate
control signals are directed to the LED display, alarms contacts, range
ID contacts, and digital to analog converter. The analog to digital
converter is a 12 bit device located in the microprocessor IC. The output
of the digital to analog converter with the help of some support
electronics produces the 4-20 mA DC and the 0-1 VDC analog
concentration signal outputs.
Signals from the power supply are also monitored, and through the
microprocessor, the system failure alarm is activated if a malfunction is
detected. Failure to communicate with the PPC will also trigger the
System alarm.
Teledyne Analytical Instruments 27