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2 Operational Theory
2.5
Electronics and Signal Processing
The Model 3020M Percent Oxygen Analyzer uses an 8031 microcon-
troller with 32 kB of RAM and 128 kB of ROM to control all signal pro-
cessing, input/output, and display functions for the analyzer. System power
is supplied from a universal power supply module designed to be compatible
with most international power sources. See chapter 5 Maintenance for the
location of the power supply and the main electronic PC boards. The Para-
magnetic Sensor has its own dedicated universal 24V power supply that
feeds the sensors internal heater and electronics.
The signal processing electronics including the microprocessor, analog
to digital, and digital to analog converters are located on the main PCB, on
the front door (see figure 5-1). The preamplifier board is mounted on top of
the motherboard. These boards are accessible by opening the front door of
the explosion proof enclosure. Figure 2-5 is a block diagram of the Analyzer
electronics.
In the presence of oxygen the chamber is rotated in the magnetic field,
but the cell generates a current to countertorque the oxygen action. This
current is converted to a voltage, which is preamplified in the sensor internal
electronics.
The preamplified signal (0-1 Volt) is fed to the 3020M amplifier for
minor processing.
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.
2.6 Temperature Control
For accurate analysis the sensor temperature is controlled internally at
O
55
C.
2-6
Teledyne Analytical Instruments
Model 3020M
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