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T400 Ozone Analyzer Operator’s Manual Theory of Operation
299
13.3.7.1. Photometer Electronic Operation
Sensor Inputs
Absorption tube
Figure 13-18: O
3
Photometer Electronic Block Diagram
Like the O
3
photometer and its subcomponents act as peripheral devices operated by the
CPU via the motherboard. Communications to and from the CPU are handled by the
motherboard.
Outgoing commands for the various devices such as the photometer pump, the UV lamp
power supply the U\V Lamp heater are issued via the I
2
C bus to circuitry on the relay
PCA which turns them ON/OFF. The CPU also issues commands over the I
2
C bus that
cause the relay PCA to cycle the measure/reference valve back and forth.
Incoming date the UV light detector is amplified locally then converted to digital
information by the motherboard. Output from the photometers temperature sensors is
also amplified and converted to digital data by the motherboard. The O
3
concentration
of the sample gas is computed by the CPU using this data (along with gas pressure and
flow data received from the instrument’s pressure sensors.
06870C DCN6332