System Description
Ammonia Scrubber
8-4 Model 42i Low Source Instruction Manual Thermo Electron Corporation
Dry Air Capillary The dry air capillary along with the pump is used to control flow in the dry
air line.
Ammonia Scrubber The ammonia scrubber is mounted internally and removes ammonia from
the sample air.
Software The processor software tasks are organized into four areas:
• “Instrument Control” on page 8-4
• “Monitoring Signals” on page 8-4
• “Measurement Calculations” on page 8-5
• “Output Communication” on page 8-5
Instrument Control Low-level embedded processors are used to control the various functions on
the boards, such as analog and digital I/O and heater control. These
processors are controlled over a serial interface with a single high-level
processor that also controls the front-panel user interface. The low-level
processors all run a common piece of firmware that is bundled with the
high-level firmware and loaded on power-up if a different version is
detected.
Each board has a specific address that is used to identify to the firmware
what functions are supported on that board. This address is also used for the
communications between the low-level processors and the high-level
processor.
Every tenth of a second the frequency counters, analog I/O, and digital I/O
are read and written to by the low-level processor. The counters are
accumulated over the past second and the analog inputs are averaged over
that second. The high-level processor polls the low-level processors once per
second to exchange the measurement and control data.
Monitoring Signals Signals are gathered from the low-level processors once per second, and then
processed by the high-level processor to produce the final measurement
values. The one-second accumulated counts representing the NO/NO
x
are
accumulated and reported for the user-specified averaging time. If this
averaging time is greater than ten seconds, the measurement is reported
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