System Description
Software
Thermo Fisher Scientific
Model 43i Trace Level-Enhanced Instruction Manual
8-5
processor that also controls the front-panel user interface. The low-level
processors all run common 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.
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 are accumulated
and reported for the user-specified averaging time. If this averaging time is
greater than ten seconds, the measurement is reported every 10 seconds.
The one-second average of the other analog inputs are reported directly (no
additional signal conditioning is performed by the high-level processor).
The calculation begins by flashing the lamp 10 times per second. After the
lamp flash, a sample and hold circuit on the input board is used to sample
the PMT output. The raw accumulated counts are scaled according to the
gain setting of the input board.
Next, the uncorrected values are determined according to a unique
averaging algorithm which minimizes errors resulting from rapidly
changing gas concentrations. This algorithm results in values which are
stored in RAM in a circular buffer that holds all the ten second data from
the previous five minutes. This data is averaged over the selected time
interval, which can be any multiple of ten between 1 and 300 seconds.
The background values, which are corrected for temperature, are subtracted
from their respective averages. The reading is corrected by the stored span
factor and by the temperature factor.
The front panel display, serial and Ethernet data ports, and analog outputs
are the means of communicating the results of the above calculations. The
front panel display presents the SO
2
concentrations. The display is updated
every 1-10 seconds, depending on the averaging time.
Monitoring Signals
Measurement
Calculations
Output
Communication
