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THEORY OF OPERATION
DOS Shell
API FIRMWARE
Memory Handling
IDAS Records
Calibration Data
System Status Data
Measurement
Algorithm
10.5.1. Adaptive Filter
The Model 400E software processes sample Gas Measurement and Reference data
through a built-in adaptive filter built into the software. Unlike other analyzers that
average the output signal over a fixed time period, the Model 400E averages over a
set number of samples, where a new sample is calculated approximately every 3
seconds -this is technique is known as boxcar averaging. During operation, the
software automatically switches between two different length filters based on the
conditions at hand.
During conditions of constant or nearly constant concentration the software, by
default, computes an average of the last 32 samples, or approximately 96 seconds.
This provides the calculation portion of the software with smooth stable readings. If
a rapid change in concentration is detected, the filter length is changed to average
the last 6 samples, approximately 18 seconds of data, to allow the analyzer to more
quickly respond. If necessary, these boxcar lengths can be changed between 1 and
1000 samples but with corresponding tradeoffs in rise time and signal-to-noise ratio
(contact customer service for more information).
Two conditions must be simultaneously met to switch to the short filter. First the
instantaneous concentration must exceed the average in the long filter by a fixed
240
Analyzer Operations
Calibration Procedures
Configuration Procedures
Autonomic Systems
Diagnostic Routines
Interface Handling
Sensor input Data
Display Messages
Analog Output Data
RS232 & RS485
External Digital I/O
Figure 10-10: Basic Software Operation
Model 400E Ozone Analyzer
Keypad
Instruction Manual
PC/104 BUS
ANALYZER
HARDWARE
PC/104 BUS
P/N 04316 Rev: B
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