Adaptive Filter; Figure 10-17: Basic Software Operation - Teledyne 300E Instruction Manual

Model 300E Carbon Monoxide Analyzer
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10.5.1. Adaptive Filter

The M300E software processes the CO MEAS and CO REF signals, after they are
digitized by the motherboard, through an adaptive filter built into the software.
Unlike other analyzers that average the output signal over a fixed time period, the
M300E averages over a set number of samples, where each sample is 0.2 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. Once triggered, the short filter remains engaged for a fixed time period to
prevent chattering.
During conditions of constant or nearly constant concentration the software, by
default, computes an average of the last 750 samples, or approximately 150
seconds. This provides the calculation portion of the software with smooth stable
readings. If a rapid change in concentration is detected the filter includes, by
default, the last 48 samples, approximately 10 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
amount. Second the instantaneous concentration must exceed the average in the
long filter by a portion, or percentage, of the average in the long filter.
P/N 04288 Rev: A
IDAS Records
Algorithm

Figure 10-17: Basic Software Operation

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