166 Theory of Operation 083730300A DCN8101
6.5 SOFTWARE OPERATION
The T300/T300M Gas Filter Correlation Carbon Monoxide Analyzer has a high
performance, Vortex86-based microcomputer running Windows CE. Inside Windows
CE, special software developed by Teledyne API interprets user commands via the
various interfaces, performs procedures and tasks, stores data in the CPU’s various
memory devices and calculates the concentration of the sample gas.
Analyzer Operations
Calibration Procedures
Configuration Procedures
Autonomic Systems
Diagnostic Routines
Memory Handling
DAS Records
Calibration Data
System Status Data
Interface Handling
Sensor input Data
Touchscreen/Display
Analog Output Data
RS232 & RS485
External Digital I/O
Figure 6-18. Basic Software Operation
6.5.1 ADAPTIVE FILTER
The T300/T300M 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 T300/T300M
averages over a set number of samples, where each sample is 0.2 seconds. This
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 Technical Support
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.
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