Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 313)

Theory of Operation Teledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 313
13.5. SOFTWARE OPERATION
The GFC7001T/GFC7001TM Gas Filter Correlation Carbon Monoxide Analyzer has a
high performance, VortexX86-based microcomputer running Windows CE. Inside
Windows CE, special software developed by TAI 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.
Windows CE
API FIRMWARE
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
Measurement
Algorithm
ANALYZER
HARDWARE
PC/104 BUS
PC/104 BUS
Linearization Table
Figure 13-18: Basic Software Operation
13.5.1. ADAPTIVE FILTER
The GFC7001T/GFC7001TM 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 GFC7001T/GFC7001TM 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 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.