Teledyne GFC-7001E - Trace CO Analyzer - Manual (Page 256)

Theory of Operation Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 256
11.5.11. SOFTWARE OPERATION
The GFC 7001E/EM Gas Filter Correlation Carbon Monoxide Analyzer has at its heart a high performance, 386-
based microcomputer running MS-DOS. Inside the DOS shell, special software developed by Teledyne
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.
DOS Shell
API FIRMWARE
Analyzer Operations
Calibration Procedures
Configuration Procedures
Autonomic Systems
Diagnostic Routines
Memory Handling
IDAS Records
Calibration Data
System Status Data
Interface Handling
Sensor input Data
Display Messages
Keypad
Analog Output Data
RS232 & RS485
External Digital I/O
Measurement
Algorithm
ANALYZER
HARDWARE
PC/104 BUS
PC/104 BUS
Linearization Table
Figure 11-19: Basic Software Operation
11.5.12. ADAPTIVE FILTER
The GFC 7001E/EM 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 GFC 7001E/EM 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.