Teledyne GFC 7001EM operation manual Software Operation, Adaptive Filter

Theory of Operation Model GFC7001E Carbon Dioxide Analyzer

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
Memory Handling	Analyzer Operations
	Calibration Procedures	PC/104 BUS
IDAS Records
	Configuration Procedures
Calibration Data	Autonomic Systems
System Status Data
	Diagnostic Routines
		ANALYZER
		HARDWARE
	Interface Handling
Measurement	Sensor input Data
	Display Messages
Algorithm	Keypad
	Analog Output Data	PC/104 BUS
	RS232 & RS485
	External Digital I/O
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.

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