Teledyne gfc 7000ta operation manual Calibration Slope and Offset, Measurement Algorithm

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer

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.

9.5.2. Calibration - Slope and Offset

Calibration of the analyzer is performed exclusively in software.

During instrument calibration (see Section 7) the user enters expected values for zero and span via the front panel touchscreen and commands the instrument to make readings of calibrated sample gases for both levels. The readings taken are adjusted, linearized, and compared to the expected values, With this information the software computes values for instrument slope and offset and stores these values in memory for use in calculating the CO2 concentration of the sample gas.

The instrument slope and offset values recorded during the last calibration can be viewed by pressing the following touchscreen button sequence:

SAMPLE	RANGE = 50.0 MGM	CO2
=XX.XX
SAMPLE	TIME = 16:23:34	CO2
=XX.XX

SAMPLE	OFFSET = 0.000	CO2
=XX.XX

SAMPLE	SLOPE = 1.000	CO2
=XX.XX

9.5.3. Measurement Algorithm

Once the IR photo-detector is signal is demodulated into CO2 MEAS and CO2 REF by the sync/demod board and converted to digital data by the motherboard the GFC 7000TA analytical software calculates the ratio between CO2 MEAS and CO2 REF. This value is compared to a look-up table is used, with interpolation, to linearize the response of the instrument. The linearized concentration value is combined with calibration slope and offset values, then normalized for changes in sample gas pressure to produce the final CO2 concentration. This is the value that is displayed on the instrument front panel display and is stored in memory by the analyzer’s DAS system.

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