Teledyne GFC 7001EM operation manual Calibration Slope and Offset, Measurement Algorithm

Theory of Operation Model GFC7001E Carbon Dioxide Analyzer

11.5.13.CALIBRATION - SLOPE AND OFFSET

Calibration of the analyzer is performed exclusively in software.

During instrument calibration (see Section 9) the user enters expected values for zero and span via the front panel keypad 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 CO concentration of the sample gas.

The instrument slope and offset values recorded during the last calibration are available for viewing from the from the front panel (see Section 3.5.4).

11.5.14.MEASUREMENT ALGORITHM

Once the IR photo-detector signal is demodulated into CO MEAS and CO REF by the sync/demod board and converted to digital data by the motherboard, the GFC 7001E/EM analytical software calculates the ratio between CO MEAS and CO REF. This value is compared to a look-up table that 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 CO concentration. This is the value that is displayed on the instrument front panel display and is stored in memory by the analyzer’s iDAS system.

11.5.15.TEMPERATURE AND PRESSURE COMPENSATION

Changes in pressure can have a noticeable, effect on the CO concentration calculation. To account for this, the GFC 7001E/EM software includes a feature which allows the instrument to compensate for the CO calculations based on changes in ambient pressure.

The TPC feature multiplies the analyzer’s CO concentration by a factor which is based on the difference between the ambient pressure of the sample gas normalized to standard atmospheric pressure. As ambient pressure increases, the compensated CO concentration is decreased.

11.5.16.INTERNAL DATA ACQUISITION SYSTEM (IDAS)

The iDAS is designed to implement predictive diagnostics that stores trending data for users to anticipate when an instrument will require service. Large amounts of data can be stored in non-volatile memory and retrieved in plain text format for further processing with common data analysis programs. The iDAS has a consistent user interface in all Teledyne analyzers. New data parameters and triggering events can be added to the instrument as needed.

Depending on the sampling frequency and the number of data parameters the iDAS can store several months of data, which are retained even when the instrument is powered off or a new firmware is installed. The iDAS permits users to access the data through the instrument’s front panel or the remote interface. The latter can automatically download stored data for further processing. For information on using the iDAS, refer to Section 7.1.

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