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Teledyne API – Technical Manual - Model 300E Family CO Analyzers Theory of Operation
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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 ze
ro a
nd 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 M300E/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
M300E/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 API 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.
04288D DCN5752