NDIR Gas Analyzer
Operational Theory 2
Teledyne Analytical Instruments., - Rev. 3
13
The data is linearized over the entire instrument range. This
linearization is inherently more accurate than the conventional process of
segmenting and optimizing the data over a narrow range.
Before being sent to the read out display or output as a voltage, the
result is de-spiked and filtered then scaled for the appropriate chart output
range. Filtering uses a selectable algorithm to damp sudden value
changes. The amount of filtering applied is determined by the operator and
generally depends on the process. Large filter values yield a
correspondingly lower instrument response but higher sensitivity.
The de-spiking filter is a software routine used to clean up the signal.
Essentially it looks at the last 5 instrument readings and discards a reading
if it varies significantly over the average. A “rolling average” method of
filtering is also applied through the software. This filtering process
depends on the filter value set by the user. Increasing the filter number
gives more weight to the last entry into the instrument reading buffer,
hence the “rolling average” is influenced to a greater degree by the last
input.
Figure 2-3 is a system block diagram which shows the functional
relationship between the electronics and the optical bench.
Figure 2-3: System Block Diagram