Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 203)

Model 9110E Instruction Manual Theory of Operation
M9110E Rev B 189
Figure 10-18: Keyboard and Display Interface Block Diagram
10.4. Software Operation
The M9110E NO
X
analyzer’s core module is a high performance, 386-based microcomputer
running a version of DOS. On top of the DOS shell, special software developed by TAI
interprets user commands from various interfaces, performs procedures and tasks, stores
data in the CPU’s memory devices and calculates the concentrations of NO
X
in the sample
gas. Figure 10-19 shows a block diagram of this software functionality.
10.4.1. Adaptive Filter
The M9110E NO
X
analyzer software processes sample gas concentration data through a
built-in adaptive filter. Unlike other analyzers that average the output signal over a fixed
time period, the M9110E averages over a defined number of samples, with samples being
about 8 seconds apart (reflecting the switching time of 4 s each for NO and NO
X
). This
technique is known as boxcar filtering. During operation, the software may automatically
switch between two different filters lengths based on the conditions at hand.
During constant or nearly constant concentrations, the software, by default, computes an
average of the last 42 samples, or approximately 5.6 minutes. This provides smooth and
stable readings and averages out a considerable amount of random noise for an overall less
noisy concentration reading.
If the filter detects rapid changes in concentration the filter reduces the averaging to only 6
samples or about 48 seconds to allow the analyzer to respond more quickly. Two conditions