Detecting Interfering Substances - Dräger Alcotest 9510 Technical Manual

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Detecting Interfering Substances

As previously mentioned, the 9510's infrared sensor operates
in the 9.5µm range of the infrared spectrum. Acetone, toluene,
and acetaldehyde, the
substances", can have a slight influence in breath analyzers
operating at the 3.4µm range of the infrared spectrum. By
shifting the operating range to 9.5µm, the 9510 is virtually free
from the influence of these compounds as they relate to a
living, breathing subject taking a breath test.
0
6 8
Absorption of ethanol at 9.5 um
Acetone/Ethanol
Isopropyl Alcohol/Ethanol
Methanol/Ethanol
Toluene/Ethanol
Dräger Alcotest 9510 Washington Technical Manual V3.1 2014
most mentioned "interfering
9.5 12
Micrometer
The 9510 also employs an alcohol specific electrochemical
(fuel cell) sensor which is not influenced by acetone or toluene.
During either a calibration or a calibration check, the fuel cell
sensor's response to ethanol (only) is memorized in the form
of a curvature analysis profile. From this analysis, the pres-
ence of methanol can be detected by comparing the fuel cell's
kinetic reactivity of ethanol compared to methanol.
If the analysis of the subject's breath reveals different curva-
ture characteristics, a message indicating that an interfering
substance was detected will be displayed and the test aborted.
During a test, the subject's breath is analyzed by both the
infrared and fuel cell sensors. There is a preset detection
threshold that both readings must fall within for a breath test to
be successful. The EC results must be within .008 g/210L or
10% of the IR reading, whichever is greater. If the two results
exceed the preset tolerance, an interference message is
displayed and the test invalidated.
NOTE: The interfering substance detection is activated in the
regular breath test sequence only. Never run a Calcheck Test
when using substances other than ethanol.
9.1 Mouth Alcohol Detection
The detection of mouth alcohol ("invalid sample") is based on
the analysis of the IR's alcohol vs. time profile taken during the
subject's breath sample. A normal profile is characterized by a
sharp increase in the concentration at the beginning of the blow
followed by a more moderate increase in the concentration until
the end of the blow. Sometimes the slope of the profile may
become zero at the end. For a regular breath test, the
concentration always increases with time and never decreases.
In the case of mouth alcohol, the alcohol vs. time profile
changes considerably. There will be sections with decreasing
concentration and thus, a negative slope. The 9510 employs
an advanced detection algorithm that can identify the various
sudden changes (positive or negative) in the slope of this curve
that are associated with mouth alcohol scenarios.
Detecting Interfering Substances
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