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6
Measuring Technologies
The Alcotest® 9510 employs two different and independent
technologies, each analyzing and quantifying a subject's
breath alcohol concentration: IR spectroscopy (Infrared) and
Electrochemical Cell (Fuel Cell) technology. This offers the
highest possible level of forensic analytical integrity.
6.1
Infrared Technology
The use of infrared technology for detection of alcohol in the
breath by Law Enforcement has been around since the late
sixties. In the early 1970's, scientists from the United States
and Germany combined worked to develop standardization on
breath testing devices utilizing infrared theory. The list of
definitions below are some of the common terms used
involving infrared technology.
Molecule: The smallest physical unit of a compound that
can exist separately and still keep the properties of the
original substance.
Wavelength: The distance between two successive points
in a wave.
Amplitude: The strength or height of a wave.
Frequency: The number of periodic oscillations,
cycles or waves per unit of time (cycles per second).
Electromagnetic
Radiation:
transmission through space or a medium (glass) in which
electric and magnetic fields are extended or transmitted as
waves.
Electromagnetic Spectrum: The complete range of
frequencies of electromagnetic radiation from the
to the highest frequency.
Infrared Energy: The part of the invisible spectrum,
contiguous beyond the red end of the visible spectrum of
electromagnetic radiation, which travels through space in
waves. Behavior of such waves is similar to that of visible
light waves.
Micron: The unit of linear measurement of electromagnetic
radiation. One micron is equal to one millionth of a meter.
The symbol µm" denotes a micrometer (e.g. 9.50µm).
6.1.1
Infrared Theory
Depending on their physical size and structure, molecules
absorb energy at specific wavelengths and areas in the IR
spectrum. Ethanol molecules absorb IR energy in two distinct
areas in the IR spectrum, the 3.4µm range and the 9.5µm
range.
6.1.2
Infrared System
The central part of the measuring system is the infrared
absorption cuvette, where the breath sample is being
observed. The cuvette comprises a chamber of 70mL in
volume with gold-coated parabolic mirrors, an electronically
modulated infrared transmitter (source) and a pyro detector
with an integrated IR filter.
Dräger Alcotest 9510 Washington Technical Manual V3.1 2014
6.2
The breath sample is transferred into the system via the breath
hose. The cuvette is heated to a minimum of 39°C to avoid
condensation and to guarantee defined conditions for the
analysis. The instrument will halt an evidential breath test
sequence with a hardware error if the cuvette temperature is
outside the range of 39°C and 50°C. The temperature at the
time of the test is also recorded in the test data records within
the instrument.
The cuvette is a multi-reflection cell which provides a long
absorption path for high precision (resolution) yet, at the same
time, has a volume of only 70mL. This small volume makes it
possible to trace the concentration-time profile very carefully
(dynamic range) because fast changes are noticed. At both
ends of the cell are gold coated parabolic mirrors which contain
the IR-source and the IR-detector plus IR-filter. The energy
from the IR-source enters the cuvette from a central orifice in
one of the mirrors onto the detector. The IR energy makes 7
passes before it is received by the IR detector.
A
form
of
energy
The infrared source, with its low thermal mass, can be
modulated at 2 Hz by a 50% duty-cycled power source. This
lowest
eliminates the need for an optical chopper or chopper-wheel.
Furthermore, the power consumption is less than 1 Watt.
The detector is a thermally compensated Pyro-IR-Detector
with very high sensitivity. It also houses the alcohol specific IR-
filter centered at 9.5µm.
The output signal is fed into a very low noise amplifier, which
brings the voltage to higher magnitude levels for further
analysis.
IR System
Measuring Technologies
7
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