Dräger Alcotest 9510 Technical Manual page 8

Absorption of Ethanol
This illustration shows an ethanol spectra. The shaded area
represents the infrared filter of the 9510. It shows the center
frequency as 9.5µm with a half band width which significantly
increases the signal to noise ratio (Resolution).
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The 9510 measures ethanol at 9.5µm because, in this area of
the IR spectrum, the cross sensitivity to potentially interfering
compounds found in the human breath is virtually non existent.
6.2.1 Beer-Lambert Law
Law of Absorption
The Beer-Lambert Law states: For a defined path length (the
sample chamber), containing
(concentration of ethanol molecules), the transmitted energy
(IR energy) will proportionally decrease with the increase in
concentration of the absorbing system.
Law Applied
In an IR chamber one end has an IR source and the other end
has an IR detector. The IR detector converts IR energy to
electrical energy. Prior to a subject test, the IR chamber
contains only ambient air. The IR detector produces a voltage
output based on the energy emitted by the IR source.
A breath sample containing ethanol is introduced into the
chamber and the ethanol will absorb some of the IR energy
causing less IR energy to reach the IR detector resulting in a
voltage decrease. An increase in the BrAC will result in a
proportional decrease in the detector's output.
Wavelength Type of Radiation
Long
Ultraviolet Light
Extreme Ultraviolet
Short Gamma Rays
Dräger Alcotest 9510 Washington Technical Manual V3.1 2014
9.5 12
Micrometer
an absorbing system
Energy Level
Radio Low
Microwaves
Infrared
Visible Light
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Visible Light
X-Rays
High
Infrared Spectrum
The illustration below shows a spectrum of human breath
containing 200 ppm ethanol. Besides ethanol, there is the
sharp absorption line of carbon dioxide at 4.2 µm and a broad
absorption band of water ranging from 5 to 8 µm. Ethanol
exhibits two strong absorption lines: one at 3.4 µm which
corresponds to the stretching of the C-H bond, and the other
centered at 9.5 µm caused by the vibration of the C-O bond.
6.3 Electrochemical Sensor Technology
The device known as an electrochemical fuel cell was
originated in 1839 by Sir William Grove. He discovered that if
two platinum electrodes were immersed in a sulfuric acid
electrolyte, and hydrogen was supplied at one electrode and
oxygen at the other, an electric current was produced as long
as gas was supplied to the device. The chemical reaction was
the same as if the hydrogen was burned, but in this case,
electricity was produced directly instead of heat. The fuel cell
was long envisioned as a desirable electrical generator, since
no moving parts were involved, the platinum (or other catalytic
material) was not consumed, and no significant heat was
developed in the process. High cost and many technological
problems have prevented the fuel cell from fulfilling its promise
as a low cost generator of electricity and its use has, to date,
been confined to relatively exotic applications such as
spacecraft and satellite power sources.
A highly important by-product of this effort has emerged in
recent years; using the fuel cell as a sensor to detect the
presence of chemical components that are capable of being
oxidized by this process.
6.3.1 Electrochemical Theory
In its simplest form, the fuel cell consists of a porous, acidic
membrane (electrolyte), which is laminated by two platinum
black plates. An electric wire is attached to each of the
platinum plates. This assembly is packed into a sealed plastic
housing which has a small hole (gas inlet) leading into a
sample chamber, where a breath sample is introduced.
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Only one platinum plate will be exposed to the breath sample.
Once ethanol reaches the platinum, a chemical reaction is
triggered. This chemical reaction produces an electrical
Measuring Technologies
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