Measuring and testing – Gas analysis – Breath analysis
Reexamination Certificate
2002-03-28
2004-09-21
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
Breath analysis
C422S084000, C436S132000, C436S900000, C600S532000, C600S543000, C180S272000, C340S576000
Reexamination Certificate
active
06792793
ABSTRACT:
BACKGROUND
The present invention relates to breathalyzers, and breath alcohol interlock devices for preventing operation of vehicles and other machines by intoxicated persons.
In the 19th century, law enforcement officials dealt with the problem of alcohol abusers by imprisoning them until they were sober. In the 20th century, the advent of high-speed transportation and complex machinery gave high priority to alcohol testing and screening. Automobiles traveling at ninety feet per second on the freeway are unforgiving of drivers with alcohol impairment. The same is true for a 300-passenger aircraft guided by an alcohol-impaired pilot attempting to land under minimum-visibility conditions. There is very little margin for error. People who operate complex equipment with their judgment impaired by alcohol may not only be a danger to themselves, but impact the safety of others.
Until recently, the main application of alcohol testing was to traffic law enforcement. The intent was to identify people suspected of driving under the influence of alcohol and remove them from the road. After arrest, law enforcement officers gave the subject a chemical test to determine his blood alcohol level. Subjects were either released or incarcerated and prosecuted, depending on what alcohol levels were illegal as dictated by state law. Until the mid-1940's, the primary means of measuring blood alcohol levels involved either blood or urine sample testing, both of which were time-consuming and expensive procedures. In the late 1940's, alcohol breath testing replaced blood and urine sample testing as a means of screening subjects and producing evidentiary results for prosecution.
In the 1980's, railroad, nuclear, Department of Defense, and maritime employees came under Federally-mandated testing requirements. In each case, new laws followed a major, alcohol-related disaster. In 1991, the United States Congress passed the Omnibus Transportation Employee Testing Act. This legislation mandated alcohol testing for transportation personnel involved in safety-sensitive jobs. This mandate included airline pilots and cabin attendants, truck drivers, railroad crews, and gas pipeline workers. The US Department of Transportation further defined unacceptable maximum alcohol levels.
Since the mid-1980s, infrared (IR) technology has been the primary means of breath alcohol testing in the United States. Current technology uses infrared measurement systems that are made more specific for alcohol by using several optical filters. Breath alcohol levels are measured this way by passing a narrow band of IR light, selected for its absorption by alcohol, through one side of a breath sample chamber and detecting emergent light on the other side. The alcohol concentration is then determined by using the well-known Lambert-Beers law, which defines the relationship between concentration and IR absorption. This IR technology has the advantage of making real-time measurements; however, it is particularly difficult and expensive to achieve specificity and accuracy at low breath alcohol concentration levels. Also, the IR detector output is nonlinear with respect to alcohol concentration and must be corrected by measurement circuits. A more favored technology uses electrochemical cells, also known as fuel cells.
The fuel cell effect was discovered in the early 1800's when a British scientist immersed two platinum electrodes in sulfuric acid electrolyte and supplied hydrogen at one electrode and oxygen at the other. The resulting reaction created a current flow between the electrodes. There was no practical application of fuel cells at that time because of high cost and technological problems. In the 1960s, researchers at the University of Vienna demonstrated a fuel cell that was specific for alcohol. This evolved into the present-day cell used in all fuel cell-based breath alcohol measurement instruments. In its simplest form, the alcohol fuel cell consists of a porous, chemically inert layer coated on both sides with finely divided platinum (called platinum black). The porous layer is impregnated with an acidic electrolyte solution, and platinum wire electrical connections are attached to the platinum black surfaces, and this assembly is mounted in a plastic case having a gas inlet that allows a breath sample to be introduced as shown in FIG.
1
.
The exact chemistry of the reaction that takes place in an alcohol fuel cell is open to some conjecture. Researchers assume that the reaction converts alcohol to acetic acid. In the process, this conversion produces two free electrons per molecule of alcohol. This reaction takes place on the upper surface of the fuel cell. H+ ions are freed in the process, and migrate to the lower surface of the cell, where they combine with atmospheric oxygen to form water, consuming one electron per H+ ion in the process. Thus, the upper surface has an excess of electrons, and the lower surface has a corresponding deficiency of electrons. When the two surfaces are connected electrically, a current flows through this external circuit to neutralize the charge. This current is a direct indication of the amount of alcohol consumed by the fuel cell. With appropriate signal processing, breath alcohol concentrations directly can be displayed. Commercial fuel cell instruments, introduced in the mid-1970s and initially suitable for non-evidential alcohol breath testing, were improved sufficiently by 1980 to be certified for evidential use by the US Department of Transportation, and by a number of state agencies and foreign governments. The fuel cell has established a reputation for specificity and linearity of response over the complete range of alcohol concentration expected in the breath. This range is from 5 to 900 ppm or its equivalent in other units of measurement.
When a precise volume of breath sample is quickly introduced into a fuel cell, the output current from the cell rises from zero to a peak, and then ultimately decays back to zero. The rate at which this happens is highly dependent on the loading across the sensor terminals.
FIG. 2
illustrates this effect, for loadings of 100 and 300 ohms, and for a shorted condition (0 ohms). Traditional fuel cell measurement instruments of the prior art have load resistors of several hundred to one thousand ohms, and the height of the voltage peak across the resistor is used as the measure of alcohol content of the sample. Although this technique produces good linearity, significant time elapses before an acceptable measurement can be obtained, and the measurement cycles are objectionably long because complete conversion of alcohol to electric current must occur prior to a new cycle, the current being limited by the load resistance of the measurement circuit.
More recent instruments have utilized lower load resistance to shorten the time to reach the peak output and speed up the recovery time, and they integrate the output signal to obtain enhanced accuracy. However, the number of positive samples analyzed in rapid succession with these prior art instruments still had to be strictly limited. Successive readings might be in error as peak fuel cell output decreased because of the time required for the cell to complete the alcohol conversion reaction. This could conceivably give readings beyond the acceptable limits for evidential measurement. In a typical unit, ten successive measurements of 0.100 gm/dl gas at three minutes between readings might result in the tenth reading being 0.095 or 0.094. Accordingly, these instruments have unfortunately been limited to no more than five positive tests per hour for maintenance of evidential accuracy. Consequently, only one subject could be tested per hour with evidential accuracy in those jurisdictions requiring two tests per subject, and a third test if the first two differed by more than a given amount, and an additional a test reading on a standard to verify calibration of the instrument. In addition, once the fuel cell output of these instruments decreases due to repeated testing, an ext
Anderson Denton L.
Ignition Lock International
Larkin Daniel S.
Sheldon & Mak
LandOfFree
Breath measurement instrument and breath alcohol interlock... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Breath measurement instrument and breath alcohol interlock..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Breath measurement instrument and breath alcohol interlock... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3237013