Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2001-04-27
2002-02-05
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C073S023310, C073S031010, C200S061030
Reexamination Certificate
active
06344798
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of sensor technology. More specifically, the present invention relates to the development of various infrared (IR) gas sensor technology applications in connection with carbon dioxide sensing, particularly as to measuring/controlling exhaust gas recirculation (EGR) to diesel engines.
BACKGROUND OF THE INVENTION
To acquire desired information of any kind, measurements of physical parameters must be made. Devices that permit these measurements are broadly categorized as sensors. The term “sensors” encompasses a broad range of technologies and devices that respond to a physical stimulus (i.e. light, heat, sound, pressure, magnetism or a particular motion) and transmit a resulting impulse, generally for measurement or operating a control.
Sensors are widely used in many different applications. Some can be as simple as the direct measurement of a thermocouple, or as complex as all-weather imaging systems. Whatever the complexity of the sensor, an interaction between the sensor and its physical environment produces some kind of signal that ultimately leads to the desired information.
In many instances, sensor technology has become a basic enabling technology. The rapid increase in the interest in sensors has been driven by numerous applications, such as analysis of selected compounds in blood, in which sensors can provide a large public benefit.
In addition, sensors are of great importance in safety-related areas, with applications ranging from assessing the integrity of aircraft to fire safety monitoring. Common research and technology issues in these diverse applications include the interpretation of spectral signatures in terms of quantities of interest, such as concentrations, temperatures or thermal properties.
For example, market demand in gas measurement platforms for determining concentration levels of carbon dioxide, is driving increased activity in CO
2
technology because in part of its utility in understanding and monitoring ventilation and Indoor Air Quality (IAQ). Building codes and standards governing ventilation in buildings, such as ASHRAE (American Society of Heating Air Conditioning and Refrigeration Engineers) Standard 62-99, have established minimum volumetric outside air requirements on a per-person basis.
Because individuals generally exhale a predictable amount of carbon dioxide, one application is to use this parameter to sense occupancy. An increasing or decreasing level of carbon dioxide can indicate ingress or egress of an indoor zone.
In addition, because outside levels are very low and constant, an indoor measurement can also provide a dynamic measure of the number of occupants of the space and the amount of low concentration outside air being introduced to dilute contaminant concentrations. As a result, a carbon dioxide measurement in a space can be used to measure or control per-person ventilation rates within a space.
Thus, while carbon dioxide is not a direct measure of indoor air quality, it has the potential to be an excellent measure of effective ventilation (mechanical ventilation plus infiltration). Generally, the higher the carbon dioxide concentration, the lower the ventilation. In other words, when indoor carbon dioxide levels are very high (i.e. above 1800 ppm) and ventilation is low (below 7 cfm/person), these conditions can allow contaminants to build up, causing irritation and discomfort.
Determining concentration levels of carbon dioxide is a powerful facility that can be useful in homes, office buildings, schools, and other commercial environments. However, implementable applications are limited by manufacturing and other costs, as well as health, safety, quality and other issues.
For example, in health and safety applications, oxygen sensors have been used to measure depletion of oxygen. However, oxygen sensors are not only expensive, but generally require periodic replacement or recalibration. Thus, it would be desirable to have an inexpensive alternative sensing method of measuring oxygen depletion.
In the automotive industry, there is also an increasing need for carbon dioxide sensor technology to improve the quality, safety and comfort of automobiles. For instance, it is known that the carbon dioxide concentration in the combustion air to an engine can be used to determine the amount of exhaust gases being re-introduced to the engine's combustion air. This is because the carbon dioxide concentration of the engine exhaust is significantly higher than ambient air (i.e. 9 percent versus 350-550 ppm).
However, conventional sensing approaches for gases in engines utilize in-situ sensors that are directly exposed to the stream of gas being measured. Exposing these types of sensors to the harsh engine environment, particularly high temperatures, impairs sensing quality and results. Thus, it would be desirable to have an alternative sensing approach, to determine carbon dioxide concentrations, that could endure the harsh environment in the engine and still produce accurate measurements.
An equally important driver in the automotive industry is the incorporation of sensors into automotive products that aid in extending human life and improving safety. In one instance, there is a need to sense the presence of an individual within a vehicle's trunk in order to prevent unwanted or accidental confinement that could lead to death.
In the area of sensor recalibration, there is an increasing need for sensors with an automatic calibration mode feature that has a fast recalibration time, and provides stable, false-free readings.
Accordingly, there is a need for an inexpensive sensor technology control approach that can be used as an indicia of concentration level characteristics of carbon dioxide. In addition, there is a need for a control approach that is suitable (i.e. standardizable) across a number of different applications.
SUMMARY OF THE INVENTION
The foregoing and other needs have been satisfied to a great extent by the present invention, which includes a very reliable method of determining concentration levels of gases, such as carbon dioxide.
More specifically, the present invention is achieved by use of a gas measurement criterion based on measuring the rate of change of carbon dioxide concentration and variations thereof, using optical methods. Optical methods are the most accurate and reliable method for measuring carbon dioxide because of its inert nature; carbon dioxide reacts poorly with other gases, and is difficult to measure reliably with sensors that depend on physical or chemical reactions.
In one aspect of the present invention, a method of measuring oxygen depletion is employed using the rate of change of carbon dioxide as a surrogate indicator of the amount of oxygen being depleted or displaced in the air. Depletion of oxygen can be measured in one of two instances.
In a first instance, if oxygen is being displaced by carbon dioxide, the natural consequence is that carbon dioxide will have to rise to very high levels to displace a significant amount of oxygen (e.g. greater than 30,000 ppm or 3 percent of CO
2
).
Conversely, and in a second instance, if oxygen is being displaced by another gas, then it follows that concentrations of carbon dioxide will ultimately begin to drop below normal atmospheric levels of 350-450 ppm. If the rate of fall of CO
2
levels drops to below 300 ppm within 24 hours or less, for example, such a drop is reasonably indicative of oxygen depletion, and a warning or control is triggered.
More accurate control levels can be established given known space volume information. Also, the rate of change of carbon dioxide can be used if the rate of change exceeds normal rates that could be expected to be generated by human occupants.
In another aspect of the invention, a carbon dioxide sensor is remotely configured in an automotive or diesel engine in order to measure and control exhaust gas recirculation (EGR) to diesel engines. EGR techniques are used to reduce the emission of certain pollutants, such as nitrogen oxide (
Baker & Hostetler LLP
Edwards Systems Technology, Inc.
Wu Daniel J.
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