Weighing scales – Self-positioning – Electrical current generating or modifying
Reexamination Certificate
2000-07-07
2002-10-15
Gibson, Randy W. (Department: 2841)
Weighing scales
Self-positioning
Electrical current generating or modifying
C073S580000
Reexamination Certificate
active
06465749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to weighing scales. More specifically, the present invention incorporates a filter in a gas stream for separating particles therefrom, and a magnetostrictive oscillating tube supporting the filter. A change of resonant frequency within the oscillating tube is used to electronically measure the mass of particles separated from the gas stream.
2. Description of the Related Art
Accompanying the operation of many machines and devices is the production of by-products. These by-products in many cases are undesirable, and in some cases will require monitoring for various process control or legally mandated reporting purposes. For example, during the operation of a diesel engine, one undesirable side-effect of rapid speed or load changes upon the engine is the production of a large quantity of carbon particulates, commonly referred to in aggregate as soot, which comes from the incomplete combustion of the diesel fuel mixture within the engine cylinders. This generation of soot is undesirable, and may be prevented using modem engine control circuitry if detected by a sensor and conveyed to an engine electronic control unit (ECU). Similarly, the proper operation of scrubbers in the smokestack or exhaust stream of a power plant, garbage incinerator, concrete plant, paper or pulp processing plant and the like may be monitored by measuring the particular content after treatment by the scrubbers. In the event of a malfunction or decreased efficacy of a scrubber, the monitor can be used to signal the need for service. Hazardous materials clean-up projects, including radioactive or contaminated materials and asbestos, will also require monitoring to ensure the hazardous materials are not displaced excessively through the air. Furthermore, in any environment where humans must exist, and more frequently co-exist with machines, there is the potential need for monitoring air for particulates.
Frequently complicating the need for adequate monitoring are factors which are dependent upon the site and the nature of the particulate to be monitored. One factor, for example in the case of a smoke stack, is the presence of large amounts of water vapor that are prone to condensation or adsorption. Any condensed or adsorbed water may be misinterpreted as additional particulate contamination, and so the sensor will most desirably be insensitive to water vapor contained within the gas or gas stream being monitored. A second factor complicating monitoring is the need for frequent or continuous sampling. Most preferably, a sensor may be placed within a smokestack or at a site and be left unattended for a predetermined period. During the unattended period, it would be most desirable for the sensor to continuously, or intermittently at predetermined times or time intervals, monitor the gas stream and record or store the results of the sensing. With the desire for automated monitoring comes the need for the sensor to operate through multiple measurement cycles without the need for repeated recalibration. A third factor complicating monitoring is the very small size and mass of contaminant particulates. In order to be air-borne, the particulates will typically be of very minute size and low mass. Sensitivity of the measuring device is very important, as is the actual retention of particulates within the measuring region. The potentially diverse size of the particulates can further complicate this retention, since different sized particles will typically be collected and retained differently strictly depending upon actual size. Another factor complicating monitoring is the industrial nature of many of the environments where the sensor will have application. During the operation of a diesel-fueled vehicle, there will typically be a large number of relatively low-frequency impacts or shocks that are unavoidably transmitted to the sensor. These shocks have been known in the prior art to overwhelm the sensor, resulting in inaccurate data generation. Furthermore, when the shocks are substantial enough, the very integrity of the sensor may be jeopardized. Finally, the industrial environment is prone to large electromagnetic pulses, which can disrupt sensitive electronic circuitry.
Monitoring of particulates has in the prior art most frequently taken the form of one or more commercial sensors, including: opacity sensors that pass illumination, whether visible or otherwise, through the gas stream, commonly referred to as nephelometers; acoustical sensors that measure the conduction of sound waves through the gas; radiation sensors that monitor the attenuation of alpha, beta or gamma particles passing through the gas stream; or ones of various mass sensors. Nephelometers are affected by the particle sizes and shapes within the gas stream, as well as the content of the gas stream, temperature and the history of the device, including potential optical blocking or interference due to accumulations of soot or other particulates within the gas stream. Consequently, these devices tend to be relatively inaccurate over time, or highly complex requiring significant maintenance. Acoustical sensors suffer from the same issues including particle size with the gas stream, chemical content of the gas stream, temperature, and particulate composition, though they tend to avoid the adverse impact of soot accumulation. Radiation sensors suffer from negative publicity in terms of radioactive contaminants, and the encumbrances associated with operation, storage and disposal of used radiation sources and radiation-exposed materials.
In view of the various limitations of the other devices, mass sensing devices have proven to be most practical for many diverse particulate measuring applications. These devices provide direct measurement of the mass of the particulates, which is a distinct advantage over the other sensing techniques outlined herein above. The basic principle behind these devices is that a mechanical system having mass in combination with a mechanical energy storage device will oscillate harmonically at a particular rate, referred to as the natural resonance frequency. This frequency is related to the system stiffness and mass. As the mass increases, such as when particles in a stream are collected, the natural resonance frequency decreases. The decrease in frequency is directly proportional to the increase in system mass. Consequently, and quite desirably, mass sensing devices have much simplicity to offer in the marketplace. Among the mass sensing devices are those gravitational sensors that provide for particle collection and weighing upon a surface parallel to the ground, wherein the collected particulate will be weighed based upon the natural force of gravity applied directly to the mass. Unfortunately, these sensors are sensitive to the direction of orientation of the sensor, and are generally also quite sensitive to shock or vibration generated externally from the sensor but coupled therewith. These sensors also do not typically have a good method for trapping or retaining particulates.
A more preferred method of sensing particulates is described as inertial sensing. Inertial sensors are designed to mechanically oscillate at a particular frequency. The addition of mass changes the natural resonance frequency of the sensor, just as with mass sensors described above, and so the frequency change can be used to directly measure the actual mass of a sample material. Among these types of sensors are oscillating fiber microbalances, where mass determination is made by monitoring the frequency change of a fiber clamped at one end and caused to oscillate with and without a mass load on the free end. These sensors tend to be fragile and susceptible to vibration or shock in the field.
Tapered Element Oscillating Microbalances (TEOM) use a tapered rod or element that oscillates at a unique frequency based upon mass loading. This technique, which has experienced particular success in the marketplace, typically incorporates a piezoelectric oscillator f
Bloom Leonard
Gamson Robert M.
Gibson Randy W.
Los Robles Advertising, Inc.
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