Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
2000-05-19
2002-04-09
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
C073S861060
Reexamination Certificate
active
06369881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical flow sensor which cross correlates digitized signals from a plurality of photodetectors that are separated in a direction parallel to a predetermined direction of gas flow and to a method of determining gas flow velocity in a predetermined direction.
2. Description of the Prior Art
Accurate flow rate measurement represents one of the biggest problems in industrial and environmental monitoring for contaminants in gaseous discharges. The problem of airborne pollution has become so acute that virtually all industries of any size are now monitored for compliance with applicable regulations or laws limiting gaseous discharges. While the determination of the concentration of pollutants, contaminants, noxious gases, and toxic gases in a gas flow has reached a satisfactory level of reliability, monitoring of the rate, and hence the volume of gas flow, has heretofore been rather inaccurate. As a consequence. The determination of the total extent of pollutants emitted from any particular facility has heretofore been uncertain.
Current technologies that estimate flow rate often rely upon a point sensor that intrudes into the path of a flowing gas, for example in the chimney or smoke stack of an industrial processing plant. The estimates for flow rate achieved with such instruments are often inadequate for industrial and environmental applications. One problem is that the intrusion of a sensor head into the flow medium, alters the resulting flow measurements. Furthermore, the flow medium being monitored is often very dirty and corrosive. Direct contact of the sensing head with the flow medium often quickly fouls the sensing head so that maintenance of the sensor is a major problem.
Attempts have been made to devise ultrasonic gaseous flow measuring devices. However, ultrasonic gaseous flow measuring instruments are very expensive and are rather inaccurate.
Since pollutants and contaminants often provide a distinctive color or conglomerated dust particles to a gaseous discharge, it is sometimes possible to visually monitor chimneys and smokestacks from a distance in order to ascertain a general estimate of rate of gaseous discharge. However, this requires a direct line of sight to the facility involved. Also, some noxious and toxic gases, such as carbon monoxide, are colorless. Moreover, visual observation is not an option at night or in inclement weather. Unfortunately, a monitored industrial facility may limit the volume of its gaseous discharges during the daytime only to increase them at night when the volume of gaseous discharge cannot be observed.
SUMMARY OF THE INVENTION
The present invention adopts an entirely new approach to measurement of the velocity of a gaseous flow. The invention utilizes an optical transmitter and an optical receiver located on opposite sides of a gas flow passageway, such as a chimney or smokestack. A beam of light is transmitted across the gas flow passageway. The receiver includes a plurality of photodetectors longitudinally separated from each other in a direction parallel to the predetermined direction of gas flow through the passageway. Particulate matter and eddies in the flowing gas produce scintillations in the beam of light transmitted across the passageway.
These scintillations are detected by all of the photodetectors on the opposite side of the passageway, but detection does not occur at the same time in each photodetector. Rather, since the particle or eddy that creates the scintillation is traveling downstream in the gas flow, the photodetector located furthest upstream will detect the scintillation earlier in time than a photodetector located further downstream. This physical phenomenon is similar to the moving shadow cast by a bird or a piece of debris being carried along on the wind.
In one broad aspect, the present invention may be considered to be an optical flow sensor for measuring gas flow velocity in a predetermined direction of gas flow. The optical flow sensor of the invention is comprised of an optical transmitter, an optical receiver, signal-controlled gain amplifier circuits, analog-to-digital converters, and a digital signal processor. The optical transmitter generates a collimated optical beam across the predetermined direction of gas flow. The optical receiver includes a plurality of receiving lenses all located in optical communication with the optical transmitter and in the path of the optical beam. The receiving lenses are separated from each other in a direction parallel to the predetermined direction of gas flow. A separate optical photodetector is provided for each of the receiving lenses. Each photodetector produces an electronic output that varies in response to scintillations occurring in the optical beam.
A separate signal controlled gain amplifier circuit is coupled to each of the optical photodetectors. A separate analog-to-digital converter is coupled to each of the gain amplifier circuits for separately digitizing outputs from each of the gain amplifier circuits.
A digital signal processor is coupled to receive inputs from all of the gain amplifier circuits. The digital signal processor determines the temporal cross variance of the digitized outputs for scintillation events detected separately by all of the photodetectors. The digital signal processor provides a path integrated flow rate in the predetermined direction of gas flow.
Preferably, the optical transmitter includes a single laser diode or an LED (Light-Emitting-Diode)and only two photodetectors are employed in the receiver. Preferably also, the optical transmitter includes a collimating lens having a diameter of about one inch focused on the laser diode, and each of the receiving lenses is about two inches in diameter and is focused on its photodetector. In the preferred embodiment of the invention the collimating lens produces a collimated optical beam.
In another broad aspect, the invention may be considered to be an optical flow sensor for measuring velocity of gas flow in a predetermined gas flow direction. The optical flow sensor is comprised of a transmitter, a receiver, signal-controlled gain amplifiers, analog-to-digital converters, and a digital signal processor. The transmitter includes an optical source and beam-forming optics for producing a collimated beam across the gas flow. The receiver is located in a line-of-sight path with the optical beam. The receiver includes a plural number of focusing receiving lenses. The receiving lenses are spaced apart from each other in a direction parallel to the predetermined gas flow direction. A separate photodetector is provided for each of the receiving lenses. Each photodetector produces an electronic output that varies with scintillation events occurring in the line-of-sight path. Separate signal controlled gain amplifiers are provided for each of the photodetectors. Separate analog-to-digital converters are coupled to each of the photodetectors for converting their outputs from analog to digital signals. The digital signal processor cross correlates the digitized signals from the photodetectors as a function of time delay between the detection of scintillation events to produce a signal indicative of velocity of gas flow in the predetermined gas flow direction.
In still another broad aspect, the invention may be considered to be a method of measuring velocity of gas flow in a predetermined linear direction. The steps of the invention include: transmitting a collimated optical beam across a volume of gas along an optical line-of-sight path intersecting the predetermined linear direction of gas flow and crossing the gas flow; receiving the transmitted optical beam with a plurality of receiving scintillation detectors spatially separated from each other in a direction parallel to the predetermined linear direction; generating a separate output signal from each of the receiving scintillation detectors in response to scintillations occurring in the gas flow; separately amplifying and digitizing each of the
Mull Fred H
Optical Scientific, Inc.
Tarcza Thomas H.
Thomas Charles H.
LandOfFree
Optical flow sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical flow sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical flow sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2833089