Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
2001-01-08
2002-08-06
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
C356S028500, C073S861000
Reexamination Certificate
active
06429926
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical flow meters for measuring flow characteristics of a fluid in a pipe. More particularly, the present invention relates to an optical flow meter in which at least part of the optical flow meter mounts within the pressurized environment of the pipe. Still more particularly, the present invention relates to optical systems that are used to focus and collect light beams inside a pressurized pipe, and which are subjected to the fluid within the pipe.
2. Background of the Invention
In pipeline operations and other industrial applications, flow meters are used to measure the flow rate of gases or liquids moving through the pipeline or tubing system. In natural gas pipelines, for example, these flow rate measurements are used for custody transfer, leak detection, control, or for other purposes. Custodial transfers of hydrocarbons and other fluids require very accurate measurements of the fluid being transferred. The flow meter typically is used as the transfer point for a custody transfer to determine the amount of fluid that has been transferred. By accurately measuring the flow rate for a particular transfer period, the volume of liquid that flows through the pipeline can be determined, and a custody transfer volume ticket can then be prepared. The pipeline transportation fee is based on the volume of product moved through the system, i.e. the custody transfer volume. Thus, a custody transfer metering system is commonly referred to in the pipeline industry as the “cash register,” and pipeline operators take great care to maintain its measurement accuracy.
Various meters have been used to measure the flow of liquids in pipelines and other tubing systems. Existing meters can be separated into three general categories for purposes of discussion. The first type of meters is obstruction meters. Obstruction meters determine fluid flow rates by introducing a physical obstruction directly into the flow of fluid, and measuring the influence of the fluid on the obstruction. One type of obstruction meter is those that introduce a flow restriction in the pipeline, such as a reduced-diameter orifice plate. The flow restriction creates a pressure drop, which can be measured and used to calculate the fluid flow rate through the restriction. In addition to orifice meters, venturi meters and critical flow nozzles also make use of flow restrictions to measure fluid flow rates. Other obstruction meters include vortex meters.
Obstruction meters have the inherent disadvantage of extracting energy from the fluid flow as a consequence of the pressure drop. The inefficiencies caused by the physical obstruction require additional pumping capacity to overcome. In addition, the physical obstruction also acts as an impediment to using pipeline pigs or other devices that scrub the interior of the pipeline. In addition, because the obstruction-type meter is placed directly in the fluid flow, the meter components may be subject to premature wear, requiring maintenance and replacement. These meters also are characterized by low turndown ratios (i.e. a limited range of flow rates for which accurate measurements are possible) due to the non-linear relationship between flow rate and pressure drop.
The second type of flow meter is kinematic meters. Kinematic meters determine the flow rate by directly sensing the actual velocity of the fluid using a turbine blade assembly that rotates kinematically with the flow. The rotational speed of the turbine is measured using a frequency transducer, and then is empirically related to flow rate using an experimentally determined coefficient. Kinematic meters provide an output that is approximately proportional to volumetric flow rate and substantially independent of density. The primary disadvantage of kinematic meters is the presence of moving parts, the obstruction to the fluid flow, the requirement of electrical power, and the physical size of the meter.
The third class of flow meters are those that use non-intrusive methods to determine flow rate. The ultrasonic meter is the only meter in this category that has been commercially developed for use in high pressure natural gas pipelines. An ultrasonic meter compares the upstream and downstream transit times of an acoustic pulse from transducers located near the inside surface of the pipe. The fluid flow therefore is unrestricted, and thus these meters do not produce any significant pressure drop. These devices, however, require a relatively long installation length (on the order of a few pipe diameters), are limited to larger pipe sizes, and can suffer from acoustic noise in the vicinity of the meter.
As noted in U.S. application Ser. No. 09/065,364, entitled “Optical Flow Meter Integrally Mounted to a Rigid Plate With Direct Optical Access to the Interior of a Pipe,” incorporated by reference herein, optical flow meters are non-intrusive flow meters that potentially overcome many of the disadvantages that exist with existing commercial flow meters, if the optical flow meter can be designed in a sufficiently compact space, with adequate access to the pipe interior.
Flow rates may be determined with optical meters by measuring the velocity of particles suspended in a representative field in the fluid flow. The particles preferably are under 100 microns in diameter, and more preferably under 25 microns in diameter. The velocity is measured by determining the time-of-flight of these particles as they move between two discrete regions that have been illuminated with light from a laser. See e.g. D. H. Thomson, “A Tracer Particle Fluid Velocity Meter Incorporating a Laser,” Jour. Of Sci. Inst. (J. Phys. E.) Series 2, Vol. 1, 929-932 (1968). The time-of-flight concept has been applied to measure the air speed of an aircraft, as described in U.S. Pat. Nos. 4,887,213, 5,046,840 and 5,313,263.
Optical techniques also have been used by numerous investigators to make measurements in laboratory environments, such as wind-tunnels and turbo machinery. See R. Schodl, “A Laser-Two-Focuse (L2F) Velocimeter for Automatic Flow Vector Measurement in Rotating Components of Turbomachines,” Transaction of the ASME, Vol. 102, p. 412 (December 1980). Additionally, UK Patent 2,295,670 describes a configuration in which laser light from an argon ion laser is split by a Rochon prism, made parallel by a lens and then focused into two spots. Scattered light produced by particles passing through the two spots is imaged onto two photoelectric converters. Velocity is determined on the basis of the transit time of the particles passing between the two spots. U.S. Pat. No. 4,125,778 discloses a similar device, except that the relative position of the two spots can be rotated using an optical component. A variation on the time-of-flight principle using individually addressable laser diode arrays was described in U.S. Pat. No. 5,701,172 to measure the velocity profile inside a high pressure natural gas pipeline through a glass window. The image of the diode array produces a series of spots in space and the light scattered by small particles is collected and converted to electrical signals. The frequency content of the signal and the spacing of the spots of light are used to determine the flow velocity. Alternatively, the patent describes the system in combination with a holographic lens placed as a window in the pipeline wall, thereby permitting multiple measurement locations along one pipe diameter. However, the requirement of a relatively large glass window in the pipeline renders this design impractical for broad commercial applications because of cost and safety concerns.
Related U.S. application Ser. No. 09/065,364, entitled “Optical Flow Meter Integrally Mounted to a Rigid Plate With Direct Optical Access to the Interior of a Pipe,” describes an optical flow meter in which the optical components are mounted in a rigid plate that is placed within the pressurized pipe environment
Daniel Pierre-Jean
Kiel Darwin E.
Sharonov Sergei A.
Williamson Ian D.
Andrea Brian
Conley Rose & Tayon PC
Nova Gas Transmission Ltd.
Tarcza Thomas H.
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