Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-03-31
2001-05-08
Lefkowitz, Edward (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S623000, C340S624000, C073S305000, C073S307000
Reexamination Certificate
active
06229448
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of storage tank fluid systems and, more particularly, to an intrinsically safe wireless overfill protection system for storage tanks.
BACKGROUND OF THE INVENTION
Industry and safety standards require that liquid storage tanks of the type located on petroleum tank farms be given periodic checks to determine the liquid level of each tank. Level indicators for such tanks typically comprise a tape and pulley apparatus with a float at one end of the tape within the tank and a mechanical level indicator at the other end.
This typical arrangement was improved on by Clarkson, U.S. Pat. No. 4,459,584 to include a transmitter for remote monitoring of liquid level, but the Clarkson system still required the use of the old tape and pulley system to monitor liquid level. This system suffered all of the common problems with the tape and pulley system in that such a system may mechanically jam, thereby disabling the movement of the float. Further, a large volume of volatile gases fills the conduit enclosing the tape and pulley, since this system is open to the tank. This feature alone presents a significant safety hazard. Further, the Clarkson system provides no means for calibration of the level detector, since it relies upon the old tape and pulley system.
We began the development of the present invention with a level monitoring and alarm system sold under the trademark Fillcheck®. This system included a transmitter that was mounted in an off-the-shelfNEMA-7 explosion-proof enclosure so as to enable it to be used in the electrically hazardous environments associated with petroleum storage tanks, pipelines, oil refineries, petrochemical plants, and fuel terminals. This type of mounting solved the problems described with regard to Clarkson, but it brought about certain shortcomings, such as the attenuation of the level signal. Mounting the transmitter and its antenna inside the explosion-proof enclosure significantly reduced the system's effective range. In this system, the explosion-proof transmitter had to be aimed toward its receiver or repeater for optimum performance. Further, that system was expensive, and the transmitter had to be equipped with a safety barrier so as to permit its connection to an external level switch, which added to system cost. That system was also heavy, in that explosion-proof enclosures are quite massive and add significantly to shipping and handling costs. Finally, explosion-proof enclosures are typically constructed of aluminum which is prone to pitting and corrosion, known as exfoliation, particularly when used in marine or coastal environments in which many refining and petrochemical facilities are located.
Thus, there remains a need for a tank level monitoring and alarm system which is intrinsically safe, minimizes the number of moving parts, and seals volatile gases within the storage tank. The present invention addresses this need in the art.
SUMMARY OF THE INVENTION
The system of this invention comprises four components: (1) a passive level switch or other passive sensor; (2) a transmitter; (3) a repeater (if required); and (4) a receiver. It provides easy installation, convenient calibration, and very low maintenance. It is specifically designed to provide fail-safe overfill protection for vessels where electrical power and/or alarm signal wiring to a supervised point are not available. Further, it is easily adapted to most systems which can include a passive sensor which provides an analog signal which is then transmitted by the system of this invention to a central monitor.
In a preferred embodiment of the invention, a mechanical level switch of appropriate design for the specific vessel is installed. The contacts of the level switch are connected to the intrinsically safe transmitter. When the switch is activated, the transmitter immediately broadcasts an alarm signal to the receiver. A relay output at the receiver is either opened or closed thus activating the alarm or other device attached to it. The relay output may also connect to a control apparatus, such as a signal transmitter to provide for remote operation of such devices as valves.
The level switch and transmitter package are powered by a secondary battery, such as for example a D cell size 3.6V lithium thionyl chloride battery. During non-alarm conditions, a supervisory signal is transmitted every 30 seconds which contains the transmitter identification and battery condition. It the receiver fails to hear from any of its transmitters, an inactive alarm is issued. Also, low battery alarms are issued before a transmitter's battery dies.
Any type of passive switching device that provides either normally open or normally closed contacts can be used with this embodiment of the invention. Further, the system of this invention is adaptable to virtually any type of passive switch or sensor which senses a parameter of interest. For storage vessels without floating roofs, a magnetic reed float switch can be used. These devices can be constructed of stainless steel, brass, or polypropylene. These float switches are available in either vertical or horizontal configurations, and can be made to virtually any length. Vertical models can optionally be equipped with a positive checking feature that enables the operator to magnetically lift the float without removing the assembly from the vessel.
The system of the present invention provides reliable, low cost, wireless overfill or other out of specification condition protection. Many areas now require overfill protection systems that operate redundantly of existing tank gauging devices. Thus, this system provides continuous fully supervised protection against conditions which routinely require monitoring. It includes a battery powered transmitter, so it needs no external electrical power at the storage tank. The transmitter is intrinsically safe (Class I Division 1 Groups C&D), and requires no FCC licensing. It has low installation and maintenance costs, and the alarms are provided with fail-safe aspects for increased reliability.
REFERENCES:
patent: 4369437 (1983-01-01), Thompson, Jr. et al.
patent: 4459584 (1984-07-01), Clarkson
patent: 5363093 (1994-11-01), Williams et al.
patent: 5642097 (1997-06-01), Martel
patent: 5708424 (1998-01-01), Orlando et al.
patent: 5762118 (1998-06-01), Epworth et al.
patent: 5946084 (1999-08-01), Kubulins
Bennett, Jr. Paul R.
Taylor, III J. Lawrence
Bracewell & Patterson, L.L
Innovative Sensor Solutions, Ltd.
Lefkowitz Edward
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