Measuring and testing – Liquid level or depth gauge – Thermal type
Reexamination Certificate
1999-08-03
2003-05-27
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Thermal type
C073S29000R, C073S204110, C073S204170, C340S622000, C374S016000, C374S045000, C374S054000
Reexamination Certificate
active
06568263
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to non-invasive detection systems and, more particularly, to a non-invasive system and method for detecting the level of fluid in a fluid containing storage vessel.
Conventional storage vessels, such as propane tanks, are beneficial both for their mobility and for their suitability to the energy needs of remote locations where access to other forms of energy is often unavailable or costly. As with any storage vessel, however, propane tanks have finite storage capacity and eventually run dry. Few are equipped with precise level detectors nor is it practicable or cost effective in most contexts to remove them individually from service for recharging. When propane tanks run dry, they can also become a safety hazard, particularly when pilot lights go out and during start-up operations.
Typical level detectors such as float-type gauges must be retrofitted to the vessels during assembly. Retrofitting usually requires that the vessel be shut down, depressurized and emptied. In operation, the gauge electronically signals an indicator located externally to the vessel; the signal corresponding to the quantity of product remaining in the vessel. Although generally effective, retrofitting these devices has been found impractical and uneconomical, as well as disruptive of operations.
Another method is level estimation using a computer. In particular, specially designed software is used to monitor usage and predict when refill or recharging is necessary. Previous liquid usage patterns are considered, as well as weather and other data. While useful, computers have been found generally unreliable in predicting runouts.
U.S. Pat. Ser. No. 5,209,115 (Bond) appears to disclose a liquid detector for thin-walled tanks including temperature sensors A, B and a heater
9
. Bond appears to disclose further that activation of the heater
9
causes different rates of increase in the temperatures sensed by sensors A, B depending upon the presence of liquid next to the tank wall
3
at the respective locations of the sensors A, B enabling detection of liquid at the respective locations. Bond, however, does not show or suggest the sensors A, B and the heater
9
contained in a modular unit which would facilitate their attachment-to the tank wall
3
. In contrast, separate mounting of each of the sensors A, B and the heater
9
on the tank wall
3
appears to be required in Bond. Additionally, Bond appears to provide a pressurant inlet
22
for the supply of pressurizing gas to the tank
1
in addition to the liquid propellant contained in the tank. Adding pressurizing gas to the liquid propellant in the tank
1
obstructs reaching thermodynamic equilibrium thereby inhibiting vaporization of the liquid propellant. This increases the proportion of the heat applied to the tank wall which increases the temperature of the tank wall rather than vaporizes the propellant. As a result, the temperature increase of the tank wall when liquid is present at the sensors A, B is closer to the increase when liquid is not so present thereby impeding indication of such liquid by the temperature difference. Moreover, the liquid detector of Bond appears to be for use in zero gravity which would inhibit convective circulation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a non-invasive system and method for detecting the level of fluid in a fluid storage vessel.
Another object of the present invention is to provide a durable, reliable and economical system and method for detecting the level of fluid in a fluid storage vessel.
A further object of the present invention is to provide a non-invasive system and method for detecting the level of fluid in a fluid storage vessel and signaling the same to a user.
Still another object of the present invention is to improve safety of fluid storage vessels, particularly in remote locations.
Yet a further object of the present invention is to provide a non-invasive system and method for detecting the level of fluid in a fluid storage vessel, which may be readily fitted to-any vessel without interruption of service or depressurizing and emptying the vessel.
Still a further object of the present invention is a system and method for detecting the rate of heat dissipation at the surface of a fluid storage vessel.
According to one aspect of the present invention there is provided a system for detecting the level of fluid in a fluid containing vessel. A device is provided for applying energy to a selected location on the vessel. A sensor in proximity to the location detects the energy level at the location during first and second time intervals. A memory device is provided for storing data representative of the energy detected by the sensor at each time interval. A logic circuit compares the amount of energy of the first time interval to that of the second time interval, and data corresponding to the level of fluid in the vessel is output to a display device. A power supply is also provided for operating the system.
In accordance with another aspect of the present invention is a system for detecting the level of fluid in a fluid containing vessel. A device is provided for applying energy to a selected location on the vessel. A first sensor in proximity to the energy location detects the energy level at the location at first and second time intervals. A second sensor, positioned at a selected distance from the surface of the fluid, detects the energy level at that position at the same time intervals as the first sensor. A memory device is provided for storing data representative of the energy detected by both sensors at each time interval. A logic circuit compares the amount of energy of the first time interval to that of the second time interval in each respective sensor, and data corresponding to the level of fluid in the vessel is output to a display device. A power supply is also provided for operating the system.
According to a further aspect of the present invention is a method of detecting the level of fluid in a fluid containing vessel, which comprises the steps of:
(a) applying energy to a selected location on the vessel;
(b) detecting the energy level at the location at time intervals using a first sensor in proximity to the energy location;
(c) detecting the energy level at that position at the same time intervals as the first sensor, using a second sensor positioned at a selected distance from the surface of the fluid;
(d) storing data representative of the energy detected by both sensors at each time interval in a memory device;
(e) comparing the amount of energy of the first time interval to that of the second time interval in each respective sensor, using a logic circuit; and
(f) outputting data corresponding to the level of fluid in the vessel to a display device.
In accordance with still another aspect of the present invention is a method of detecting the level of fluid in a fluid containing vessel, which comprises the steps of:
(a) applying energy to a selected location on the vessel;
(b) detecting the energy level at the location at a first time interval using a sensor in proximity to the energy location;
(c) storing data representative of the energy detected by the sensor at the first time interval in a memory device;
(d) detecting the energy level at the location during the second time interval;
(e) storing data representative of the energy detected by the sensor at the second time interval in the memory device;
(f) comparing the amount of energy of the first time interval to that of the second time interval using a logic circuit; and
(g) outputting data corresponding to the level of fluid in the vessel to a display device.
REFERENCES:
patent: 3161050 (1964-12-01), Exner
patent: 3461446 (1969-08-01), Sergeant
patent: 3465315 (1969-09-01), Alexander et al.
patent: 3485100 (1969-12-01), Petersen
patent: 3696675 (1972-10-01), Gilmour
patent: 4036053 (1977-07-01), Jenkins
patent: 4065967 (1978-01-01), Beeston
patent: 4089209 (1978-05-01), Grana et al.
patent: 4135186 (1
Cygan Michael
Larkin Daniel S.
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