Measuring and testing – Liquid level or depth gauge – Hydrostatic pressure type
Reexamination Certificate
2000-10-24
2003-01-28
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Hydrostatic pressure type
C073S302000, C073S864350, C073S299000
Reexamination Certificate
active
06510736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to devices for measuring the quantity, or more accurately the depth or pressure head, of a volume of liquid in a container. More specifically, the present invention relates to air bubble tube or “purge” type systems, wherein a gas is pumped to the bottom of the liquid tank and the pressure of the gas is measured to determine the pressure head, and thus the depth, of the liquid in the tank.
2. Description of the Related Art
The determination of a liquid quantity in a tank or other container is of great importance in a number of different fields, including the bottling and beverage industry (in both manufacturing and retail levels), vehicle fuel systems, closed lubrication systems, and a number of other applications. Accordingly, a number of different principles of measuring the quantity of a liquid in a tank or container, have been developed in the past. These different principles range from a simple calibrated stick, rod, or sight gauge, to float and arm type systems (as commonly used in vehicle fuel tanks), capacitance type systems for certain liquids, pressure sensing transducers disposed in the container bottom, to air bubble or “purge” type systems related to the present invention.
The air bubble or purge system operates essentially by providing pressurized air, which is forced through a tube extending downwardly to the bottom of the tank or container. When the air pressure is slightly above the liquid pressure at the tube outlet, the air pressure will force air bubbles from the lower or outlet end of the tube, thereby stabilizing the air pressure within the tube. This air pressure may then be equated to the pressure head of the liquid, and thus the depth of the liquid in the container. By knowing the volume of the container, a determination of the quantity or volume of liquid in the tank or container is made.
However, such purge systems as developed in the prior art have various drawbacks and deficiencies. Conventionally, such purge systems have relied upon a separate mechanical pressure regulator, which regulates pressure from a relatively high pressure source (pneumatic pump, compressed air source, etc.). Where a motor is used to supply the air pressure for such systems, the motor must be somewhat larger and more powerful than required to produce pressure sufficient to equal the pressure head of the liquid, as the motor must provide sufficient additional pressure over and above the regulated pressure. This, and the fact that the motor must run continuously, result in considerable energy usage and render such systems impracticable for many applications. Moreover, the mechanical regulators used in such systems are relatively delicate, requiring frequent adjustment due to vibration, ambient temperature and pressure changes, etc, and thus are not suitable for installations in vehicles, factory lines, etc.
Thus, a need will be seen for an air bubble or purge type liquid measuring system which overcomes these and other deficiencies in the prior art. Rather than using a continuously operating motor to supply the air pressure for the system, the present invention actuates the pneumatic motor only as necessary to supply air (or other gas) to the down tube or dip tube which extends into the liquid tank or container. The motor is controlled by a precision regulator and novel electrical and pneumatic circuitry providing such precision control. The present purge type system is capable of providing liquid depth sensing to extremely precise tolerances if desired, on the order of the diameter of a single bubble escaping from the dip tube. This, and other features, provide numerous advantages in the bottling industry, auto manufacturing industry, and other areas where precision filling of containers is required.
The present depth sensing system also lends itself well to applications in vehicle fuel tanks and systems, as the present system does not require any electrical wiring or circuitry within the fuel tank or system. The only intrusive elements within the tank or container, are the dip tube and vent tube which supply the pressure information to the sensing apparatus. Heretofore, such systems were impracticable for use in such vehicle fuel systems due to their weight, bulk, energy usage, maintenance requirements, and relative lack of sensitivity due to the relatively large continuous use motors required and the regulators used. The present system provides numerous advantages over such prior art devices.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 1,731,928 issued on Oct. 15, 1929 to Edward E. Johnson, titled “Constant Liquid Level Apparatus,” describes a device, for maintaining an essentially constant liquid level within a closed tank, filling the tank as the level drops and shutting off flow to the tank as the level rises to the point desired. The Johnson system operates on an entirely different principle than the purge line system of the present invention, with Johnson utilizing a pair of complementary mercury type switches in his system. Moreover, Johnson does not disclose any means of displaying the depth of the liquid in the tank, as he has no motivation to do so due to the constant level maintained by his system.
U.S. Pat. No. 2,502,578 issued on Apr. 4, 1950 to John I. McDaniel, titled “Liquid Level Control Device,” describes a system utilizing a pair of electrodes within a tank. When the liquid level drops below the lower electrode, a motor is energized to pump liquid into the tank. When the liquid level reaches the higher electrode, the motor is shut off. The McDaniel device thus uses an entirely different principle of operation from that of the present invention, and controls the liquid level only through a relatively broad range determined by the difference in heights of the two electrodes. Moreover, McDaniel does not provide any display of liquid quantity with his system.
U.S. Pat. No. 2,734,458 issued on Feb. 14, 1956 to Thomas B. Hayes, titled “Pump Speed Control Arrangement,” describes a compound system controlling a pump motor primarily by means of a “liquid rheostat” (i. e., a series of capacitor plates) within the tank. The capacitance of the plates varies as the liquid level varies, thereby controlling the speed of an output pump motor. Hayes also utilizes a pair of floats, with the lower float cutting off the motor and the higher float causing the motor to run at maximum speed. The inclusion of electrical components within the tank, and the lack of any liquid level display, both teach away from the present invention with its purge type system providing an extremely accurate readout of liquid level in a tank or container.
U.S. Pat. No. 3,213,795 issued on Oct. 26, 1965 to John W. Parks et al., titled “Fluid Handling System,” describes a bubble tube or purge type device wherein pressure from the pneumatic system is supplied to a smaller tank having two compartments. The first compartment receives the pneumatic pressure, while the second compartment contains a series of capacitance plates (“liquid rheostat”) therein. When the level of the main tank drops, the pneumatic pressure drops, causing the level of the auxiliary tank first chamber to rise and the second chamber to fall, thereby exposing more of the plates to control a reduction in the pump motor speed. The pneumatic motor runs constantly, unlike the present invention, to provide the required air supply to operate the system. Moreover, Parks et al. do not provide any display of the liquid level in the tank(s).
U.S. Pat. No. 3,794,789 issued on Feb. 26, 1974 to Johnnie J. Bynum, titled “Pressure Sensitive Control For Pump Regulator,” describes an electrical pump control circuit which shuts down the liquid pump in the event the pump cannot draw sufficient liquid, thereby preventing pump motor burnout. The Bynum system operates by measuring the pneumatic pressure captured within a closed tank. If
Jackson André K.
Larkin Daniel S.
Litman Richard C.
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