Apparatus for measuring the liquid contents of a tank

Apparatus for measuring weight, level and or volume of a volatile liquid in a sealed container, comprising: a housing, capable of sustaining high pressure; a load cell, located within the pressure housing, mounted on an external pipe flange at the top of a sealed container having known cross section and containing a liquid of a known specific gravity; a displacer weight of known weight and length passing through the pipe flange opening and suspended above the bottom of the container. The apparatus, operating on the inferential method of determining liquid quantity by weight in a sealed vessel, works on the principle that when there is no liquid in the tank, the load-cell and its meter system sense the maximum weight of a displacer cylinder which is the null or "Zero" point for measurement. The buoyancy of the displacer weight in the liquid then reflects the volume in the container via a meter/computer display.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for measuring the amount of 
liquid in a tank and, more particularly, to an apparatus for measuring the 
weight, level and/or volume of a liquid in a sealed container. 
2. General Background 
The prior art suggests a number of methods and apparatus for measuring the 
liquid level in a tank. Some utilize ultrasonics while others use a float 
system in combination with the magnetostrictive principle. Other apparatus 
rely on sensor arrays to determine the mass of the liquid in a container 
then calculating the volume based on the mass, specific gravity of the 
liquid and adjusting for temperature variations. All such devices and 
systems have one thing in common, they all have various degrees of error. 
Each system strives to reduce the error, and in doing so, the systems 
become more complicated. One such system is disclosed by Zfira in U.S. 
Pat. No. 5,157,968. Zfira discloses a system for measuring the specific 
gravity, weight, level and/or volume of a liquid in a container. However, 
Zfira employs a dual system, one for measuring specific gravity where the 
liquid may change from time to time and the second for measuring the mass 
of the liquid thus determining the quantity of liquid in the container. 
The system requires two load cells, two body weights and two transmitters 
to send data to a computer monitoring system which, in effect, produces 
two input signals, thereby, inducing a second error factor. Any system 
which relies on multiple sensors or inputs compounds its potential for 
error. The Zfira patent does not disclose a means for operating under 
pressure. The known systems are usually relatively complicated and are 
limited as to the types of liquid measured without using multiple sensors. 
Such systems do not address the need for a simple system having a single 
input for measuring a known type of material, contained in a vessel, 
designed for storing a specific volatile liquid. In some such cases, it is 
essential that the apparatus be capable of operating while under pressure 
and be calibrated without opening the enclosure or otherwise disturbing 
the integrity of the vessel. 
SUMMARY OF THE PRESENT INVENTION 
It is an object of the present invention to provide a simple and efficient 
apparatus which may be used for measuring the mass, level and/or volume of 
a volatile liquid under pressure, in a container, regardless of its 
temperature variation. 
Another object of the invention is to provide an apparatus which can 
monitor the mass of liquid in a sealed tank or vessel in real time, as the 
level changes, with only one input signal. Still another object of the 
invention is to provide a load cell apparatus for taking such measurements 
in a pressure tested housing for mounting to a container's existing pipe 
flange. According to the present invention, there is provided an apparatus 
for measuring the mass and/or volume of a liquid of known specific 
gravity, in a container of known cross sectional area. The apparatus is 
comprised of; a load cell device at the upper end of the container, 
mounted in a pressure tested housing, attached to the tank or container's 
spool flange, in a vertical position; a sealed, hollow, cylindrical 
free-body having a uniform cylindrical configuration of a known cross 
sectional area and weight, the free-body extending through the interior of 
the container, with the upper end of the body supported by the load cell, 
with the lower end of the free-body clear of the container bottom, the 
free-body being adaptable in length, depending on the container depth, the 
free-body referred to herein as a displacer, having a diameter and weight 
which depends on the container depth, specific gravity of the fluid to be 
measured, and in some cases, the size of the container flange, the 
displacer being of sufficient length so that it would normally be only 
partially submerged by the liquid in the container; and a power 
supply/signal conditioner located adjacent the load cell for excitation of 
the load cell and electrically transmitting the signals generated by the 
load cell as a result of movement by the displacer's buoyancy in the 
liquid, to a remote computer for interpretation of the tank's mass and/or 
volume of the liquid in the container. 
This method of measurement, known as an inferential method of determining 
liquid quantity by weight in a sealed vessel, works on the principle that 
when there is no liquid in the tank, the load-cell and its meter system 
senses the maximum weight of the displacer which is the null or "Zero" 
point for measurement. As the known liquid rises, the load cell senses 
less strain due to the buoyancy of the displacer cylinder at a given 
specific gravity, depth and pressure. Although the liquid in the container 
expands with temperature increase, the liquid level on the displacer 
cylinder will increase and the specific gravity of the fluid will 
proportionately drop. The load cell will not see any change since the 
total weight of the liquid in the tank has not changed. Therefore, there 
is no need for temperature compensation of measured values since the free 
body or displacer cylinder sees only the weight of the fluid it displaces 
and not simply the liquid level.

DESCRIPTION OF TEE PREFERRED EMBODIMENT 
The present invention 10 as first seen in FIG. 1, is comprised of a dome 
shaped, pressurable housing 12 having a heavy, external flange collar 14 
for coupling to a mating flange 16 on a container or vessel 18, as best 
seen in FIG. 3, with the dome of the housing 12 fitted with a threaded 
coupling 20 at its peak and externally plugged with a hex-head, pipe plug 
22 having a lifting ring 24 secured thereto. The housing 12 further 
contains a support bar 26 secured internally for supporting a load cell 
28. A load cell 28 is attached to the internal support bar 26 via a bolt 
30 and is fitted with a pipe nipple 32 secured at one end to the load cell 
28 thereby providing a conduit for the load cell cable 34. An externally 
threaded pipe nipple 36, which penetrates the side wall of the housing 12, 
is also provided and is seal welded at its open end to the load cell 
nipple 32. A transmitter/meter 40 having a power supply and a signal 
conditioning system may be threadably attached directly to the penetration 
nipple 36 for receiving and connection of, the load cell power and signal 
cable 34. Regardless of its location the power supply/signal conditioner 
provides excitation voltage to the load cell and receives signals from the 
load cell for transmission to a remote computer. An eyelet 42 is provided 
at the lower end of the load cell 28 for pivotal attachment 44 of a 
hollow, sealed, displacer 46 which is of known weight and length. The 
cylinder body or displacer 46 is capable of length adjustment as best seen 
in FIG. 2. 
Because many varying and different embodiments may be made within the scope 
of the inventive concept herein taught and because many modifications may 
be made in the embodiments herein detailed in accordance with the 
descriptive requirement of the law, it is to be understood that the 
details herein are to be interpreted as illustrative and not intended to 
limit the invention.