Measuring and testing – Liquid level or depth gauge – Float
Reexamination Certificate
2000-12-20
2002-07-16
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Float
C073S319000, C340S623000
Reexamination Certificate
active
06418788
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to a Hall sensor configured linear displacement transducer which contains magnet that is float activated by way of a spring-float system with precise magnitudes of liquid buoyancy, spring constants, and float density. Together, the linear displacement transducer and the spring-float system combine to form a submersible head unit of this device. The analog output voltage of each of the Hall sensors within the head unit are communicatively connected (either by wired or by wireless connection) to a remote electronic signal conditioner. Depending upon the operational configuration of the floats in the system and the original initialization of the device, the electronic conditioned signal provides two possible measures. When the head unit is configured as a liquid density meter and is completely immersed in a liquid, the combination of the submersible head unit and the electronic signal conditioner constitutes the liquid density meter that provides for measuring and monitoring the density (specific gravity) of the liquid. When the head unit is configured as liquid level meter and is immersed in a container which hold the liquid, the combination of the submersible head unit and the electronic signal conditioner constitutes the liquid level meter that provides for measuring and monitoring the level (height) of the liquid in the container.
2. Description of the Related Art
There are many different types of devices that use different technologies to measure either the density of a liquid or the level of a liquid in a container. In this invention, the basic operating principle of either application can be categorized as being a float-activated device that is responsive to the buoyancy force of the float in the liquid. From physics, the buoyancy force produced by a float in a homoglneous liquid is equal to the weight of the liquid that is displaced by the float. Since buoyancy force is linear with respect to the density of the liquid within which the float is submerged, the measure of the buoyancy force yields a measure of the density of the liquid. Further, since buoyancy force is linear with respect to the volume of liquid displaced by the float within the liquid, then the measure of buoyancy force of a float within a liquid within a container yields a measure of the level (height) of the liquid within the container.
The measure of buoyancy force produced by a float in a liquid is generally dependent upon the measure of the displacement of the float within the liquid by way of a displacement transducer. The liquid density/liquid level meter in this invention uses a distinctive linear displacement transducer that is based on the operating principles of Hall sensors. This distinctive linear displacement transducer is coupled with a spring float system whose parameters meet precise performance criteria.
Discussed below are many conventional liquid density or liquid level measuring devices that are based on the principle of a float-activated system. In a general sense, they differ from each other in regards to the different transducer means that each one utilizes for detecting the relative position of the float in the liquid.
In U.S. Pat. No. 3,089,502, a conventional hydrometer bulb acts as a float that activates the position of a magnetic core of a differential transformer whose output voltage monitors the position of the bulb so as to measure the liquid density.
In U.S. Pat. No. 3,954,010, a float activates the on/off position of the sight line of a beam of light into a light sensor and this is the means for detecting the position of the float in the liquid.
Both U.S. Pat. No. 3,964,317 and U.S. Pat. No. 4,400,978 utilize a similar principle whereby a float activates the position of an electrical sensing coil that is in the vicinity of a stationary magnet. A force-balance restoring current is established in the coil to restore the coil to a neutral position and the magnitude of this current is a measure of the buoyancy force and density of the liquid.
In U.S. Pat. No. 4,015,477, a float activates the position and radius of curvature of a magnetostrictive sensitive wire that is electrically sensed to measure the displacement of the float and, thus, the buoyancy force of the liquid.
In U.S. Pat. No. 4,981,042, a float activates the position of a lever that is connected to the float by way of a pivot assembly. The position of the lever is sensed electronically to measure the displacement of the float to determine the buoyancy force and, thus, the density of the liquid.
In U.S. Pat. Nos. 5,253,522 and 5,471,873, a float activates the position of a toroidal magnet that surrounds a sonic waveguide. A reference magnet also surrounds the waveguide and is positioned at a distance away from the float magnet. An electrical impulse wave is sent along the waveguide and both magnets provide a reflected torsional (magnetostrictive) pulse. The time difference between the reflected signals from the two magnets is indicative of the relative position of the float in the liquid and, thus, the buoyancy force and density of the liquid.
In U.S. Pat. No. 5,447,063, a float activates the tilt of one end of a balance beam. A sensor employs a differential transformer to detect the magnitude of the tilt, thus providing a measure of the buoyancy force and density of the liquid.
In U.S. Pat. Nos. 5,744,716 and 5,847,276, a float activates a pair of force transducers that give a direct measure of the buoyancy force and, thus, the density of the liquid.
U.S. Pat. No. 4,920,797 describes a liquid level sensor with a spring-float assembly and a displacement transducer. In U.S. Pat. No. 4,920,797, two springs hold a single float, which activates the position of a magnet in the vicinity of a Hall sensor.
In addition to the principle of float-activated systems, there are many other different technical approaches to measuring either liquid density or liquid level. Briefly, they are refractive index, vibrating tube, capacitive, vibrating plate, vibrating pipe, radiation, differential pressure, Coriolis meter, inductance coil, and bubble probe.
SUMMARY OF THE INVENTION
This invention utilizes a linear displacement transducer whose operating principle is based on the voltage-generating characteristic of Hall sensors. Hall sensors are devices that produce a voltage that is proportional to the magnitude of the transverse magnetic field that intercepts the sensitive plane of the sensor. Edwin H. Hall first discovered the Hall principle (reference: R. P.Winch, Electricity and Magnetism, 1963, Prentice Hall) in 1879.
The Hall sensor linear displacement transducer acts as the proximity-sensing element in the operation of this invention. Hall sensors (two or more) are configured on a non-magnetic sensor fixture assembly such that the sensors are equal-angularly spaced about the circular periphery of the cylindrical sensor fixture. Within the sensor fixture is a concentric borehole that allows for a nonmagnetic actuator rod to move axially between the Hall sensors. An axially aligned permanent magnet is embedded within the actuator rod. The Hall sensors provide an output voltage that is proportional to the magnitude of the radial (transverse) magnetic field that intercepts the sensitive plane of the sensor. As the magnet moves axially in a lateral slide-by approach with respect to the sensors, each of the sensors generates an output voltage that is continuous and linear with respect to the displacement.
A cylindrical (or a rectangular) permanent bar magnet is used in this invention to provide the magnetic field for the Hall sensors. The magnetic field associated with a permanent magnet depends upon the geometry and the magnetization of the magnet. In addition, the magnitude and the direction of the magnetic field depend upon the point of observation with respect to the magnet. From a head-on observation of the field on the longitudinal axis at a distance from one of the poles of the magnet, the field has a direction that is parallel to the longitudinal a
Foley & Lardner
Frank Rodney
Williams Hezron
LandOfFree
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