Method and apparatus for determining liquid level
First Claim
1. An apparatus for measuring the level of liquid in a tank comprising:
- (a) an elongate ferromagnetic element adapted to be mounted vertically within the tank;
(b) means for applying to one end of said element an ultrasonic pulse which propagates through said element;
(c) at least first and second magnet means adjacent said element, one above the other, each of said magnet means being responsive to the passing of said ultrasonic pulse to produce corresponding first and second electrical pulses in said element;
(d) means for mounting said first magnet means fixed in position;
(e) a float supportable by the surface of said liquid and carrying said second magnet means, whereby the vertical position of said second magnet means corresponds to the level of said liquid;
(f) electrical signal sensing means coupled to said element to receive said electrical pulses; and
(g) timing means coupled to said sensing means to produce an output signal responsive to the time period between said first and second electrical pulses.
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Abstract
An ultrasonic level measuring system is disclosed for determining by a time-ratioing technique the level of a liquid within a storage tank. An instrument sensor assembly, including a waveguide formed of a tensioned, ferromagnetic wire having a low thermoelastic coefficient is vertically supported within a storage tank containing a liquid. The waveguide is positioned to span both the tank liquid and vapor spaces. Two permanent magnets are positioned in close proximity to the waveguide at a known dimensional separation which defines the calibration span of the system. The waveguide and magnets are housed in a protective shield which acts as a process barrier and which is convoluted over a substantial portion of its length allowing the instrument sensor assembly to be easily transported and installed. A float, housing a permanent magnet, is positioned concentrically about the instrument sensor assembly to rise and fall with the liquid level.
An ultrasonic transducer is formed of a field coil wrapped about a section of permanently magnetized, magnetostrictive wire. The magnetostrictive wire is butt welded to the top end of the waveguide.
The field coil is excited by a current pulse introducing a torsional ultrasonic pulse into the waveguide. As the ultrasonic pulse passes each of the three magnets (i.e., the top, float and bottom magnets), a low level voltage pulse is generated across the waveguide. The voltage pulses are detected and amplified by sensing circuitry and coupled to a signal processing unit. The processing unit produces an output signal indicative of the liquid level by ratioing the time interval between the float and bottom magnets to the time interval between the top and bottom magnets. The resulting ratio is scaled by being multiplied by the known distance between the top and bottom magnets, (i.e., the calibration span) to produce a measure of the liquid level in the tank.
50 Citations
24 Claims
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1. An apparatus for measuring the level of liquid in a tank comprising:
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(a) an elongate ferromagnetic element adapted to be mounted vertically within the tank; (b) means for applying to one end of said element an ultrasonic pulse which propagates through said element; (c) at least first and second magnet means adjacent said element, one above the other, each of said magnet means being responsive to the passing of said ultrasonic pulse to produce corresponding first and second electrical pulses in said element; (d) means for mounting said first magnet means fixed in position; (e) a float supportable by the surface of said liquid and carrying said second magnet means, whereby the vertical position of said second magnet means corresponds to the level of said liquid; (f) electrical signal sensing means coupled to said element to receive said electrical pulses; and (g) timing means coupled to said sensing means to produce an output signal responsive to the time period between said first and second electrical pulses. - View Dependent Claims (2, 3)
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4. An apparatus for measuring the level of liquid in a tank comprising:
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(a) an elongate ferromagnetic element adapted to be mounted vertically within the tank; (b) means for applying to one end of said element an ultrasonic pulse which propagates through said element; (c) first, second and third magnet means adjacent said element and responsive to the passing of said ultrasonic pulse to produce corresponding first, second and third electrical pulses in said element; (d) means for mounting said first and third magnet means fixed in position one above the other; (e) a float supportable by the surface of said liquid between said first and third magnet means and carrying said second magnet means, whereby the vertical position of said second magnet means corresponds to the level of said liquid; (f) electrical signal sensing means coupled to said element to receive said electrical pulses; and
,(g) timing means coupled to said sensing means to produce an output signal responsive to the ratio of;
(1) the time period between said second and third electrical pulses, and (2) the time period between said first and third electrical pulses.
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5. An instrument for determining the level of liquid within a storage tank, comprising:
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(a) a ferromagnetic transmission medium adapted to be supported within such tank to span the vapor/liquid interface; (b) a first element adjacent said medium for generating a magnetic field about a first reference point along the transmission medium, said first point defining the maximum measurement level; (c) a second element adjacent said medium for generating a magnetic field about a second reference point along the transmission medium, said second point defining the minimum measurement level; (d) a third element interdisposed of the first and second elements and moveable with the liquid level, said third element for generating a magnetic field about a point on the transmission medium substantially at the liquid level; (e) means for generating a torsional ultrasonic pulse, said means being coupled to the transmission medium such that such ultrasonic pulse is introduced to the medium; (f) wherein the distance between the first and second elements is fixed at a predetermined dimension and, as said ultrasonic pulse passes each of said first, second and third points a respective voltage pulse is generated across the transmission medium; (g) sensing circuitry coupled in parallel with the transmission medium for sensing each of said generated voltage pulses; and
,(h) wherein the time-ratio of the three generated pulses is a measure of the liquid level. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A system for determining the level of liquid within a storage tank, comprising:
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(a) a section of ferromagnetic wire adapted to be supported vertically within such tank to span the vapor/liquid interface, said ferromagnetic wire made of a material having a low thermoelastic coefficient; (b) an ultrasonic pulse generator for applying to the upper end of said ferromagnetic wire a torsional ultrasonic pulse which propagates downwards through said ferromagnetic wire, said pulse generator including; (I) a section of magnetostrictive wire coupled to the upper end of said ferromagnetic wire, said magnetostrictive wire having a permanent, circumferential, magnetic polarization; (II) a field coil wrapped about said magnetostrictive wire; (III) a current source coupled to said field coil, said current source for exciting said coil with a current pulse producing an axially aligned magnetic field about the magnetostrictive wire; and
;(IV) wherein said axially aligned field interacts with said circumferential field to produce a pulsed torsional ultrasonic pulse in said ferromagnetic wire; (c) first;
second and third permanent magnets mounted one above the other and adjacent to the ferromagnetic wire, each of said magnets responsive to the passing of said ultrasonic pulse to produce respective first, second and third electrical pulses in said ferromagnetic wire;(d) a float supportable by the surface of such liquid between said first and third magnets and carrying said second magnet such that the vertical position of said second magnet corresponds to substantially the level of such liquid; and
,(e) sensing circuitry coupled in parallel with said ferromagnetic wire for sensing the presence of said electrical pulses, said sensing circuitry producing first, second and third digital signals which characterize the first, second and third electrical signals respectively and the time ratio of which is a measure of liquid level. - View Dependent Claims (17, 18, 19, 20)
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21. A method of determining the level of liquid within a tank, comprising:
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(a) introducing a torsional ultrasonic pulse into a ferromagnetic waveguide adapted to be supported vertically within such tank; (b) sensing the propagation of said ultrasonic pulse by a first, second and third datum points to produce a series of three time-related pulses the ratio of which is a measure of the level of such liquid, said datum points being defined by respective first, second and third magnets means situated along said waveguide; and
,(c) wherein said first datum point is a tank top reference, said second datum point is a level reference and is movable with the liquid surface and, such third datum point is a tank bottom reference. - View Dependent Claims (22, 23, 24)
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Specification