Abstract:
A wave guide probe for use with direct-read tank level gages to provide electric signal output is disclosed. The apparatus comprises a translucent tube, a wave guide probe, and an electronics assembly. The translucent tube is for containing a fluid interface. The wave guide probe is positioned in the translucent tube. The electronics assembly is operably associated with the wave guide probe for actuating the wave guide probe and producing an electrical output signal representative of a location of the fluid interface in the translucent tube. The apparatus provides both electronic and optical level indications and is well suited for tank applications.

Description:
FIELD OF THE INVENTION 
       [0001]    In certain aspects, this invention relates to improved level gages. In other aspects, this invention relates to methods for improving level gages. 
       BACKGROUND OF THE INVENTION 
       [0002]    Level gages are used to determine liquid level in opaque tankage. The simplest and most reliable type is a liquid sight monitor, also known as a direct reading level gage, or sight glass. It comprises a vertical translucent tube, generally constructed of glass or plastic, positioned outside of the tank and connected to the tank so that the liquid level in the tube is the same as the liquid level in the tank. An operator can determine the liquid level in the tank simply by viewing the liquid level in the tube. Direct reading tubular level gages are commonly employed on tanks having a working pressure of less than about 300 psig. 
         [0003]    Other types of level gages for tanks generally rely on electronics and/or a float for operability. An advantage of an electronic gage is that the level reading can be near instantaneously transmitted to a remote location for a continuous level readout. The electronic level signal can be used in automated process control. A potential drawback to the use of these types of gages is failure. Electronics and floats can both fail, making it extremely difficult to accurately determine the liquid level in the tank. It is also inherently difficult to verify that the signal produced by these types of gages is indeed representative of liquid level in the tank. 
         [0004]    Redundant systems are known. However, there exists need for providing redundancy in an increased cost-effective manner, and for cost effectively retrofitting existing sight glass systems to provide an electrical signal output for remote monitoring and automated control. 
       OBJECTS OF THE INVENTION 
       [0005]    It is an object of this invention to provide a redundant system for monitoring liquid level in tankage. 
         [0006]    It is another object of this invention to provide an electronic signal representative of the liquid level in a tank for transmission to a remote location. 
         [0007]    It is a further object of this invention to provide a cost-effective technique for retrofitting an existing sight glass system for an electronic output representative of liquid level. 
       SUMMARY OF THE INVENTION 
       [0008]    In one embodiment of the invention, there is provided an apparatus comprising a translucent tube, a wave guide probe, and an electronics assembly. The translucent tube is for containing a fluid interface. The wave guide probe is positioned in the translucent tube. The electronics assembly is operably associated with the wave guide probe for actuating the wave guide probe and producing an electrical output signal representative of a location of the fluid interface in the translucent tube. The apparatus is redundant and it is easy to calibrate the electronic signal to yield values representative of the position of the fluid interface. 
         [0009]    In another embodiment of the invention, there is provided a method for providing a tank having a sight glass level gage mounted on its side with an electrical output signal representative of a fluid level in the tank. The tank is provided with a sight glass level gage of the type comprising a generally vertically positioned translucent tube having an upper end and a lower end. A lower flow path means connects a lower end of the tube with an interior of the tank. An upper flow path means connects an upper end of the tube with the interior of the tank. The connections and the translucent tube are positioned so that a fluid interface in the translucent tube is representative of a fluid level in the tank. The method is carried out by positioning a wave guide probe in the translucent tube, and providing an electronics assembly operably associated with the wave guide probe for actuating the wave guide probe and producing an electrical output signal representative of a location of the fluid interface in the translucent tube. 
         [0010]    The method provides a simple and inexpensive way to convert direct level reading systems into electronic systems that can be monitored at a remote location, while at the same time preserving the direct read feature which permits errors to be detected. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a side view, partly in schematic, showing a direct reading level gage according to the prior art. 
           [0012]      FIG. 2  is a frontal view of a probe according to an embodiment of the invention that can be installed in a prior art system as shown in  FIG. 1  to provide electrical output signals. 
           [0013]      FIG. 3  is a side view, partly in schematic, showing the probe of  FIG. 2  installed in the equipment of  FIG. 1 . 
           [0014]      FIG. 4  is an exploded view of another embodiment of the invention. 
           [0015]      FIG. 5  is a side view of a level gage and transmitter assembly containing the invention shown in  FIG. 4 . 
           [0016]      FIG. 6  shows a front view of an electronic hardware assembly which can be used in an embodiment of the invention. 
           [0017]      FIG. 7  is a side view of the electronic hardware assembly shown in  FIG. 6 . 
           [0018]      FIG. 8  shows schematically shows a Sensor Assembly which can be used in an embodiment of the invention. 
           [0019]      FIG. 9  shows as a block diagram a system of preferred electronic components which can be used in an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In one embodiment of the invention, there is provided an apparatus  2 ,  102  comprising a translucent tube  4 ,  104 , a wave guide probe  6 ,  106 , and an electronics assembly  8 ,  108 . The translucent tube is for containing a fluid interface. The wave guide probe is positioned in the translucent tube. The electronics assembly is operably associated with the wave guide probe for actuating the wave guide probe and producing an electrical output signal representative of a location of the fluid interface in the translucent tube. The apparatus is redundant and it is easy to calibrate the electronic signal to yield values representative of the position of the fluid interface. 
         [0021]    The translucent tube can be the same in size as employed in prior art direct-reading apparatus. See  FIG. 1 . Generally speaking, the translucent tube has an inside diameter in the range of from about 0.5 inches to about 4 inches, and a length in the range of from about 1 to about 50 feet. Usually, the translucent tube has an inside diameter in the range of from about 0.75 inches to about 1.25 inches and a length in the range of from about 5 feet to about 25 feet. The wave guide probe according to the invention is sized to fit in the translucent tube. Generally, the wave guide probe has an outside diameter in the range of from about 0.1 to about 0.5 inches. 
         [0022]    In one embodiment, the wave guide probe comprises a nonmagnetic outer tube  12  and a magnetostrictive wire  14  axially positioned in the outer tube. A magnetic annularly shaped fluid-interface-seeking float  16  rides the outer surface of the nonmagnetic outer tube so as to be in the annulus between the nonmagnetic outer tube and the translucent tube when the apparatus is in use. If desired, however, a radar-principled device could be used. 
         [0023]    If desired, a plurality of magnetic annularly-shaped fluid-interface-seeking floats can ride the tube to enable the detection of multiple interfaces. For example, in  FIGS. 4 and 5 , a float  116  can be provided with an apparent density to seek an upper interface, for example, gas/oil, and a float  116 ′ can be provided with a greater apparent density so that it seeks a lower interface, for example, oil/water. In the illustrated embodiments, the translucent tube is also partially surrounded by an optional protective shield  18 ,  118 . 
         [0024]    The electronics assembly comprises a housing  25 ,  125 , an electric pulse generator  300 , and a torsion sensor  302 . The housing is positioned on an upper end of the wave guide probe. The electric pulse generator is positioned in the housing for transmitting an electric pulse through the magnetostrictive wire  6 . The torsion sensor is positioned in the housing for sensing a torsional strain induced in the magnetostrictive wire by the magnet in response to the electric pulse and producing an electrical output signal representative of a position of the magnetic annularly-shaped fluid-interface-seeking float. 
         [0025]      FIG. 6  shows a front view of the electronic hardware assembly. The front face carries pushbuttons  306  for operator input and configuration and a diagnostic connector  308  for allowing access to internal electrical signals. A display  310  is provided for local display functions. 
         [0026]      FIG. 7  is a side view of electronic hardware assembly. Electronic module  311  contains the elements shown in  FIG. 9 . A wiring/filter printed circuit board  312  is mounted aft for providing interconnection between the Electronic Module and the Sensor Assembly shown in  FIG. 8  as well as for connection with field wiring. 
         [0027]      FIG. 8  shows the Sensor Assembly in schematic form. The torsion sensor  302  has the nonmagnetic tube  6  extending from one end, and a wiring harness  214  extends from the other end for connection to the circuit board. In practice, a brief current pulse is applied to the wire  10 . A torsional disturbance is created when a suitable magnetic field is present near the wire. The torsional disturbance subsequently propagates through the wire at a constant velocity. A mode conversion device located at the end of the sensor assembly converts the torsional disturbance into an electrical signal which is passed to the electronic module for processing. 
         [0028]      FIG. 9  is a block diagram of preferred electronic components. Power is provided to the circuit board at connector  316 . The electronics module contains a microprocessor PCB assembly  318 , a magnetostrictive PCB assembly  320 , and a user interface, all operatively connected with circuitry. 
         [0029]    In another embodiment of the invention, there is provided a method for providing a tank, such as a prior art tank  200  in  FIG. 1 , having a sight glass level gage  202  mounted on its side with an electrical output signal representative of a fluid level  204  in the tank. The sight glass level gage is of the type comprising a generally vertically positioned translucent tube  4  having an upper end and a lower end. A lower flow path means  220  connects a lower end of the tube with an interior of the tank. An upper flow path means  222  connects an upper end of the tube with the interior of the tank. The upper flow path means, the lower flow path means, and the translucent tube are positioned so that a fluid interface in the translucent tube is representative of a fluid level in the tank. The method is carried out by positioning the wave guide probe  8  in the translucent tube, and providing an electronics assembly operably associated with the wave guide probe for actuating the wave guide probe and producing an electrical output signal representative of a location of the fluid interface in the translucent tube. The improved device with the added functionality can be as shown in  FIG. 3 . 
         [0030]    Because the method is for adapting a prior art device for electrical signal output at minimal expense, the translucent tube from the device being improved is preferably not replaced. Generally speaking, the translucent tube has an inside diameter in the range of from about 0.75 inches to about 2.00 inches and a length in the range of from about 1 foot to about 25 feet. The wave guide probe has an outside diameter in the range of from about 0.25 to about 0.50 inches and is sized to fit the tube. 
         [0031]    Although a radar wave guide probe can be used, a magnetostrictive probe may be preferred. In the magnetostrictive probe embodiment, the wave guide probe comprises a nonmagnetic outer tube with a magnetostrictive wire axially positioned in the outer tube. It is positioned in the translucent tube so as to form an annulus between the nonmagnetic tube and the translucent tube. A magnetic annularly shaped fluid-interface-seeking float is positioned in the annulus between the nonmagnetic outer tube and the translucent tube. 
         [0032]    For use, an electric pulse is transmitted through the magnetostrictive wire. Passage of the pulse by the magnet induces a torsional strain wave which travels back up the wire. The torsional strain induced in the magnetostrictive wire by the magnet in response to the electric pulse is sensed. An electrical output signal representative of a position of the magnetic annularly shaped fluid-interface-seeking float is then produced for transmission, such as by wire, radio wave, or light wave, to a remote monitoring and/or control location. 
         [0033]    While certain preferred embodiments of the invention have been described herein, the invention is not to be construed as being so limited, except to the extent that such limitations are found in the claims.