Abstract:
A simple, inexpensive, non-mechanical apparatus for monitoring the changing fluid level in a remote pre-existing container, without requiring access to the bottom (of the outside) of the container. Visual display of the level is in 10, 10% increments to full capacity. The 10 increments are available on a connector as data output for process control, if required. The level can be presented as “% Full”, Gallons, Feet, or whatever units are appropriate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The proposed system is intended to measure, remotely, the changing levels in primarily water-based fluid in an enclosed tank.  
         [0002]     Many systems are currently available to provide a display of the level of the liquid in a tank.  
         [0003]     U.S. Pat. No. 5,705,747 to Bailey discloses a system and method of displaying a level of a liquid contained in a tank, wherein the level of the liquid is measured using a sensing device and includes a user interface, a processor, and a scaleable graphical display.  
         [0004]     This is a complex, sophisticated system intended for a more demanding application requiring elapsed time related data and requires a special tank.  
         [0005]     U.S. Pat. No. 3,548,657 to Panerai et al, discloses a system which provides a vertical bar display representative of the level of the liquid using specific optical light-transmitting sensing device. The sensing device includes a plurality of optical reflection prisms simultaneously and uniformly illuminated by a luminous source located on one wall of the tank.  
         [0006]     This is a complex, sophisticated system intended for a more demanding application requiring a special and elaborate sensing system pre fitted to the tank.  
         [0007]     U.S. Pat. No. 4.987,776 to Koon discloses a storage installation which is capable of storing a variety of free-flowing materials, both conductive and non-conductive, includes a level sensing device which may be disposed either exteriorly or interiorly thereof. The device has either one or a plurality of level sensor and sensor circuit pairs which are preferably disposed vertically within a non-electrically conducting tube which may be hermetically sealed from contact with the stored material. The level sensors comprise respective sensing capacitors, each having effectively a single plate construction. Grounded electrical contacts, if relatively adjacent, may comprise the other side of the effective sensing capacitor. Electrostatic force lines flow outward from the sensing capacitor(s), and are differentially interfered with by the presence or absence of materials or objects to be sensed. Such interference affects the dielectric constant of the respective sensing capacitor, which can in turn be detected to drive a level indicator display.  
         [0008]     This is a capacitance sensing system, complex, sophisticated and intended for a more demanding application requiring a special and elaborate sensing system pre fitted to the tank. Also requires an oscillator.  
         [0009]     U.S. Pat. No. 4,780,705 to Beane discloses an overfill sensing system uses a capacitive sensor ( 12 ) on the interior of a tank for sensing the presence of a liquid to cease the filling process. The capacitive sensor ( 12 ) includes a sensing capacitor ( 16 ) and a reference capacitor ( 18 ) on separate arms of a bridge circuit ( 22 ). An oscillator ( 28 ) supplies an AC signal to the bridge circuit ( 22 ) divided by a variable resistor ( 30 ) to balance the bridge ( 22 ). A comparator ( 24 ) receives the output on each arm of the bridge ( 22 ) to sense a differential therebetween. When a liquid reaches the sensing capacitor ( 16 ), the capacitance changes from a predetermined capacitance, thereby changing the differential. A control circuit ( 14 ) is responsive to the differential at the output of the comparator ( 24 ) for visually indicating the status of the filling process and ceasing the filling process from the filling facility when a liquid has been detected.  
         [0010]     This is a capacitance sensing system, complex, sophisticated and intended for a more demanding application requiring a special and elaborate sensing system pre-fitted to the tank. Also requires an oscillator.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     It is thus the object of this invention to provide a simple system that fulfills a limited area of utilization. The proposed system provides an inexpensive, simple solution with no moving parts or special sensors and does not require access to the bottom of the tank, as in many cases, the tank is below ground or the problem of possible leaking has to be addressed. Unlike prior systems the invention can be fitted to a preexisting underground tank with limited access to the top of the tank and provides remote display over 300 feet from the tank being monitored. Also, as the invention is unique in its simplicity, it is restricted in its use as follows. 
    1. The fluid being monitored must have a conductivity greater than 16.3 μS/cm     2. The size of the tank must be known and fixed.     3. The fluid must not adhere excessively to the probe    
 
         [0015]     This eliminates its use for most oil based products but has many applications in the domestic, agricultural and industrial arena as follows:  
         [0016]     Successful tests have been carried out using this system with the following fluids:  
                                                           Rain water   Tap-water   Ground water           Pond water   Well-water   Swimming pool water           Milk   Beer   Wine           Ammonia   Bleach   Liquid detergent           Liquid fertilizer   Insecticide   Vinegar           Waste water   Septic Water                      
 
         [0017]     See table 3 and 4 for more detailed information.  
         [0018]     A pre-calibrated probe specifically designed for the user&#39;s application is one of the key design features. The probe was designed to have the maximum invulnerability to problems of contamination encountered by other similar systems. Unfortunately the length of the probe has to be anticipated in accordance with the depth of the levels being measured but can be made available in standard sizes or made to order. The standard 5 foot version is detailed and the changes necessary for a 4 foot version also described All have a standard 1¼ inch plumbing fitting. The system has been tested successfully to lengths over 300 feet and as small as 2 inches on the prototypes. It is anticipated that the users will be using standard sizes so mass production would not be a problem.  
         [0019]     The probe consists of 10 conductive plates mechanically placed at 10% increments along the length of the probe. As the fluid level rises and falls successive contact is made to the plates and the remote display is illuminated in 10% increments. Digital data is available.  
         [0020]     Other systems are generally more complicated and expensive and prone to failure in a hostile environment. This system is simple, inexpensive to produce, has no moving parts and does not use special sensors or transducers. The display electronics box with its power source can be at least 300 feet away from the measurement point providing true remote operation.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0021]     Note: Use the block diagram of  FIG. 2  to reference the sub assemblies, their drawings and FIG. Numbers.  
         [0022]      FIG. 1  is a diagram of the embodiment of a typical system as used on the prototype and preproduction version. A 5 foot deep, below ground tank was used for this purpose and for making drawings  FIG. 3 - FIG. 5 .  
         [0023]      FIG. 2  is a block diagram showing the complete system and its components referencing the appropriate assemblies and their drawings.  
         [0024]      FIG. 3  shows the mechanical detail of the integrated assembly. Inner probe, outer sheath, electronics box and interconnecting cables.  
         [0025]      FIG. 4  shows the mechanical details of the outer sheath  
         [0026]      FIG. 5  shows the mechanical details of the inner probe.  
         [0027]      FIG. 6  shows how the design would be changed for the embodiment of a 4-foot deep system.  
         [0028]      FIG. 7  is a complete electronic schematic of the electronics box.  
         [0029]      FIG. 8  shows the detail of the plate connection and associated parts.  
         [0030]      FIG. 9  shows the detail of the probe connector assembly  007 .  
         [0031]      FIG. 10  shows the detail of interconnecting cable assembly  003   
         [0032]      FIG. 11  shows the mechanical assembly of the display electronics box.  
         [0033]      FIG. 12  shows the detail of display electronics box interconnecting cable assembly  004   
         [0034]      FIG. 13  shows connection detail of Optional Data Output J 1 .  
         [0035]      FIG. 14  shows the display electronics box front panel  
         [0036]      FIG. 15  shows the drilling data of the front panel.  
         [0037]      FIG. 16  shows a photograph of the Electronics Display Box pre production version.  
         [0038]      FIG. 17  shows a photograph of the probe assembly (5 foot version). 
     
    
       [0039]     Table 1: A complete parts list of the components illustrated in  FIG. 7 , &amp;  14  is given in Table 1.  
         [0040]     TABLE 2: A complete parts list of the components illustrated in  FIG. 1-5  is given in Table 2  
         [0041]     TABLE 3: Sample measurements were carried out on common materials to test their compatibility. The results are shown in Table 3.  
         [0042]     TABLE 4: Table 4 was included for comparison of some published figures of EC (electrical conductivity) and their respective TDS (Total Dissolved salts) for naturally occurring water.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     There are many ways of monitoring the fluid level in a tank ranging from “looking into it”, using a dip stick, a mechanical float system or an external hydraulic eye glass to the most sophisticated computer controlled systems with elaborate sensors. The proposed system provides an inexpensive simple solution with no moving parts, or special sensors and does not require access to the bottom of the tank, as in many cases, the tank is below ground or the problem of possible leaking has to be addressed (See  FIG. 1 ). The power supply and electronics/display box may be 300 feet from the tank being monitored (see  FIGS. 1 &amp; 3 ) and only one electronics/display box is required to serve any number of tanks to be monitored.  
         [0044]     The key to reliable operation of the system over and above other systems available, is having a well defined on and off state for the indication of the liquid levels. This requirement was addressed in the design philosophy in the following manner:  
         [0045]     Contamination and malfunction of the measurement sensors or transducers is eliminated by not using small intricate expensive devices at all. Instead, a relatively large surface area (9 square inches) metal plate is used to detect each measurement increment. Details of the plates are shown in  FIG. 8 .  
         [0046]     Further definition of the exact turn on condition is achieved by the choice of the decision making circuits for the indicators in the electronics control box. This important aspect is fully described in the section below labeled “Electronic Circuit Theory of Operation”.  
         [0000]     Electronic Circuit Theory of Operation  
         [0047]     Refer to electronic schematic  FIG. 7 :  
         [0048]     PB  1  is a normally open push button switch. When a reading is to be taken, PB 1  “READ” is pressed LEDs  1  through LED  10  will illuminate in accordance to the fluid level in the vessel 10% through 100%. We shall use the 10 % reading circuit for the purpose of this description and the design is merely repeated for the 20% to 100% circuits.  
         [0049]     Q 1  is a PNP Bipolar Junction Transistor configured as a “normally off” switch. Under standard conditions the turn on voltage between the base and emitter connection was found to be 0.745 Volts. Normally open switch WL 10  and associated series resistance R 31  represent the fluid level reaching conducting the 10% plate or not.  
         [0050]     NOTE: R 31  represents the resistance of the fluid, once contact is made, and is not an actual component but is included, purely for demonstration of the theory of operation.  
         [0051]     WL 10  will close when the fluid level reaches 10%. R 2  was chosen as 6.8 Kohms such that 0.745 Volts or greater would appear at the base of Q 1  if R 31  was less than 61 Kohms. R 21  was chosen to limit the current flowing through LED  1 . R 1  was included as protection from static, interference and inadvertent shorting of the probe. The values used through out, were determined theoretically using normal electronics design techniques. They were then verified on a computer simulation and proven, with extensive “in the field” experiments to determine the most practical values using standard readily available components.  
         [0052]     The actual values of the components will vary considerably with manufacturer&#39;s tolerances and the prevailing conditions but extensive experiments have shown the components used, to provide correct performance and the best overall realization under the most demanding conditions.  
         [0053]     R 31 , (representing the resistance of the fluid) will vary considerably depending on the actual fluid being measured. 61 Kohms was used as the worse case scenario in the standard design presented here. Resistance values above this level will not provide reliable operation. It is therefore necessary to equate this value in terms of Electrical Conductivity (EC) for the fluid in question. It is normal to express the EC of fluids in units of μS/cm or derivatives thereof as shown in table 3. The probe design provides a +20% safety factor yielding 16.3 μS/cm as the minimum electrical conductivity of acceptable fluids. Fluids with lower EC values will not work reliably with the standard version of the proposed apparatus. (However R 2  may be increased in value to accommodate lower EC values for more specific requirements).  
         [0054]     It can be readily seen that the standard apparatus as described will function perfectly on all the common fluids it was claimed to.  
         [0055]     The 10 increments of “% Full” are made available as parallel data output at connector J 1  (see  FIGS. 7 &amp; 13 ).  
         [0056]     A complete parts list of the components illustrated in  FIGS. 7 , &amp;  14  is given in Table 1 
                                                     TABLE 1                       REF. No   Part   Description   Qty   Notes                                R1, 3, 5, 7, 9, 11, 13,   7001   330 Ohm ¼ watt   20           15, 17, 19, 21, 22,       5% resistor       23, 24, 25, 26, 27,       28, 29, 30       R2, 4, 6, 8, 10, 12,   7002   6.8 Kohm ¼ watt   10       14, 16, 18, 20       5% resistor       LED 1-10   7004   Red LED Everlight 5 mm   10       PB 1   7005   Push Button N/O switch   1       V1   7006   9 Volt Battery   1       BC1   7009   Battery Clip Connector   1       Q1-10   7007   2N3906 PNP Transistor   10       BD 1   7008   Circuit Board   1   Wired in accordance with  FIG. 7         BX1   7010   Electronics Box   1   Part # TB-4 All Electronics Corp       FP1   7011   Front Panel   1   See  FIG. 14         Ancillary Materials               Connecting Wire   6 foot               Solder 60/40                  
 
         [0057]     A complete parts list of the components illustrated in  FIG. 1-5  is given in Table 2 
                                                     TABLE 2                       REF. No   Part   Description   Qty   Notes                                CP1, 2, 3, 5, 6, 7, 8, 9, 10   8001   Conduction Plate   10   Fabricated as shown in  FIG. 8         CR1, 2, 3, 4, 5, 6, 7, 8, 9, 10   8002   Crimp Terminal   10   Ring term #22-#18 wire 8-10 stud       LK1, 2, 3, 4, 5, 6, 7, 8, 9, 10   8003   Stainless Steel Lock   10               Washer # 10       NT1, 2, 3, 4, 5, 6, 7, 8, 9, 10   8004   Stainless Steel Nut   10               # 10       BLT1, 2, 3, 4, 5, 6, 7, 8, 9, 10   8004   Stainless Steel Bolt   10               ½″ # 10       GR1, 2   8005   Grommet 9/32ID 9/16   2   Mouser Part # 5167-208       ANG1   8006   PVC angle ¾″ × .08 × 6′   1       CP1   8007   PVC Threaded End   1               Cap 1¼″   1       EI1   8008   PVC Elbow 1¼″   1       Cable assemblies   8009   Standard DB 25 Male to   1   Modified in accordance with               Male Printer Cable                       3″ Aluminum Adhesive   1               Tape. 6 foot role               PVC adhesive 8 oz   1                  
 
         [0058]     Sample measurements were carried out on common materials to test their compatibility.  
                                               TABLE 3                           Measurements were made on sample fluids using a proprietary       conductivity meter. The instrument was calibrated using a reference       standard conductivity solution of Potassium Chloride, traceable to NIST       standard reference certified material. Potasium Chloride Calibration       Solution 1413 μS/cm at 25 Degrees C.                Fluid Material   Conductivity                            Distilled water   3   μS/cm           Collected Rain Water   29   μS/cm           Bottled Drinking Water   53   μS/cm           Pool Water   245   μS/cm           Pond water   395   μS/cm           Chlorinated filtered Farm Tap water   454   μS/cm           Light Beer   900   μS/cm           Swimming Pool Water   1400   μS/cm           1% Low Fat Milk   1999+   μS/cm           Orange Juice from Concentrate   1999+   μS/cm           Guinness Stout   1999+   μS/cm           Burgundy Wine   1999+   μS/cm           Black Coffee   1999+   μS/cm           White Coffee   1999+   μS/cm           Household Ammonia   1999+   μS/cm           Dishwashing Detergent   1999+   μS/cm           Household Bleach   1999+   μS/cm           Septic tank sample   1999+   μS/cm                      
 
         [0059]     As there is such large variance in the solutions and their concentrations these measurements were intended to just give a rough idea of the relative conductivity of various common solutions. All measurements were carried out at approximately 25 Degrees C.  
                                                   TABLE 4                           There follows for comparison some published figures of EC (electrical       conductivity) and their respective TDS (Total Dissolved salts) for naturally       occurring water.       CONDUCTIVITY AND TOTAL DISSOLVED SALT VALUES                    EC   TDS               (μS/cm)   (mg/L)                            Divide Lake   10   4.6           Lake Superior   97   63           Lake Tahoe   92   64           Grindstone Lake   95   65           Ice Lake   110   79           Lake Independence   316   213           Lake Mead   850   640           Atlantic Ocean   43,000   35,000           Great Salt Lake   158,000   230,000           Dead Sea   ?   ˜330,000