LIQUID CONTAMINATION DETECTION METHOD AND DEVICE

Abstract: A method and device for detecting a liquid contaminant (16) in a body of another liquid which relies on a difference in electrical conductivity between the contaminant and the liquid body respectively. The device includes a sensor circuit (3) having two parallel paths - a detection path (7) and a reference path (9), and the detection path includes two contacts (4, 5) which engage the liquid body so that a liquid bridge (6) extends between them. A power source (10) is connectable to the sensor circuit to cause current to flow through that circuit and current will flow through the reference path regardless of the conductance of the liquid bridge. That reference path flow provides a reference from which various conditions of operation can be determined, including malfunction of the device.

Description: . . This invention relates to a method and device for detecting the presence of one liquid within a body of ? another liquid. One useful application of the invention is in detecting the presence of water in hydrocarbon fuels 5 and it will be convenient to hereinafter describe the invention with particular reference to that example application. The invention has other applications however, such as detection of oil or other contaminants in water. Water in fuel detectors have been proposed in the Q past and one such device is the subject of U.K. patent 1378895. That earlier device is not entirely satisfactory for several reasons. For- example, its manner of operation makes it suitable for limited application only and it is difficult to tell whether the device is working correctly 5 so that dangerous situations can go undetected. It is an object of the present invention to provide a sensor for a device of the foregoing kind which is of relatively simple construction and is usable in a wide range of applications. It is a further object of the 0 invention to provide such a device which has a fault indicating facility such that any serious malfunction in the sensor can be detected. According to one aspect of the present invention there is provided-a sensor for detecting the presence of a liquid ^ contaminant in a body of another liquid, said sensor including two contacts arranged in spaced relationship and being adapted for simultaneous engagement with said liquid body to form a liquid bridge between said contacts, an electrically conductive circuit including a reference path and a detectxon path arranged in parallel relationship, said detection path including said contacts and the liquid bridge therebetween, and terminal means through which a source of electrical energy can be connected to said circuit to cause current to flow therethrough, whereby the current flow through said circuit varies with variation in the electrical conductivity of said liquid bridge and a particular range of current flow through said circuit can be selected as indicating the absence of said contaminant and the absence of a fault in said circuit. According to a further aspect of the invention there is provided a method of detecting the presence of a liquid contaminant in a body of another liquid, including engaging two spaced contacts with said liquid body to form a liquid bridge between those contacts said contacts and said intervening liquid bridge forming at least part of one path of an electrically conductive circuit having a refer- '-. ence path which is parallel to said one path, applying an electrical potential across said circuit so that current flows through at least said reference path, and selecting a current flow range as indicative of the absence of said liquid contaminant in said liquid bridge, whereby variations in said current flow from said selected range indicates either the presence of said Ixquxd contaminant or the presence of a fault in said circuit. A sensor as referred to above is conveniently made as a separate unit for use with other conponents as necessary to carry out a contamination detection procedure. For example, the sensor may be connected to an indicator which responds to the current flowing through the sensor circuit to^indicate whether the liquid body is contaminated. The indicator may rely on the magnitude of the current flowing through the sensor circuit for that purpose. In % another application, the sensor may be connected to control •s means which responds to variations in the current flow 5 through the sensor circuit to control some other device or apparatus such as a valve. A method and device as referred to above can be used to detect the interface between two bodies of liquid such as engaging bodies of oil and water moving through a conduit. 10 In that event the detection is more for the purpose of control than to reveal a contamination and consequently the reference to "contamination" as used throughout this specification is to be read in sufficiently wide terms as to embrace such an interface situation. 15 The essential features of the invention, and further optional features, are described in detail in the following passages of the specification which refer to the accompany¬ ing drawings. The "drawings however, are merely illustrative of how the invention might be put into effect, 0 so that the specific form and arrangement of the features (whether they be essential or optional features) shown is not to be understood as limiting on the invention. In the drawings: Figure 1 is a diagrammatic representation of one form - 5 of sensor according to the invention as used in one particular application. Figure 2 is a view similar to figure 1 but showing the presence of a contaminant in the liquid being monitored. Figure 3 is a cross-sectional view of one form of 0 sensor usable in the situation of figure 1. Figure 4 is a diagrammatic representation of a device incorporating the sensor of figure 3. Figure 5 is a graph relative to operation of the device according to figure 4. Figure 6 is a diagrammatic view of the sensor of figure 3 in another application. Figure 7 is a view similar to figure 6 but showing a modification of the mounting of the sensor. Figure 8 shows yet another application of the sensor of figure 3. Figure 9 shows a variation of the arrangement shown in figure 8. The concept upon which the invention is based can be applxed in various ways and to a wide variety of situations. Figures 1 and 2 represent, in basic diagrammatic form, the concept of the invention as applied to one situation such as the detection of water contamin¬ ation in hydrocarbon fuels. The body of fuel 1 to be monitored is contained in a tank 2 for example and a sensor 3 has two contacts 4 and 5 which are exposed to the fuel 1 so that a liquid bridge 6 extends between those contacts 4 and 5. The contacts 4 and 5, and the intervening bridge 6, form part of a detection path 7 of a sensor circuit 8 and that circuit 8 also includes a reference path 9 which is arranged in parallel with the detectxon path 7. A battery 10, or other power source which could be an AC source, is connected to the sensor circuit 8 to cause a current to flow through that circuit 8. In a practical application of the invention a 9 volt battery is used for the power source. Also in the example shown, a connected into the circuit 8 so as to respond to current flow in that circuit 8 to cause deflection of a needle 12 across a panel or scale 13. For the particular situation under consideration the deflection of the needle - 12 will increase as the magnitude of the current through the circuit 8 increases. _ Hydrocarbon fuels have a very low conductivity (.e.g., the conductance of aircraft fuel might be as low as 300 peco-mho) and consequently in the clean or uncontaminate fuel condition as represented by figure 1, the current flow through the circuit 8 will be predominantly through the reference path 9. Any flow through the detection path 7 can be ignored for the purposes of the present discussion. The current flow through the reference path 9 can be represented as Ir .and that will be the total current flow across the circuit 8 save for a possible small current flow through the detection path 7 which is being ignored as discussed above. The meter scale 13 is divided into a clean fuel zone 14 and a contaminated fuel zone 15 and current Ir is such as to deflect the needle 12 into the zone 14. In that regard, .the circuit 8 can be prearranged to provide a current flow Ir of suitable magnitude for the purpose of achieving a clean fuel reading whilst being sufficiently small as not to present a danger in a volatile fuel environment. It is of some significance that there is current flow through the circuit 8 in the clean fuel situation. That flow creates a visible meter response which provides—. ^ ■ ζ- - i\ -~- Λ f ~ a reference for other^conditions such as failure of the power source which might otherwise escape attention with adverse consequences. Figure 2 represents a condition in which water 16 is present in the fuel 1 and consequently increases the conductivity of the liquid bridge 6. That increase in conductivity will, under circumstances discussed below, cause a detectable increase in current flow through the detection path 7 of the circuit 8. In figure 2, that flow is represented as IC and the total current flow across the circuit is represented by It which is the sum of Ir and Ic. The increase in current causes the needle 12 to be deflected into the zone 15 of the meter scale 13 thereby showing that the fuel is contaminated. The detection path 7 preferably has a resistance value independent of that established by the liquid bridge 6 so that a short circuit within the circuit 8 will cause additional deflection of the needle 12 into the fault zone 17 of the meter scale 13. That contributes to the efficiency of the device in avoiding misinterpretation between contaminated fuel and short circuit conditions. In the circuit 8 shown in figures 1 and 2 a resistor 18 is included in the detection path 7 for the foregoing reason. A resistor 19 is also included in the reference path 9 for a reason hereinafter made clear. Figure 3 shows in cross section one form of sensor 3 according to the invention. That particular sensor 3 xncludes a body portion 20 formed of metal or other * - electrically conductive material and having an externally threaded neck section 21 at one end. A cavity or bop_g22 ~~~~ is formed through the end 23 of the body portion 2Q and a probe 24 is secured to that end 23 to close off the bore * 22. In the example shown, the probe 24 extends axially , from the body portion end 23 and is secured to the body 5 portion 20 by screw threaded engagement within the end portion of the bore 22. -Obviously, other forms of connectio could be adopted. The probe 24 as shown includes a sheath 25 of polytetrafluoroethylene or other electrically insulating 0 material which is screw threaded at one end for connection to the sensor body portion 20. A conductive element 26 extends axially through the sheath 25 and the exposed outer end portion of that element 26 forms the contact 4. That contact 4 may be gold plated or otherwise treated 5 to provide a stable surface. The exposed end surface 23 • of the body portion 19 forms the other contact 5. As shown, the resistors 18 and 19 are located in the body portion bore 22 in spaced relationship and are contained within an electrically insulating sleeve 27. 0 It is preferred that the resistors 18 and 19 are held in spaced relationship by a coil compression spring 28 which also forms a conductor between those resistors 18 and 19. The resistor 18 is in electrically conductive relationship with the inner end 29 of the probe element 26 and the resistor 19 is in electrically conductive relationship with the body portion 20 at the base 30 of the bore 22. A connector 31 comprising an input terminal 32 and an earth terminal 33, is connected to the body portion 20 and in the arrangement shown the earth terminal 33 is 0 a socket connected to the body portion 20 in conductive relationship. The input terminal 32 is a pin or the like which extends between coils of the spring 28 so as to be clamped between those coils in a positive conductive relationship. An insulating^sleeve 34 surrounds part of the terminal pin 32. In the arrangement shown in figure 3, the body portion 20 forms a part of each of the circuit paths 7 and 9 and the spring 28 also forms a part of each of those paths 7 and 9. Obviously, different sensor constructions may be adcjϊted and AC rather than DC power supply may be used. Figure 4 provides a diagrammatic representation of one form of indicator means 35 usable with the sensor of figure 3. The indicator 35 includes the meter 11 as previously described and a meter circuit 40 which is connected to the sensor terminals 32 and 33 as shown. The meter circuit 40 may take any appropriate form, but in the arrangement shown includes a signal amplifying transistor 36 to ensure adequate movement of the meter needle 12 and a thwristor 37 to compensate for temperature drift i-h the circuit 40. Potentiometers 38 and 39 are provided for calibration of the circuit 40 to obtain appropriate read¬ out on the meter scale 13 under the various conditions of operation. In particular, the meter circuit 40 is calibrated relative to the sensor circuit 8 so that the meter needle 12 will be in the scale zone 14 when an uncontaminated fuel bridge 6 exists between the contacts 4 and 5. In that regard, the resistance value of the resistor 19 is selected according to the conductivity of the uncontaminated fuel 1 so-there will be preferential current flow through the reference path 9 under clean fuel conditions. That resist- ance value is also selected to provide a suitable balance or stabilisation for the total system. In the event of a malfunction in the reference path 9 or failure of the power source 10, the meter needle 12 will locate within the fault zone 41 of the scale 13 so as to reveal the existence of that malfunction or failure. An interface zone 42 may be provided on the scale 13 as shown in figure 4. The -needle 12 is located in the interface zone 42 when water is present in the fuel body 1 in small quantities.- e.g., in the form of a fine mist of water 16. The indicator device 35 is arranged to respond to the presence of free water in the fuel body 1 and measurable quantities of such water do not generally exist at a conductance below approximately 5000 peco-mho. That conductance, or thereabouts, may be selected as the beginning of the clean fuel zone 14 of the scale 13. Figure 5 is a graph of the conductance in peco-mho as against water suspension reckoned in parts per million. The graph is divided vertically into a number of regions identified as A,B,C,D,E, and F.respectively. Regions A, B, C, and F correspond to zones 41, 14, 42, and 17 respectively of the meter scale 13. Regions D and E together correspond to zone 15 of the scale 13. Regions B and E~ also correspond generally to the influence imposed on the sensor circuit 8 by the resistors 19 and 18 respectively. Furthermore, region D represents water present in the form of micro-sized droplets, hereas region E represents the presence of water in slug or globule fo_ 0. It will be appreciated from the foregoing description that the present invention provides a relatively simple yet effective means for detecting the presence of water in fuel whilst also providing a fault detection facility. The arrangement is such that a relatively small current flow is adequate for operation of the device and even under short circuit conditions the current flow is not so high as to be dangerous in a volatile fuel environment. The invention has been so far described in relation 10. to detection of water in a fuel tank and in that situation the sensor 3 is generally located at the bottom of the tank 2, but any other suitable location could be adopted. If desired, several sensors 3 may be connected to a single tank 2. The .sensor 3 is also usable in association with pipe lines and other conduits for flowing streams of liquid, and in that event it is generally convenient to connect the sensor 3 into the top of the pipe 43 as shown in figure 6. In the figure 6 arrangement, a socket 44 forms 2° a continuation of the sensor body 20 and also forms the contact 5. If a higher level of sensitivity is required, the distance between the contacts 4 and 5 can be reduced by containing the probe 24 within the socket 44 and providing the socket 44 with a restricted opening 45 as 5 shown in figure 7. Figure 8 shows another form of installation of the sensor 3 involving detection of oil in water. In that arrangement, water 16 flows through the pipe 44 and because of its conductivity provides a conductive bridge between the- contacts 4 and 5, The sensor 3 is connected through line 46 to a control device 47 and power may be supplied through line 48. When a globule of oil 49 engages the probe contact 4 the conductivity of the liquid bridge will be significantly reduced so that current flow is at least substantially confined to the reference path 9. The control device 47 may respond to that by generating an audible and/or visual signal. In one arrangement, that signal will continue to be generated until manual operation of a reset switch 50. If desired, the control device 47 could also be arranged to operate a valve or other apparatus when the signal is generated. The arrangement of figure 9 is more suited for detecting relatively small quantities of oil in water. In that arrangement, the probe 24 is confined within a compartment 51 formed within the sleeve 44 and closed at its lower end by a wall 52. A tube 53 projects through the wall 52 and has a plurality of openings 54 through which water 16 (with oil 49 if present) can be directed intq.- the compartment 51. A vent tube 55 enables a continuous flow into and out of the compartment 51 and the presence of oil 49 is sensed in the manner previously described. If desired, a tap 56 may be provided to exhaust collected oil from the compartment 51. The sensor 3 is clearly usable in a great variety of situations. For example, it may be used to locate the interface between bodies of water and oil respectively moving in tandom through a pipe line. Such situations arise where regulations require oil transport pipes to be temporarily filled with water when not transporting oil Accurate location of the water/oil interface can reduce wastage of oil in such situations. Similarly, the sensor may be used in finding the oil/water interface in slosh tanks as used in oil refineries, again with a significant reduction in oil wastage. Finally, it is to be understood that various alterations, modifications and/or additions may be introd-*-; uced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention as defined in the appended claims. *

Claims: CLAIMS . ~ A sensor for detecting the presence of a liquid contaminant in a body of another liquid, said sensor including two contacts arranged in spaced relationship and being adapted for simultaneous engagement with said liquid 5 body to form a liquid b-cidge between said contacts, an electrically conductive circuit including a reference path and a detection path arranged in parallel relationship, said detection path including said contacts and the liquid bridge therebetween, and terminal means through which a 10 source of electrical energy can be connected to said circuit to cause current to flow therethrough, whereby the current flow through said circuit varies with variation in the electrical conductivity of said liquid bridge and a particular range of current flow through said circuit can 15 be selected as indicating the absence of said contaminant and the absence of a fault in said circuit. 2. A sensor according to claim 1, including a body portion, said contacts being connected to said body portion and being exposed externally thereof for engagement with 20 said liquid body. 3. A sensor according to claim 2, wherein one of said contacts forms part of said body portion and the other said contact is electrically insulated from said body portion. -. 4. A sensor according to claim 3, wherein said body portion 25 has a neck section for insertion into an opening of a wall of a liquid carrying member, and a probe located at said neck section for exposure to said opening, said other contact is exposed at an outer terminal end of said probe and said one contact is formed by part of said neck section. 0 5.. A sensor according to claim 4 f wherein said probe has an electrically insulating sheath over a substantial part of the length thereof projecting from said body portion. 6. A sensor according to any one of claims 2 to 5, wherein - said body portion is formed of an electrically conductive material, and said terminal means includes a power input terminal and an earth terminal which are connected to said body portion in non-conductive and conductive relationship respectively. 7. A sensoraccording to any preceding claim, wherein each said circuit path includes a respective resistor. 8. A sensor according to claim 7, 'wherein the resistor in said reference path has a resistance which is substantially higher than that of the detector path resistor and which is related to the conductivity of said liquid body when not contaminated so that said current will preferentially flow through said reference path in the absence of said contamination. 9. A sensor according to claim 7 or' 8 when appended directly or indirectly to claim 4, wherein said body portion is composed of electrically conductive material, a cavity is formed within said body portion, said resistors are located within said cavity in spaced relationship, said reference path resistor is connected to said body portion in electrically conductive relationship, said detection path resistor is connected to said probe contact in electrically conductive relationship, and conductor means interconnects said resistors in a series relationship. 10. A sensor according to claim 9, wherein said probe includes an insulating sheath connected to said body porti and an electrically conductive element extending through said sheath so as to be insulated from said body portion, an outer end of said conductive element forms said probe contact and an inner end thereof is in electrically conductive relationship with said detection path resistor. 11. A sensor according to claim 9 or 10, wherein said resistors are retained in spaced relationship by spring means and said spring means forms said conductor means. 12. A sensor according to claim 11 when appended to claim 6 wherein said spring means is a coil compression spring, said input terminal includes an electrically conductive element which is accessible -from the outside of said body portion and which engages between coils of said coil compression spring in electrically conductive relationship, and said earth terminal is located on said body portion adjacent said input terminal and is electrically insulated from said input terminal. 13. A sensor according to claim 12, wherein said earth terminal is in electrically conductive relationship with both said neck part and said reference path resistor through said body portion. 14. A device for detecting the presence of a liquid contaminant in a body of another liquid, including a sensor according to any preceding claim, power supply means connectable to said sensor circuit and being operable to cause an electrical current to flow through that circuit, and indicator means connectable into said sensor circuit and being responsive to said current to indicate the magnitude of said current. 15. A device according to claim 14, wherein said indicator means includes, a meter having a graduated panel and a pointer movable over that panel, and a meter circuit connectable to said sensor circuit so as to be responsive to current flowing through said sensor circuit to cause deflection of said pointer across said panel and to vary that deflection according to the magnitude of said current. 16. A device according to claim 15, wherein said panel is divided into a plurality of zones including an opening circuit zone, a correct reference zone and a contaminant zone, and said pointer is located at said open circuit zone when inadequate current is flowing through said sensor circuit, is located in said correct reference zone when said current is within said selected range and is located in said contamination zone when said current is outside of said selected range. 17. A device according to claim 16, wherein said pointer is located in said contamination zone when said current flow is of greater magnitude than said preselected range and that zone is graduated to indicate the degree of said contamination. 18. .A device according to any one of claims 15 to 17, wherein said panel includes a short circuit zone and said pointer is located in that zone when a short exists within said sensor circuit. 19. A method of detecting the presence of a liquid contaminant in a body of another liquid, including engaging two spaced contacts with said liquid body to form a liquid bridge between those contacts, said contacts and said intervening liquid bridge forming at least part of one REA path, of an electrically conductive cipcuit having a reference path which is pa.ra.llel to said one path, applying an electrical potential across said circuit so that current flows through at least said reference path, and selecting a current flow range as indicative of the absence of said liquid contaminant in said liquid bridge,„whereby variations in said current flow from said selected range indicates either the presence of said liquid contaminant or the presence of a fault in said current. 20. A sensor for detecting the presence of a liquid contaminant in a body of another liquid substantially as herein particularly described with reference to what is shown in the accompanying drawings.

Inventors: HEEPS BRIAN HAMILTON, HEEPS, BRIAN, HAMILTON
Applicants: REPCO RES PTY LTD, REPCO LIMITED
Application year: 1982
Main classification: G01N27
IPC codes: G01N27, G01R27