FLUID LEVEL DETECTION AND MONITORING SYSTEM

Abstract: A fluid level detection and/or monitoring system, e.g. for vehicle radiators (17), has a probe unit (10) fitted to the fluid container (17) and a monitoring unit (30) giving a visual and audible indication (34-40) of the fluid level (21) in the container (17). The probe unit (10) has a number of probes (24-28) in a tubular body (11) open at its lower end. Air bleed holes (22) in the upper end of the probe unit (10) allows air to enter or leave the probe unit (10) with a restricted flow to damp any fluid level change in the probe unit (10) to overcome any transient changes in the fluid level (21) in the container (17) due to flow surges, cavitation and/or frothing, the bleed holes (22) also preventing air being trapped in the probe (10) and artificially depressing the fluid level in the unit (10). The monitoring unit (30) has a series of lights (34-39) which are extinguished as the fluid level (21) falls. An audible buzzer (40) indicates that a critical level (29) is being reached, and the machine being monitored is shut off when the critical level (29) is reached before any damage to it can occur.

Description: Title: "FLUID LEVEL DETECTION AND MONITORING SYSTEMS" BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to fluid level detection and/or monitoring systems which are particularly suitable for detecting and/or monitoring fluid levels in tanks, containers and other vessels. Specific applications for the invention including monitoring the coolant level in vehicle engines and the hydraulic fluid level in hydraulic motors and pump circuits. (2) Brief Description of the Prior Art Many types of detection and/or monitoring systems have been proposed for such applications. Examples of these are disclosed in Australian Patent No. 282,500 (Ford Motor Company of Canada Limited); Australian Patent Application No. 75785/74 (Marston Radiators Limited) and U.S. Patent Nos. 4,182,363 (Fuller); 3,947,692 (Payne); 3,905,236 (Henry) and 3,186,224 (Mair) . While it is relatively easy to accurately monitor the fluid level in a substantially static application, e.g. in a brake fluid reservoir in a vehicle, many problems arise where the fluid to be monitored is flowing, e.g. as in an engine radiator or a hydraulic fluid tank. The major problem in such applications is to provide a detector means which is highly sensitive and accurate, and yet will not yield false readings or be misled by transient changes in the fluid level due, e.g., to flow surges, cavitations and/or frothing. Many complex fluid level probe assemblies (e.g. as disclosed in U.S. Patent No. 4,182,363) have been proposed to satisfy these stringent requirements but do not appear to have been wholly satisfactory to the present. In addition, many of the detection and. monitoring systems presently available only indicate when a critical level has been reached (e.g. as disclosed in Australian Patent No. 282,500) and so are purely passive systems. They do not provide an early warning that a problem is deve ' loping, nor do they shut off the machine which they are monitoring before any damage can occur. Finally, of the electrical and/or electronic systems available, many suffer failure or give inaccurate readings in the field due to electrolysis or chemical build-up on the probe(s) . BRIEF SUMMARY OF THE INVENTION With the above problems in mind, it is an object of the present invention to provide a detection and monitoring system which can discriminate between major and transient changes in the fluid level being monit¬ ored to enable the actual level of the fluid to be correctly measured. It is a preferred object to provide a system which gives a progressive warning that a critical level or other parameter is being reached. It is a further preferred object to provide a system where audible and/or visible warnings are given of the approach of the critical level or parameter and which may slow down the equipment being monitored. It is a still further preferred object to provide a system where only a low detection current is passed through the probes in the detection unit and the probes are self-cleaning, overcoming the problems of electro¬ lysis and chemical build-up. Other preferred objects will become apparent from the following description. In one aspect, the present invention resides in probe unit for a fluid level detection and/or monitor¬ ing system including: OMFI a substantially tubular body adapted to be mounted in a fluid container, the fluid level of which is to be monitored; an opening at the lower end of the body to allow fluid in the container to enter the interior of the body; and at least one probe in the interior of the body adapted to carry an electrical current when the probe is in engagement with the fluid in the interior of the body; wherein: at least one air bleed hole is provided in the body adjacent its upper end in communication with the container, the bleed hole or holes enabling a restricted flow of air between the container and the interior of the body to enable the fluid level in the interior of the body to change when the fluid level in the container changes, the restricted flow of air damping the change of the fluid level in the interior of the body to overcome any transient changes in the fluid level in the container due to flow surges, cavit¬ ation and/or frothing of the fluid in the container. In a second aspect the present invention resides in a fluid level detection and/or monitoring system including: a probe unit including: a substantially tubular body mounted in a fluid container, the fluid level of which is being monitored; an opening at the lower end of the body allowing fluid in the container to enter the interior of the body; a plurality of probes in the interior of the body, the probes being of incrementally different lengths and each adapted to carry an electrical current when in engagement with the fluid in the interior of O PI of the body; and a monitoring and indication circuit including: an input connected to each probe; an amplifying means amplifying the input signal from each probe; a plurality light means connected to the amplifying means, each light means being operable when a respective probe is in engagement with the fluid in the interior of the body; wherein: at least one air bleed hole is provided in the body adjacent its upper end in communication with the container, the bleed hole or holes enabling a restricted flow of air between the container and the interior of the body to enable the fluid level in the interior of the body to change when the fluid level in the container changes, the restricted flow of air damping the change of the fluid level in the interior of the body to overcome any transient change in the fluid level in the container due to flow surges, cavit¬ ation and/or frothing of the fluid in the container; and the light means being respectively switched off as the fluid level in the interior of the body, and in the container, falls towards a critical level. n addition to the damping effect by the bleed hole(s), they also prevent an artificial depression of the fluid level in the interior of the body of the probe unit as would occur if air became trapped at the top of the probe unit. Preferably a number of probes are provided in the probe unit, the shortest indicating that the container is substantially full of fluid and the longest indicating that the fluid level has fallen to the critical level. Preferably the light means, e.g. a LED, connected to the longest probe is normally switched on and the OMPI_ electrical circuit connected to that probe incor¬ porates a switch means operable to shut down the machine, the fluid level of which is being monitored. Preferably the electrical circuit connected to the next longest probe incorporates an audible warning means to indicate to the operator of the machine that the critical level is being approached. BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, a preferred embodiment will now be described with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of the detection and monitoring system fitted to a vehicle radiator, the probe unit being shown in sectional side view; FIG. 2 is a plan view of the probe unit; and FIG. 3 is the circuit diagram of the monitoring unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The probe unit 10 is moulded of suitable plastics material and has a tubular body 11, with an internal bore 12, which is closed at its upper end by a cap 13 which has a hexagon head. The body is provided with a screw- headed portion 14 below the cap to receive a complement¬ ary screw-threaded clamping ring- 15 which is used to clamp the probe unit in an opening in the header tank 16 of a vehicle radiator 17 above the cooling tubes 18. (The radiator has cooling fins 19 and a pressurized filler cap 20) . The level of the coolant in the radiator 17 is indicated at 21. A number of bleed holes 22 are provided in the body 11, just below the screw-threaded portion 14, to allow a restricted flow of air into, and out of, the bore 12 as the fluid level 23 in the bore changes. The bleed holes 22 provide two functions. Firstly, they prevent the fluid level 23 in the probe unit 10 from being O PI artificially depressed as would occur if a volume of air was trapped in the top of the probe unit. Secondly, the restricted flow of air in and out of the bore 12 (to the header tank 16) damps any sudden changes in the fluid level 23 in the probe unit which otherwise would occur with flow surges, cavitation and/or frothing in the header tank. Thus the fluid level 23 in the probe unit accurately reflects the actual fluid level 21 in the header tank 16. Five probes 24-28 are moulded into the cap 13 and each is provided with a screw-type terminal. The probes 24-28 extend into the bore 12 to different depths, the difference in depths being set at integral steps of, e.g., 0.5" (1.2cm.). The longest probe,28, is used to indicate that the coolant level has fallen to the critical level 29, at which operation of the engine has become unsafe. The probe may be spaced, e.g. 0.25" (0.6cm.) above the top of the cooling tubes 18 as experiments have indicated that overheating of the engine will occur when the tops of the cooling tubes 18 are no longer covered in coolant. The monitoring unit 30 may be contained in a housing (not shown) mounted in the operator's cabin of the vehicle in clear view of the vehicle operator. The monitoring unit 30 has an electronic circuit unit 31, the inputs of which are connected to the probes by wires 32, a display unit 33 with six coloured light emitting diodes (LEDs) 34-39, and an audible buzzer 40, and is connected to the vehicle battery B. Referring to FIG. 3, the positive rail 41 of the electronic circuit 31 is connected to the ignition coil (not shown) and the engine run side of the ignition switch (also not shown) via poles 42, 43 respectively, diodes 44 ensuring the correct polarity of the unit. A capacitor 45 is provided across the positive and ground -£JR£ _ OMPI (or earth) rails 41, 46 to remove any ripple currents from the circuit. Each probe 24-28 is connected to a respective input pole 47-51 by a respective wire 32. Each input pole 47-49 is connected to a respective switching transistor 52-54 via a current limiting resistor 55-57 and a diode 58-60 respectively (the diodes 58-60 ensuring the correct polarity of the unit is maintained) . The transistors 52-54 are biassed by biassing resistors 61-63 respectively so that when a current flows through the probes 24-26 (probes being in engagement with the coolant) , the transistors 52-54 are switched on and their respective collector currents are amplified by an integrated circuit 64 to cause a current flow through the LEDs 34-36 which are coloured green. Probes 27 and 28 are provided with similar circuits to operate LEDs 37 and 38 which are coloured orange. LED 39, which is coloured red, is connected across the positive and ground (earth) rails 41, 46 and is always illuminated when the monitoring unit 30 is switched on. A switching and amplifying circuit 65 is provided in parallel with the circuit 66 connecting the LED 37 to the probe 27. This circuit incorporates a similar switching and amplifying circuit to that of circuit 66 but the LED 37 (and its resistor 67) are replaced by a switch 68 which, when current is flowing through the probe 27, maintains a normally closed relay 69 open. This relay, when closed, connects the audible buzzer 40 to the positive rail 42 to indicate that the critical level is being approached. In ' the particular example given above, the coolant level 21 is now 0.5" (1.2cm.) above the critical level 29. A similar switching and amplifying circuit 70 O PI { ■ fA to the circuit 65 is connected to probe 28. This circuit 70 incorporates a switch 71 which maintains a normally closed relay 72 open but which, when the current through the probe 28 is interrupted, is closed to ground the ignition coil of the engine to shut it down. (In a diesel engine, the relay 72 would be connected to the diesel pump solenoid) . At this time, orange LED 48 is switched off, leaving only the red LED switched on, indicating that the coolant level 21 is now below the critical level 29. In operation, the coolant is added to the radiator 17 until the LEDs 34-39 are switched on. The coolant level 21 is now at its maximum and all of the probes 24-28 are in engagement with the coolant. When the fluid level 21 falls below the tip of probe 24, the current through the probe is interrupted. Transistor 52 is switched off, switching off the first green LED 34. When the coolant level 21 falls a further 0.5" (1.2cm.), probe 25 is also no longer in engagement with the coolant and so the second green LED 35 is switched off. Similarly, the third green LED 36 is switched off when the coolant level 21 falls a further 0.5" (1.2cm.). When the coolant level 21 falls below the tip of the probe 27 (and is therefore less than 0.5" (1.2cm.) above the critical level 29) the current through probe 27 is interrupted and so the first orange LED 37 is switched off. Simultaneously, the current through the switching and amplifying circuit 66 is interrupted, switch 68 is closed, closing relay 60 to operate the audible buzzer 40. The noise from the buzzer 40, and the illumination of only the second orange LED 38 and red LED 39 should cause the operator to stop the vehicle and replenish the coolant in the radiator 17. However, if the operator OMPI ignores these warnings, the coolant level 21 will continue to fall until the critical level 29 is reached. At this point, probe 28 is no longer in engagement with the coolant and so the current through the probe is interrupted. The second orange LED 38 is switched off (leaving only the red LED 39 illuminated) and simultaneously, the current through the switching and amplifying circuit 70 will be interrupted. Switch .71 is. closed, closing the relay 72 and the ignition coil of the engine is grounded (or earthed) , shutting off the engine. When the coolant has been replenished, the switch 72 is mechanically reset and the engine can be restarted provided the coolant level 21 is above the critical level 29. As the probes 24-28 are connected to the positive rail 41 of the monitoring unit 30, the probes are connected as anodes with the radiator 17 acting as the cathode. This arrangement overcomes any damage to the probes due to electrolytic action and/or chemical build-up on the probes and so the probes are continuously self-cleaning. The amplifying circuits in the monitor ensure that the unit will operate with only a very low detection current and so allow the unit to operate even when the probes are only damp or are covered with wet dirt or other rubbish. It will be readily apparent to the skilled addressee that the system may be used to monitor the fluid level in any type of container including, iner alia, monitoring the hydraulic oil level in a supply tank for a hydraulic motor/pump system. In a modified form of the probe unit 10, the probes 24-28 may be removably fitted in the cap 13 and/or may be provided with terminals to receive spade-type connectors fitted to the wires 32. OMPI Similarly, in a modified form of the monitoring unit 30, the switching and amplifying circuitry may be provided in a single integrated circuit. The unit hereinbefore described has the following features, inter alia: (a) the probe unit, with its bleed holes, allows . the fluid level in the probe to rise and fall with the fluid level in the container but still overcome transient changes in the level, e.g. due to flow surges and frothing; (b) The unit progressively indicates that a critical level is being approached and so the operator can take remedial action before the machine is shut down; (c) the anode-type probes are self-cleaning; (d) the unit can operate with very low detection currents through the probes; (e) the combination of the lights, buzzer or horn and the shut down of the machine provide effective protect¬ ion for the machine; (f) the unit cannot be bypassed or deactivated by the operator of the machine, to enable the machine to continue to operate when the fluid level falls below. the critical level, as disconnection of the unit from its power source operates the switch(es) which shut down the machine. The machine will be shut down if any interruption of the supply of power to the unit occurs, and not just when the fluid level falls to the critical level; and (g) the unit indicates that the coolant level in a vehicle radiator, filled when cold, has fallen after the thermostat has opened to allow the coolant to enter the engine, and that additional coolant should be added to the radiator to bring the coolant level in the radiator back to its maximum level. Various changes and modifications may be made to the embodiment described without departing from the scope of the present invention as defined in the appended claims. OMPI

Claims: CLAIMS : 1. A probe unit for a fluid level, detection and/or monitoring system including: a substantially tubular body adapted to be mounted in a fluid container, the fluid level of which is to be monitored; an opening at the lower end of the body to allow fluid in the container to enter the interior of the body; and at least one probe in the interior of the body adapted to carry an electrical current when the probe is in engagement with the fluid in the interior of the body; wherein: at least one air bleed hole is provided in the body adjacent its upper end in communication with the container, the bleed hole, or holes enabling a restricted flow of air between the container and the interior of the body to enable the fluid level in the container changes, the restricted flow of air damping the change of the fluid level in the interior of the body to overcome any transient changes in the fluid level in the*container due to flow surges, cavitation and/or frothing of the fluid in the container. 2. A probe unit as claimed in Claim 1 wherein: the air bleed hole or holes further prevent an artificial depression of the fluid level in the interior of the body as the fluid level in the container is increased by enabling air in the upper part of the body to be bled to the container. 3. A probe unit as claimed in Claim 1 or Claim 2 including a plurality of probes wherein: the probes are of incrementally increased length to respectively indicate different fluid levels in the container; the critical fluid level in the container being OMPI just below the longest of the probes. 4. A fluid level detection and/or monitoring system comprising: a probe unit including: a substantially tubular body mounted in a fluid container, the fluid level of which is to be monitored; an opening at the lower end of the body allowing fluid in the container to enter the interior of the body; a plurality of probes -in the interior of the body, the probes being of incrementally different lengths and each adapted to carry an electrical current when in engagement with the fluid in the interior of the body; and a monitoring and indication circuit including: an input connected to each probe; an amplifying means amplifying an input current from each probe; and a plurality of light means connected to the amplifying means, each light means being operable when a respective probe is in engagement with the fluid in the interior of the body; wherein: at least one air bleed hole is provided in the body adjacent its upper end in communication with the container, the bleed hole or holes enabling a restricted flow of air between the container and the interior of the body to enable the fluid level in the interior of the body to change when the fluid level in the container changes, the restricted flow of air damping the change of the fluid level in the interior of the body to overcome any transient change in the fluid level in the container due to flow surges, cavitation and/or frothing of the fluid in the container; and O PI the light means being respectively switched off as the fluid level in the interior of the body, and in the container, falls towards a critical level. 5. A system as claimed in Claim 4 wherein: the probe unit includes a plurality of probes of incrementally increasing length to respectively indicate different fluid levels in the container; and the critical level is just below the longest of the probes. 6. A system as claimed in Claim 5 wherein the amplifying means includes: a respective switching and amplifying circuit interconnecting each probe and a respective light means, each light means being switched off when the electrical current flow through its respective probe is interrupted by the fall of the fluid level below the respective probe. 7. A system as claimed in Claim 6 wherein: the probe unit is fitted to the radiator of a vehicle; and the switching and amplifying circuit for the longest probe includes* a further switching circuit operable to shut off the engine of the machine cooled by the radiator when the fluid level in the radiator falls to the critical level below the longest probe. 8. A system as claimed in Claim 7 wherein: a further switching circuit is provided in the switching and amplifying circuit for the second longest probe, the further switching circuit being operable to operate an audible warning means indicating that the fluid level in the radiator is approaching the critical level. 9. A system as claimed in Claim 7 or Claim 8 wherein: each electrical current flows from the monitoring circuit, through a respective probe, through the coolant in the radiator to the radiator, the probes acting as anodes and the radiator as a cathode, the direction of flow of the OMPI electrical currents preventing chemical build-up on the probes and preventing electrolytic deterioration of the probes. OMPI

Inventors: MASSEY LEO JOHN, WILMS JOHN RAYMOND, MASSEY, LEO, JOHN, WILMS, JOHN, RAYMOND
Applicants: DRANMONT PTY LTD, DRANMONT PTY. LTD.
Application year: 1983
Main classification: G01F23
IPC codes: G01F23