GB2086576A - A fluid level monitoring device - Google Patents

Abstract

A fluid level monitoring device particularly adapted for monitoring the level of fuel in a fuel tank 11 of a boat comprises a tube (12) containing a plurality of float switches (17, 18, 19) set at different levels to commute when the fluid level passes that particular value. Each float switch (17, 18, 19) operates an associated relay to energise associated lamps, de-energise previously energised lamps and to energise an associated warning horn which can be silenced by operation of a switch so that audible warning can be provided at each change of level from one range to another and a visual indication of the existing range provided continuously. <IMAGE>

Description

SPECIFICATION Fluid level monitoring device The present invention relates to a fluid level monitoring device, and particularly to a device which is specifically adapted for monitoring the level of liquid fuel in fuel tanks.

It is common practice in large liquid-fuelled vehicles such as aircraft and ships to store the liquid fuel in a plurality of tanks rather than a single tank in order to make use of available spaces which might otherwise be wasted. In aircraft, because the state of balance of the aircraft is highly critical to its performance, the tanks are all inter-connected and the levels of fuel therein maintained within close limits. In ships, on the other hand, it has been common practice merely to provide a manually operable valve to close off supply from one tank and to open supply from another when the fuel in one tank has been completely used up. It has been thought that the fuel level in the tanks was an unimportant factor in determining the equilibrium state of the vessel.

However, it has now been found that where certain classes of vessel are provided with two main storage tanks, one on either side of the centre line, the complete emptying of one tank while the other remains full can seriously affect the equilibrium of the vessel, particularly in the case of a fishing vessel where it may be required to haul nets over the side of the vessel. It is believed that hauling full nets over the side of the vessel which also housed a full fuel tank at a time when the fuel tank on the other side of the vessel was empty has contributed to a situation where the vessel has turned over and sunk.

In order to obviate the repetition of such accidents and also to help vessels maintain a better state of equilibrium, it has been proposed that the fuel levels in lateral tanks should never be allowed to exceed a predetermined threshold difference. This, however, involves constant monitoring by the responsible members of the crew to maintain a continuous check on the fuel level in each tank. As far as fishing boats are concerned this is a particular problem since the vessel may remain for long perods with the engines idling or completely stopped during which no fuel is being used. Consequently, and also because of the pressure of other duties, the watch on the fuel levels can be forgotten, particularly if the motors are then used for a series of short running operations which utilises a negligable amount of fuel.This can lead to a situation where the running of the engines does not automatically remind the responsible members of the crew that the fuel levels might require checking.

Because of the violent nature of the movement of a vessel they cannot be fitted with the conventional full range gauges utilising a float on a pivoted arm operating a variable rheostat or other adjustable electrical component, and for this reason the level of fuel in a ship's fuel tank is often only determinable by means of the dipstick and there is no continuous monitoring of the level.

The present invention seeks to provide a simple and effective device for providing a continuous monitoring of levels of liquid in a tank, which is particularly suitable for monitoring the level of fuel in a ship's tank or tanks. It will be appreciated that since ships use their fuel relatively slowly it is not necessary to provide a continuous indication of the exact amount of fuel in the tank. In fact, it is sufficient for the captain to know that he has a given proportion of the original supply. For this reason the liquid level monitoring device requires only to provide an indication that the liquid level is above or below one or more selected threshold values.In a limiting case it would be sufficient for a single threshold value to be selected although for a more complete characterisation it is preferred that three threshold values are employed these being set to indicate when the liquid level in the tank reaches three-quarters of the maximum volume, half the maximum volume and a selectable minimum volume as a "fuel low" warning. This latter may conveniently be set to provide an indication when the tank has one hundred gallons of fuel remaining.

According, therefore, to one aspect of the present invention a fluid level monitoring device comprises level sensing means for detecting when the level of the fluid exceeds a pre-determined value, and means responsive to the level sensing means for providing an output signal having a first value when the fluid level is above the said pre-determined value and a second value when the fluid level is below the said pre-determined value.

This corresponds to the provision of the above mentioned minimum requirement of monitoring a single fluid level. There may be further provided an audible warning device operable to produce an audible warning when the said output signal changes from one value to the other. This then draws the attention of the crew to the commutation of the indicator from one side of the set fluid level to the other. Of course, in order to avoid the audible warning device becoming a nuisance, there may be provided means for silencing this when it has performed its function of drawing attention to the change in indicated level.

However, no corresponding such means should be provided to switch off the fluid level monitoring device which, preferably, should operate continuously, or at least whenever the fluid is being drawn from the tank.

Although described herein particularly in relation to the monitoring of the level of liquid fuel in a tank, the present invention is, of course, applicable to the monitoring of the level of any liquid where the attainment of a critical threshold level may be of interest. The term fluid will be understood to include not only liquids, but also fluidised beds of particulate material which may change in level.

The two values of the output signal may be both positive (or both negative) with respect to a zero or earth value in order to provide an indication at all times that the system is working. Alternatively, and preferably, one of the said two values is zero in order to minimise the current consumption of the device.

The level sensing means may be of any suitable type able to commute from, for example, a contact open to a contact closed position or vice versa, and conveniently a float switch of conventional type can be employed for this purpose. In a preferred embodiment of the invention the float switch energises a relay which has means for latching to hold the contact in a closed position when energised.

Likewise, a similar relay for operating the audible warning device may be provided, the circuit being such that switching the audible warning device off does not affect the state of energisation of the relay supplying the visual indicators.

As mentioned above it is preferable to monitor a plurality of levels ofthe liquid, and for this purpose a plurality of level sensors may be provided each operable over a limited, but adjustable range of values to provide an output indication when the liquid level passes a critical threshold value within their range of adjustment. Each individual level sensor may be provided with a respective visual indicator, the visual indicators all being arranged in a row so that the position of the illuminated indicator can provide an analogue indication of the fuel level.

The audible indicator may be common to all level sensors and repeatedly energised upon commutation of respective sensors.

Preferably the level sensors are float switches each float of which has a limited travel for commuting the switch contacts as the float liquid level passes their respective range. Such float switches may conveniently be mounted slidably on a common upright guide and immersed in the liquid the level of which is to be monitored.

In order to avoid surge effects which occur due to the movement of the ship at sea, it is preferred that the tank containing the liquid the level of which is to be monitored has a separable upright tube in communication therewith at a low level, the upright guide and float switches being mounted within the tube so that long-term variations in the liquid level, which are due to the fuel being used, will be transmitted to the level of liquid in the tube whereas movements of the liquid due to wave motion of the sea are limited.

Although such movements can be limited to a certain extent by the arrangement described above they cannot be eliminated entirely, and to prevent "hunting" of the device due to commutation of one or more switches upon rapid changes of liquid level there are preferably provided timer means in the electrical circuit which operate to delay commutation of the relay for a pre-determined or adjustable time delay.

Since the monitoring device provides a continually illuminated lamp to indicate instantaneous fuel level rangethere are preferably provided means for accommodating variations in ambient illumination conditions in order to avoid annoyance when the ambient light level is low whilst at the same time being able to provide sufficient brightness for a clear indication when the ambient light level is high. Such a light dimming arrangement may include a light sensitive electrical element in a supply circuit for the indicator lamps. Such a light sensitive element may conveniently be a photoresistor connected in a voltage dividing circuit supplying the base of a switching transistor which is connected with its collectorlemitter path in series with a relay coil whereby to control the relay to switch in when the ambent light level is low.The relay may include a plurality of contacts connected in series with the indicator lamps and operable, when closed, to connect additional resistors in series with the indicator lamps whereby to cause dimming when the ambient light level is low.

The present invention also comprehends a fuel level monitoring system in which a plurality of illuminable lamps provide a continuous indication of the range of levels of fuel in a tank, there being provided an audible indicator operable to generate an audible indication whenever the device commutes from indication of one level to indication of another. The indicator lamps may be conventional incandescent lamps or, alternatively, may be light emitting diodes.

The invention also comprehends a multiple tank fuel control system in which fuel is drawn from one tank at a time and there are provided means for transferring fuel from one tank another where the difference in fuel level exceeds a pre-determined or adjustable threshold value.

One embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a fuel tank equipped with a fuel monitoring device according to the present invention; Figure 2 is a schematic circuit diagram of the fuel level monitoring device; and Figure 3 is a circuit diagram of a light dimming circuit constituting part of the embodiment of Figures 1 and 2 Referring now to the drawings, and particularly to Figure 1, there is shown a tank generally indicated 11 containing the liquid fuel the level of which is to be monitored. Alongside the tank 11 is a vertical tube 12 which communicates with the tank 11 through transverse passages 13, 14 one at a high level and one at a low level of the tank.

Within the upright tube 12 there is located a central guide rod 15 on which slide the floats of three float switches 17, 18, 19. The range of movement of the float switches 17, 18, 19 is determined by suitable end stops adjustably mounted on the central shaft 15. These may be in the form, for example, of spring clips which can be readily moved to determine the required position of the associated float. The central shaft 15 is held in its mid position by suitable upper and lower brackets (not shown).

All the electrical leads from the float switches are taken from the upper end of the tube 12.

Referring now in particular to Figure 2 the three float switches 17, 18, 19 are illustrated as normally open contacts, the "normal" state being considered as that when the float is raised to its highest position due to the liquid level being greater than that at which the float switch commutes. The three float switches 17, 18, 19 are connected in parallel between a positive power supply line 20 and a negative power supply line 21. Each of the float switches 17,18,19 is connected in series with an associated relay coil A, B, C respectively. The float switch 19 is located at the lowermost position of the three to indicate the emergency reserve level.The float switch 18 is located at an intermediate position, for example to indicate that the fuel level in the tank represents the tank being half empty, and in series with the float switch 18, in addition to the relay coil B, there are also provided normally closed contacts C2 of the coil C in series with the float switch 19. Likewise, the uppermost float switch 17, which is located at a level such as to indicate that the tank is three-quarters full, has in series therewith, in addition to the relay coil A, a set of normally closed contacts B2 of the relay coil B in series with the intermediate float switch 18.

The positive power line 20 is connected by three sets of contacts Al, B1 and C1 to three individual warning light circuits. The contacts Al, B1 and C1 are normally open, and close when the associated relay coil A, B and C is energised. The contacts Al are connected in series between the positive line 20, a warning lamp unit 22 and the negative line 21. The warning lamp unit 22 consists of two individual warning lamps in parallel with one another. This duplicated arrangement ensures that even should one of warning lamps fail, there will still be a visual indication provided by the remaining warning lamp, and the fact that one warning lamp has failed will also be evident so that steps can be taken to replace it in good time.

In parallel with the warning lamps 22 is an audible alarm circuit comprising a diode 23 connected in series with a set of relay contacts D2 and an audible warning device 24 in the form of a horn or buzzer.

The contacts B1 are connected to a warning lamp unit 25, again comprising two lamps in parallel like the lamp unit 22. The lamp units 25 are connected between the contact B1 and the negative supply line 21 and, similarly, a further lamp unit 26 is connected between the relay contact C1 and the negative supply line 21. Diodes 27, 28 respectively connect the relay contacts B1 and C1 to the relay contacts D2.

These contacts D2 are normally open, and close upon energisation of a relay coil D which is connected in series with the parallel arrangement of silencing switch 29 and latching contacts D1 via three respective diodes 30, 31, 32 to the three float switch circuits : the diode 30 being connected to a point between the contacts B2 and the relay coil A, the diode 31 being connected to a point between the contacts C2 and the relay coil B, and the diode 32 being connected between the float switch 19 and the relay coil C.

The circuit described above operates as follows: When the tank 11 is full, all the float switches 17, 18, 19 are open since the associated floats are held in their uppermost position by their buoyancy. In this condition all three lamp units 22, 25, 26 are deenergised and the monitoring unit provides no illuminated output. When the level in the tank has fallen to the commutation point of the float switch 17 the contacts close energising the relay coil A and closing the relay contacts Al so that the upper lamp unit 22 is illuminated. At the same time, via the diode 30, the relay coil D is energised, latching in the contact D1 and closing the contact D2 so that the horn 24 is energised via the diode 23.The diodes 27, 28 prevent illumination of the lamp units 25, 26 by reverse current flowing therethrough, and likewise the diodes 31,32 prevent a reverse current flow energising either the coil B or the coil C.

Although not shown in the circuit the relay coils A, B and C are provided with timer units preventing their associated contacts from switching for a predetermined time after the associated float switch has closed. This prevents surge in the tanks from providing spurious results. The timers may provide a delay of, typically, fifty seconds although the time delay relays used can be varied to provide a delay of up to 120 seconds if required. Shortly after closure of the float switch 17, then, the lights 22 are illuminated due to energisation of relay A and closure of the relay contact Al and at the same time current is fed through the diode 30, the push button switch 29 and the coil D to energise the relay contacts D1 and D2 thus allowing power to be supplied via the relay contacts Al and the diode 23 to the horn 24.To silence the horn 24the push button switch 29 is operated reducing the current in the coil D and opening the contacts D2.

As the fuel level in the tank falls between the upper level determined by the setting of the float switch 17 and the mid level determined by the setting of the float switch 18 the lamps 22 remain illuminated indicating that the tank is between three-quarters and half full. Upon reaching the half-full condition the float switch 18 closes energising the relay coil B which opens the contact B2 thereby de-energising the coil A and turning off the lights 22. At the same time the contacts B1 are closed energising the lights 25 and, via the diode 31, re-energising the relay D.

Power from the positive supply line 20 can then be fed via the now closed relay contact B1 and the diode 27 through the now closed relay contacts D2 to the horn 24 which is again energised. Once more silencing of the horn 24 can be effected by depression of the push button switch 29.

The lamps 25 remain illuminated whilst the fuel tank level remains between half full and the level determined by the setting of the float switch 19. The horn 24 is energised upon commutation of the float switch so that attention can be drawn to the change in state of the fuel tank monitoring circuit. This again happens when the fuel falls to the minimum level determined by the setting of the float switch 19 since, in these circumstances, the relay coil C becomes energised opening the contacts C2 and de-energising the relay coil B. The contacts C1 are correspondingly closed permitting the lamp 26 to be illuminated whilst the lamps 25 are extinguished by the opening of the contacts B1 as the powder is removed from the coil B due to opening of the relay contacts C2 upon energisation of the relay coil C. At the same time via the diode 32, the coil D is energised and, via the diode 28 power is supplied through the contacts D2, closed upon energisation of coil D, to the horn 24 which again sounds an alarm to indicate that the minimum level has been reached.

The lamps 26 remain energised at all times when the fuel level is below that set by the float switch 19, although again the horn 24 can be silenced by depressing the push button switch 29 in the manner described above. The circuit is automatically re-set simply by filling the tank with fuel so that the float switches become opened as the floats rise by their natural buoyancy.

In Figure 3 there is shown a circuit for providing dimming of the lights with a reduction in the ambient illumination level. This comprises a relay E connected between a positive supply line 20 and a negative supply line 21 which may be the same supply lines as in the circuit of Figure 2. Between the relay coil E and the negative supply line is connected the collector/emitter of the transistor 33 the base of which is connected in a potential divider circuit comprising a variable resistor 34 a fixed resistor 35 and a temperature sensitive resistor 36. The setting ofthe variable resistor 34 will depend upon the normal illumination level, the values of the thermistor 36 and the ambient illumination level at which switching of the transistor 33 is desired.

The relay E has a plurality of normally open relay contacts which are connected in series between the positive supply line 20 and respective resistors 37, 38,39 which are to be connected in parallel across the lamps being controlled. In this case the resistor 37 would be connected across the lamp 22, the resistor 38 would be connected across the lamp 25 and the resistor 39 would be connected across the lamp 26 with the relay contact being located between the associated parallel resistor and the respective contacts Al, B1 and C1. The switching of the contacts El, E2 and E3 will, of course, be entirely independent of the switching of the float switches 17, 18, 19 and will take place regardless of whether any, or indeed none of the lamps 22,25,26 are illuminated as the ambient light varies to either side of the threshold at which the transistor 33 is triggered into conduction.

Claims (18)

1. A fuel level monitoring system, particularly for marine vessels, in which a plurality of visual indicator means provide a continuous visual indication of the range within which the level of fuel in one or a plurality of tanks lies, there being provided an audible indicator operable to generate an audible indication whether the device commutes from indicating one level to indicating another level.

2. Afluid level monitoring device, comprising level sensing means for detecting when the level of fluid exceeds a predetermined value and means responsive to the level sensing means for providing an outlet signal having a first value when the fluid level is above the said predetermined value and a second value when the fluid level is below the said predetermined value, and means for providing either a visual or audible indication signal when commutation from the first value to the second value occurs.

3. A fluid level monitoring device as claimed in Claim 2, in which one of the said values of the output signal is zero.

4. A fluid level monitoring device as claimed in Claim 2 or Claim 3, in which the level sensing device has normally open contacts which commute to a closed contact state when the fluid level falls below the said predetermined value.

5. Afluid level monitoring device as claimed in any of Claims 2 to 4, in which there are provided means for silencing the said audible warning device after commutation of the signal from its first value to its second value has initiated operation thereof.

6. A fluid level monitoring device as claimed in any of Claims 2 to 5, in which there are provided a plurality of level sensors each responsive to the attainment by the fluid of a predetermined different level, and operable to provide commuted output signals upon attainment of the associated respective level by the monitored fluid.

7. Afluid level monitoring device as claimed in Claim 6, in which the audible warning device is common to the sensors for each level, respective sets of visual indicators being provided for each level.

8. Afluid level monitoring device as claimed in Claim 6 or Claim 7, in which each of the said plurality of level sensors is adjustable over a certain range of values to provide an output indication when the liquid level passes a critical threshold value within the associated range of adjustment thereof.

9. Afluid level monitoring device as claimed in any of Claims 2 to 8, in which the fluid level sensors are float switches having means for allowing a limited range of travel for commuting the associated switch contacts thereof as the liquid level passes a respective range.

10. A fluid level monitoring device as claimed in Claim 9, in which the said float switches are all mounted slidably on a common upright guide for immersion in a fluid the level of which is to be monitored.

11. Afluid level monitoring device as claimed in any preceding claim, in which a liquid the level of which is to be monitored is contained in a tank having an associated separate upright tube in communication therewith at least at a low level, the upright guide and the said float switches being mounted within the said tube whereby variations in the liquid level which are due to movement of the tank can be minimised.

12. A liquid level monitoring device as claimed in Claim 10 or Claim 11 in which the said float switches operate respective relays which latch upon energisa-i tion thereof.

13. A liquid level monitoring device as claimed in any of Claims 2 to 12 in which the circuit includes delay means for delaying commutation of the said output signal from its first value to its second value for a predetermined time period after the said liquid level has passed the critical threshold value, whereby to avoid commutation due to surge effects from movement of the tank containing the liquid the level of which to be monitored.

14. A liquid level monitoring device as claimed in any of Claims 2 to 12, in which the visual indicator comprises one or a plurality of lamps one or more of which is illuminated at any one time to indicate the current range of values of the liquid level, there being means for varying the brightness of the lamp in dependence on the ambient illumination conditions.

15. A liquid level monitoring device as claimed in Claim 14, in which the circuit includes a dimmer device for reducing the intensity of illumination of the lamps when the ambient light level is low, the dimmer including a light sensitive resistor.

16. A liquid level monitoring device as claimed in Claim 15, in which the light sensitive resistor is connected in a voltage dividing circuit supplying the base of a switching transistor which is connected with its collector/emitter path in series with a relay coil whereby to control the relay to switch in, with an associated additional resistor in the lamp circuit, when the ambient light level falls below a critical threshold value.

17. Amultipletankfuel control system in which fuel is drawn from one tank at a time and there are provided means for transferring fuel from one tank to another when the difference in fuel levels exceeds a predetermined or adjustable threshold value.

18. Afuel level monitoring device substantially as hereinbefore described with reference to the accompanying drawings.