WO2012174582A1

WO2012174582A1 - System and method for determining fluid level

Info

Publication number: WO2012174582A1
Application number: PCT/AU2011/000751
Authority: WO
Inventors: Noel Mancuso
Original assignee: Pioneer Waste Management Holdings Trust Pty Limited
Priority date: 2011-06-21
Filing date: 2011-06-21
Publication date: 2012-12-27

Abstract

A level sensing assembly (100) for measuring a level of a fluid in a reservoir (400) is provided. The level sensing assembly (100) includes a guide assembly (102) and a float (104) adapted to be guided by the guide assembly (102) to rise and fall with the level of the fluid, and in doing so to vary the length of a signal path travelled by a level sensing signal. The length of the signal path may be used by a level sensor (130) to determine the level of the fluid.

Description

System and method for determining fluid level

Field of the invention

The present invention relates to systems and methods for sensing the level of a fluid in a fluid reservoir. The systems and methods describe are particularly useful in sensing the level of pulp slurries, and it will be convenient to describe the invention in relation to that exemplary, though non-limiting, application.

Background of the invention

A wide variety of systems make use of level sensors. For example, many waste treatment and/or disposal systems operate by temporarily storing fluid waste in a holding tank. The holding tank is periodically emptied and the fluid waste transported elsewhere for disposal or further processing.

For example, PCT applications PCT/AU2004/001460 (published on 6 May 2005) and PCT/AU2008/000685 (published on 20 November 2008) describe putrescible organic waste treatment systems which process putrescible organic waste into a pulp slurry and transfer the pulp slurry to a holding tank. The systems described in these two PCT applications automatically control the addition of water during the processing and transportation of the waste to the holding tank such that a minimum (or reduced) amount of water is used, thereby creating a relatively dense and viscous pulp slurry. Due to the density/ viscosity, the surface of the pulp slurry in the reservoir is typically uneven. n order to prevent over-filling, the holding tank is provided with a level sensor. While a variety of level sensing technologies exist, however, the characteristics of the relatively dense and viscous pulp slurries produced by the systems disclosed in the aforementioned PCT applications are such that providing a cost-effective solution for reliably providing accurate level information can be difficult. For example, traditional float sensors (i.e. sensors which float with the fluid and trigger an electrical, magnetic, or mechanical switch on reaching an actuation level) can be buried by the weight of the pulp slurry and fail to rise with the level of the fluid. Additionally, due to the viscosity of the fluid the workings of the float sensor may be impeded, either preventing the float from rising (during filling of the reservoir) or, in the instance of a pivot/hinged type float switch, preventing the float from falling (during/after emptying of the reservoir),

Traditional sonic sensors, on the other hand, are typically well suited to measuring the level of "flat" surfaces - e.g. fluids with low viscosity such as water or similar. For dense and viscous slurries, such as putrescible organic waste slurries, however, the surface area is rarely even. This uneven surface compromises the accuracy and reliability of measurements from sonic sensors, as level signals may hot be returned (or returned directly) to the sensor from the fluid surface. . ·

In the even that a level sensor does not operate correctly, the holding tank may be overfilled and explode. At best this may create a large mess and be expensive (both in terms of having to replace the holding tank and other damaged components and having to clean up the mess), and at worst may present a safety risk - either due to the explosion itself, or the contents of the holding tank which are released on the explosion.

Accordingly, it would be desirable to provide systems and/or methods capable of determining the level of dense/viscous fluids with a relatively high degree of accuracy and/or reliability. Alternatively, or in addition, it would be desirable to provide the public with a useful alternative to existing level sensing systems and methods.

-Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention

In one aspect the present invention provides a level sensing assembly for determining a level of a fluid in a reservoir, the level sensing assembly including: a guide assembly; and a float adapted to be guided by the guide assembly to rise and fall with . the level of the fluid and in doing so to vary the length of a signal path travelled by a level sensing signal, the length of the signal path for use by a level sensor in determining the level of the fluid.

The level sensing assembly may include the level sensor. In a second aspect the present invention provides a level sensing assembly for determining a level of a fluid in a reservoir, the level sensing assembly including: a level sensor; a guide assembly; and a float adapted to be guided by the guide assembly to rise and fall with the level of the fluid and in doing so to vary the length of a signal path travelled by a level sensing signal emitted by the level sensor, the length of the signal path for use by a level sensor in determining the level of the fluid.

In either or both of the above aspects:

The signal path may be the path between the level sensor and a target area.

The target area ma be maintained at or above a surface level of the fluid by the float and may be adapted to direct the level sensing signal to a signal receiver: of the level sensor.

The level sensor may include an emitter for emitting the level sensing signal along the signal path; the. guide assembly may guide the float such that the target area moves along the signal path, and in use the level sensing signal may be reflected back to the receiver of the level sensor by the target area. The guide assembly may include a stop against which the float rests when not buoyed up by fluid, the guide assembly in use allowing for fluid flow beneath the float when at rest against the stop.

The float may be approximately spherical in shape.

The target area may be a surface of the float. Alternatively, the target area may be provided on a target carried by the float. The target may be a plate which is maintained substantially parallel to the surface level of the fluid by the float. The target may include one or more bearing formations for bearing on the guide assembly to maintain an orientation of the float and/or target. The or each bearing formation may be a tab.

The guide assembly may include at least one rod for guiding travel of the float. The guide assembly may include a plurality of rods for guiding travel of the float. The plurality of rods may be arranged to form a cage about the float. The level sensor may be in communication with a computer processing device and may be adapted to send sensed level information to the computer processing device. The computer processing device may be configured to process the sensed level information received from the level sensor and output level-based information to one or more users. Level-based information may be output to one or more users by one or more output means selected from a group including: displaying levels-based information on a display means; playing level-based information oil a speaker; sending level-based information to one or more email addresses; sending a short-message-service message including level-based information to one or more phone numbers; sending a voice message including level-based information to one or more phone numbers; posting level-based information to a website accessible by a user; and sending level-based information to a pager.

Level based information may include information selected from a group including: a path length between the target area and the level sensor; an estimated volume of fluid in the reservoir;, an estimated remaining capacity of the reservoir; an estimated time until the reservoir will be at^! full capacity; and a recommended time at which the reservoir should be emptied.

The reservoir may be adapted to receive and hold fluid waste from a waste processing unit via one or more inlet pipes.

The computer processing device may be configured to control operation of the waste processing unit according to the sensed level information. The waste processing unit may be a putrescible Organic waste processing unit; The fluid may be a pulp slurry; .

In a further aspect the present invention provides a fluid reservoir for fluid produced by a waste treatment system, the fluid reservoir including a level sensing assembly according to any one of the above statements. In a still further aspect the present invention provides a putrescible organic waste treatment system including a waste processing unit for processing putrescible organic waste and transporting said processed waste to a fluid reservoir as described above. In a still further aspect the present invention provides a method for determining a level of a fluid in a reservoir, including: directing a level sensing signal at a target area carried by a float; receiving a returned level sensing signal from the target area; and determining the level of the fluid based on characteristics of a signal path travelled by the level sensing signal, wherein the float is adapted to be guided by the guide assembly to rise and fall with the level of the fluid and in doing so to vary the. length of the signal path. .

The characteristics of the signal path include the distance of the signal path, and/or the time taken between directing the level sensing signal at the target area and receiving the returned signal. As used herein, except where the context requires otherwise; the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives^ components, integers or steps.

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief description of the drawings

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 provides a perspective view of a level sensing assembly in accordance with an embodiment of the invention.

Figures 2A and 2B provide partial perspective views of the base of the level sensing assembly shown in Figure 1 , respectively without and with the float visible.

Figure 3 provides a perspective view of the float assembly of the level sensing assembly shown in Figure 1; . Figure 4A provides a perspective depiction of a fluid reservoir with the level sensing assembly of Figure 1 installed therein;

Figures 4B provides a sectional elevation depiction of the reservoir of Figure 4A. Figure 5 provides a block diagram of a computing' system suitable for use with embodiments of the present invention; and

Figure 6 provides a schematic diagram of a putrescible organic waste treatment system including the fluid reservoir of Figure 4 and level sensing assembly of Figure 1. Detailed description of the embodiments

Figures 1 to 3 provide perspective and partial perspective views of a level sensing assembly 100 in accordance with an embodiment of the invention. Typically (and as depicted in Figure 4) level sensing assembly 100 will be installed in a fluid reservoir such as a holding tank into which a fluid is pumped/otherwise transported. Level sensing assembly 100 includes a guide assembly 102 and a float 104.

In this instance the guide assembly 102 includes four rods 106 extending between a base . 108, in the form of a ring, and a top plate 1 10. The rods 106 form a cage about the float 104. Each of the four rods 106 is provided with a threaded end 112 which is received through an aperture in the base 108, allowing the rod to be secured to the base 108 by use of a complementally threaded bolt 1 14. This allows the base 108 to be easily secured/removed which, in turn, allows the float 104 to be placed inside/removed from the guide assembly 102. As can be most easily . seen in Figure 2A, a crossbar 1 16 extends across the centre of the base 108 (i.e. along a diameter) and is secured at each end to the base 108 (in this instance by welding, however other fastening/securing means could also be used). The crossbar 1 16 provides an elevated stop for the float 104 which prevents the float 104 from resting on the base of the reservoir in which the sensing assembly 100 is installed, and/or from resting on the inner edge of the ring of the base 108 (which could inadvertently create a seal between the float 102 and the base 108). By mounting the crossbar 1 16 atop the base 108 a flow gap exists between the bottom of the crossbar 1 16 and the bottom of the base 108, allowing fluid flow beneath the crossbar 116. Top plate 1 10 includes a central aperture (obscured) for receiving a level sensor device, and a plurality (in this case four) of peripheral apertures 118 by which the top plate 1 10 can be secured in place using bolts or other fasteners. In this instance rods 106 are welded to the top plate 1 10, however alternative securing means are, of course, possible. The float 104 of the present embodiment is a substantially spherical, air-filled hollow ball. As can be seen, the diameter of the float is such that the float is received between the four rods 106 of the guide assembly 102 and is free to travel up and down within the guide assembly 106. The float 104 cannot, however, escape the guide assembly 102, ensuring that the float 104 moves along a sensing axis of a level sensor 130 (discussed below).

It will be appreciated that alternative floats and/or guide assemblies are possible. Generally speaking, the shape/construction of the float and guide assembly will be such that the float can freely travel up. and down as the fluid level changes, and that the float provides a target area that remains elevated above the surface of the fluid and "visible" to the level sensor 130. For example, the float could be a hollow geometric "solid" of an alternative shape, such a cube, a cylinder, a prism, or other shape. By way of further example, the guide assembly 102 could be formed of a fewer or greater number of rods. For example, the guide assembly could be formed of two or three rods with the float shaped/adapted to be guided up and down between the rods. Further alternatively, the guide assembly could be formed of a single rod, with the float adapted < to be guided up and down the single rod (e.g. by being fnovably connected to the rod by, for example, a sleeve or collar of slightly greater diameter to the rod and able to travel along the rod).

Sensing assembly 100 also makes use of a level sensor 130. The level sensor 130 may be provided as a part of the sensing assembly 100, though could also be supplied as a separate/user installable component. By way of non-limiting example, the level sensor 130 may be a distance sensor which determines the distance between the sensor and the float (or a target carried by the float). Suitable distance sensors may include optical distance sensors (e.g. laser distance sensors) and sonic distance sensors, though typically sonic distance sensors are more cost-effective than optical/laser distance sensors. Taking a sonic distance sensor as an example, and generally speaking, a transducer is used to emit a level signal (i.e. a sound wave) towards a target area (in this case the float 102 or a target carried on the float 102). The level signal is reflected by the target back to the transducer, where it is received (i.e. the echo of the sound wave) and the level sensor measures the time taken for the echo of the emitted sound wave to be returned from the target. From the. measured time, and with reference to the speed of the sound wave, the distance between the sensor and the target can then be determined by simple calculation. For the purposes of description, this embodiment will be described with the level sensor 130 being a ToughSonic® TSPC-30 series ultrasonic distance sensor manufactured by Senix Corporation. It will be understood, however, that alternative ultrasonic distance sensors may be used, or indeed alternative types of distance sensors. Level sensor 130 is mounted to/carried by the top plate 1 10 and defines a sensing axis of the sensing assembly 100 - i.e. the direction in which sensing signals are emitted from an emitter of the level sensor 130, and returned to/received by a receiver of the level sensor 130. In this case the body of the level sensor 130 includes a threaded shaft which is received through the centrally located aperture in the top plate 1 10 and secured in place by a correspondingly threaded nut. Relevant connections to the sensor 130 (e.g. connection to a computing system 500 as described below for data and control communications with the sensor 130, and a power connection) are provided for by cables 132 which extend from the top of the sensor 130.

Float 104 includes a target area 152 which during use is maintained above the surface level of the fluid so as to be easily receptive to signals sent by the level sensor 130. The path travelled by the level sensing signal between the level sensor 130 and the target area 152 is referred to as the signal path.

In the present embodiment the target area 152 is provided on. a rectangular target plate 154. The target area is adapted to receive the level signal from the level sensor 130, and reflect the level signal back to the level sensor 130. In order to maintain a stable and substantially level orientation, which assists wit the accuracy/reliability level _.sensing, the edges of the plate 152 are provided with upturned tab formations 156, each of which being sized arid positioned so as to stabilise the plate 312 against one of the rods 106 and prevent the ball from spinning/rotating in the guide assembly 106. In this way the guide assembly 102 keeps the target plate 154 (and target area 152) aligned with the sensing axis of the sensing assembly 100 as the float 104 rises and falls with fluid level fluctuations.

In alternative embodiments the surface of the float 104 may itself be the target of the level sensor 130 (in which case the target area 152 is the surface of the float 104), or the target area 152 may be provided by alternative target devices or components which are integrally formed on/with or carried by the float 104. Depending on the level of accuracy required, the sensing assembly 100 (or a computing system processing the sensed data as discussed below) may be configured to adjust the raw sensor readings to account for the elevation of the target area 152 above the surface of the fluid level. For example, if the properties of the fluid are such that the target area is, on average, maintained a level of x cm above the surface level of the fluid, then this can be taken into account during processing by adding x to any distance measurement. Where high precision is not required, however, such adjustment may not be necessary, recognising that in measuring a point above the actual surface level of the. fluid the reported surface level will be higher than the actual surface level (providing an inherent overestimation and safet gap). · '

By keeping the target area 152 above the surface level of the fluid the level sensor 130 can easily measure the distance to the target area 152, allowing for relatively reliable and accurate levels to be obtained. This is in contrast to the known prior art, where level signals are bounced off the surface of the fluid itself, which (depending on the characteristics of the fluid) can make accurate and reliable level readings difficult or impossible.

The components of the level sensing assembly 100 (e.g. the guide assembly 102, the float 104j and the target 152 if a separate target is provided) may be manufactured from any material suitable to the environment in which the sensing assembly 100 is to be used. Typically these will be materials that will not corrode or otherwise degrade due to exposure to the fluid the level of which is being determined, limiting both damage to the level sensing assembly 100 components and contamination of the fluid in which the assembly 100 is placed. In addition, and as described in further detail below, where the reservoir is evacuated by a pumping operation, the materials should be sufficiently strong/rigid to be able to withstand forces generated when fluid (which may be quite dense and viscous) is pumped out of the fluid reservoir. Further, float 104 should also be sufficiently lightweight and buoyant so as to rise and fall with the. fluid level and not get trapped beneath the surface of the fluid. Where the sensing assembly 100 is being used to determine the level of organic waste pulp in a fluid reservoir, stainless steel is a suitable material as it will not degrade by exposure to the waste material, and. is strong enough to withstand suction forces generated during a tank pumprout operation. Further, a spun stainless steel (or similar) provides for a float 104 that does not become trapped under the surface level of the fluid. The components of the level sensing assembly 100 could, of course be manufactured from alternative materials; Such materials may, for example, include plastics such as high density polyethylene.

Turning to Figures 4A and 4B, perspective and sectional elevation depictions of a fluid reservoir 400 with the level sensing assembly 100 (as described above) are provided. As will be appreciated, level sensing assemblies in accordance with embodiments of the present invention could be used with a wide variety of reservoirs, tanks etc, and as such reservoir 400 is provided by way of non-limiting example only.

Reservoir 400 is a holding tank moulded from high density polyethylene. A floor 402 of the reservoir 400 is sloped downwardly from one end 404 to the other 406 to assist in pump-out operations. The upper end of wall 406 is fitted with an outlet pipe 408 capped by a camlock 410 for connection to a hose Or similar by which fluid in the reservoir 400 is pumped out and info (for example) a tanker. Inside the reservoir 400 outlet pipe 408 is provided with an elbow 412 such that the internal end 414 of the outlet pipe is located at the bottom of the foot 416 of the, reservoir 400. The top wall 418 of the reservoir 400 is fitted with an inspection/access lid 420, a one-way air inlet vent/valve 422 (to allow air into the reservoir 400 during pump out operations), and a one-way outlet vent/valve 424 (to allow air/other gases to escape the reservoir 400). In this instance the outlet vent 424 is fitted with a filter (e.g. a carbon filter) to reduce odours being released. Reservoir 400 is also provided with an inlet 428 by which fluid is introduced into the reservoir 400.

Installed inside the fluid reservoir 400 is a level sensing assembly 100 as described above. The sensing assembly 100 is installed such that as the fluid level in the tank 400 increases/decreases the float 104 is guided by the guide assembly 102 to rise and fall substantially vertically. Where the fluid reservoir 400 is a closed reservoir as shown, the base 108 and top plate 1 10 of the guide assembly 102..may be respectively secured to the floor and ceiling of the reservoir 400, such that the rods 106 extend substantially vertically therebetween. Additional or alternative struts or supports could, of course be used, though care should be taken not to unduly disrupt the flow of fluid in the reservoir 400 (which could, for example, increase pump out times). While the level sensing assembly 100 could, of course, be located at any position in the fluid reservoir, in applications where the fluid is a highly viscous fluid (e.g. an organic waste pulp slurry as discussed below), locating the level sensing assembly 100 in a corner of the tank as shown can be advantageous. By locating the assembly 100 in a corner drag during a pump-out operation (generated due to the viscosity of the fluid flowing past/through the components of the level sensing assembly) is reduced/minimised, which in turn provides for a more efficient pump-out operation.

In use. waste fluid is pumped into the fluid reservoir 400 via inlet 428. As the level of the waste in the tank 400 rises, the float 104 also rises, its movement being restricted by the guide assembly 102 so as to maintain alignment with the level sensor 130. As discussed above, when the tank 400 is empty, float 102 rests on the crossbar 116 provided at the base of the guide assembly 102. This elevates the float 102 from the floor of the tank 400 (and the base 108 of the guide assembly 102) allowing fluid to easily circulate around the float as it is pumped in to the tank 400.

Level sensor 130 is configured to periodically determine the distance to the target area 152 of the float 104 and output a level signal to a computing system 500 (described below). The frequency at which the level sensor emits a signal to determine the position of the target area may.be set as is appropriate for the environment i which the sensing assembly 100 is used. For example, in reservoirs subject to relatively rapid level changes, a polling frequency of 2 seconds (or even shorter) may be appropriate. Alternatively, for reservoirs not subject to rapid level changes, a longer polling frequency may be appropriate.

Figure 5 provides a block diagram of one example of a computing system 500 suitable for use in receiving and processing data/signals from the level sensor 130 and controlling level sensor 130. The computing system 500 includes at least one processing unit 502. Typically, the processing unit 502 will include a single processing device (e.g. a microprocessor, programmable logic controller,; or other computational device), however the processing unit may include a plurality of processing devices. Through a communications bus 510 the processing unit 302 is in data communication with volatile memory 504 (e.g. random access memory including one or more DRAM modules) and non-volatile memory 506 (e.g. one or more hard disk drives, solid state disk drives, and/or ROM devices such as one or more EPROMs). Instructions and data to control operation of the processing unit 502 are stored on the volatile and/or non-volatile memory 504 and 506. The computing system 500 also includes one or more peripheral interfaces 508 which allow the system 500 to interface with (e.g: send data to and/or receive data from) a plurality of peripheral devices. Level sensor 130 is one such peripheral device, and may interface with the system 500 via (for example) an RS-232 or RS-485 interface. Other interfaces (such, as USB, firewire etc) are, of course possible.

Additional peripheral devices will, typically, also be provided. These may include, for example, a display device 312 (e.g. an LCD screen, LED screen, or other display device), and one or more user input devices 314 (e.g. a keyboard, pointing device, and/or user operable buttons/switches). As will be appreciated, a wide variety of additional peripheral .input/output interfaces may also be provided depending on other functions to be provided by the computing system 500. By way of non non-limiting example, these may include interfaces for interfacing with touch-screens; devices connected via USB, Firewire, eSata, serial ports, parallel ports; flash memory devices (such as SD cards, Compact Flash cards etc); and drives (such as compact disc drives, DVD drives, Blue-Ray drives). Computing system 500 also includes a communications interface 316. A variety of communications interfaces are possible, for example a GSM modem or a Network Interface Card allowing for wired or wireless connection to a network. Using the communications interface 514 the computing system 500 can communicate with other computing systems via a network 518. These may be local devices on a local area network, and/or devices accessible via a public network such as a mobile network or the Internet.

Control of the computer system 500 is achieved , by computer software programs/applications run on the computer system 500. These programs include computer- readable instructions which are executed by the processing unit 502 to implement the relevant actions. By way of non limiting example, computing system 500 may be a PC running an operating system such as Windows® 7. Alternative computing systems and operating systems are, of course, possible. .

The level signal provided by the level sensor is received by the computing system 500 and, typically, stored (along with information such as date and time and identification information - e.g. a serial number or other identifier of the level sensor 130) in a database on memory 506. The. level signal is then processed by the computing system 500 to provide users with level-based information. The level-based information may include a variety of information based directly on the level information and/or on ancillary information, such as historical level or other data. By way of non-limiting example, level-based information may include information such as: raw level data (e.g. the sensed distance between the target area 152 and the level sensor 130); tie volume of fluid sensed in the tank (e.g. based on the distance between the target area 152 and the level sensor 130); the remaining capacity of the tank 400 (e.g. based on the sensed volume of fluid and the known capacity of the tank 400); an estimated time until the tank will reach full capacity (e.g. based on usage statistics); a recommended time at which the fluid reservoir should be emptied (e.g. based on current capacity and usage statistics).

In addition, the level-based information can be used to provide information/statistical data on reservoir and waste usage. For example, when pumping a reservoir out the volume pumped out can be determined according to the most recent sensed level. In many circumstances measuring, the volume pumped out in this manner will be simpler/more cost effective than doing so using flow sensors of similar to directly calculate the volume of fluid pumped. The volumetric data on pump-out operations can then be used for billing_i purposes (e.g. where disposal is charged at , a per-litre rate) and other environmental reporting data. Once again, this usage information may be made available to reservoir users to allow them to view their waste usage patterns over a given time period. As will be appreciated, a wide variety of rules may be employed as to what level-based information is communicated, how level-based information is communicated, when level-based information is communicated, and where level-based information is communicated to. For example, level-based information may be continuously displayed/updated on a dedicated display unit (e.g. 512) provided on the fluid reservoir 400 and/or at the source of the fluid being . transported to the fluid reservoir (such as the display of the Putrescible organic waste treatment system 600 discussed below).

LeVel-based information may also, or alternatively, be periodically communicated to users by, for example, emailing email addresses provided in a mailing list of relevant users r sending messages (e.g. sms's and/or automatically generated voice messages) to phone numbers provided in a phone list of relevant users, and/or paging relevant users. Relevant users may, for example, be the operator/owner of the fluid reservoir and the organisation responsible for collecting fluid from the fluid reservoir.

Computer system 500 may be configured to send such communications directly via a communications interface 516, or may be configured to send level based information to a further computing device which, in turn, is configured to send the communications. By way of example, computing device 500 may include a GSM modem which sends level-based information to a distribution list of phone numbers. In addition, or alternatively, computing device may include an Internet connection interface (e.g. a network interface card) and send communications to users via a network such as the Internet. System 500 may be programmed to send communications each time a level signal is received at system 500 from the level sensor 130 or only when a level signal indicative of a change in the level of the fluid is received by the system 500. More typically, however, communications will only be sent when particular threshold levels are sensed (e.g. 50%, 80%, 90%). Further, system 500 may be programmed with multiple predefined thresholds, and configured to take different actions depending on which threshold has been reached. For example, when the level sensed indicates the tank 400 is at 50% capacity, a communication may be sent to a "regular" distribution list of email addresses/phone numbers. If, however, the level sensed indicates the tank 400 is at 95% capacity, a communication may sent to an "important" distribution list of email addresses/phone numbers. By way of further example, computer system 500 may be configured to make reservoir and level-based information available via a user-accessible web-site (reservoir information may, for example, include a reservoir identifier, the physical location of the reservoir, the owner/operator of the reservoir, the next scheduled emptying of the reservoir, etc). Access to such a website may be limited by requiring a user account and/or valid login/authentication details. As will be appreciated, such an arrangement allows for relevant parties to monitor the level-based information of a fluid reservoir 400 from anywhere. This may be particularly advantageous where a single organisation owns/uses, or is responsible for emptying, a number of separate fluid reservoirs. In this case a single website may be provided showing level-based information for all fluid reservoirs relevant to a particular user. Each individual fluid reservoir may be uniquely identified (for example based on physical location, a serial number, or other information) and level-based information provided in a way that allows the user to quickly and easily determine the levels of all relevant tanks. This may, for example, be by a display showing the relevant tanks (and associated information) along with a visual representation of the capacity and current level of each tank. The tanks may, for example, be displayed in a list or table, or may be displayed on a map, each tank being positioned on the map according to its actual location. Further, the visual representation of each tank may be colour-coded according to the sensed level. For example, tanks with a sensed fluid level below a predefined "safe" threshold (e.g. 60%) may be shown in green, tanks with a sensed fluid level above a predefined "danger" threshold (e.g. 90%) may be shown in red, and tanks with a sensed fluid level between the "safe" and "danger" thresholds may be displayed in yellow. Various intermediate thresholds/colour codings may, of course, also be used. This allows a user to very quickly review all tanks under their responsibility in order to determine which (if any) of the tanks need to be emptied as a matter of urgency, which are substantially empty, and which are in-between. This information may also be used by collection agencies to efficiently plan tank -emptying runs, particularly where tank information is displayed on a map and a user can visually determine the relative ¾ physical locations of the various tanks. Alternatively, the information may be input into an algorithm to automatically plan the most efficient path for a collection run (i.e. one that provides a shortest path covering all tanks that are. considered to need emptying).

Generally, computing system 500 will also be programmed to control the operation of various components of the system(s) which deliver fluid to the fluid reservoir 400 according to the level-based information. For example, if the level-based information is such at the tank 400 is at (or approaching) capacity, system 500 may control relevant .components/systems to prevent further fluid being transported to the fluid reservoir. .

For safety, computing system 500 may also be programmed to interpret any fault signal received from .the level sensor 130 (or, in fact, absence of a signal from the level sensor 130 as could occur, for example, if the sensor 130 had ceased operating) as being a full tank 400 and prevent further fluid being transported to the tank 400.

As noted above, one (non-limiting) application of a level sensing assembly such as assembly 100 described above is in putrescible organic waste treatment systems. Figure 6 provides a schematic diagram of a putrescible Organic waste treatment system 600 including the fluid reservoir of Figure 6. System 600 is similar to the system described in PCT/AU2008/000685 (publication number WO 2008/138069, . titled 'Putrescible organic waste treatment" and published on 20 November 2008), the contents of which are hereby incorporated by reference.

Putrescible organic waste treatment system 600 that includes a comminution unit 602 having an outlet 604 that is in fluid communication with fluid reservoir 400. The comminution unit 602 includes an internal chamber 604 which is used to receive putrescible organic waste. The internal chamber 604 is located above a comminution means 606 which is used to comminute and masticate the, putrescible organic waste. The system 600 also includes a control panel 608 that is used to display information and control the comminution unit 602. The comminution means 606 in the form of a grinding unit which is operable by a motor

610 to comminute putrescible organic waste into a pulp or , slurry during a comminution operation. The comminution unit also includes a mechanical brake 612 for stopping the grinding unit 606. It will be appreciated that in alternative embodiments, other comminution units may also be used, for example cutting blades, and the motor 610 may be either internal or external to the comminution unit, and the brake 612 need not be provided. .

A water supply 614 is also connected to the comminution unit 602 and is controlled by the computing device 622. Water from the water supply 614 is introduced into the comminution unit 602 at the internal chamber 604 by water jet 618 and at the grinding unit 606 by water jet 620. If required additional water inlet jets may be provided in the comminution unit 602. For example, if a pump is used to pump the waste pulp from the comminution unit 602 to the fluid reservoir 400 (as opposed to the vacuum arrangement described below) an additional water inlet may be placed between the grinding unit 606 and the pump to prime the pump before use. In addition, one or more jets may be directed to spray on the under-surface of the lid 638 to ensure no waste material becomes stuck thereon. Putrescible organic waste treatment system 600 also includes a computing device 622.

This may be a device such as computing system 500 described above. Computing device 622 is programmed to receive information regarding the operating parameters of the comminution means from the comminution means, and oh the basis of that information control the grinding unit 606 and the water supplied to the comminution unit during comminution of the putrescible 1,7 organic waste. Computing device 622, also receives information from the/level sensing assembly 100. : ^{■ '}

For example, the motor 610 may be fitted with a load sensor 624 for sensing the load on the motor 610. For relatively soft waste, such as vegetable matter, the load sensor 624 will read only a low load and the computing device 622 will not supply a large amount of water. In contrast, for harder waste such as bones and/or seeds etc, the load sensor 624 will read a high load and the computing device 622 .will supply a greater amount of water to aid in the comminution and transport of comminuted waste. Additionally, when a suitably small load is detected on the grinding unit 606 the computing device 622 can interpret this to be that there is no more material requiring comminution and switch the grinding unit 606 off.

Finally, if the load on the motor 610 is sensed to exceed a predetermined value, or to exceed a predetermined value for a predetermined time, the computing device 622 can be programmed to interpret this as an indication that the grinding unit 606 has become stuck and should either be shut off or the direction of rotation changed (as discussed below) in order to prevent damage to the grinding unit 606 or the motor 610.

When the computing device 622 cuts power to the grinding unit 606 (for example at the end of a cycle or in the event of a blockage/jam or some other fault) the computing device 622 also operates the brake 612 in order to halt the rotation of the comminution means 606. Although without power the comminution means 606 would, of course, eventually stop turning of its own accord (and therefore a brake 612 is not strictly necessary) by providing a brake 612 the grinding unit 606 will come to a halt in a shorter period of time, allowing for stoppage time (either due to a malfunction or merely time between cycles) to be minimised.

By supplying water according to the load of the comminution means 606 the computing device 622 can automatically determine and add the appropriate; amount o water to ensure that any one or more of the following pulp characteristics are produced by the comminution unit: a defined pulp density; a range of pulp densities; a defined moisture content; a range of moisture contents; flow characteristic; or a range of flow characteristics. The density, moisture content and flow characteristics may be selected to ensure the most efficient transportation of the pulp waste material, or selected to optimise the pulp waste material for further use. For example, the further use of the pulp waste material may be transportation to a biogas plant for use in a digester for the production of biogas.

The computing device 622 can be programmed to introduce a predetermined volume of water during each comminution cycle. An appropriate volume of water per cycle may be between 2 to 5 litres, this volume divided between the water jets 618 and 620. Alternatively, the computing device 622 can be programmed to vary the amount of water supplied according to the load on the motor 610.

Water jets 618 and 620 are fed by a mains water line 614 which includes an on/off control valve 626. Valve 626 is a variable valve and is able to vary the flow of water from between 0% to 100% of the total available water flow, depending on the desired flow characteristics and pulp density required The outlet 628 of the comminution unit 602 is connected to the fluid reservoir 400 via outlet line 630. In one embodiment, fluid reservoir 400 is fitted with a vacuum pump 632 for depressurising the fluid reservoir 400. In this case waste from the comminution unit 602 is transferred through the pipes by the suction created in the sealed fluid reservoir 400. Alternate arrangements for transportation of the waste pulp through the system are, of course, possible. For example, instead of fitting the fluid reservoir wjth a vacuum pump 632 to create a vacuum for waste transportation, a standard pump 634 may be installed to pump the waste from the comminution unit_s602 to the tank 400.

Fluid reservoir 400 is also connected to an outlet (e.g. pipe 408) which includes an interface (such as camlock 410). Preferably the valve 408 is manually operable to enable an operator to , empty the fluid reservoir 400 independently of the comminution Unit 602 and computing device 622.

The system 600, with the exception of the fluid reservoir 400, may be incorporated within a single unit so as to be conveniently located adjacent; a food preparation or processing area, for example in a kitchen or a food processing plant. Such a unit' may be appropriately , sized, for example to a size similar to that of a domestic clothes washing machine.

The comminution unit 602 further includes a lid 638 which pivots about pivot joint 640 and is used to cover the chamber 604 when the comminution unit is in operation. The lid is designed to be lifted by an electronic actuator (not shown) which is also linked to computing device 622. As a safety measure, the computing device 622 is programmed not to allow the comminution means to operate when the lid is open.

The upper part 604 of the chamber is provided with sloping walls so as to funnel the putrescible organic waste material onto the grinding unit 606. The water jet 618 (which may be one of multiple jets placed around the periphery of the upper part 604 of the chamber) is directed onto the surface of the funnel to produce centrifugal flow of water and thereby ensure that all waste material is substantially funnelled onto grinding unit 606. The grinding unit 606 comminutes and masticates the putrescible organic waste material in the presence of the water to produce a putrescible organic waste pulp. The computer processing device 622 is, also configured to store a log of data concerning the operation of the comminution unit 602 and the level ^' of fluid reservoir 400. As described above, relevant information may then be communicated to one or more users in a variety of ways. Information processed, logged, and or communicated may include, for example: the number and type of comminution cycles performed by the comminution unit; the total time which the comminution unit 602 has been operated for; the load information as sensed by the load sensor 624; the control operations selected by a user; the configuration of the controller 622 (such as communicatiori settings, ^'griridihg unit 606 settings, door 640 settings); the volume of water used during the comminution cycles; how the capacity of the fluid reservoir 400 has changed with each comminution cycle; the present capacity of the fluid reservoir 400; machine faults.

This data, both operational and statistical, may be used to determine, for example, if and when upcoming maintenance of the various components (such as the motor 610 or grinding unit 606) of the comminution unit 602 may be required, when the fluid reservoir 400 will require emptying, and general statistical information such as the efficiency of the comminution unit 602 with respect to water usage.

Use of the comminution system 600 will now be described. The lid 638 is raised by an operator of the comminution unit 602, or automatically by the actuator means. Putrescible organic waste is loaded in the chamber 604. The lid 638 is closed and the operator, using the control panel 608, initiates the operation of the comminution unit 606, and a signal is sent to the computing device 622 which initiates a comminution cycle. The computing device 622 actuates the valve 626 so that a jet of water is supplied to the chamber 604 and (if required) the grinding unit 606.

The jet 618 is located at a position on the cone to cause the fluid to travel centrifugally to ensure that the waste material is swept off the walls of the chamber 604. The opening of the internal chamber 604 leads onto the grinding unit 606 allowing the grinding' unit 606 pulp the material to a predefined size. The valve 626 is actuated for a period of time set by the computing device 622 utilising information received from the load sensor 624 to supply volume of water to water jets 618 and 620 so that an optimal Waste pulp will be produced. The operation of the grinding unit 606 itself is also controlled by the controller 622 on the basis of the sensed load on the motor 610. ; . ^; " '

The optimal pulp density is determined to ensure that the pulp is optimal for transportation to and from the fluid reservoir 400.

In the case where the waste for a particular cycle is comprised essentially of a liquid or . has liquid components, for example such as oils, gravies, juices, sauces and the like, the system 600 may be optionally operated without the comminution means 606 being operated, whilst the waste is delivered to the fluid reservoir 400. Such liquids provide high energy feedstock for digestion by a biodigestor. It will be appreciated that although such liquids may be introduced into the system and be added to a pulp already contained within the fluid reservoir 400, the predetermined water content or density can be maintained by the addition of water, or alternatively by decanting excess \vater should there be an excess.

Once the fluid reservoir 400 contains pulp fluid at optimal or predetermined density, the contents of the fluid reservoir 400 can be periodically evacuated/removed by transportation such as by waste transportation truck. The waste pulp may, for example, be transported to a biogas production plant which utilises the waste pulp as production feed for the production of a biogas. The level sensing assembly 100 of the fluid reservoir 400 sends the level signal to the computing device 622. As discussed above, the computing device 622 can then displays level- based information on the control panel 22 to allow users to determine when the level of the tank 400 is approaching full. When the waste in the fluid reservoir 400 reaches a predetermined level the computing device 622 may be programmed to display to the user that only a set number of comminution cycles will be allowed before the must be emptied. Once the set number of cycles have been performed (or in the event that a predefined "full" capacity of the tank 400 is reached) the computing device 622 will prevent operation of the system 600 until the tank 400 has been emptied. As a safety mechanism the computing device controller 30 also prevents operation of the comminution unit 602 if no signal is received from the level sensing assembly 100. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A level sensing assembly for determining a level of a fluid in a reservoir, the level sensing assembly including: a guide assembly; and a float adapted to be guided by the guide assembly to rise and fall with the level of the fluid and in doing so to vary the length of a signal path travelled by a level sensing signal, the length of the signal path for use by a level sensor in determining the level of the fluid.

2. A level sensing assembly according to claim 1 , wherein the signal path is the path between the level sensor, and a target area.

3. A level sensing assembly according to claim 2, wherein the target area is. maintained at or above a surface level of the fluid by the float and is adapted to direct the level sensing signal to a signal receiver of the level sensor.

4. A level sensing assembly according to any one of claims 1 to 3 , wherein: the level sensing assembly includes the level sensor; the level sensor includes an emitter for emitting the level sensing signal along the signal path; the guide assembly guides the float such that the target area moves along the signal path,

^• and in use the level sensing signal is reflected back to the receiver of the level sensor by the target area.

5: A level sensing assembly according to any one of claims 1 to 4, wherein the guide assembly includes a stop against which the float rests when not buoyed up by fluid, the guide assembly in use allowing for fluid flow beneath the float when at rest against the stop.

6. A level sensing assembl according to any one of claims 1 to 5, wherein the float is approximately spherical in shape.

7. A level sensing assembly according to any one of claims 2 to 6, wherein the target area is a surface of the float. ,

8. A level sensing assembly according to any one of claims 2 to 6, wherein the target area is provided on a target carried by the float.

5 9. A level sensing assembly according to claim 8, wherein the target is a plate which is maintained substantially parallel to the surface level of the fluid by the float.

10. A level sensing assembly according to claim 8 or claim 9, wherein -the target : includes one or more bearing formations for bearing on the guide assembly to maintain an orientation of the float and/or target. 0

11. A level sensing assembly according to claim 10, wherein the or each bearing formation is a tab.

12. A. level sensing assembly according to any one of claims 1 to 11, wherein the!⁵' guide assembly incl udes at least one rod for guiding travel of the float.

13. A level sensing assembly according to any one of claims 1 to 12, wherein the,5 guide assembly includes a plurality of rods for guiding travel of the float. ^'

14. A level sensing assembly according to claim 13, wherein the plurality of rods are arranged to form a cage about the float.

15. A level sensing assembly according to any one of claims 1 to 14, wherein the level sensor is in communication with a computer processing device and is adapted to send0 sensed level information to the computer processing device.

16. A level sensing assembly according to claim 15, wherein the computer processing device is configured to process the sensed level information received from the level sensor and output level-based information to one or more users.

17. A level sensing assembly according to claim 16, wherein level-based information5 is output to one or more users by one or more output means selected from a group including: displaying level-based information on a display means; playing level-based information on a speaker; sending level-based information to one or more email addresses; sending a short- message-service message including level-based information to one or more phone numbers; sending a voice message including level-based information to one or more phone numbers; posting level-based information to a website accessible by a user; and sending level-based information to a pager.

18. A level sensing assembly according to claim 16 or claim 17, wherein the level based information includes information selected from a group including: a path length between the target area and the level sensor; an estimated volume of fluid in the reservoir; an estimated remaining capacity of the reservoir; an estimated time until the reservoir will be at full capacity; and a recommended time at which the reservoir should be emptied.

19. A level sensing assembly according to any one of claims 1 to 17, wherein the reservoir is adapted to receive and hold fluid waste from a waste processing unit via one or more inlet pipes.

20. A level sensing assembly according to claim 19 when dependent on any One oil claims 15 to 18, wherein the computer processing device is configured to control operation of the waste processing unit according to the sensed level information.

21. A level sensing assembly according to claim 19 or claim 20, wherein the waste processing unit is a putrescible organic waste processing unit and fluid waste is a pulp slurry.

22. A fluid reservoir for fluid produced by a waste treatment system, the fluid reservoir including a level sensing assembly according to any one of claims 1 to 21.

23. A putrescible organic waste treatment system including a waste processing unit for processing putrescible organic waste and transporting said processed waste to a fluid reservoir according to claim 22.

24. A method for determining a level of a fluid in a reservoir, including: directing a level sensing signal at a target area carried by a float; receiving a returned level sensing signal from the target area; and determining the level of the fluid based on characteristics of a signal path travelled by the level sensing signal, wherein the float is adapted to be guided by the guide assembly to rise and fall with the level of the fluid and in doing so to vary the length of the signal path.

25. A method for determining a level of a fluid in a reservoir according to claim 24, wherein the characteristics of the signal path include the distance of the signal path.

26. A method for determining a level of a fluid in a reservoir according to claim 24 or claim 25, wherein the characteristics of the signal path include the time taken between directing the level sensing signal at the target area and receiving the returned signal.