AU2021221642A1 - Fluid-Level Sensing and Monitoring for Wastewater - Google Patents

Abstract

A pressure sewer comprising a sewerage tank for temporarily storing fluid in the form of sewage and/or wastewater, a radar distance sensor mounted inside the tank at or near 5 the top for determining a distance from the sensor to a surface of the fluid stored in the tank, a pump for pumping stored fluid out of the tank, a controller arranged to control supply of power to the pump, wherein the controller is arranged to receive an output signal from the sensor, the output signal being indicative of a measured fluid level in the tank. 10 4/9 110 100- 120 s0 121 122 212 140 126 Figure

Description

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Fluid-Level Sensing and Monitoring for Wastewater

Technical Field Described embodiments generally relate to pressure sewer systems, in particular methods and apparatus for sensing and monitoring fluid levels in such systems.

Background Pressure sewer systems are the best option to provide a sewer service to properties in instances where a conventional gravity system is not practical or cost effective. This may be because the number of properties served is low, the terrain is hilly so the gravity flow of sewage might not be possible, or there might be a high risk of groundwater contamination or tough terrain (such as bedrock), which would make construction of a conventional system very difficult. A pressure sewer system can be installed relatively economically at most sites, regardless of the terrain. It requires only shallow trenches and relatively small diameter piping within the property boundary.

Pressure sewer systems involve the use of a fluid reservoir, such as a tank, buried in the ground to receive sewerage from a dwelling or building. All wastewater generated by the property (i.e. from toilets, baths, sinks, showers, a washing machine and dishwasher) can be fed into the tank, although greywater (i.e. wastewater from non toilet plumbing) may be collected separately for reuse onsite if desired. The pressure sewer tank contains a pump within the fluid reservoir to pump fluid out of the reservoir and into a reticulated sewer system comprising fluid conduits to transport the sewage to a suitable processing station. The pumping unit inside contains a grinder that breaks up the organic solids and other soft material, reducing this to a liquid slurry that can more easily be conveyed to the reticulated sewer without causing pipe blockages.

The pressure sewer system relies on proper functioning of the pump to ensure that the collected sewage is periodically removed from the tank, so as to avoid the fluid reservoir becoming too full and overflowing. In the event the pump does not operate in a timely manner to evacuate the waste fluid from the fluid reservoir, this can lead to an undesirable overflow and/or leakage of sewage from the fluid reservoir. This overflow can be a very unpleasant experience for the inhabitants of the dwelling.

Conventionally the control system for the pressure sewer pump utilises a fluid level sensing means (such as a float switch) to detect the sewage fluid level in the reservoir.

Level sensing applications within sewer tanks normally require contact based measurement solutions that are prone to suffer long term from ingress issues, contaminants and are costly.

It is desired to address or ameliorate one or more shortcomings of prior pressure sewer systems, or to at least provide a useful alternative thereto.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Summary According to one aspect of the present invention there is provided a pressure sewer comprising: a sewerage tank for temporarily storing fluid in the form of sewage and/or wastewater; a radar distance sensor mounted inside the tank at or near the top for determining a distance from the sensor to a surface of the fluid stored in the tank; a pump for pumping stored fluid out of the tank; and a controller arranged to control supply of power to the pump, wherein the controller is arranged to receive an output signal from the sensor, the output signal being indicative of a measured fluid level in the tank.

In embodiments, the sensor communicates wirelessly with the controller, and may include a battery for suppling electrical power.

The controller may be configured to compare the fluid level to a fluid level threshold stored in the memory of the controller and to cause the pump to operate to pump fluid out of the tank when the fluid level is greater than or equal to the fluid level threshold.

The controller may be further configured to receive a float switch output signal from a float switch in the tank indicative of a high fluid level, the controller being configured to operate the pump in response to the float switch output signal.

In embodiments, the float switch is coupled to the sensor which wirelessly conveys the float switch output signal to the controller.

In accordance with the present invention there is also provided a pump control system for a pressure sewer, comprising: a radar distance sensor mounted at or near the top inside a pressure sewer tank, for determining a distance from the sensor to a surface of fluid stored in the tank; a controller arranged to control supply of power to a pump for pumping stored fluid out of the tank, wherein the controller is arranged to wirelessly receive an output signal from the sensor, the output signal being indicative of a measured fluid level in the tank.

Brief description of the drawings Embodiments are described in further detail below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a pressure sewer installation at a residential property; Figure 2 is a is a diagram of a pressure sewer tank illustrating fluid levels and volumes; Figures 3 (A)-(D) are diagrammatic illustrations of wastewater cycles in a pressure sewer tank; Figure 4 shows a central vertical cross-section through a pressure sewer tank, diagrammatically illustrating an embodiment of the present invention; Figure 5 is a cutaway view of a pressure sewer tank in situ, incorporating an embodiment of the present invention; Figure 6 shows a fluid level sensor according to an embodiment of the invention; Figure 7 is a sectional view through the fluid level sensor of Figure 6; Figure 8 is a block diagram of a wired fluid level sensing and pump control system according to an embodiment of the invention; Figure 9 is a block diagram of a wireless fluid level sensing and pump control system according to an embodiment of the invention; Figure 10 is a block diagram of a wired fluid level sensing circuit.

Figure 11 is a block diagram of a wireless fluid level sensing circuit; and Figure 12 is a block diagram of a wireless-to-wired data conversion circuit.

Detailed description

Referring in particular to Figure 1 there is shown a pressure sewer installation 100 comprising a pump control system 110 operating in cooperation with a buried sewerage tank 120. The pump control system 110 constitutes an above-ground part of installation 100 while the sewerage tank 120 and associated components form the in-ground part. The sewerage tank 120 has a fluid reservoir 122 that is arranged to receive waste water (e.g. sewage) from a domicile or other building 102 via an inlet conduit 126. The fluid reservoir 122 houses a pump 124 therein, with the pump 124 being arranged to, on demand, pump fluid out of the reservoir 122 via a fluid outlet conduit 128 into a reticulated sewerage network of fluid conduits 130. Access to the reticulated sewerage network is typically beyond the property boundary 103 of the building 102.

The in-ground components of installation 100 also include a level sensor 112 and a float switch 212. The level sensor 112 is conventionally a form of contact-based measurement solution such as a pressure transducer, for example, and is in electrical communication with the pump control system 110 via suitable means, such as an electrical cable. The pump 124 operates under the control of pump control system 110, turning on and off in response to the action of a suitable pump contactor (relay) that supplies mains power to the pump 124 from a mains power supply.

The conventional level sensor 112 may be arranged to have the sensing head generally submerged below the level of fluid 140 in order to obtain a constant accurate measure of the fluid level within the fluid reservoir 122 and provide a constant (or sufficiently regular as to be effectively constant) output signal to the pump control system 110. Float switch 212 is provided as a high level fail safe, so that when the fluid level in the reservoir 122 gets above the shutoff level of the float switch 212, the float switch 212 provides a fluid level high signal to pump control system 110, which causes pump 124 to begin pumping fluid out of the reservoir 122 (if it was not already doing so).

Pump control system 110 is the above-ground part of installation 100 and may be located on a wall or other position for easy access by inhabitants of the domicile 102 or maintenance personnel. Details of an exemplary pump control system may be found in the specification of Australian patent AU 2014250705, the contents of which are incorporated herein by reference.

Figure 2 is a diagram of a pressure sewer tank illustrating a simplified form of fluid levels and volumes relevant to operation of the pump 124 in pressure sewer tank 120. Figures 3 (A)-(D) are diagrammatic illustrations of wastewater cycles in a pressure sewer tank in use. Referring to these drawings, a residual volume 152 of the tank represents the ordinary minimum volume of fluid during operation. The operating volume 154 has a lower level 153 at the top of the residual volume, and an upper level limit at 155. In use, when wastewater is discharged through inlet conduit 126 into the tank (Figures 3(A) and 3(B)), the level of fluid 140 in the tank rises. When the fluid level reaches the top of the operating volume at level 155 the pump control system energises the pump 124 to evacuate fluid from the tank 120 through outlet conduit 128. The pump remains on until fluid level in the tank reaches the lower operating level limit 153 (Figure 3(C)).

Over the operating volume 154 is an alarm volume 156. The upper limit level 157 of the alarm volume is at or about the level of the input from the inlet conduit 126 into the tank 120. Over the alarm volume the tank 120 has emergency storage volume 158. In the event that fluid in the tank rises to above the alarm level 157 (Figure 3(D)) the pump controller issues an alarm, which may include local audio and/or visual indications as well as communication with a central service provider.

In order to control the pressure sewer system as outlined above the system must include a means for detecting or measuring the level of fluid in the tank 120. Conventionally, fluid level sensing in pressure sewer tanks has been accomplished using contact-based level measurement solutions, e.g. sensors that require contact with the fluid to operate. While such sensors have widespread use in this application, collected data shows that the contact based level measurement solution can account for 2% of pressure sewer failures due to water ingress related failures. Although this may be a small number, overall, it will be appreciated that any sewer system failure can have very unpleasant consequences for the building occupants.

Accordingly, embodiments of the present invention introduce a non-contact fluid level sensing system incorporating a low power, high precision, pulsed short-range radar sensor. Figures 4 and 5 show a pressure sewer tank and a pressure sewer system, respectively, according to embodiments of the invention and including a radar level sensor. The radar level sensor 50 is an in-ground component that is installed within the volume of reservoir 122 near the top of the tank 120 and beneath the tank closure 121. Figures 6 and 7 show a sensor unit 50, according to embodiments of the invention, in isolation.

The sensor unit 50 is in use supported inside the tank 120, near the top opening, beneath the tank closure 121. The sensor unit 50 includes circuitry, described below, contained in a moulded housing 52. A mounting structure 54 is provided at the rear of the housing for mounting the sensor unit 50 to the inside of the rim 123 of the pressure sewer tank 120 (Figure 4). For example, the mounting structure 54 may be in the form of a plate or flange designed to interfit with existing formations on the rim of the tank or tank closure.

The sensor unit 50 includes a sensing, processing and communications circuitry on a printed circuit board 55 contained within the housing 52. The sensor unit circuitry includes a high precision, pulsed short-range radar sensor 56 in the form of a one chip system in package (SiP) solution with embedded radio and antenna. The radar sensor emits and receives radio wave signals (represented diagrammatically by arrows 80) by way of a radar lens component 60. The purpose of the lens 60 is to direct the emissions from the radar sensor 56, to an extent possible, toward the bottom of the tank and thus toward the surface 141 of fluid 140 in the tank (Figure 4). Reflections of the pulsed radio wave emissions are also detected by the radar sensor 56 and used to determine the distance from the sensor to the reflecting surface (i.e. the fluid surface 141). With prior knowledge of the distance from the mounted sensor to the tank bottom, the measurement made by the radar sensor 56 is representative of the fluid level in the tank.

The radar sensor 56 does not require an aperture to beam through, in other words, the housing 52 and lens 60 together may be made sealed against fluid ingress. Moreover, in some embodiments (described in further detail below) the sensor unit circuitry is operated by battery power and communicates wirelessly, meaning that no openings in the housing are necessary through which to pass power or communication cabling to the pump control system 110. A battery 58 for powering the sensor circuitry is seen in Figure 7.

Two versions of radar level sensing circuitry according to embodiments of the invention are disclosed herein: one that communicates with the pump control system via wires, and another that communicates wirelessly. Either one may be battery powered, although the advantages of using battery power are more evident in the case of the wireless version. Figure 8 is a general block diagram of a pump control system 110 coupled with a wired fluid level sensing circuit 600 according to an embodiment of the invention. Figure 9 is a general block diagram of a pump control system 110 coupled with a wireless fluid level sensing circuit 400.

In embodiments of the invention, the pump control system 110 may comprise a OneBox wastewater management device available from Iota Services Pty Ltd.

Referring to Figure 8, the wired radar level sensing circuit 600 is coupled to the pump control system by way of a 24V power supply connection 601 and a 4-20 mA current loop interface 602. In use the radar sensor determines the distance to the liquid level in the tank, and transmits this parameter to the pump control system through the interface 602. As noted above, embodiments of the invention utilise a high-level float switch (HLFS) 212 for failsafe fluid level control as is known conventionally. In the wired version of the radar level sensing circuitry the HLFS 212 is connected to communicate directly to the pump control system 110 via wired connection 213.

Figure 10 is a block diagram showing the main functional components of the wired radar level sensing circuit 600. The radar sensor 601 comprises an Al11 radar sensor integrated circuit available from Acconeer. The Al11 radar sensor is a 60 GHz pulsed coherent radar (PCR) short-range device capable of measuring the distance to one or multiple objects in the range of 60-2000 mm with millimetre accuracy. Characteristics of the Al11 radar sensor include: • Material detection - Detection of materials with different dielectric constants • Low power consumption - Milliwatt power consumption enables integration into battery-driven devices • Optimized integration - Small one chip solution with embedded radio and antenna without the need for an aperture " Robustness - Radio band operation without interference from noise, dust, colour nor direct or indirect light.

The circuit 600 includes a coordinating micro-controller 602, for example an nRF52840 available from Nordic Semiconductor, which utilises a STM32 core and includes NFC and BLE5 interfaces built in. The Al11 radar sensor has its own API's to communicate with the controller circuit 602 built in, although embodiments of the invention use a TI SN74AVC4T774 level transceiver to convert the 3V3 volts of the processor to 1V8 for the radar sensor. The controller circuit 602 in use executes on board firmware to read the distance measurements taken by the radar sensor 601, convert the distance measurement into a corresponding fluid level, and transmit the fluid level information to the pump control system. A digital output from the controller 602 is passed to digital-to-analog converter circuit 611 which produces a 4-20 mA analog signal, available for output at wired interface 612. The wired interface 612 comprises a four-wire cable for transmitting digital and analog signals, and also includes electrical power supply for the circuit 600. The wired interface may comprise 4-20 mA analog signal wires including: 1. 24 VDC; Analog signal (4-20 mA); Optional error signal (0-5 V). The 24 VDC line is coupled as input to a DC/DC step-down converter circuit 611 which converts the input 24 VDC to 3.3 VDC for electrical power to the controller circuit and all internal peripherals. The wired interface may also include digital signal wires coupled to receive output directly from the controller 602.

Although the fluid level measurement information is conveyed from the wired circuit 600 to the pump control system by a wired interface, the circuit 600 nevertheless includes wireless communication facilities as well. As seen in Figure 10, a near-field communication (NFC)interface circuit 607 is provided for pairing and updating the device configuration (e.g. micro-controller data) including, for example, the distance to the bottom of the tank, the maximum tank height, etc. A wireless interface 604 is also provided for transmitting and receiving digital signals and micro-controller firmware upgrades. The wireless interface communicates with the controller circuit 602 by way of Bluetooth LE protocol stack 603, which can be used in master and slave modes and can be implemented inside the nRF52840 micro-controller as a Nordic Software Device.

Referring to Figure 9, the wireless radar level sensing circuit 400 is outlined in block diagram form with a wireless communications link to the pump control system 110. The OneBox wastewater management device employed as the pump control system in embodiments of the invention does not include short-range wireless communication facilities. Accordingly, a wireless-to-wired data converter circuit 500 is provided to receive wireless signals (e.g. Bluetooth LE) from the wireless sensing circuit 400 and convert them into wired signals appropriate for input to the OneBox device. Coupling the data converter circuit 500 to the OneBox pump control system 110 is a 24V power supply 501, an analog 4-20 mA level signal connection 502, a digital HLFS signal connection 503 and an analog 0-5V signal connection 504. In order to take full advantage of the wireless communications arrangement, the float switch 212 in this case is coupled to the wireless sensing circuit 400, rather than being connected directly to the pump control system as for the wired version previously described.

Figure 11 is a block diagram showing the main functional components of the wireless radar level sensing circuit 400. The fluid level sensing functions of the circuit 400 are fundamentally the same as previously described in connection with the wired circuit. A radar sensor 401, comprising an Al11 radar sensor integrated circuit available from Acconeer, is controlled by a micro-controller 402 (Nordic Semiconductor nRF52840) to periodically determine the distance from the sensor to the tank fluid surface. In this wireless version of the radar level sensing circuitry the HLFS 212 is connected to communicate with the controller circuit 402 via interface 406. The wireless circuit 400 is powered by battery 405; for example a D cell primary ER34615H primary lithium battery may provide for 10 plus years wireless operation through Bluetooth to the pump control system 110. In embodiments, the wireless circuit version also includes a STMicroelectronics STC31001ST battery gauge IC for battery level reporting to the controller circuit. As for the wired circuit, an NFC interface 407 is provided that can pair with the circuit 500 or a mobile device for updating configuration data such as distance to the bottom of the tank, maximum tank height, etc.

In place of a wired interface to the pump control system, the wireless sensing circuit 400 conveys data to the data converter circuit 500 by way of Bluetooth LE signalling using the in-built Bluetooth LE wireless protocol stack 403 and wireless interface 404. The wireless-to-wired data conversion circuit 500 has corresponding wireless interface 505 and Bluetooth LE protocol stack 506 implemented as a function of micro controller 515. The controller circuit 515 receives data from the wireless sensing circuit 400 indicating the distance to obstacles from the radar sensor 401 and converts it into a fluid level measurement. The controller circuit 515 also receives data from the wireless sensing circuit indicating the state of the HLFS. The fluid level measurement is converted into a 4-20 mA analog signal by digital-to-analog converter circuit 509 that is then communicated to the pump control system 110 by way of the wired interface

510. The HFLS state is communicated to the pump control system by digital signal wires. Also included in the data conversion circuit 500 according to embodiments of the invention are: * NFC reader 507 for pairing with the wireless level sensing circuit 400 * DC/DC stepdown converter for converting input 24 VDC from the wired interface into 3.3 VDC for the on-board circuits * Digital-to-analog converter 511 for signalling battery levels and error conditions by way of a 0-5 V analog error signal * Buzzer 512 for signalling NFC, BLE pairing status and errors * Buttons 513 including reset and user buttons for pairing slave devices * LEDs 514 for indicating wireless connection, pairing and error states.

Embodiments of the present invention as described herein can provide a non-contact, radar based level sensor at a fraction of the cost of the current contact based level sensor solutions. Up to 500 metre wireless connection is possible between the level sensor in the sewer pit and the pump controller that it interfaces too, unlike the current contact based solution that is only wire based and thus requires cabling to the pump controller. Moreover, the present invention is envisaged to be of higher reliability, whereas at present the contact based level measurement solution may account for 2% of pressure sewer failures due to water ingress related issues.

Embodiments have been described herein by way of example, with reference to various possible features and functions. Such embodiments are intended to be illustrative rather than restrictive. It should be understood that embodiments include various combinations and sub-combinations of features described herein, even if such features are not explicitly described in such a combination or sub-combination.

Claims (7)

CLAIMS:

1. A pressure sewer comprising: a sewerage tank for temporarily storing fluid in the form of sewage and/or wastewater; a radar distance sensor mounted inside the tank at or near the top for determining a distance from the sensor to a surface of the fluid stored in the tank; a pump for pumping stored fluid out of the tank; a controller arranged to control supply of power to the pump, wherein the controller is arranged to receive an output signal from the sensor, the output signal being indicative of a measured fluid level in the tank.

2. The pressure sewer of claim 1 wherein the sensor communicates wirelessly with the controller.

3. The pressure sewer of claim 2 wherein the sensor includes a battery for suppling electrical power.

4. The pressure sewer of claim 1, 2 or 3 wherein the controller is configured to compare the fluid level to a fluid level threshold stored in the memory of the controller and to cause the pump to operate to pump fluid out of the tank when the fluid level is greater than or equal to the fluid level threshold.

5. The pressure sewer of any one of claims 1 to 4 wherein the controller is further configured to receive a float switch output signal from a float switch in the tank indicative of a high fluid level, the controller being configured to operate the pump in response to the float switch output signal.

6. The pressure sewer of claim 5 wherein the float switch is coupled to the sensor which conveys the float switch output signal to the controller.

7. A pump control system for a pressure sewer, comprising: a radar distance sensor mounted at or near the top inside a pressure sewer tank, for determining a distance from the sensor to a surface of fluid stored in the tank; a controller arranged to control supply of power to a pump for pumping stored fluid out of the tank, wherein the controller is arranged to wirelessly receive an output signal from the sensor, the output signal being indicative of a measured fluid level in the tank.