GB2525142A

GB2525142A - A method & apparatus for detecting and measuring the level of liquid within a channel

Info

Publication number: GB2525142A
Application number: GB1320451.6A
Authority: GB
Inventors: Brian Back
Original assignee: RADIO DATA NETWORKS Ltd
Current assignee: RADIO DATA NETWORKS Ltd
Priority date: 2013-11-19
Filing date: 2013-11-19
Publication date: 2015-10-21
Anticipated expiration: 2033-11-19
Also published as: GB2525142B; GB201320451D0

Abstract

A method / apparatus is described for detecting the presence and level of fluid 14 in a channel based on the premise that there exists a temperate difference between the fluid and the air/gas above it. The method uses an array of temperature sensors 1. The temperature sensor array 1 may be suspended in the channel such that it is free to move. The temperature sensor array may be activated in response to detection of the presence / flow of fluid in the channel using a second sensing means. The second sensing means may comprise an accelerometer which detects movement of the sensor caused by movement of the liquid in which it is immersed or a capacitance sensor that detects change in dielectric permittivity. During bouts of heavy rain it is common for sewers to become overwhelmed. To prevent a backlog that could cause customers' homes to be flooded, the sewer system is provided with overflows that carry excess rainwater/effluent to a discharge point, usually a local watercourse or the sea. The system may be used to detect the presence and level of fluid in the sewer system.

Description

A Method & Annaratus for DetectinQ and Measurina the Level of Liquid within a Channel The present invention relates to a method and apparatus for detecting and measuring the level of liquid within a channel. It is considered to be particularly suitable for detecting and measuring the level of water / effluent within a sewer or passing out through a sewer overflow within the sewerage network or a storm drain.

Sewers arc used to collect raw effluent and waste for both domestic and industrial locations. Drains are used to collect rainwater or groundwater. Whereas combined sewers collect a mixtures of effluent, rainwater and groundwater. The level of effluent within the sewer varies significantly depending upon rainfall and or other events such as blockages, industrial discharges or combinations of any of the above.

During bouts of heavy rain it is common for the sewers and storm drains to become overwhelmed due to finite hydraulic capacity. To prevent a backlog in the sewer which could cause customers to be flooded, the sewers are provided with overflows often referred to as combined sewer overflows [CSOs], that carry excess rainwater and effluents mix to a discharge point, usually a local watercourse or the sea, often collectively referred to as receiving waters.

Combined sewer overflows are consequently a significant source of environmental pollution. Water companies are generally obliged to report all known spills to environment authorities. Similarly, blockages or obstnictions with sewers can cause levels to build up and again lead to pollution either in dry or wet weather and not necessary at the overflows. Spills of this nature are often referred to as surcharges or sewer flooding.

At present, the occurrence of a spill through a combined sewer overflow, a pollution incident or a surcharge into property is too often reported by members of the public who have observed the spill or the debris /pollution incident has left behind.

Fines may be imposed on the water companies in the event of a sewage spill in particular if the spill was caused by a preventable event such as a blockage or equipment failure rather than heavy rainfall. There is therefore an incentive for water companies to be aware of a spill or blockage as soon as possible in real time in order to correlate the event against rainfall plus there is also a duty placed in many countries upon water companies to warn bathers and sheilfishery operators about the risk of pollution.

Previous attempts to provide early warning of spills and blockages include the use of float switches, ultrasonic level gauges, capacitance probes, dielectric transducer, pressure transducer, doppler flow, air bubbler level gauges and velocity transducers.

Each of the above has been seen to have various shortcomings which have given rise to missed events, stuck readings and false positive or negative events. Causes of such issues include total submersion; salt caking in coastal locations; corrosion, ingress; fat, oil and rags build up; mechanical entanglement; sediment build-up and incorrect calibration at setup.

The present invention was conceived with the aim of overcoming or at least ameliorating some if not all of the aforementioned problems.

According to a first aspect of the invention there is provided a method suitable for detecting the presence of a liquid within a channel, the method comprising: using one or more temperature sensors to identify the presence of a temperature gradient within the channel attributable to an interface between the fluid within the channel having a first temperature and gas above the fluid having a second temperature, the first and second temperatures being different.

The invention relics on the temperature of the liquid within the channel being different (and usually higher) than the temperature of the gas above, and also that any temperature differences within the liquid and gas are smaller than the difference betwixt the liquid and the gas.

In the case of effluent/water within a sewer the difference in temperature between the effluentlwater and the air above is expected to around or above 1°C, and usually between 1°C -4°C. It is therefore preferred, for the aforementioned purpose at least, that any temperature sensor(s) used are accurate to within 0.5 °C or less.

A tempcraturc scnsor can be incorporatcd into a unit that can be casily installed, c.g.

by suspending from thc top of channcl making entry into the channel by thc installcr of unnecessary (as is required for ultrasonic, pressure, air bubble level, microwave/radar & Doppler flow sensors). Tt also allows for a unit of simple design that can be positioned/shaped to minimise ragging and collection of F.O.G. (fat, oil grease). Temperature sensors are also believed to be less affected by the accumulation of F.O.G. than capacitance sensors.

In a preferred embodiment, there is provided an array of temperature sensors ananged to measure the temperature at various depths within the channel. This provides a convenient means to sense either in quick succession or simultaneously the temperature at different depths within the channel.

An array of tcmpcratc sensors also provides a convenicnt mcans to dcrivc a valuc indicative of the level of the water within the channel by identif'ing the position (depth) of the temperature gradient. It is thereby possible to monitor the change in liquid level within the channel. If the position of the sensors are known, the level can be derived by identifying which pair of adjacent sensors show noticeably different temperatures.

It is further preferred that a further sensing means is used to detect the presence of the fluid and/or fluid flow. In one preferred embodiment detection by the further sensing means of the presence of the fluid and/or fluid flow within channel initiates a process for identifying the level of the liquid within the channel. This way the temperature sensor array, which has a relatively high power usage, can be left in an off state unless liquid is detected. Examples of sensing means that may be used as the second sensing means include accelerometers that detect the movement of the sensor caused by movement of the liquid in which it is (at least partly) immersed, or a capacitance sensor that detects the change in dielectric permittivity.

Using two sensing means also provides an ability to veri' that the temperature sensor array is working. For example if the second sensing means detects the presence of a fluid but this is not followed by a reading from the temperature sensors, an alert can be raised to physically check the sensor unit.

It is preferred that the method includes suspending a sensor unit comprising the temperature sensor array, and optionally also the further sensing means, into the channel. This provides a convenient means to install the sensor without the need to enter the channel. This can provide significant saving where the sensor unit is to be installed in a drain/sewer of which entry requires numerous health and safety conditions to be met.

It is preferred that the method comprises suspending the sensor unit such that it is free to move in response to the flow and/or change in depth of the liquid within the channel. This reduces the likelihood of ragging up of the sensor. The freedom of movement also allows an accelerometer to identify the presence of liquid when used as the further sensing means.

It is a preferred that during installation, the sensor unit is suspended within the channel so as to sit above a normal level of liquid within the channel. This allows the sensor unit to detect events where the liquid level exceeds normal limits whilst conserving power usage.

It is preferred that the sensor unit is suspended into the channel from a flexible linkage. The linkage may be a cable, which may also be used as a conduit to provide power to the temperature sensor array and/or further sensing means, and may also be used to transfer data from the sensors to a remote unit.

The position of the sensor unit within the channel may be set by adjusting the length of a flexible linkage, preferably shortening of the flexible linkage is achieved through coiling.

The method may in theory be used to detect and/or measure the level of any liquid with any channel, though it is expected to be used primary in relation to monitoring the level of water in rivers or other waterway and more favourably effluent/water within a sewer/sewer overflow/storm drains, where the gas comprises air.

The sensor unit may be suspended from a frame or a wall supporting a manhole cover or sewer overflow chamber. This removes the need for the installer to fully enter the sewer.

The invention may also described in the form of apparatus, and therefore according to a second aspect of the invention there is provided apparatus for detecting a liquid within a channel, the apparatus comprising: an array of temperature sensors to measure temperature at different depths within the channel; a processor arranged to receive signals from the temperature sensors and to identify from said signals the presence of a temperature gradient within the channel indicative of an interface between the liquid and a gas above.

It is preferred that the processor is arranged to determine from identity and/or position information of the temperature sensors in the array the level of the fluid within the channel. This could be executed in various ways though a preferred way is to identify the difference in temperatures sensed by pairs of temperature sensors which are directly adjacent to each other in the array (preferably the sensors are arranged one above the other) with thc level of thc liquid/gas interfitce being present between the -measuring the largest differential in temperature. Another possible method is to identify the temperature sensor sensing a temperature which is noticeably different than the others and between the readings of the others. This indicates that the liquid/gas interface lies at approximately the level of this sensor, the difference being attributable to the sensor being submerged part of the time due to turbulence at the liquid's surfhee.

The invention will now be described by way of example with reference to the following figures in which: FIgure 1 a side view of a water level sensor suspended by a flexible linkage to a control unit; Figure 2 is a side section of the water level sensor of Fig 1 having an accelerometer; Figure 3 is a side section of the water level sensor of Fig 1 having a dielectric sensor; Figure 4 is an illustration of the level sensor of Fig 3 mounted to a wail of a sewer to detect slow rising level of effluent in the sewer; FIgure 5 is an illustration of the level sensor of Fig 2 mounted adjacent to an overflow channel of a sewer to detect a spill through the overflow; and Figure 6 illustrates the arrangement of Fig 5 in the event that a spill is taking place.

The assembly in Fig 1 comprises a sensor unit 1 suspended by a flexible linkage 2 from an upper unit 3 housing a power source, wireless transmitter and controller (not shown).

As shown in Fig 2 the sensor unit 1 has an outer sleeve 4 that preferably has moderate thermally conductivity, and resistance to water and corrosive substances. An example of a suitable material is acrylic though other materials such as stainless steel, may be used in certain instances; it is currently believed that materials with a thermal conductivity between 0.1 W/m.K and 43 W/m.K will be suitable.

Inside the sleeve 4 is housed a circuit board 5 to which are attached a plurality of temperate sensors 6 (e.g. of semi-conductor device form). The temperature sensors 6 are arranged to be in direct contact with the inner surface of the sleeve 4 to provide good thermal conductivity between the sensor 6 and the outside surface of the outer sleeve 4.

The temperature sensors 6 are spaced apart (preferably at equal distances) by a distance that is significantly greater than the distance between each temperature sensor 6 and the most proximate point of the outer surface of the outer sleeve 4. This, in conjunction with the moderate thermal conductivity of the outer sleeve 4, reduces the likelihood of false readings caused by the conduction of heat upwards from the submersed parts of the sleeve 4 to the portion of the sleeve 4 above the water line.

The spacing between the sensors 6 depends on a number of factors including the sensitivity required of the device; the distance between the temperature sensor and the outer surface of the outer sleeve; and the thermal conductivity of the material. In the instance of using an acrylic sleeve of 3mm in thickness, a spacing of 2.5cm is thought to be satisfactory.

The number of temperature sensors fitted is set at manufacture in proportion to the length of the sensor unit 1, the desired precision in the level to be achieved.

Also housed within the sensor unit 1 is a dual axis accelerometer 7, 8 and a micro controller 9. The functions of the controller 9 may be provided by a programmable microchip in combination with other circuitry.

As an alternative to the accelerometer 7, 8, Fig 3 illustrates a sensor unit 1 having a dielectric sensor 10.

Air voids within the sleeve 4 are filled using an encapsulent such as a thermally conductive resin. The removal of air voids prevents the sleeve from filling with watet'liquid as a result of osmotic travel through the sleeve wall.

A data/power connection between the sensor unit 1 and the upper housing 3 is provided by one or more cables that also act the flexible linkage 2. The flexible linkage 2 permits the sensor unit I to move in response to flow of effluent. As well as allowing the accelerometers 7, 8, detect the presence of effluent through this movement, it has the additional benefit of reducing the build up of rags and F.O.G. on the sensor unit 1.

In Fig 4, the upper housing 3 is mounted to a wall within a sewer at a point that can he safely reached from the surface without need to enter the sewer. The length of the flexible linkage 2 is adjusted, through coiling (which may be held using a fastener) to lower and set the height of the sensor unit 1 within the sewer. Typically the sensor unit 1 is set to sit just above the normally expected level of effluent within the sewer.

When the sewage level rises as illustrated by 12 in Fig 4 such that it partly submerges the sensor unit 1, the dielectric sensor 10 detects a change in the dielectric permittivity of the surrounding medium and sends a signal to the controller 9. In response, the controller 9 wakes the temperatures sensors 6. The controller 9 may also, in response, cause a signal to be sent via the wireless transmitter in the upper housing 3 to a remote control station.

Each temperature sensor 6 sends signals to the controller 9 that arc indicative of the temperature at its vicinity. The controller 9 through knowledge of the location (relative of otherwise) of each temperature sensor 6 can deduce the level by identifying the position of the temperature gradient from the sensors which are submerged in the effluent to the sensors that are in the air above the effluent. This can be done, for example, by calculating the difference in temperature sensed by adjacent pairs of temperature sensors, and identifying the pair that senses a significantly different temperature, e.g. above 1°C. The level of the effluent can therefore be determined to be between that pair of sensors 6. For example, if the sensors 6 are identified from bottom to top as A-L, and that following signals received from each of sensor the controller 9 determines that there is a temperate differential between E and F which is sufficiently large to indicate that the liquid level lies between these sensors, the controller 9 can store/and or send this information via the transmitter to the control station. Alternatively or in addition it may be fed to additional processing circuitry to identify whether an alarm should be generated. If the initial position of the sensor unit is known and the position and spacing of the sensors 6 relative to the sensor unit I a quantitative measurement could also be derived.

Of course if the temperature sensors 6 are only to be used to identify the presence of effluent and not the level, it is not necessary to known the location of the sensors, and by merely identifying that at least one the sensors senses a temperature significantly different from the others is enough to indicate that a water/air interface exists.

Fig 6 illustrates the sensor unit of Fig 2 arranged at the entry of a sewer overflow.

The flow of effluent through the overflow causes the sensor unit to move from the orientation illustrated in Fig 5. This movement is detected by at least one of the accelerometers 7, 8 that sends a signal to controller 9 that in turn initiates an effluent level reading to be made.

Accelerometers 7, 8 are preferred for this application as there is a risk that F.O.G.

build up on the sensor unit I could cause a dielectric sensor 10 to provide a false positive and thereby unnecessarily extend the activation period of the temperature sensors, the associated alarms generated and may also have detrimental impact on battery life.

The controller 9 generates an alarm signal, and level signal which are passed through the flexible linkage to the wireless transmitter whence they are broadcast to a remote receiving station. -10-

Alternatives to the above embodiments include using, rather than a wireless transmitter, a direct cable to the receiving station, which might be or include a handheld receiver or computer system, rather than a wireless link.

In a frirther altemative, rather or in addition to transmitting data, the apparatus may include a data logger which is periodically read or automatically sends a distress message when the levels exceed pre-set limits.

Although it is preferred that the flexible linkage also provides a data/power path, it is possible that the linkage may take another form, such as of a chain, and for a separate non-load bearing cable(s) be used to provide the power/data path.

The controller 9 may optionally be housed in the upper housing 3 rather than in the sensor unit 2.

Claims

Claims 1. A method suitable for detecting the presence of a liquid within a channel, the method comprising: identifying the presence of a temperature gradient within the channel attributable to an interface between the liquid within the channel having a first temperature and gas above the liquid having a second temperature, the first and second temperatures being different.
2. A method according to claim I comprising using an array of tcmperature sensors ananged to measure the temperature within the channel at various depths.
3. A method according to claim 1 or 2 wherein the level of the liquid within the channel is derived by identifying the position of the temperature gradient.
4. A method according to claim 3 wherein a further sensing means is used to detect the presence of the fluid and/or fluid flow.
5. A method according to claim 4 whereby detection by the further sensing means of the presence of the fluid and/or fluid flow within channel initiates a process for identifying the level of the liquid within the channel.
6. A method according to claim 2 -S comprising suspending a sensor unit comprising the temperature sensor array into the channel.
7. A method according to claim 6 wherein the sensor unit comprises the further sensing means. -12-
8. A mcthod according to claim (3, 7 or 8 whcrcin the sensor unit is suspended such that it is free to move in response to the flow of the liquid within the channel 9 A method according to claim 8 wherein the sensor unit is suspended into the channel from a flexible linkage.10. A method according to claim 8 or 9 wherein the sensor unit is suspended within the channel so as to sit above a normal level of liquid within the channel in order that the sensor unit will detect when the level of liquid within the channel rises above the nornial level.11 A method according to any claim 4 -10 wherein the farther sensing means comprises an accelerometer.12. A method according to any claim 4 -11 wherein the further sensing means comprises a capacitance sensor.13. A method according to any claim 6 -10 wherein the position of the sensor unit within the channel is set by adjusting the length of a flexible linkage about which senor unit is suspended.14. A method according to claim 13 wherein the length of the flexible linkage is adjusted by coiling.15. A method to detect the level of effluent within a sewer/sewer overflow/storm drain according to any previous claim.16. A method according to claim 15 when dependent upon claim 6 where the sensor unit is suspended from a frame andlor a wall supporting a manhole -13 -cover or sewer overflow chamber such that the installer does not have to frilly enter the sewer.17. Apparatus for detecting a liquid within a channel, the apparatus comprising: an array of temperature sensors to measlLre temperature at different depths within the channel; a processor arranged to receive signals from the temperature sensors and to identi' from said signals the presence of a temperature gradient within the channel indicative of an interface between the liquid and a gas above the liquid.18. Apparatus according to claim 17 wherein the processor is arranged to determine from identity and/or position information of the temperature sensors in the array, the level of the liquid within the channel.19. Apparatus according to claim 17 or 18 comprising a second sensing means to detect the presence of liquid within the channel.20. Apparatus according to claim 19 comprising means, in response to detection by the second sensing means of the presence of liquid within the channel, to activate the temperature sensor array.21. Apparatus according to claim 19 or 20 comprising means to generate an alert signal in response to the detection of the presence of liquid within the channel by the second sensing means.22. Apparatus according to claim 19, 20 or 21 wherein the second sensing means comprises an accelerometer. -14-23. Apparatus according to any claim 19 -22 wherein the second sensing means comprises a dielectric transducer.24. Apparatus according to any claim 17-23 wherein the array of temperature sensors is housed in a sensor unit ananged to be suspended into the channel.25. Apparatus according to claim 24 wherein the sensor unit is attached for suspension from a flexible linkage.26. Apparatus according to claim 24 or 25 wherein the scnsor unit further houscs the second sensing means.27. Apparatus according to claim 24, 25 or 26 wherein the sensor unit has an outer casing and wherein the temperature sensors are ananged to be in thermal contact with the outer casing.28. Apparatus according to claim 27 wherein the sensors are in direct contact with the outer easing.29. Apparatus according to claim 27 or 28 wherein the temperature sensors are spaced apart by a distance greater than the distance between each temperature sensor the outer surface of the outer casing.30. Apparatus according to any claim 27 -29 wherein the outer casing has a thermal conductivity between 0.1 W/m.K and 43 W!m.K inclusive.31. Apparatus according to any claim 19 -23 comprising a power source housed in a housing connected to the sensor unit via the flexible linkage.32. Apparatus according to any claim 17-31 comprising a transmitter to transmit data from and!or derived from sensors within the sensor unit.-15 - 33. Apparatus according to claim 32 wherein the transmitter is housed in a housing connected to the sensor unit via the flexible linkage.34. Apparatus according to any claim 27 -33 wherein thc outer casing is filled with an encapsulant.