GB2444552A - Conductive probe for sensing liquid levels in drainage systems - Google Patents

Abstract

A probe for detecting the liquid level in drainage systems (e.g. sewerage systems) comprising at least a pair of stainless steel electrodes 10, 20 wherein each electrode is substantially surrounded by a hollow sheath 100. The sheath is open at its bottom end to allow liquid to enter and rise up within the sheath and comprises a vent (e.g. a longitudinal slot) to allow expulsion of air displaced by rising liquid levels. The device may comprise a third shorter electrode 30, wherein one electrode is common and the other two are arranged to sense a level of retained liquid and a flood condition respectively. The electrodes are provided with a plurality of pre-weakened portions along their length to alter the electrode length. The device and system comprises a means for transmitting readings (e.g. antenna 210) from the probe to a remote station for monitoring the condition of a drain network.

Description

IMPROVEMENTS IN MD RELATING TO CONDUCTIVE PROBES

The present invention relates to a conductive probe for sensing the presence or absence of a liquid. The invention finds particular, but not exclusive, use in the field of monitoring of drainage systems. In particular, an application utilising such a probe is disclosed for monitoring domestic and industrial gully or drain systems.

It is known in the prior art to detect the presence of a liquid, which is at least partially conductive, by means of a pair of electrodes separated by a short distance, such that if a liquid is present between the electrodes, a current may pass between the electrodes and be detected.

In the absence of a partially conductive liquid, then the open circuit between the electrodes prevents any significant current flowing. Such systems are well known as level sensors in a variety of situations e.g. industrial processes and the like.

In domestic and industrial drainage systems e.g. sewerage systems, it can be important to ascertain rapidly whether a main sewer is blocked and causing waste water further up the systems to back up. The results of this can be unpleasant, especially if foul waste backs up to an extent whereby it escapes from drains or gullies close to households.

Up until now, there has been no satisfactory method of assessing when a main sewer is blocked until such back up or overflow occurs. It is clearly unpleasant for everyone involved and can be very costly to remedy.

An aim of embodiments of the present invention is to ameliorate these problems by providing a system which is able to provide an early warning of blockages in a main sewer.

According to the present invention there is provided an apparatus and method as set forth in the appended claims.

Preferred features of the invention will be apparent from the dependent claims, and the description which follows.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 shows a pair of electrodes according to the prior art; Figure 2 shows a pair of electrodes according to an embodiment of the present invention; Figure 3 shows a gully monitoring device according to an embodiment of the present invention; Figure 4 shows the gully monitoring device of Figure 3 in situ; and Figure 5 shows an alternative embodiment of the present invention.

Figure 1 shows a pair of electrodes 10, 20 which may be used to detect the presence or absence of a partially conductive liquid. The pair of electrodes may be suitably placed into a receptacle for liquid, and if the liquid is at a level whereby it bridges the gap between the electrodes 10, 20, then suitable circuitry attached to the electrodes can be used to detect a small current flow, indicating that the liquid is at least at the level of the electrodes. In the absence of any liquid bridging the gap between the electrodes 10, 20, then an open circuit exists between the electrodes and no significant current will pass between them.

Such an arrangement of electrodes is perfectly acceptable for most instances where the liquid is clean and free from Contamination. However, in certain situations, the liquid may be dirty and may contain waste matter which can collect around the electrodes and result in an unexpected reading, erroneously indicating that the electrodes are immersed in a liquid, whereas they may in fact only be fouled by waste matter.

In a particular embodiment of the present invention, used in situations where it is desirable to use a liquid sensor to detect the height of a liquid in a gully or drain system, there is a very real chance that the electrodes, if of the form shown in Figure 1, would become fouled by waste matter, such as dead leaves and litter. Particularly in the case of leaves, which may be partially decayed, these can hold enough moisture to give a false reading of a liquid level when in fact the true level of the liquid is below the electrodes. This can result in false positive readings, which can prove troublesome.

A further problem in this particular situation is that water will from down from above and, if it is flowing in sufficient quantity, a continuous stream can also bridge the gap between the electrodes, falsely indicating a level of water which is not accurate.

In order to address this particular problem with the prior art electrode system, an embodiment of the present invention utilises the pair of electrodes 10, 20, from the prior art, but is adapted to surround each of them with a separate hollow sheath 100. The sheath is open at at least its bottom end, allowing liquid to enter the sheath and rise up it, depending upon the level of the water.

The sheath 100 is open at its upper end, or at least provided with an air vent to allow any air in the sheath to escape once the liquid level rises.

By use of such an arrangement, a rising liquid level will still bridge the gap between the two electrodes, whilst alleviating the problem of waste matter fouling the electrodes by being able to directly contact both the electrodes, and so give a false reading.

This configuration also prevents false readings by large quantities of liquid falling and running down the probe.

The sheath 100 ensures that only liquid rising from below will be registered.

The particular configuration shown in Figure 2 is only one that may be adopted as long as there is some form of shielding around the electrodes 10,20 which prevents solid matter from bridging the gap between the electrodes whilst still allowing the liquid to bridge the gap.

Figure 3 shows a device according to an embodiment of the present invention which is suitable or use in giving an early indication of possible problems with a sewer. The device is arranged to be fitted to a gully of a property in an unobtrusive manner.

Generally, rain water falling on the roof of a property is collected in gutters and then flows down a drain pipe to the base of the property, at which point, it empties into a gully, which then flows on into a main sewer. If the main sewer becomes blocked or obstructed so that waste water (and possibly foul waste) begins to back up, then it is these gullies which will be affected first.

The device 200 of Figure 3 is a self-contained device arranged to continually sample the level of a liquid in the gully and to periodically transmit certain information regarding that level to a remote monitoring station, either on a pre-determined basis or when polled by said station.

There may be one or more remote monitoring stations, supplemented, if necessary by a plurality of repeaters or hubs.

The gully monitoring device 200 comprises an external waterproof housing 205, preferably constructed from a moulded or extruded plastics material. Protruding from the upper surface of the device 200 is an antenna 210, for communicating with the remote monitoring station. Also contained within the housing is a battery for powering all circuitry, a suitable programmed microprocessor and associated working and storage memory and a transmitter or transceiver for communicating with the remote monitoring station.

Immediately below the antenna 210, the main housing 205 accommodates the circuitry required to monitor the liquid level in the gully and to transmit this information via the antenna 210.

Positioned respectively just above and below the approximate mid-point of the housing 205 are upper and lower placement rings 215, 220. These rings are provided to hold the device 200 in position in the grating. To fit the device to a gully, a suitable hole is created (e.g. by use of a hole-saw) in the plastic grating of the gully and the device 200 is fitted therein, with the rings 215, 200 effectively sandwiching the device in place.

Protruding from the lower surface of the housing 205 is the liquid sensor 225, comprising the pair of electrodes 10, 20 and sheathing elements 100, described previously with reference to Figure 2. In addition to the two electrodes 10, 20, described previously, there is provided, additionally, a third electrode 30. The provision of three electrodes in this way allows for further functionality for the device. In particular, the three electrodes 10, 20, 30 are effectively two discrete sensors, with the central electrode 20 being common to both. The notation 10' is used to refer to the sensor composed of electrodes 10 and 20. The notation 30' is used to refer to the sensor composed of electrodes 20 and 30.

The electrodes 10, 20, 30 are composed of stainless steel to ensure that they do not corrode in use. They may *1 further be provided with a plurality of pre-weakened portions along their lengths so that they be easily set to the correct lengths by merely snapping off any excess before the sheathing 100 is fitted.

When the device 200 is positioned for use in a gully, the longer of the electrodes 10, 20 are dimensioned to sit in the sump 305, which usually retains water at all times.

This is shown clearly in Figure 4, which shows the device located for use in a typical gully 300. It can be seen clearly that the sheathing 100 surrounding the three electrodes 10, 20, 30 extends into the sump as do electrodes 10, 20, whereas electrode 30 is positioned well above the normal level of the retained liquid.

By placing electrodes 10, 20 in the surnp in this way, it is possible to verify that the standing water is actually present. Its absence can indicate a leaking gully, which can result in waste water seeping into underfiow spaces and cellars, which can cause problems. In drought periods, it is possible that the sump will be dry, but the occurrence of a drought will be known and this can be accounted for.

Furthermore, it may be possible to infer from a negative reading from probe 10' that the device 200 is not correctly positioned and may have been removed, which may require further investigation.

When the device periodically takes readings from sensors 10' and 30', such readings may be stored locally for a period or transmitted immediately to the remote monitoring station. Depending on the readings from each sensor, different data may be transmitted to the remote station.

For instance, if sensor 30' indicates that it is immersed in water, then an alarm signal or message may be transmitted immediately to the remote monitoring station so that appropriate action may be taken. This action may include dispatching an investigation team to unblock the sewer, if necessary. This is particularly to occur if a neighbouring gully shows the same problem. A long-term record is kept in an attempt to identify any systemic problems, such as under-sized sewers or those which have a tendency to become blocked.

Located on the lower part of the housing 205 is a light sensor 230. This is arranged to be positioned inside the gully, just below the level of the grating or grille. The reading from the light sensor can be used to infer that a local blockage from e.g. fallen leaves may be blocking the gully. For instance, if the device 200 transmits a message during the hours of daylight, but the light sensor indicates darkness, then this may indicate a problem with that particular gully. In such a case, any readings from that gully may be disregarded and a technician may be sent to investigate, if desired.

When a device 200 according to an embodiment of the invention is used as part of an integrated monitoring system, there are likely to be a large number (perhaps 20 in a typical Street of terraced houses) of similar device deployed in a given area, all communicating with a local hub and then on to a remote monitoring station via a radio link.

In normal use, the device 200 is configured to transmit approximately every 4 hours to the hub. A random element is added to the timing so that the period varies from transmission to transmission. Each local hub is in communication with approximately 50 devices 200, so there is some likelihood of collision between transmissions from different devices. The random factor helps to avoid this in practice. Since each device 200 only transmits for about 1 second in every 4 hours, there are effectively over 14,000 slots' available. Thus, even if one transmission from a particular gully is lost due to a collision it is unlikely to happen on the next transmission and this rate of loss is deemed acceptable.

The remote monitoring station is further linked to a central data gathering point, usually a control centre of a water authority or similar organisation with responsibility for maintaining the sewer system in a given area.

The link from the remote monitoring station to the central point is by a separate radio scheme, preferably GPRS (General Packet Radio Service). The information can give an up to the minute picture of the situation across the network of sewers and drains. Certain conditions can cause alarms to be triggered, thus allowing emergency action to be taken to mitigate potential problems.

The probe 225 does not need to take the form shown in Figures 2 and 3. An alternative configuration is shown in Figure 5. Here, a perspective view of an alternative arrangement of sheath 310 is shown. Rather than the three electrodes 10, 20, 30 being arranged linearly, they are arranged with each at the vertex of a triangle. The functionality is identical as that described previously.

The sheath 310 is then placed over the electrodes once they have been shortened, if necessary. The sheath 310 is a length of extruded plastics material having a generally circular cross-section and divided internally into three 1200 sectors 315. Running longitudinally along each of the sectors is a slot or discontinuity 320. This slot 320 acts as a vent so that as liquid rises up the sheath 310, the air present can be expelled through the slot 320.

The functionality of the sheath 310 is essentially the same as has been describe earlier. Liquid is able to rise up the sheath and create the appropriate contact between the electrodes, but the ingress of waste material or solids is prevented or at least hindered, such that false readings may be avoided or minimised.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features

disclosed in this specification (including any

accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (14)

1. A probe for detecting a liquid level, comprising a pair of conductive electrodes, wherein each electrode is substantially surrounded by a sheath.

2. The probe of claim 1 wherein the sheath is a hollow tube which surrounds each electrode.

3. The probe of any preceding claim wherein the sheath comprises a vent to allow air expelled by a rising liquid level to be expelled.

4. The probe of claim 3 wherein the vent comprises a longitudinal slot running along at least a part of the sheath.

5. The probe of any preceding claim wherein the electrodes comprise stainless steel.

6. The probe of any preceding claim further comprising a third electrode, shorter than the pair of electrodes.

7. The probe of any preceding claim wherein the electrodes are provided with a plurality of pre-weakened portions along their length.

8. A device for monitoring the condition of a drain, said device comprising a probe according to any preceding claim.

9. The device of claim 8 comprising means for transmitting a reading from the probe to a remote station.

10. The device of claim 8 or 9, comprising three electrodes, whereby one electrode is common and the other two are arranged to sense a level of retained liquid and a flood condition respectively.

11. A system comprising a plurality of devices as claimed in any of claims 8 to 10, further comprising a remote station for receiving transmissions from each device for monitoring the condition of a drain network.

12. A conductive probe substantially as herein described, having particular reference to the accompanying drawings.

13. A drain monitoring device substantially as herein described, having particular reference to the accompanying drawings.

14. A system as substantially herein described, having particular reference to the accompanying drawings.