GB2444512A - A rain gauge - Google Patents

Abstract

A rain gauge 1 comprises an elongate housing 20, at the top of which is positioned a primary funnel 10. The funnel 10 can be varied in size for different applications of the rain gauge. Rain entering the primary funnel 10 falls downwards to the impact retarder 30. After leaving the impact retarder 30, any collected water falls to the secondary funnel 40 positioned directly below the impact retarder 30. Positioned inside the secondary funnel is a flow regulator device 50. The flow regulator device 50 is provided so that a consistent flow rate through the exit of the secondary funnel 40 is achieved regardless of the input flow rate to the secondary funnel 40. Once water leaves the exit of the secondary funnel 40, it falls a distance through the housing before hitting a sensor 60, which is operable to detect and count drops leaving the funnel 40.

Description

Improvements in and relating to rain gauges The present invention

relates to rain gauges used to record an amount of rainfall over a given period of time.

Such devices have a number of applications, including meteorological study, environmental monitoring and other such applications.

Prior art rain gauges range from the very simple standard rain gauge, which consists of a funnel attached to a graduated cylinder which directly captures rainfall into the funnel, the amount of which is then read from the graduated cylinder at a later time. The amount of water collected in the cylinder is directly related to the rainfall over a given period. Such devices are very simple, but the resolution of sampling available with such a device is not very great at all. This means that if a minute-by-minute or hour-by-hour reading of rainfall is required, then the standard rain gauge must be visually inspected as required. This is clearly inconvenient.

To address such problems with the standard rain gauge, various attempts have been made to automate the process of recording rain fall. Chief amongst these is the so called "tipping bucket rain gauge". Such a rain gauge consists of a large cylinder, at the top of which is a funnel which collects and channels the rain. The rain falls onto one of two small buckets or levers which are balanced relative to each other. After a certain amount of rain falls, the lever tips and this triggers an electrical switch which is used to record a certain amount of rainfall. This process is repeated with the tipping bucket alternating between its two rest positions.

The resolution of such a rain gauge is determined by the amount of rainfall which is required to cause the tipping bucket to switch position.

A problem with the tipping bucket rain gauge is that the rainfall may stop before the lever has tipped and so some rainfall is effectively not recorded correctly. When the next period of rain begins it may take no more than one or two drops to tip the lever which would give an unrealistically high reading for that moment in time.

These inaccuracies do not render the tipping bucket rain gauge suitable for all uses.

Embodiments of the present invention seek to address shortcomings with prior art gauges, whether disclosed herein or not.

According to the present invention there is provided an apparatus as set forth in the appended claims. Preferred features of the invention will be apparent from the dependent claims, and the description which follows.

Advantageously, embodiments of the present invention provide a greater resolution than prior art devices and do not require periodic emptying, meaning that they may be deployed in a wider variety of locations.

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. shoes a cross sectional view of a first embodiment of the present invention; Figure 2 shows a second embodiment of the present invention; and Figures 3A to 3C show detailed views of part of the embodiment of Figure 2.

Figure 1 shows a cross sectional view through a rain gauge 1 according to an embodiment of the present invention.

The rain gauge 1 comprises an elongate housing 20, at the top of which is positioned a funnel 10 for collecting rainfall.

The funnel 10 can be varied in size for different applications of the rain gauge. If the area of the entry to the funnel is large, then the gauge can be made sensitive to even light drizzle. If the entry level is made small, then the system is better suited for monitoring large storms. Depending upon the use to which the rain gauge will be put, the entry area of the funnel can be set accordingly.

The entry to the funnel 10 may be covered with netting or gauze to prevent the ingress of waste matter, such as leaves. It may also act to deter birds from nesting in the funnel.

Rain entering the funnel 10 faIls downwards to impact retarder 30 which, in this particular embodiment, comprises a plurality of glass marbles. The function of the impact retarder 30 is to slow the speed of incoming rain so that any water leaving the impact retarder 30 leaves at essentially the same rate regardless of the speed of the incoming rainfall. Marbles are selected as they are easily available, do not absorb water and the path created between several marbles, acts to slow the incoming rainfall.

It should be understood that the impact retarder 30 is not necessary in all embodiments, and in some cases, it may be omitted.

After leaving the impact retarder 30, any collected water falls to the secondary collecting funnel 40, positioned directly below the impact retarder 30. The secondary funnel 40 is positioned in the housing 20 such that there is a tight seal around its edge such that any water falling from the impact retarder 30 enters the secondary collecting funnel and none travels around the edge of the funnel. The dimensions of the secondary collecting funnel 40 must be known, and consistent, to enable rainfall calculations to be made on a basis of the number of measured drops.

Positioned inside the secondary collecting funnel 40 is a flow regulator device 50. The flow regulator device 50 is provided so that a consistent flow rate through the exit of the secondary collecting funnel 40 is achieved regardless of the input flow rate to the secondary collecting funnel 40.

Some characteristics of the flow regulator device 50 are that: it should be of a non absorbent material; it should not expand when wet; its structure should be consistent along its length; and, that it should be fibrous along its length, thereby allowing multiple flow paths through the neck of the funnel 40.

The flow regulator device 50 also acts to filter out any small solid material which have entered the rain gauge.

In practice, it has been found that a suitable material for the flow regulator is a short length of nylon rope or rope of any other suitable synthetic material. In use, the short length of nylon rope is knotted at its top end so that the knotted portion sits in the neck of the funnel and a short length of the rope extends through and down the neck. Water entering the funnel 40 therefore flows through the synthetic material of the flow regulator device 50 and exits the funnel 40 with a consistent drop size, largely regardless of the rate of rainfall.

Once water leaves the exit of the secondary collecting funnel 40, it falls a distance through the housing 20, before hitting sensor 60, which is operable to detect and count drops leaving the funnel 40. The sensor 60 comprises at its upper surface, a membrane upon which falling water falls. This membrane acts like a drum skin such that falling drops are amplified by hitting it.

Positioned beneath the membrane is a microphone arranged to sense any impact on the membrane and pass any such signals onto a detecting circuit which is arranged to be triggered by such impacts and to count the number of such impacts and their time of arrival. Relatively straight-forward electronic circuitry can be implemented to achieve this effect.

An example of an acoustic system which may be used comprises a piezo-electric transducer which converts mechanical energy (i.e. a falling drop) into electrical energy in the form of a short pulse. A microprocessor is able to count such pulses, after they have amplified and possibly further processed, and so measure the amount of rainfall on this basis.

The microprocessor counts drops for a preset period (e.g. 1 minute) and then stores the reading for later retrieval or transmission.

Considering the operation of the rain gauge as a whole, incoming rainfall enters the primary collecting funnel 10, from where it falls into the secondary collecting funnel 40, whereupon it flows into flow regulator device 50, which ensures that water leaving the funnel 40 does so at a substantially consistent speed and with a consistent drop size, indicative of the incoming rainfall.

Optionally, an impact retarder 30 is disposed between the primary and secondary funnels and acts to stop direct rainfall from entering the secondary funnel, forcing rain through the flow regulator device and possibly causing misleading readings.

The functional effect of the flow regulator device 50 is that uniform drops of water emerge from the funnel 40 at a frequency which can be directly correlated with the amount of rainfall.

The drops descend through the tube 20 to contact the sensor 60, which is arranged to record and log the falling drops to give a direct indication of the amount of rainfall. The bottom of the tube 20 is open so that water may just fall through the bottom of the tube to the ground.

Figure 2 shows an alternative embodiment 100 of the invention. The primary collecting funnel 10 and impact retarder 30 are as previously described. The difference lies in the means used to record drops issuing from the secondary collecting funnel 140, which is adapted especially for this purpose.

Rather than use a sensor located at the bottom of the tube 20, a sensor 200 is added to the funnel 140.

Figures 3a to 3c show the operation of the sensor 200.

Figure 3a shows a detailed view of the funnel 140 and the sensor 200. The sensor 200 comprises two electrodes 210, 220. The first electrode 210 penetrates the lower portion of the funnel 140 such that it crosses all or part of the diameter of the funnel's exit tube.

The electrode 220 extends vertically upwards such that it presents an end point towards the exit of the funnel 140.

Figure 3b shows the situation where a drop of water is just exiting the funnel 140. At this particular moment in time, the drop of water bridges the gap between the two electrodes 210, 220 and the sensor 200 is able to detect presence of the drop by the change in resistance measure between the two electrodes.

When the drop of water exits the funnel and clears the second electrode 200, the resistance between the two electrodes reverts to its former open-circuit value and the sensor records the whole episode as shown in Figures 3a to 3c as a single drop.

Whether the first embodiment of Figure 1 or the second embodiment of Figure 2 is used, the output of the sensor or 200 is identical -a train of pulses, each of which indicates the passage of a single drop through the secondary funnel.

There is no simple mathematical relationship between the various design factors of the gauge, but through a process of experimentation, it is possible to derive what is herein termed a gauge constant', which defines the volume of each drop which is later measured.

In practice, it has been found that a consistent drop size can be achieved through selection of the variables: the width of the secondary funnel outlet, the width of the funnel material at the funnel outlet, and the speed at which the accumulated water is allowed to get to the secondary funnel outlet. By varying these, it is possible to arrive at a situation where a substantially consistent drop size is achieved, e.g. O.lmL. This volume may then be equated with the amount of rainfall, measure in mm or cm.

By use of appropriate logging techniques, these pulses are equated with a certain amount of rainfall, which can be determined by suitable calibrating the device according to primary funnel 10 diameter and properties of the flow regulator device 50.

The logging equipment required to record rainfall can be located local to the device 1 or it may be positioned remotely, with a suitable wired or wireless data link provided as needed.

The logging equipment can be arranged to send periodic reports to a the monitoring station and/or arranged to trigger alarm conditions in the case of a sudden heavy downpour of rain. Such an arrangement can be very useful to water authorities who desire rapid warning of heavy rain so that any problems with sewers can be dealt with urgently.

Embodiments of the invention may be deployed in a variety of different locations, as required. Typical locations could include on lamp posts or other items of street furniture.

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 (16)

1. A rain gauge comprising: a housing; a primary collecting funnel, located at the top of the housing; a secondary collecting funnel, located internal to the housing, below the primary collecting funnel; a flow regulating device to regulate liquid flow through the secondary collecting funnel; and sensing means to detect drops of water emerging from the secondary collecting funnel.

2. A rain gauge as claimed in claim 1 further comprising an impact retarder disposed between the primary and secondary collecting funnels, the function of which is to retard the incoming rainfall before it enters the secondary funnel.

3. A rain gauge as claimed in claim 2 wherein the impact retarder comprises a plurality of glass marbles.

4. A rain gauge as claimed in any preceding claim wherein the flow regulating device comprises a plurality of fibres disposed within the secondary funnel.

5. A rain gauge as claimed in claim 4 wherein the plurality of fibres comprise a short length of rope.

6. A rain gauge as claimed in claim 4 or 5 wherein the fibres are of synthetic material.

7. A rain gauge as claimed in claim 6 wherein the synthetic material is nylon.

8. A rain gauge as claimed in any of claims 5 to 7 wherein the rope is knotted at one end and the other end extends through the exit from the funnel.

9. A rain gauge as claimed in any preceding claim wherein the sensing means comprises an acoustic sensor to detect each drop falling from the secondary funnel.

10. A rain gauge as claimed in claim 9 wherein the acoustic sensor comprises a piezo-electric device.

11. A rain gauge as claimed in claim 9 or 10 wherein the sensor further comprises a membrane upon which falling drops impact.

12. A rain gauge as claimed in any of claims 1 to 8 wherein the sensing means comprises a conductive sensor arranged to detect each drop emerging from the secondary funnel.

13. A rain gauge as claimed in claim 12 wherein the conductive sensor comprises a first electrode running through the exit tube from the sensor and a second electrode positioned adjacent the exit from the funnel such that a drop emerging from the secondary funnel will bridge a gap between the two electrodes.

14. A rain gauge as claimed in any preceding claim further comprising data logging equipment to record drops.

15. A rain gauge as claimed in any preceding claim further comprising communication means to transmit recorded data to a remote location.

16. A rain gauge substantially as herein described and having particular reference to the accompany drawings.