An accurate and precise rainfall gauge having no moving parts

Abstract

The present invention is a new type of rain gauge that achieves high resolution and accuracy without employing any moving parts. It consists of a rain collecting funnel leading to a small laminar-flow bell syphon, the syphon being electrically connected to an electronic circuit and sensor to signal when, and for what duration, the syphon operates. The circuit detects and records both the start and end of each syphon discharge cycle as the discharge water closes and then breaks an electrical circuit. The syphon discharges rain water at a known, constant rate. The measurement of rainfall depth (amount) is achieved by recording the aggregate time for which the syphon operates (the aggregate duration of the short intervals between contact closure and contact breakage by water) in any period of interest (hour, day, etc). 20 25 20 47 04 22 J un 2 02 5 A B S T R A C T 2 0 2 5 2 0 4 7 0 4 2 2 J u n 2 0 2 5

Description

TECHNICAL FIELD The present invention relates to the improved measurement and automatic recording of the amount of rainfall received at a place. Such measurements are widely required by Government weather and climate agencies, as well as in areas of application including agriculture and flood warning systems. BACKGROUND OF THE INVENTION Prior art in the measurement and automatic recording of rainfall is technologically diverse. However. worldwide the most widely-used gauge design is the "tipping-bucket", a form of rainfall gauge that originated in the 17th century. A tipping-bucket rainfall gauge consists of a pair of unbalanced buckets mounted back-to-back, and able to rotate on an axle. In tippingbucket rain gauges, each bucket fills and overbalances in turn, in a see-saw-like fashion, and the estimation of rainfall is made from a tally or count of how many tips have occurred in an hour, a day, or other period. This prior art is attended by a number of difficulties. The devices are mechanical, and subject to corrosion, bearing wear and friction, and other weather-related effects that require re-calibration and maintenance perhaps once or twice per year. This can be costly and difficult, particularly for gauges deployed in remote locations. However, an inherent and particularly problematic limitation of these gauges is that in increasingly intense rainfall, they systematically under-record rainfall amounts by 10-30% or more. This occurs because as the buckets fill, overbalance, and tip, water from the collecting funnel can continue to flow into the bucket but without causing any additional tip. This water remains unmeasured and therefore unrecorded, and the count of tips does not accurately reflect the amount of rainfall caught by the gauge. Tipping-bucket gauges suffer from a number of other issues, notably incomplete emptying of the buckets once they have overbalanced and tipped. Complete emptying is often limited by surface tension, which retains films or droplets of water against the inner surfaces of the bucket. The retained water tends to result in bucket filling and tipping sooner than should be the case, so tending to over-estimate the rainfall. The error from this cause alone can amount to 6% - 8%. Because they rely on balanced 2025204704   22 Jun 2025 buckets, tipping-bucket rainfall gauges are also extremely sensitive to being mounted off-level. Additionally, they are difficult to calibrate, this normally being done by careful, repeated adjustment of stop-screws that alter the angle of rest of the buckets on their pivoting axle. This is an exacting and time-consuming process, and one that does not readily permit high accuracy to be achieved. The present invention eliminates many of the limitations of tipping-bucket rainfall gauges. The limitations of a mechanical system of buckets balanced on an axle are completely removed as the present invention contains no moving parts. In this way, the present invention eliminates any requirement for annual or twice-yearly lubrication, maintenance, and recalibration to account for wear. The present invention eliminates the problem of unmeasured inflow of rainwater during the tipping action, and so eliminates this major source of error, which is commonly referred to as "undercatch" or "dynamic error". SUMMARY OF THE INVENTION The present invention replaces the measurement of the count or tally of bucket tips, as required when using a tipping-bucket rain gauge, with the detection and recording of the total time through which a small laminar-flow syphon is discharging. The syphon used in the present invention empties when it has become filled with a volume of just a few millilitres. This is less than the volume of a typical tipping-bucket. The flow from the syphon begins and ends very sharply. In rainfall of common intensities, said syphon drains every one to two minutes, taking just over 2 seconds to drain. Syphon action is driven by gravity and depends on the cohesive forces between water molecules. Thus, by way of example, in one hour of steady rainfall the syphon might drain 30 times, for a total draining time of about 60 seconds. For the remainder of the time, the syphon chamber is simply filling slowly with water draining from the collecting funnel. Rain water collected by the funnel above can continue to flow into the syphon during drainage. In contrast to what occurs in tipping-bucket rain gauges, this inflow is not unmeasured, but rather simply lengthens the syphon draining time by a few tenths of a second. This duration is accurately recorded by the special electronics that form an integral part of the present invention. Thus, the present invention eliminates one of the most troubling issues with tipping-bucket gauges, namely the major "undercatch" 2025204704   22 Jun 2025 errors (of up to 30% or even more) that occur in heavy rain. These can in principle be allowed-for by complex 'dynamic calibration' and the creation of correction procedures that can be applied in data processing. In practice, however, many users do not have the capacity to apply complex corrections, and the accurate adjustment of the delicate balance settings of the tipping buckets by means of rather coarse stop screws remains essential but it still difficult to achieve. In fact, some manufacturers of tipping-bucket rain gauges include a small syphon fitted below the rain collecting funnel, the purpose being to feed a steadier inflow to the tipping-buckets than would occur if they received water directly from the funnel above. The steadier flow from the syphon is intended to reduce the effective range of intensities for which the tipping-buckets have to be calibrated. The present invention monitors the flow of such a syphon directly, which completely obviates the need to have the complex, mechanical tipping-buckets at all. In summary, the present invention replaces the counting of bucket tips, and instead simply records the time for which a small laminar-flow syphon discharges rainwater. Extensive laboratory and field trials have confirmed that the present invention can achieve accuracies in the recording of rainfall depth of 0.1%. Furthermore, given that the syphon operates on a smaller volume of water than a typical tipping-bucket, the present invention allows greater sensitivity in the recording of rainfall, including the times of onset and cessation of rainfall. This is critical when rainfall intensity needs to be estimated from rain gauge data. The present invention thus improves on the "tipping-bucket" principle in several ways: a) it eliminates all moving parts, and so eliminates the problems arising from bearing wear, corrosion, or other issues, greatly simplifying manufacture and assembly and associated costs. Furthermore, there are no stop-screw adjustments and no need for the stop-screw settings and the free rotation of the buckets on their bearings to be checked and adjusted at regular intervals; b) it eliminates the need for so-called 'dynamic calibration' that is intended to facilitate the correction of undercatch. Dynamic calibration is complex and time-consuming, but is necessary for proper quantification of the error inherent in tipping-bucket gauges as rainfall intensity increases; 2025204704   22 Jun 2025 c) it provides better sensitivity (typically 0.13 mm of rainfall) than most tipping-bucket gauges (most often these have a sensitivity of 0.2 mm of rainfall), and hence can more accurately record the beginning and end of rainfall, which are key parameters needed to estimate the rainfall intensity from rainfall depth and rainfall duration; d) it provides greater accuracy: typically, errors of 0.1% are achievable, whereas most prior art is limited to 2%-5% error at best, and errors of up to 30% or more in heavy rainfall. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an embodiment of the invention using only one sensing electrode (4) mounted near the outlet of the syphon drain tube (5) and insulated from it by a collar of non-conductive material (3). In this configuration, the second electrode connection would be made to the metal casing of the rain gauge (6) and hence to the water that flows from the collecting funnel. These funnels are most commonly made from brass or copper. Vertical arrows in the syphon drain tube in Figure 1 show the direction of water flow from the syphon. Figure 2 shows an embodiment of the invention using two sensing electrodes (4) both mounted near the outlet of the syphon drain tube (5) and insulated from it by a collar of non-conductive material (3). The two electrodes (4) would be fabricated from light-gauge stainless steel or equivalent. Tinned copper wire or equivalent can also be used successfully to form the sensing electrodes. Vertical arrows in the syphon drain tube in Figure 2 show the directionn of water flow from the syphon. Figure 3 presents a schematic layout of the two components of the present invention. These are as follows: 2025204704   22 Jun 2025 (a) the syphon (2) mounted below the rainfall collecting funnel (1) and enclosed within the rain gauge casing (6); (b) the associated control electronics. The electronic components include the circuitry (7) to detect contact closure and breakage between the two sensing electrodes (4) by water discharged from the syphon drainage tube, the microcontroller (8), the LCD data display (9), and the SD card data recording system (10). Two connecting signal wires (11) run from the two sensing electrodes within the rain gauge to the contact closure and breakage circuit (7). Pairs of arrows connecting the modules (7, 8, 9, and 10) symbolise the paths of signal flow among the electronic components. These signal pathways are implemented using standard digital communication buses. DETAILED DESCRIPTION OF EMBODIMENTS The syphon (2), insulating collar (3) and sensing electrodes (4) of the present invention are housed within the cylindrical casing (6) of the rain gauge and immediately beneath the funnel that collects rainwater (1). The present invention thus has two key sub-components within the gauge casing: the miniature syphon (2) and two sensing electrodes (4) separated by a small gap that would be bridged by the stream of water released from the syphon when it emptied. This stream of water, which lasts for a little over 2 seconds, bridges the two sensing electrodes and closes an electrical circuit. The sensing electrodes are insulated from the metallic syphon outlet tube (5) by an annular insulating collar (3). Alternatively, the syphon could be 3D-printed in non-conductive resin to which the sensing electrodes could be attached directly. The sensing electrodes can be retro-fitted to an existing rainfall gauge such as a tipping-bucket gauge, eliminating the need for the purchase of a complete new gauge housing. The novel electronics and data recording system (7,8,9,10) that receive and process the signal from the two sensing electrodes form the second key component of the present invention. This component can be mounted within the casing of a rainfall gauge, or more remotely in a separate waterproof enclosure or building. The signal can be transmitted tens of metres using ordinary electrical signal wire. 2025204704   22 Jun 2025 The second key sub-component of the present invention includes several electronic modules, including the electronic circuit that detects when water bridges the two sensing electrodes (4). This circuit has to be particularly sensitive, because rain water can be very dilute. Thus, a high-gain circuit is needed, and therefore includes a Darlington pair of transistors for current gain, followed by a single-supply operational amplifier for additional voltage gain. The circuit is able to operate the gauge with water having extremely low specific electrical conductivity (down to less than 0.1 gS cm-1, which is considerably lower than the conductivity of de-ionised water). Natural rainwater typically has a specific electrical conductivity in the range from a few gS cm-1 to many tens of gS cm-1. This sensing circuit feeds a voltage signal (a logical 'HIGH' signal) to a 48 MHz microcontroller (8) and hence to the data collection and logging modules via an optical coupler. Optical coupling is adopted to allow for the shift in voltages between the electronic sensing circuit (nominally operating on 12 V DC from a battery) and a typical data logger having a maximum permissible voltage input of less than 12 V (often in the range 1 V to 5 V). The microcontroller (8) also drives an LCD data display (9). The data collection and logging circuit for the present invention is based on a programmed microcontroller that runs code specifically designed for management of the rainfall measurement and recording system of the present invention. The code handles time-keeping to the millisecond, as required to time the operation of the syphon, keeps track of clock and calendar data, and the writing of the syphon operating durations, all time- and date-stamped, to SD (secure digital) data storage card. The microcontroller also writes, in real time, relevant data (file name, duration of syphon operations, amount of rainfall received) to an LCD (liquid crystal display) panel so that operation of the gauge can be monitored if required (e.g. at a weather observing station or research installation). The use of a programmable microcontroller means that the operating codes can readily be customised as required, for instance to report hourly rainfall amounts (or amounts tallied through other time intervals) if required.

Claims

1. A rainfall measuring and recording device (rain gauge), said gauge having no moving parts, and equipped with electronic circuitry capable of detecting and recording contact closure and contact breakage across two sensing electrodes by rain water being discharged from a small laminar flow syphon, and with the ability to electronically time and record the durations of the intermittent discharges of rainwater from the said syphon.

2. A rainfall measuring and recording device (rain gauge), as claimed in Claim 1, one of the two sensing electrode being the metal housing of the rainfall measuring and recording device (rain gauge), and the other sensing electrode established via an insulated electrical contact mounted just below the outlet tube of the syphon, and equipped with electronic circuitry capable of detecting and recording contact closure and contact breakage across said sensing electrodes by rain water being discharged from a small laminar flow syphon, and with the ability to electronically time and record the durations of the intermittent discharges of rainwater from the said syphon.

3. A rainfall measuring and recording device (rain gauge), as claimed in Claim 1, the two sensing electrodes both being mounted just below the outlet of the syphon, and equipped with electronic circuitry capable of detecting and recording contact closure and contact breakage across said sensing electrodes by rain water being discharged from a small laminar flow syphon, and with the ability to electronically time and record the durations of the intermittent discharges of rainwater from the said syphon.

Images