IL298652B2 - Capacitive Precipitation Gauge - Google Patents

Description

TECHNICAL FIELD This invention relates to capacitive transducers, and more particularly to variable capacitance transducers for determining amount and intensity of water precipitations in agriculture, as well as for measuring the level of electrically conductive fluent materials within a container.

BACKGROUND OF THE INVENTION 1. Applications 70% of fresh water is used in agriculture. Over half of the average home's water use goes to residential landscaping. Irrigation control systems known in the art typically employ a time clock and controller coupled to one or more electrically actuated or activated valves. Considerable inefficiency and poor performance can result when using pre-programmed watering controls as described above. For example, such watering systems typically irrigate during rainstorms, thus resulting in wasted water.

Overwatering is not only costly but may promote shallow roots, which in turn increase the plants susceptibility to disease. Between 2003 and 2012, about 12.5 million hectares were allegedly disturbed by plant diseases, mostly in Asia and Europe.

Keeping track of rainfall amounts is a great way to cut costs and conserve water while retain a beautiful, lush healthy landscape.

Another area of concern is that crops in grape vineyards, apple and pear orchards, cotton and potato fields, etc. are prone to diseases, developing from freestanding water on the leaves. Golf courses, (and other sports fields), are among the highest per-hectare users of fungicide treatment. Their high expenditure will make the precipitation gauge, having a leaf wetness sensor, an immediate cost saving device in utilizing the disease prevention models. When the farmer knows that his field has had a certain number of hours of surface wetness at a certain temperature, he can use fungicides to reduce or prevent the disease. Such precision use of fungicides can reduce spraying costs by 50% and give far better disease control. In greenhouses, prevention of condensation on crops, which usually takes place at night and causes fungal crop diseases, requires either heating or ventilation or both. To save on operating expenses of dehumidification devices, they should only be activated when necessary. A more reliable indication of the onset of condensation might be obtained by using a leaf wetness sensor (artificial leaf,) over which it is easy to detect the initial stages of dew formation. Once detected, a signal may be transmitted to the control system (heating, ventilating and/or dehumidification).

In long cooled storing of agricultural produce (fruits, vegetables, spices and so on) there is a problem of product weight and quality losses which are caused by the loss of water. To reduce these losses there is installed a humidifier which increases the humidity in the storage. On the other hand, deterioration of harvested agricultural produce is hastened greatly when moisture is allowed to remain or collect on the surface of the product, usually as a result of water condensation. The negative consequences of water condensation include inhibition of gas exchange, leakage of solutes from the damaged areas and enhancement of microbial growth. To increase humidity in the cooling rooms controllably, without condensation, the humidifier should only be activated when necessary. Wetness sensor can be used for either monitoring or controlling high humidity without condensation on the surface of agricultural products during their postharvest life (storage, transportation, marketing). Therefore, a reliable and cheap precipitation gauge, including a rain gauge and wetness sensor, could be an important instrument of optimal water using in agriculture. 2. Rainfall measurement There are some patents on this subject, describing probable solutions and problems.

German Patent Application DE 4231235 to SCHMITZ MICHAEL, describes integrating rainfall gauge, in which the rain is collected through a funnel into a U-tube of small capacity equipped with, e.g., a capacitive or ultrasonic level sensor.

According to United States Patent Application 20220155487 to JAHN; Felipe ; et al., some criteria drastically influence the achievement of the real amount of rain by a tipping bucket rain gauge.

One of the problems is the inclination of the device in relation to the plane where it is installed; this problem can cause large measurement errors, reaching or even exceeding 20%. The most aggravating factor to this problem is that the technician responsible for reading the device can take months to detect the failure, as it needs to be done inloco, or even never to detect, due to the difficulty of access to the place that was installed, being that in some cases access to the equipment is only by helicopter, boats, among other expensive and difficult means of availability.

Another problem related to the measurement errors of a tipping bucket rain gauges, which it seeks a solution, is that due to the equipment being installed in open and remote areas, it is subject to impregnation of dirt, which can lead to clogging in the region of the catchment funnel, by the accumulation of leaves, bird droppings, dead insects, etc.; or in the failure to detect the pulse generation, which measures the movement of the tipping bucket, due to its mechanical locking, caused by some external factor, such as the presence of an anthill; or caused by an internal factor, such as the bearing damaged resulting in its locking, or by the non-functioning of the pulse generating device, or failures in the sensor. The detections of these failure can take weeks or months, which could represent weeks or months of invalid data.

Also, by the fact that this equipment is used in open areas and is subject to bad weather, the support where the equipment is installed, is subject to the same vibrations. These vibrations, if excessive, can lead to measurement errors, as they can cause disturbances in the equipment resulting in erroneous data, reducing the equipment's operating reliability.

In conclusion, there are following problems in using conventional rain gauges in agriculture: • The tipping bucket rain gauge is easy to be affected by rain intensity, and its measurement error increases with rain intensity increasing. These errors can amount to 20% for some types of tipping bucket gauges [1]. • They are known to miss many small and large rainfall events • They have mechanical transmission parts that need to be regularly maintained and are temperature dependent. Mechanical locking can be caused by some external factor, such as the presence of an anthill, or the bearing damaging resulting in its locking, or by the non-functioning of the pulse generating device • Inclination of these devices causes the measurements errors • They are affected by an accumulation of salt and dirt on the measurement areas, bird droppings, dead insects, etc. • They are affected by vibrations caused by wind and heavy rain. Noise in the weight measurement due to the water input must be filtered out appropriately • The widely used cheap rain gauges are relative cheap but not precise enough, while the precise instruments are expensive • Existent capacitive rain gauges are very expensive because of the need to compensate the measurement dependence from temperature, dielectric constant and electrical conductivity of the water, external electromagnetic field interference, vibrations and water condensation on the electrodes 3. Surface wetness measurementOne of the devices for sensing wetness and humidity control is a dew sensor. This sensor in fact mimics the condensation of humidity on a natural surface such as on leaves, without control of the temperature of the sensor, and thus in fact is very reliable since it directly mimics the natural process of condensation. Various measurements have shown a good correlation between the temperature of the leaf and the temperature of the dew sensor at night. Thus, such a sensor is suitable for use in detecting condensation of water on various surfaces, such as leaves in greenhouses, giving a warning when a humidity of the air is too high, a situation which occurs for example at night, which is a cause of many plant diseases. Such a warning may operate various drying mechanisms to lower again greenhouse humidity.

In fact, at night the dew sensor, is more suitable for use than humidity meter in greenhouses, since it indeed reflects the true and natural situation of condensation on surfaces, which is a better predictor to the state of the leaves than humidity content detected by humidity meters.

The most popular method for wetness detection nowadays is based on measuring the electrical impedance between two electrodes, which are shorted by water. Conventional dew sensors such as those used in greenhouses typically employ a pair of spaced electrical wires, the resistance between which drops from approximately megohms to 3 megohms when dew bridges the two wires. But such devices are electrically noisy and have changeable sensitivity that depends on salts precipitation and pollution on the sensor. Another problem with such devices is that generally require high voltage and the exposure of the conductors and leads which features renders them vulnerable to corrosion by the weather. The corrosion is especially rapid in the presence of high voltages used in the range of 1 to 20 volts.

Example of another technology is PHYTOS 31 LWS Dielectric Leaf Wetness Sensor of METER Group, Inc. USA. It measures both the onset and duration of wetness on a simulated leaf, which in turn predicts when the onset of certain diseases or infections may occur. It uses capacitance technology, so it can sense sub-milligram levels of water condensing on the surface, including frost and ice formation. That way you can establish a threshold that not only indicates when the sensor is wet, but also senses how much water there is. This kind of moisture clarity reduces guesswork and worry about accurately predicting disease conditions [2]. The LWS measures the dielectric constant of a zone approximately 1 cm from the upper surface of the sensor. The surface coating is hydrophobic — similar to a leaf with a hydrophobic cuticle. The sensor matches the wetness state of these types of leaves but may not match the wetness duration of pubescent leaves or leaves with less waxy cuticles. The accumulation of dust and debris will cause the dry output to increase and change the Boolean threshold. It needs cleaning the sensing surface with a moist cloth periodically or when elevated dry output is detected. If using the LWS in areas with unusually high radiation loads, Campbell Scientific recommends applying Revivex UV Protectant every 45 days [3]. 30 There are some patents on this subject, describing probable solutions and problems.

U.S Patent 4,626,774 is directed to a dew-point measuring instrument which has a capacitive dew-point sensor which is cooled by a cooling device to the dew-point temperature measured by a temperature sensor. A phase measuring circuit measures the phase angle of the impedance of the capacitive dew-point sensor. The measured phase angle is used as a gauge for the contamination of the dew-point sensor.

U.S Patent 4,948,263 is directed to a dew point sensor for a dew-point measuring device for measuring the water vapor dew point in gases comprising a sensor surface which is exposed to the gas to be measured and on which, upon cooling, the dew-point temperature water vapor condenses. Mounted on the sensor surface are two electrode structures which comprise electrode portions which are arranged a uniform interval parallel to each other and which are covered with a moisture-insensitive insulating layer. The reaching of the dew-point temperature is determined by measuring the impedance or capacitance between the two electrode structures. The distance between the electrode portions, arranged parallel to each other, of the two electrode structures is of the order of magnitude of the diameter of the largest condensation droplet forming on reaching the dew-point temperature, or smaller than said diameter, and the thickness of the insulating layer is small compared with the distance between the electrode portions.

U.S Patent 5,402,075 is directed to a capacitive moisture sensor includes insulator means; capacitance means including a sensing capacitor having a plurality of spaced capacitive sensor conductors mounted with the insulator means for exposure to the atmosphere; and first and second electrodes mounted with the insulator means remote from the spaced capacitive sensor conductors; means for applying a periodic input current across the first and second electrodes; and means for detecting a change in capacitance between the first and second electrodes indicative of moisture bridging at least two of the capacitive sensor conductors.

U.S. Patent No. 6,926,439 to Zlochin concerns dew point hygrometers based on condensation of dew on ends of optical fibers, or on surfaces of an optical prism. The surfaces of the dew forming ends are rough (grinded) and dew formed thereon increases light transmittance.

U.S. Patent No. 6,575,621 to Zlochin describes a capacitive dew sensor comprising: a first electrode separated from the ambient environment by a coating which does not allow penetration of humidity and electrolyte there through; an insulator mounted on said first electrode, a second electrode formed on the exposed outer surface of the insulator when water containing electrolytes condenses or precipitates on said exposed outer surface of the insulator to form a continuous layer; electric wires connecting the two electrode structures to a measuring circuit for applying a current to said first and second electrode structures, so as to detect a change in capacitance between said first and second electrode structures when water layer is present. An absorbent material can be mounted on the exposed outer surface of the insulator, thereby speeding the dew condensation onset and to increase the sensitivity of the sensor. But absorbent material slowing water evaporation from the sensor in the drying cycle of greenhouse or cooling room humidity control.

Thus, there remains a need for wetness control apparatuses which provide improved surface wetness measurement despite contamination and application of fertilizers, pesticides, herbicides and other chemical treatments which may be routinely applied to the plants and soil. 4. Liquid level measurement The proposed capacitive precipitation gauge is based on the liquid level sensor.

Liquid level sensors are widely used in various fields. For example, a level sensor can be applied in a rain gauge, to monitor rainfall. In addition, a liquid level sensor can also be used for the detection of liquid level in a tank for the purpose of controlling process pumps or inventory control, toilet monitoring and intelligent control, controlling the level of a liquid in a boiler and a coffee machine, In many industrial processes, the amount of liquid medium accumulated in a storage or process vessel is an important process variable. Knowledge of the liquid inventory therein present allows better operation of the process. Liquid level information may be a process parameter necessary for the actuation of pumps, heaters, and other common process equipment. The ability to monitor liquid levels accurately allows the efficient operation of a process and contributes to the quality of typical industrial products.

One traditional liquid level sensor determines the liquid level using image identification technology, as shown in U.S. Pat. No. 7,982,201.

Another traditional liquid level sensor uses ultrasound detecting technology to determine the liquid level, as described in U.S. Pat. No. 4,610,164.

In addition, optical moisture sensors are used. For example, U.S. Patent No. 5,005005 to Brossia, et al. (1991) includes a fiber optic probe system for automatic and real time detection of the presence or absence of a substance in an environment by monitoring variations in light energy transmitted through an optical fiber having a specially processed sensitive probe area. The sensitive probe area is positioned on, about or within the environment where a substance is to be detected. Because of differences in optical indices of refraction and energy absorption characteristics of different substances, the presence of different substances at the processed sensitive area will cause different proportional and characteristic attenuation of the light energy passing through the optical fiber. Changes in light energy transmission can be interpreted automatically to provide an indication of the condition of an environment.

However, theses traditional liquid level sensors are expensive and complicated, and are no user-friendly nor easy to use.

Prior art liquid level sensors, such as fuel sensors for motor vehicles, usually include a float that rides on an upper surface of the fuel in a fuel tank. The float is typically connected to one end of a pivot arm while the other end of the pivot arm typically includes a wiper mechanism that brushes against a resistor strip when the arm is rotated due to a change in fuel level in the tank. Such sensors are prone to wear, mechanical and/or electrical breakdown or inaccurate liquid level detection.

Variable capacitance probes have been developed to overcome these drawbacks.

Contemporary capacitive liquid level sensors, used for dielectric media, typically employ a parallel plate capacitor configured to be immersed or embedded in the medium so that a portion of the medium becomes embedded between the parallel plates and functions as a dielectric between the plates. The capacitance provided by such a capacitor is used as part of an RC oscillator circuit having an oscillation frequency which varies with changes in the dielectric property of the small portion of the medium between the plates. The frequency of the oscillator circuit is used as an indicator of the moisture content of the medium.

Another traditional capacitive liquid level sensors are used for electrically conductive liquids. They are two type [4]: • Dielectric Type (D-Type) - capacitive proximity sensors are configured with two sensing electrodes integrated in the oscillator. The sensing field projects away from the sensor face and entrance of any object into the sensing field will increase the capacitance, resulting in oscillation. Such sensors will detect all materials, insulative or conductive. These sensors are often called "shielded" and they may be flush mounted. • Conductive Type (L-Type) - capacitive proximity sensors are configured with only one sensing electrode integrated with the oscillator. Entrance of a conductive material into the field provides the second coupling electrode which then causes oscillation. Such sensors are excellent for "looking through" an insulative material such as rubber, glass or paper in order to detect a conductive material such as water, or metal. These sensors are often called "unshielded" and they may not be flush mounted.

Conductive media typically has an electrical conductivity > 20 μS/cm. Conductive material can easily be detected by all sensor types whether they have a GND electrode or not. In conductive media the dielectric constant is irrelevant for the sensing distance.

The sensing distance is influenced by the size of the object and its grounding. Non-conductive media typically has an electrical conductivity < 20 μS/cm. In general sensors with a GND electrode are recommended for non-conductive media. If a non-conductive object is moved into the sensor field, the field increases depending on the dielectric constant and the size of the material to be detected, increasing the capacity of the measuring field [5].

There are some patents on this subject, describing probable solutions and problems.

A capacitive moisture sensors is proposed in U.S. Pat. No. 4,941,501 to Bireley. The device described in this patent employs a multi-vibrator type RC oscillation circuit that reacts to the impedance between a pair of electrodes located in the soil and a variable capacitance having a value dependent upon the moisture content of the soil being monitored. However, as noted above, RC oscillation circuits are highly susceptible to the conductivity of the medium being monitored. Bireley's variable capacitance signal is provided by a pair of plate-type electrodes coated with a dielectric material. However, as noted above, dielectric coating on sensor electrodes can adversely affect the accuracy of sensor (as well as increasing the manufacturing complexity and cost).

As another example, U.S. Pat. No. 5,103,368 to Hart describes a capacitive fluid level sensor which senses level by charging a plurality of capacitors in sequence. The capacitors are formed by two concentric tubes which are vertically oriented in a tank. The vertical orientation allows the fluid to be the dielectric between the plates. As the fluid level falls, a greater area of the plates is exposed to air as the dielectric, which changes the capacitance of the capacitor. For irregular shaped tanks, the capacitors are arranged in a non-linear manner. After each capacitor is charged for a fixed time interval, the resultant voltage is compared with a known voltage to obtain an output signal representing liquid depth.

U.S. Pat. No. 6,766,728 to Fogagnolo , et al., describes device for controlling the level of a liquid in a boiler of a coffee machine. The device, in which the boiler is connected with an external cylindrical container made of dielectric material, comprises 30 a capacitive sensor, coupled externally of cylindrical container, and means for detecting the changes in the capacitance of the capacitive sensor, thereby generating an electric signal representative of the liquid level in the boiler, and for controlling the liquid flow into the boiler.

In U.S. Patent No. 8,161,814 to Calcote, April 24, 2012, Self-calibrating capacitive transducer for determining level of fluent materials is disclosed. A capacitive transducer for detecting the level of liquids and other materials has one or more antenna probes connected to an integrated chip normally associated with touch-screen displays. Each antenna probe operates independently and senses the level condition of wet or dry flowable materials such as water, oil, fuel, grain, and so on. The antenna probes may be formed as insulated conductive wires or conductive traces between layers of a stiff or flexible substrate, such as a PCB, with the substrate material serving as the insulating layers. Each antenna probe has a different length representing different depths of the material being measured to provide dynamic calibration of the level condition independent of the material type and ambient conditions.

Transducers for determining liquid level are often used in vehicles, industrial equipment and other systems and components. Such transducers typically operate by detecting a change in an electrical property of the transducer which varies in accordance with the liquid level. The probe section is adapted for mounting inside or outside a tank, vessel or other container for measuring a level. The probe section in accordance with an exemplary embodiment of the invention preferably includes a primary antenna probe and a plurality of secondary antenna probes formed as elongate electrically conductive electrodes or traces on an elongate electrically insulating substrate. The primary probe is preferably constantly immersed in the material being measured while the secondary probes are used to dynamically calibrate the primary probe during measurement.

In U.S. Patent No. 9,983,042 to Huang, apparatus for detecting liquid level is disclosed. An embodiment of the invention provides a liquid-level sensor to detect liquid-level information of a liquid to be tested in a container. The sensor includes an electrode, a sensing circuit, an amplifier and a controller. The electrode is disposed on the outer surface of the container, comprising a first electrode and a second electrode. The sensing circuit is coupled to a first electrode and a second electrode and receives a clock signal to generate a first voltage signal and a second voltage signal. The amplifier receives the first voltage signal and the second voltage signal to output an output voltage. The controller acquires liquid-level information of the liquid to be tested according to the output voltage and a voltage-volume table.

In U.S. Patent No. 10,385,559 to Canfield, toilet monitoring and intelligent control is disclosed. A toilet monitor uses a toilet tank water level sensor producing a toilet tank water level measurement signal. A processor detects rate of change of the measurement signal and conditionally produce a responsive actuation signal in response to the detected rate of change. A transducer connected to receive the actuation signal and transmit information, provide a humanly-perceptible indication, generate a data log and/or control an electronic water supply valve.

The sensor includes an uninsulated conductor and an insulated conductor. The uninsulated conductor, when immersed in the water of a toilet tank, provides direct electrical current conduction path into the water. The amount of conduction depends on several factors including the mineral content of the water. The uninsulated conductor and the surrounding water it is conductively connected to forms one plate of a two-plate capacitor. The other conductor is insulated and is thus not electrically connected to the surrounding water in the toilet tank. This other conductor acts as a second plate of the two-plate capacitor. The equivalent circuit is thus a 2-plate variable capacitor--with the capacitance between the two plates varying based on the level or height of the water into which the conductors are immersed as well as the mineral content, temperature and other characteristics of that water, and the length of at least the insulated conductor.

Due to the very high impedance of RC oscillator the sensor exhibits no substantial variation in accuracy over a wide range of liquid or water impurities, conductivity, temperature, depth of submersion, or variation of metals that might be used to construct uninsulated conductor.

The processor logs the rate of change for later retrieval and water usage tracking. The sensor is configured to be disposed inside the tank and has a length that is less than the extent of the water level change within the tank, and the processor uses the measurement signal to extrapolate the measurements based on the extent of the water 30 level change within the tank. The processor is configured to sleep and to wake up at time intervals to sample the rate of change. The toilet tank monitor is battery powered and has no on/off switch.

In U.S. Patent No. 11,079,267 to Gill, isolated capacitive liquid level probe is disclosed. The device includes a first insulated electrode along with a second insulated electrode in the rod that is immersed in an electrically conductive liquid the depth of which is to be measured, contained in a tank. The device is so constructed that any signal generated in the coil of the first transformer that is connected to the measurement circuit caused by a change in any external magnetic field relative to the measurement circuit is in anti-phase with the corresponding signal generated in the coil of the second transformer that is connected to the measurement circuit. A problem is encountered with such a construction in the presence of stray external electromagnetic radiation, for example, in that the resulting changes in the external electromagnetic field may adversely interfere with the measurement which is made.

The readings obtained from prior art capacitive-type sensors are subject to variation and inaccuracies based on several variables. For example, a change in the dielectric constant of either the liquid being measured or the gas above the liquid can significantly affect sensor readings. Pressure and temperature changes of the liquid or gas can result in significant shifts to the dielectric constants of the liquid and gas, which introduces inaccuracies to the sensor readings. Because prior art sensors fail to compensate for such variances and inaccuracies, their usefulness is limited to applications where pressure and temperature (and therefore, dielectric constant) is substantially constant, or where precision is not a requirement. Additionally, many prior arts level sensors must be calibrated at the time the sensor is installed for service, thus complicating the sensor's installation and setup.

Although variable capacitance probes have been developed, they are cost-prohibitive in many applications and are typically limited to measure a certain type of liquid, since different liquids will have different dielectric properties.

The electronics associated with capacitive measurement and dielectric properties compensation are relatively expensive and are thus priced out of markets where there is a long-felt need for low-cost and highly accurate liquid level transducers.

In addition, a variable capacitance probe designed to measure fuel level normally cannot be used for measuring water level due to the different dielectric properties associated with different liquids.

What is needed, therefore, is a sensor which can consistently measure liquid level with a high degree of accuracy regardless of dielectric changes which may occur in the liquid or gas due to temperature changes, pressure changes, and other changes affecting the dielectric constants. The sensor should be capable of being calibrated at the factory so that calibration need not be performed when the sensor enters service.

OBJECTS OF THE INVENTION It is an object of the present invention is to provide a cheap precipitation gauge, with improved watering control, based on the actual watering needs of the irrigated zone or zones, while reducing or eliminating wasted water and preventing frequent manual adjustment of the controller due to daily, episode or seasonal fluctuations in weather conditions. It must provide reliable operation based on moisture content despite application of fertilizers, pesticides, herbicides and other chemical treatments which may be routinely applied to the soil being irrigated.

Another object of the invention is to provide a precipitation gauge, which is versatile, rugged, low maintenance and low in cost, as well as to be capable measuring extremes high and low of precipitation and moisture events.

It is a further object of the present invention is to provide a precipitation, condensation and moisture sensors that can be used in various applications including, for example, but not limited to: greenhouses and cooling rooms humidity control, as well as conductive liquid level monitoring in tanks.

Accordingly, several objects and advantages of the invention are: (a) to ensure reliable operation over a long period of time, (b) to reduce cost of the device, (c) to reduce the power consumption of the device by using low power capacitance SUMMARY OF THE INVENTION These and other objects are provided by a reliable and cheap Capacitive Precipitation Gauge (CPG), monitoring amount and intensity of water precipitation in agriculture and meteorology at unstable environmental conditions, as well as at salt/dirt deposition and water vapor condensation on the sensitive elements. It includes a capacitive Rain Gauge (RG), a capacitive Wetness Sensor (WS), and a temperature meter.

The Rain Gauge can accurately track both rainfall and sprinklers’ output, providing essential data for irrigation management and timing. It delivers accurate measured values for both amount and intensity of rainwater precipitation at both light and heavy rain. The Rain Gaige is based on the change in capacitance of the electronic capacitor as a result of the change in the water level. The water surface area, around the capacitor’s first electrode, serves as the sensitive surface of the capacitor’s second electrode. With the help of an innovative structure of the electrodes, it is protected against instability of the water level, environmental electromagnetic disturbances, deposition of dirt and salt, as well as condensation of water vapor on the first electrode. Moreover, it includes a reference capacitor for self-calibration at changeable ambient temperature.

The Wetness Sensor intends for measuring small amount of rainfall and can be used as additional reference for RG self-calibration. It is based on continuous measurements of electronic capacitance change caused by wetness change of a water absorbent sheet.

Moreover, the Wetness Sensor accurately tracks moisture on surfaces like plant leaves in open field, providing, together with the temperature meter, essential data for timing and reducing plants’ spray treatments. It measures both the onset and duration of wetness on a simulated leaf, which in turn predicts when the onset of certain diseases or infections may occur.

In addition, it can be used for dew condensation control in greenhouses and cooling rooms.

In this Wetness Sensor the problem of solid contaminants (salts, dust and so on) deposited on the outside surface of the sensor and electrode’s corrosion are significantly reduced by using a water layer as a one of the capacitor’s electrodes. It includes two electrode structures, connecting each of the electrodes to a measuring circuit. The first electrode structure is formed when a water (including some electrolytes which are naturally present in the atmosphere) condenses or precipitates on the exposed outer surface of the absorbent sheet. The second electrode structure is an electrically insulated conductive structure, isolated from the ambient atmosphere. A measuring circuit is connected through wires to apply a current to both first and second electrode structures to detect a change in capacitance between them.

The Capacitive Precipitation Gauge is provided in certain example embodiments. In one embodiment, the present invention concerns a precipitation gauge, intended for measuring amount and intensity of rainfall and other water precipitations at unstable environment conditions of agriculture and meteorology, consists of: ✓ a rainfall collector of electrically conductive water, ✓ a primary capacitor including: • at least one first electrode in form of a vertical elongate tube, made of insulated electrically conductive material, located within the rainfall collector • at least one second electrode, including an assembly, surrounding the first electrode, formed by a grounded electrically conductive cup, having top horizontal surface, and the conductive water that is in physical contact with the first electrode outer surface and in electrical contact with the grounded electrically conductive cup • a floating body, sliding along the first electrode inside the electrically conductive cup as result of the level changes of the water, intended for prevention salt and dirt accumulation, as well as water vapor condensation on the first electrode outer surface and damping the water level instability • wherein the contacted area of the conductive water with the first electrode is changed due to the water level changes, that, in turn, causes the capacitance changes of the primary capacitor, correlated with the water level changes ✓ a wetness sensor for measuring small amount of rainfall or other water precipitation, including a second capacitor that formed by: • at least one third electrode, including an assembly of a vertical electrically conductive bare grounded tube and a water absorbent sheet, having a top and bottom surfaces, attached to the upper horizontal end of the electrically conductive bare grounded tube by a conductive fixing cover, which in electrical contact with both the absorbent sheet top surface and electrically conductive bare grounded tube • at least one fourth electrode, formed by an insulated electrically conductive grid, attached to the bottom surface of the water absorbent sheet • wherein the capacitance of the second capacitor depends on existing and amount of water between the top and bottom surfaces of the water absorbent sheet ✓ a siphon, intended for the rainfall collector self-emptying, that includes assembly of: • the grounded electrically conductive cup, surrounding the first electrode • a non-conductive tube, mounted inside the first electrode tube, where its top end is at some distance from the top horizontal surface of the grounded electrically conductive cup • wherein the rainfall collector is self-emptied after said water level achieves to said non-conducive tube top end, inside said grounded electrically conductive cup ✓ a measuring circuit, providing an output signal, indicating changes in capacitance of the first and second capacitors, during rainfall or other water precipitation, ✓ a central processing unit connected to the measuring circuit, programmed to compute amount and intensity of the rainfall or other water precipitation every given time, ✓ a wireless data transmitter to transmit the measurement data to user’s devices.

In other embodiment of the present invention, the wetness sensor is used for measuring dew condensation and wetness duration on plant leaves and determining water condensation on agricultural products in cooling rooms.

In additional embodiment of the present invention, the water level measurement device of the precipitation gauge can be used for measuring the water level in all types of tanks in industry, meteorology and automatic home installations. It has advantages in the areas of measuring the amount of rain, the coolant level of engines in unstable conditions such as a car radiator, managing fertilization systems of crops in greenhouses and in open areas, controlling residential water supply systems, etc.

This embodiment concerns a fluid level meter of conductive liquid in a vessel, based on electrical capacitors, immersed into said liquid, including: • at least one first electrode in form of a vertical elongate tube, made of insulated electrically conductive material • at least one second electrode, including an assembly formed by the conductive liquid with a grounded electrically conductive tube, surrounding said first electrode; the conductive liquid is in physical contact with the first electrode outer surface and in electrical contact with the grounded electrically conductive tube • the first and second electrodes form a primary capacitor • a floating body, sliding along the first electrode inside the grounded electrically conductive tube during the liquid level changes, intended for prevention salt and dirt accumulation on the first electrode outer surface and damping the liquid level instability • a measuring circuit, providing an output signal, indicating changes in capacitance between the first and second electrodes during the liquid level changes • electric leads connecting the two electrodes tothe measuring circuit for applying an electrical field to them • a central processing unit connected to the measuring circuit, programmed to compute the liquid level changes every given time • a wireless data transmitter to transmit the liquid level changes to user’s devices • wherein the contacted area of the first electrode with the conductive liquid is changed due to its level change, that, in turn, causes the capacitance changes of the primary capacitor, correlated with the liquid level changes In the following, the present invention will be further described with reference to some non-limiting drawings and examples. 30 BRIEF DESCRIPTION OF THE DRAWINGS The objects, features, and advantages of the invention its organization, construction and operation will be best understood from the following detailed description, taken in conjunction with the accompanying drawings, on which: FIG. 1 illustrates a principal scheme of the capacitive precipitation gauge with a central siphon.

FIG. 2 illustrates a principal scheme of additional embodiment of the capacitive liquid level meter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described more fully hereafter with reference to the accompany drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the elements are not necessarily drawn to scale.

Reference is now made to FIG. 1 shows a principal scheme of a preferable embodiment of the present invention, illustrating a capacitive precipitation gauge with a central siphon. It includes a rainfall collector 1, having a funnel 2. A primary capacitor, which measures rain and other water precipitations, includes a first electrode, forming by an insulated conductive tube 3, electrically isolated from a surrounding rainwater 4. The second electrode of the capacitor is formed by surface of the rainwater 4 that is in physical contact with the insulated conductive tube 3 and in electrical contact, via a conductive grounded capped tube 5, with a measuring circuit 6, which placed under the rainfall collector 1. The rainwater is conductive since it contains naturally appearing salts present in the atmosphere. When rainwater level is changed, the area of the second electrode is changed and, as a result, the capacitance changes somewhat from 20 to 5picofarads that measured by the measuring circuit 6.

A floating disk 7, placed inside the conductive grounded capped tube 5, slides along the insulated conductive tube 3 and intends for cleaning its surface from salt/dirt deposition. Moreover, it prevents water vapor condensation on the surface of the insulated conductive tube 3 that can cause the measurement instability and errors. An assembly of the insulated conductive tube 3 and the conductive grounded capped tube 5, together with the floating disk 7, serves as mechanical damper in case of water level instability caused by rainfall and wind. Moreover, the conductive grounded capped tube 5, around the insulated conductive tube 3, prevents the gauge from the environmental electromagnetic interference, which decrease the water level measurement accuracy.

A siphon tube 8 is mounted inside the insulated conductive tube 3. When rainwater level is reached to the upper point of the siphon tube 8, the rainwater begins running out via the siphon from the rainfall collector 1 and it is self-emptied.

Further, a capacitive wetness sensor 9, including a second capacitor, is mounted at the top end of the rainfall collector. It is used for measurement of small amount of rainfall. It measures, also, presence, amount, and duration of dew, precipitated on the plans’ leaves. Moreover, it used as the reference of the higher point of the primary capacitor measuring range for compensations of environmental temperature changes and the sensitive elements contamination of the primary capacitor. A first electrode of the wetness sensor is formed by a conductive grounded tube 10, a water absorbent fabric sheet 11, attached to the upper end of the conductive grounded tube 10 by a conductive fixing cover 12. The second electrode of the wetness is formed by a grid 13, made of an insulated electrical wire, mounted closely to the fabric sheet bottom surface. When the fabric sheet 11 is wet, the capacitance between it and the grid 13 increased. Besides the fabric sheet wet area, the capacitance value depends, also, on amount of water between upper surface of the fabric sheet and the grid 13 surface. In this way, small amount of rainfall can be measured.

Moreover, the fabric sheet is served as artificial leaf for measurement of wetness present and duration on plant’s leaves. Water condensation or precipitation on the artificial leaf causes increasing conductive area of the wetness sensor first electrode that, in turn, increases tits capacitor capacitance. The condensed water is conductive 30 because it contains naturally appearing salts present in the air. The electrodes are connected to a measuring circuit 6.

In addition, a grounded conductive tube 14 together with the insulated conductive tube form a third reference capacitor, that used as the reference of the lower point of the primary capacitor measuring range for compensations of environmental temperature changes and primary capacitor electrodes contamination.

Furthermore, a temperature meter 15 is placed under the rainwater collector 1.

The precipitation gauge is further equipped with a wireless communications device to wirelessly communicate with a monitoring network, LAN or the like via Wi-Fi, WAN, Bluetooth or any other convenient wireless technology.

Claims (12)

1./ CLAIMS. What is claimed is: 1. A precipitation gauge, intended for measuring amount and intensity of rainfall and other water precipitations at unstable environment conditions of agriculture and meteorology, consists of: a) a rainfall collector of electrically conductive water b) a primary capacitor including: • at least one first electrode in form of a vertical elongate tube, made of insulated electrically conductive material, located within said rainfall collector • at least one second electrode, including an assembly, surrounding said first electrode, formed by a grounded electrically conductive cup, having top horizontal surface, and said conductive water that is in physical contact with said first electrode outer surface and in electrical contact with said grounded electrically conductive cup • a floating body, sliding along said first electrode inside said electrically conductive cup as result of the level changes of said conductive water, intended for prevention salt and dirt accumulation, as well as water vapor condensation on said first electrode outer surface and damping the water level instability • wherein the contacted area of said conductive water with said first electrode is changed due to said water level changes, that, in turn, causes the capacitance changes of said primary capacitor, correlated with the water level changes c) a wetness sensor for measuring small amount of rainfall and other water precipitation, including a second capacitor that formed by: • at least one third electrode, including an assembly of a vertical electrically conductive bare grounded tube and a water absorbent sheet, having a top and bottom surfaces, attached to the upper horizontal end of said electrically conductive bare grounded tube by a conductive fixing cover, which in electrical contact with both the top surface of said absorbent sheet and said electrically conductive bare grounded tube • at least one fourth electrode, formed by an insulated electrically conductive grid, attached to the bottom surface of said water absorbent sheet • wherein the capacitance of said second capacitor depends on existing and amount of water between the top and bottom surfaces of said water absorbent sheet d) a siphon, intended for said rainfall collector self-emptying, that includes assembly of: • said grounded electrically conductive cup, surrounding said first electrode • a non-conductive tube, mounted inside said first electrode tube, where its top end is at some distance from the top horizontal surface of said grounded electrically conductive cup • wherein said rainfall collector is self-emptied after said water level, inside of said grounded electrically conductive cup, achieves to said non-conducive tube top end e) a measuring circuit, providing an output signal, indicating changes in capacitance of said first and second capacitors, during the water precipitations f) a central processing unit connected to said measuring circuit, programmed to compute said water precipitations amount and intensity every given time g) a wireless data transmitter to transmit said measurement data to user’s devices.

2. The precipitation gauge according to claim 1, wherein said wetness sensor sensitivity may be changed by changing said water absorbent sheet material and thickness.

3. The precipitation gauge according to claim 1, wherein said wetness sensor capacitor serves as reference for said primary capacitor self-calibration during the rainfall, to reduce the environment temperature influence on the measurement accuracy.

4. The precipitation gauge according to claim 1, wherein, during the rainfall, electrical resistance between said electrically conductive bare grounded tube and said insulated electrically conductive grid of said wetness sensor is used as means for correction of measurement errors caused by variations of salts content in the water.

5. The precipitation gauge according to claim 1, wherein said floating body includes a fifth horizontal insulated electrode that forms, with said water horizontal surface, a third alignment capacitor that is used for the measurement and correction of the precipitation gauge inclination relative to the vertical, during its installation and working.

6. The precipitation gauge according to claims 1 or 5, wherein said fifth electrode is, also, used, for regular calibration of said primer capacitor in the field to reduce influence of its contamination, the water mineral content and temperature, as well as external electromagnetic interference.

7. The precipitation gauge according to any one of claims 1 to 6, wherein for reducing influence of contamination, the water mineral content and temperature, as well as external electromagnetic interference on its measurements, it additionally includes a fourth reference capacitor, intended for said primer capacitor self-calibration in the field, comprising: • at least one sixth electrode in form of an elongate tube, made of insulated electrically conductive material • at least one seventh electrode in form of an electrically conductive tube, surrounding said sixth electrode

8. The precipitation gauge according to claim 1, wherein said wetness sensor is used for measuring dew condensation and wetness duration on plant leaves and determining water condensation on agricultural products in cooling rooms.

9. A fluid level meter of conductive liquid in a vessel, based on electrical capacitors, immersed into said liquid, including: • at least one first electrode in form of a vertical elongate tube, made of insulated electrically conductive material • at least one second electrode, including an assembly formed by said conductive liquid with a grounded electrically conductive tube, surrounding said first electrode; said conductive liquid is in physical contact with said first electrode outer surface and in electrical contact with said grounded electrically conductive tube • said first and second electrodes form a primary capacitor • a floating body, sliding along said first electrode inside said grounded electrically conductive tube during said liquid level changes, intended for prevention salt and dirt accumulation on said first electrode outer surface and damping the liquid level instability • a measuring circuit, providing an output signal, indicating changes in capacitance between said first and second electrodes during said liquid level changes • electric leads connecting said two electrodes to said measuring circuit for applying an electrical field to them • a central processing unit connected to said measuring circuit, programmed to compute said liquid level changes every given time • a wireless data transmitter to transmit said liquid level changes to user’s devices • wherein the contacted area of said first electrode with said conductive liquid is changed due to its level change, that, in turn, causes the capacitance changes of said primary capacitor, correlated with the liquid level changes.

10. The fluid level meter according to claim 9, intended for liquid level measurement at the bottom of said vessel, wherein said first electrode includes an insulated third electrode attached to said vertical elongate tube bottom end that forms an additional second capacitor with said conductive liquid horizontal surface of said second electrode.

11. The fluid level meter according to claims 9 or 10, wherein said first and third electrodes forms third reference capacitor, intended for regular calibration of said first and second capacitors in the field.

12. The fluid level meter according to claim 9, wherein said coaxial first and second electrode tubes are cylindrical. The inventor: Igal Zlochin, 1./62 Dolphin Str. Tirat Carmel, 3950814