Abstract:
A rain gauge device is provided that uses a plurality of conductivity sensors to determine liquid levels. Certain rain gauge devices include a plurality of conductivity sensors fixed along the length of a support member, wherein each conductivity sensor comprises at least two selectable electrodes for sensing the presence of a liquid by measuring a conductivity of the liquid between these electrodes when a liquid is present between the sensing electrodes, and an electronic command unit adapted to apply a voltage between a common electrode and a selected electrode. Level measuring devices are also provided that comprise a collector, a measuring tube, a plurality of conductivity sensors and an electronic command unit for applying a voltage across the conductivity sensors and for converting the conductivity measured into a digital output for each increment. Methods of use and operation are also provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to level measurement devices for liquids and more particularly, to level measurement devices that sense liquid levels by detecting the rail to rail voltage between a queried level sensing electrode and a reference electrode. Accordingly, the reference electrode is either “on” or “off” depending upon whether a liquid is present at a queried level electrode. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many devices have been proposed for measurement of rain. One of the most primitive means for measuring rain is placing a tube marked with measurement increments in an outdoor area exposed to the rain. Other means include the use of sight glasses, magnetic and mechanical float level sensors (including magnetostrictive, resistive chain level sensors), pneumatic level sensors (nitrogen bubblers), microwave/radar level sensors, optical level sensors, ultrasonic or sonar level sensors, hydrostatic pressure sensors. 
         [0003]    The tipping bucket rain gauge is another alternative to the standard rain gauge for measuring rainfall. Two specially designed buckets tip when the weight of 0.01 inches of rain falls into them. When one bucket tips, the other bucket quickly moves into place to catch the rain. Each time a bucket tips, an electronic signal is sent to a recorder. To calculate the rainfall for a certain time period, the number of marks on the recorder is multiplied by 0.01 inches. The tipping bucket rain gauge is especially good at measuring drizzle and very light rain events. If the recorder is equipped with a clock, you can determine how much rain fell during certain time periods without actually being present at the station. However, one weakness of the tipping bucket rain gauge is that it often underestimates rainfall during very heavy rain events, such as thunderstorms. 
         [0004]    Unfortunately, the prior art conventional rain gauge devices suffered from a variety of disadvantages. Many devices suffered from low reliability, low accuracy, excessive maintenance and/or recalibration requirements, low repeatability or precision, high cost, and high failure rate mainly because the conventional rain gauge device utilized moving parts, which increased the occurrence rate of failures attributable to such parts. And, many of these conventional rain gauge devices do depend, in some fashion, upon the physical properties of the fluid such as density and temperature, and thus require recalibration and/or reconfiguration of the rain gauges in different conditions. 
         [0005]    Additionally, the prior art level rain gauge devices are not suited for precisely measuring rainfall accumulation over time and are not well adapted to providing necessary warnings of impending floods. This is a major draw back in the prior art. Increasing urban development, subsidence of land due to consumption of ground water, and increasing severity of weather conditions are increasing the frequency and severity of flooding in many areas. The National Oceanic &amp; Atmospheric Administration (NOAA) estimates around 5,321 flash flood deaths in the United States between from 1960 to 2006. NOAA warns that flash floods and floods are the number one weather-related killer, with around 140 deaths recorded in the United States each year. Floods on average are also responsible for $4.6 billion in damages in the each year in the United States alone. 
         [0006]    Given the gravity of flooding problems in the United States and abroad, a need exists for accurate and reliable measurement devices capable of measuring an accumulation of rainfall that are able to warn surrounding residents and weather stations of flood conditions and thereby allow for sufficient time to evacuate low-lying areas. Accordingly, it would be desirable to have rain gauge devices that rely less on moving parts, and the density properties of fluids in order to obtain an accurate measurement heading. Importantly, a gauge that provides a simple “on” “off” signal at a measurement increment is needed. Accurate measurements of rainfall also can be used to check alternate rainfall measurements such as radar, and calibrate them, in order to predict aquifer usage for crop watering, and predict water supply shortfalls. On a small scale, a homeowner could better judge how often to water his land, noting that areas served by radio or television stations are large and their coverage area varies greatly not only in the amount of rain measured but in whether there was rain. 
       SUMMARY OF THE INVENTION 
       [0007]    The rain gauge according to the invention uses and electric potential supplied to a common electrode to count the number of level increments in a measurement tube. When the measurement tube is full, the gauge empties the measurement tube, and begins the count at the bottom again. 
         [0008]    More particularly, when battery power is applied to the circuitry of the rain gauge according to the invention, a DC to AC circuit generates a current limited power for a common electrode. 
         [0009]    The 5 volt power supply also powers a microcontroller and other circuitry. The microcontroller drives an optical switch to close periodically as an indication of correct function, and a lamp flashes at the same time the optical switch is closed, indicating the same thing to an attending service person. The microcontroller selects detection points, i.e., electrodes to “poll”, one at a time, starting with the bottom of the tube until the selection is above the water line. At each selection the current detector informs the current detector informs the microcontroller that current is present, which drives a reed relay to output one switch closure, and advance to the next selection. When the “N”th switch detects water, in addition to driving the reed relay, the solid state switch turns a custom solenoid to quickly empty the tube. Note that the detection electrodes alternate left and right of the common electrode instead of a single row. In this way the electrodes are twice as far apart so that a drop of water hanging between electrodes doesn&#39;t falsely advance the selection. An on board button or an off board switch closure will also turn on the dump solenoid, usually to begin from scratch once each day. 
         [0010]    Advantages of the rain gauge devices of the present invention include, but are not limited to, high reliability, accuracy, high repeatability, low cost, and low failure rate. Additionally, the lack of moving parts in certain embodiments reduces the failures that would be attributable to such parts such as wear out, or the sticking of a magnetic float. Furthermore, because rain gauge devices of the present invention do not depend upon the physical properties of the fluid such as density and temperature, recalibration and/or reconfiguration of the rain gauge devices of the present invention are not needed. Also, the signal output is a rail to rail voltage 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying figures, wherein: 
           [0012]      FIG. 1  is a drawing of an exemplary rain gauge device according to first embodiment of the invention. 
           [0013]      FIG. 2  is a flow diagram of the electronic control unit of the first exemplary embodiment of the invention. 
           [0014]      FIGS. 3A and 3   b  are flow diagrams for the operation of the rain gauge device according to the first embodiment of the invention. 
           [0015]      FIG. 4  is a drawing of the collector according to the first exemplary embodiment of the invention. 
           [0016]      FIG. 5  is a drawing of the circuit board of the first embodiment of the invention. 
       
    
    
       [0017]    While the present invention is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0018]    The present invention generally relates to rain gauge devices for liquids and more particularly, to rain gauge devices utilizing conductivity sensing electrodes and methods thereof.  FIG. 1  is a drawing of a level measuring device according to an exemplary embodiment of the present invention. Level measuring device  100  comprises collector  110 , housing  170  and indicator devices  180 . Generally, the collector is connected to the housing and the housing is connected to the indicator devices, though the means and devices adapted to form those connections will be discussed in more detail below. 
         [0019]    As shown in  FIG. 4 , collector  110  is a vessel generally adapted to receive any falling liquid, e.g., rainfall, etc. and includes a funnel-like bottom portion  108  with at least as many sidewalls of a depth necessary to make a container-like structure. Located at the bottom of collector  110 , at the apex of the funnel-like portion  108 , is a hole  104  for connection to housing  170 . The hole  104  and the funnel-like portion may be centered, or as in the case of the exemplary embodiment, slightly off-center so as to minimize the distance between the collector  110  and the housing  170 . The hole may also include threading to removably connect the collector  110  to the housing  170 ; however, threading is not necessary. 
         [0020]    Preferably, collector  110  is a rectangular vessel with a screen  112  adapted to prevent large objects from entering the collector  110  positioned at either the top of the collector or inside the vessel portion. However, collector  110  might not have a screen, might be a conical funnel or any other such shape as could be calibrated to provide a mathematical relationship between the liquid in the collector and the liquid in the gauge (to be discussed in more detail below), collector  110  could even have a partial lid. Furthermore, collector  110  is constructed out of any material that would be robust in the collection of rain or other liquids. For example, collector  110  could be fabricated from aluminum, copper, stainless steel, or a strong synthetic material such as plastic for general usage, collector  110  might be made of a robust material such as a powdered metal in instances for applications where heavy rain could damage the collector, or collector  110  could be fabricated from polytetrafluoroethylene or similar, for use when measuring rain mixed with reactive chemicals, i.e. acid rain 
         [0021]    Referring back to  FIG. 1  and as previously mentioned, the collector  110  is connected to the housing  170 . Housing  170  includes a connecting tube  115 , a measuring tube  120 , and an electronic command unit  140 . Connecting tube  115  is provided to removably connect the collector  110  and the measuring tube  120 . As such, the connecting tube includes threads on both the distal and proximal ends so that the connecting tube may be screwed into place. However, one skilled in the art will appreciate that threading is not necessary on either the collector or the connecting tube  115 , and connecting tube  115  could be permanently attached to one or both of the collector and the measuring tube via friction fit, adhesive or some other similar attachment means. Connecting tube  115  may be fabricated from the same types of material as used to fabricate the collector  110 , but, it is not necessary for collector  110  and connecting tube  115  to be fabricated from exactly the same materials in the same device. One skilled in the art will also recognize that collecting tube  115  may not be entirely necessary, and accordingly some embodiments of the invention may connect the collector  110  directly to the measuring tube  120 . 
         [0022]    Connecting tube  115  connects the collector  110  to measuring tube  120 . Measuring tube  120  includes a shell  119 , long sensor electrode  172  and several level sensor electrodes  174  formed on a support member  130 , and valve  150 . Generally, shell  119  is a tube housing the liquid to be measured and the sensor electrodes  172  and  174 . It is preferable that the shell  119  is transparent, insulating material i.e., fabricated from glass, transparent plastic, or the like, so that the sensor electrodes  172  and  174  can be easily viewed for error diagnostic purposes and the electrodes  172  and  174  are electrically isolated. However it is not necessary that the shell  119  be transparent or insulating (although shells fabricated from conductive materials require the addition of insulators for the invention to be operable) and shells fabricated from other materials are within the scope of this disclosure. 
         [0023]    The long sensor electrode  172  and level sensor electrodes  174  are disposed on a support member  130  inside the shell  119 . The long sensor electrode  172 , disposed bisecting and down the length of the support member  130 , provides a voltage which the incoming rain connects to the level sensor electrodes  174 . The level sensor electrode  174 , formed on alternating sides of and perpendicular to the long sensor electrode  172 , each receive an electric potential through the water. Importantly, the sensor electrodes  174  are disposed according to the mathematical relationship between the area of the measuring tube  120  and the area of the planar surface  106  of the collector  110 . Namely, the ratio of the area of the planar surface  106  to the area of the tube  120 , multiplied by the desired measured increments, provides the spacing for the electrodes. 
         [0024]    For example, where the ratio of the area of the planar surface  106  to the area of measuring tube  120  is 24/1, as in the exemplary embodiment of  FIG. 1 , then the level of liquid in the measuring tube  120  would be 24 times the level of liquid in the collector  110 . Thus, for a desired measurement resolution of 1/100 of an inch or 0.01 inches, the level sensor electrodes would be placed 0.24 inches apart, i.e., sensing electrode S 1  is 0.24 inches vertically below sensing electrode S 2 . Sensing electrode S 2  is 0.24 inches below S 3 , and so forth. Thus, one skilled in the art will recognize the various combinations for number of electrodes, measurement resolutions and collector areas that can be accommodated with the above formulae, without departing from the spirit and the scope of this disclosure. 
         [0025]    Moreover, while there are multiple methods for fabricating the support member  130 , the long sensor electrode  172  and the multiple level sensor electrodes  174 , preferably, support member  130  is fashioned from an insulator, i.e., a circuit board, so that the long sensor electrode  172  and each of the level sensor electrodes  174  are electrically isolated. Sensor electrodes  172  and  174  and associated electrical connections to the electronic command unit  140  are thereby formed as wiring on the support member using standard printed circuit board techniques. It is further preferred, as shown in  FIG. 5 , that the same board used to mount the circuitry of the electronic command unit  140  is used as the support member  130 , and that the connection from the sensor electrodes  172  and  174  be formed as traces thereon. This configuration allows for easy replacement of circuitry components and uniform installation. However, the support member  130  and board mounting the electronic command unit  140  could be formed as separate members so that measuring tube  120  may be immersed in a liquid or fluid. Electronic command unit  140  may be in also be in or covered with a liquid-tight insulator, e.g., potting compound that doesn&#39;t absorb moisture, to prevent damage to the electronic components of the electronic command unit  140 . Moreover, one skilled in the art will recognize that there are many more alternatives and/or equivalent methods for mounting the sensor electrodes and providing wired connections between the sensor electrodes and the electronic command unit, all of which are incorporated herein. 
         [0026]    Finally, the measuring tube  120  includes valve  150 , which releases liquid from measuring tube  120 . Valve  150  is preferably formed at the bottom of measuring tube  120 . Valve  150  may be any commercially available valve that provides a tight seal to measuring tube  120 , however, in preferred embodiments, valve  150  is a high-flow solenoid valve capable of coupling to the electronic command unit  140  and providing a quick, wide opening to allow for the rapid discharge of liquid. 
         [0027]    As shown in  FIG. 1 , the measuring tube  120  is connected through the sensor electrodes  172  and  174  to the electronic command unit  140 , which will now be described in detail with reference to  FIG. 2 . The electronic command unit includes a electrode select circuit  400 , a DC/AC converter  402 , a microcontroller  404  having a memory  406 , power supply  408 , switches  410 , common electrode  414  programming access point  416 , remote dump switch  418 , on board push button  420 , solenoid  422 , switch output  424 , and auxiliary output  426 . Common electrode  414  is connected through a current detector to a DC/AC converter  42  and power supply  408 . Together the current detector, DC/Ac converter  402  and power supply charge common electrode  414 . 
         [0028]    The microcontroller  404  forms “the brains” of the invention. The microcontroller  404  converts a digital signal indicative of the liquid level received from the current sensor when electrode select circuitry  400  draws current, into an output “count”, or switch closure. Microcontroller  404  is connected to the DC/AC converter  402 , power supply  408 , access points  420 ,  418 , and  416 , custom solenoid  422 , switch closure output  424 , and auxiliary output  426 . The microcontroller  404  couples to the DC/AC converter  402  to control the power delivered from the power supply  408  to the common electrode  414 . Microcontroller  404  also connects to the electrode select circuitry  400  to both send a “polling” signal to each of the switches  410  and receive a signal from the current detector indicative of the water level in the measuring tube. Microcontroller  404  controls both the solenoid  422 , which dumps the measuring tube, and an output terminal, which generates a switch closure to a remote location. The microcontroller  404  may also be coupled to an auxiliary output, in case data from the switches from the switches needs to be processed in another way, e.g. converted to a display, instead of just sending pulses to reflect proper functioning. Microcontroller  404  is also joined to several actuators  402 ,  418 , and  416 . On board push button  420  activates solenoid  422  through the microcontroller  404 . Remote dump switch  418  is remotely connected to the solenoid through the receiver associated with remote dump switch  418  and programming access  416  allows a programmer to access microcontroller memory  406  to program the microcontroller  404 . 
         [0029]    While power supply  408  may continuously power the level measuring device, power supply  408  might also include a timer (not shown) The timer could have a “run” mode, a “sleep” mode and a “poll” mode. When there is no liquid in the collector  110 , the timer shuts off the power supply  408 , or enters “sleep” mode. After a certain time interval, the timer re-powers the circuitry of the device and goes into “poll” mode, i.e., powers on the system and checks the microcontroller  404  for a signal for a pre-determined time period. If a signal is received by the microcontroller  404 , the microcontroller  404  sends a signal to the timer to switch to “run” mode. The timer then periodically checks the microcontroller  404  to see whether input data is being received by the microcontroller  404 . If no data is being received by the microcontroller  404 , the timer switches the circuitry of the device back to “sleep” mode. In this way, the timer enables the level measuring device to conserve power. 
         [0030]    Although many variations exist for querying a plurality of sensing electrodes, and such variations are recognized as within the skill of a person of ordinary skill in the art with the benefit of this disclosure, the operation of the level measuring device according to an exemplary embodiment of the present invention will now be described with reference to  FIGS. 1 &amp; 2 . In its simplest form, rain is received by collector  110 , and travels through the connecting tube  115  to the measuring tube  120 . Simultaneously, the long sensing electrode receives power from power supply  408 . If there is a liquid present in the measuring tube, current flows to a level sensing electrode  174 . The microcontroller  404  polls the level sensing electrodes  174 , S n , n being equal to one of the plurality of level sensing electrodes formed on the support member  130 , to determine the presence of water and then outputs a switch closure and increments n so that the system can poll the next electrode. Once the electronic command unit receives no voltage from the nth electrode, the microcontroller  404  holds the count for the first electrode not conducting, i.e. The value of (n) stored in memory for that electrode polled to conduct. Periodically, microcontroller  404  re-polls the electrodes to determine whether electrode n is conducting, and if so continues on to n+1. If the highest possible level sensing electrode in the measuring tube is evaluated as in the presence of liquid, the microcontroller also sends a signal to dump the contents of the measuring tube  120 . 
         [0031]    To compensate for rain passing through the measuring tube  120  during the activation of solenoid  422 , the microcontroller calculates the missed rain based on the rainfall rate just prior to dumping, and accumulates fractional hundredths of an inch until that result exceeds 1/100 inch of rain. Then an extra switch closure is emitted at  424  during dump. For example, let the error add up to 0.008 inches during one dump. If during the next dump an error of 0.005 inches is calculated, then the total rain missed would be 0.013 inches. The extra switch closure is sent, and the accumulated error is reduced to 0.003 inches to be included in the next dump&#39;s calculation. For predictability during manual dumps the accumulated error us zeroed out. This helps to check factory calibration and offers a clean start for those who empty the rainwater daily, thus avoiding complications from long term evaporation. 
         [0032]    The operation of the rain gauge according to the invention will now be described in reference to  FIGS. 3A and 3B . The microcontroller is initialized in step  600 , i.e., turned on, and the scan position for the microcontroller is set at bottom level in step  602 . In step  604 , the microcontroller queries the power supply to ensure that the battery voltage is above a minimum voltage. If so, it sets an invalid scan position to lower power consumption in step  606 . The microcontroller then sets an alarm flag to enable a double blinking light in step  612  and then re-queries the battery voltage to see if it&#39;s below the minimum in step  620 . As long as the battery voltage is below a minimum amount, the system returns to step  604 , where the battery voltage was initially queried. If the battery voltage is determined to be above a minimum a mount again, the microcontroller checks to see if a manual or an external dump is requested in step  608 , and if such a request has been made, the microcontroller resets the fractional pulses to zero in step  610 , runs a dump cycle in steps  634 , checks to make sure the dump is successful in step  638  and then sets the scan position to a bottom level in step  642 , thereby returning once again to step  604 . If the manual or external dump is not request in step  608 , the scan position is queried too make sure that it&#39;s not the maximum level step  614 . If the scan position is greater than the maximum level, the water in the measuring tube is checked to see if it&#39;s within maximum and minimum range in steps  616 , the fractional pulses are incremented according to rainfall rate and dump time in  628 , the system queries whether fractional pulses are greater than or equal to one in step  630 . If so, the queued pulses are increment and the fractional pulses are decreased in steps  632 . until the fractional pulses are less than one and a dump cycle can be run in step  634 . If the scan position in step  614  is below a maximum level, then the microcontroller queries the scan position to see if it is conductive in step  618 . The rainfall rate is calculated in step  624 , and the scan position is conductive, the queued pulses are incremented in steps  622 . The rainfall rate is calculated in step  624 , and the scan position is advanced in step  626 . The system then returns to steps  604  where the battery voltage is queried. If the scan position is not conductive in step  618 , the battery voltage is re-queried in step  604 , and the process begins again. It should be noted that after dump cycle  634 , in step  638  the microcontroller queries the system to make sure that the dump was successful, and if the dump was not successful, sets an alarm flag in step  636  and waits to receive an external or manual dump. If an external or manual dump signal is received, the alarm flag is cleared in step  640  and the scan position is returned to a bottom level in step  642 . 
         [0033]    The dump cycle will now be described in greater detail with reference to  FIG. 3B . In step  500 , the drain valve is opened and an LED is activated. In step  502  the scan position is set to the dump position and in step  504  the microcontroller queries the system to see whether the dump attempts are less than the maximum dump attempts. If so, in step  506  the dump timer is set and in step  508  the microcontroller checks to see whether the timer is cleared. If not, the microcontroller ensures that the battery voltage is above the minimum in step  510  and in step  512  checks to see whether or not it is a first dump. If it is the first dump, the microcontroller checks to see whether or not it is conductive in step  514  and if so, the system returns to clearing the dump timer in step  508 . If the scan position is not conductive the drain valve is closed and the LED is deactivated in step  516 . In step  518  the post-dump delay timer is set and the system waits for it to expire. In step  520 , the microcontroller checks to see whether or not the current scan position is conductive, and if not, sets a scan position to the bottom level in step  522  and in step  530  it signals that there was a successful dump and returns to the main loop. If the current level is conductive in step  520 , then the dump attempt counter is incremented ( 532 ) and then the drain valve is open is step  534 . The system returns to checking whether the dump attempts are greater than the maximum dump attempts in step  504 . If the dump attempts are greater than the maximum dump attempts in step  504 , an alarm flag is set to double blink ( 524 ), in step  526  the scan position is set to invalid to lower the power consumption in step  526  and in step  528  there is a failure indicated and the program returns to the main loop. 
         [0034]    The above description is of the general features of device  100 , however there are many other additions to the devices that one skilled in the art could incorporate into the exemplary embodiments. For example, an embodiment could employ a six inch plastic tube that measures a liquid column of fluid with the described herein 0.24 inch spacing between level sensing electrodes. The collector would therefore have an opening 24 times the measuring tube circumference, and each increment between the level sensing electrodes would represent 1/100 of an inch of rain. The next to highest electrode would cause the solenoid valve to dump, and the next 6 inch column of water would be measured. The circuitry to perform these operations would be a 12 volt battery with a five volt regulator supplying power to the microcontroller. An oscillator would generate a 600 HZ AC voltage and the AC voltage would be transformed from 5 volts to 120 volts rail to rail. The microcontroller would scan the electrodes, i.e., one at a time and look for a change between liquid conduction and open circuit. At the next to last electrode, the microcontroller would signal the solenoid to send a dump signal and the measuring would start again at the next successive number in the electrode count. An embodiment implemented as described has an accuracy of approximately 1%. 
         [0035]    One skilled in the art will appreciate the advantages of the instant invention including, but not limited to, low maintenance operation (routine debris removal is all that is needed), ability of the unit to communicate with remote terminals, digital measurement capabilities, no required calibration of the sensors, individual sensing points may be internally hardwired and may be fully encapsulated between a stainless steal backing and an ABS front strip, a special circuit may be added to reduce possible damage by lightning or system transients, all construction materials may be compatible with hazardous environments in outdoor applications, low cost construction, and temperature changes down to just above freezing do not affect the sensor&#39;s accuracy. 
         [0036]    The present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.