Abstract:
A magnetostrictive precipitation gage includes a catch tube having an upper opening configured to receive precipitation therein. A vertical magnetostrictive rod and corresponding magnetic float linearly displaceable thereon are used to determine the fluid level within the catch tube. More particularly, as the fluid level fluctuates in the catch tube, so will the vertical position of the float, which interacts magnetically with the magnetostrictive rod. Accordingly, the vertical position of the float may be detected to determine the fluid level within the catch tube, and calculations regarding precipitation may be performed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to precipitation gages and, more particularly, relates to a precipitation gage using a magnetostrictive transducer to measure precipitation levels. 
     2. Discussion of the Related Art 
     Precipitation gages are well known to include a generally cylindrical cavity having an upwardly facing opening configured to collect precipitation, such as rain or snow. Conventional precipitation gages typically include mechanical mechanisms that output signals indicative of the amount of precipitation within the cylinder. For instance, a precipitation gage may include a spring or other type of compressive element that is positioned at the bottom of the cylinder and compresses as precipitation accumulates within the cylinder. The amount of compression is thereby converted to the amount of precipitation based on the known spring constant. 
     Another precipitation gage currently used includes a pressure transducer that outputs signals corresponding to the amount of pressure sensed within the cylinder, which will change according to the amount of precipitation within the cylinder. 
     The amount of spring compression or, alternatively, the signals output by the pressure transducer are fed into a data manipulation system, which translates the signals into measured precipitation levels. Unfortunately, these precipitation gages are subject to fluctuations due to the wide variations in ambient temperature that occur throughout a given year, which affect the sensitivity of the spring constant, and additionally affect the ambient pressure which could thereby limit the effectiveness of a pressure transducer. Spring gages are additionally costly to manufacture. 
     What is therefore needed is a precipitation gage that is robust to temperature fluctuations, and that is relatively inexpensive to manufacture. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention, a magnetostrictive precipitation gage includes an elongated catch tube having an upwardly facing opening and a base and is configured to receive precipitation therein. A magnetostrictive transducer includes a rod extending upwardly from the base and a corresponding buoyant magnetized float that is linearly displaceable along the rod. Therefore, as precipitation accumulates within the catch tube, the rod senses the placement of the float and the magnetostrictive transducer outputs voltage signals to a data logger, which is configured to process the voltage signals and output data reflecting the precipitation levels over a given period of time. 
     These as well as other features and characteristics of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiment of the invention will be described with reference to the accompanying drawings. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
     FIG. 1 is a perspective view of a precipitation gage in accordance with one embodiment of the present invention; 
     FIG. 2 is a sectional side elevation view of the precipitation gage of FIG. 1; 
     FIG. 3 is a top plan view of the precipitation gage of FIG. 1; 
     FIG. 4 is a rod cover that may optionally be used in combination with the precipitation gage of FIG. 1; 
     FIG. 5 illustrates a schematic circuit usable in combination with the data collection circuitry in accordance with the precipitation gage of FIG. 1; 
     FIG. 6 is a schematic view of an evaporation pan gage employing a magnetostrictive transducer in accordance with the preferred embodiment; 
     FIG. 7 is a perspective view of a precipitation gage in accordance with another embodiment of the present invention; 
     FIG. 8 is a sectional side elevation view of the precipitation gage of FIG. 7; and 
     FIG. 9 is a top plan view of the precipitation gage of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIGS. 1-3, a precipitation gage  10  includes an elongated cylindrical catch tube  12  having a bottom wall  14  and defining an inner cavity  15  having an upper opening  16 . The upper walls  17  of the catch tube  12  are beveled so as to prevent the accumulation of snow on the catch tube, which could result in the accumulation of inaccurate precipitation levels within the catch tube  12 . The diameter of the catch tube is preferably between 6 and 12 inches, and is uniform throughout the tube so as to provide accurate measurements of precipitation. The upper walls  17  of the catch tube  12  are beveled so as to prevent the accumulation of snow on the catch tube, which could result in the accumulation of inaccurate precipitation levels within the catch tube  12 . The catch tube  12  may be made of a plastic, metal, fiberglass, or any other material suitable for collecting precipitation. A larger diameter of catch tube  12  is preferable so as to provide a greater sampling area for the precipitation gage.  10 . In operation, it is desirable to partially fill the catch tube  12  with antifreeze initially so that as precipitation falls, it melts, thereby increasing the accuracy of the precipitation gage  10 . The antifreeze also prevents fluid already in the gage from freezing. As precipitation accumulates, the antifreeze will become dilute, so the initial charge of antifreeze should be sufficiently deep so as to provide adequate protection as the catch tube  12  fills. A surface coating of oil on the top of the fluid in the catch tube  12  prevents evaporation of the fluid. 
     The precipitation gage  10  includes a magnetostrictive transducer  13  having a generally cylindrical magnetostrictive rod  18  extending upwardly from the bottom wall  14 . The upper walls  17  of the catch tube  12  are beveled so as to prevent the accumulation of snow on the catch tube, which could result in the accumulation of inaccurate precipitation levels within the catch tube  12 . Preferably, the rod  18  has a length of one foot to provide high precision in measurement, or can be up to two or three feet long for gages where considerable precipitation is expected with infrequent maintenance. It should be appreciated that a shorter rod  18 , while providing for greater accuracy, would necessitate emptying of the precipitation gage  10  at more frequent intervals. It has been determined that the precision of a gage  10  having a one-foot rod is approximately 0.005 inches using a commonly available data logger  26 . 
     A float  20  is mounted on the rod  18  for sliding displacement therealong, and contains a generally circular magnet therein. As a result, as the fluid level  22  lowers and rises within the catch tube  12 , the float  20  will be displaced up and down accordingly. The rod. 18  includes a magnetostrictive wire extending from the tip of the rod  18  through the bottom wall  14  and into a magnetostrictive transducer head  24 . The head  24  may be protected by the ambient environment by providing a housing that is attached to the outside of bottom wall  14  so as to encapsulate the head. For the sake of convenience and clarity, the combination of the housing and magnetostrictive transducer head will hereinafter referred to as the head  24 . The head  24  encloses electronics for use in combination with magnetostrictive wires enclosed within the rod  18  to produce a voltage output indicating the location of the float  20  with reference to the rod  18 . The magnetostrictive transducer is powered by a power supply  30  via electrical wire  32 . It has been determined that a relatively accurate and linear response may be obtained using a 12-volt power supply. One such magnetostrictive transducer is described in more detail in U.S. Pat. No. 4,839,590, the disclosure of which is hereby incorporated by reference. It should be appreciated, however, that alternative magnetostrictive transducer designs exist, and the present invention is not intended to be limited to the configuration described above. 
     With continuing reference to FIG. 1, a data logger  26  is connected to the magnetostrictive transducer head  24  via an electrical wire  28  that inputs varying voltage signals corresponding to the fluid level  22 , as indicated by the interaction between rod  18  and float  20 , from the head  24 . The data logger includes electronic circuitry to compute and output statistical information regarding precipitation levels that are experienced over a given period of time. While the catch tube  12  is illustrated as being generally cylindrical in accordance with the preferred embodiment, it should be appreciated that the tube may be of any other suitable configuration, for example, rectangular. Accordingly, the catch tube  12  is not intended to be limited to cylindrical structures. 
     Conventional magnetostrictive transducers may output voltages ranging from zero to 10 volts, while conventional data loggers are capable of reading up to 2.5 volts, and sometimes up to 5 volts. Accordingly, referring now to FIG. 5, the electrical connection  28  includes a voltage splitter  31 , which reduces the relatively high voltage output from head  24  to acceptable values that are processed by the data logger  26 . Specifically, the voltage splitter  31  includes a resistor  33  that is connected in series with a resistor  35  and the data logger  26 . One having skill in the art will recognize that the voltage drop in this configuration will equal the resistance of resistor  35  divided by the sum of resistances of resistors  33  and  35 . Accordingly in the illustrated embodiment, a ten voltage output from the head  24  will input to the data logger  26  as 10*(33/133)=2.5 volts. It should further be appreciated that if resistor  33  was modified to include a resistance of 33 kilo-ohms, the resulting input to the data, logger would equal 5 volts. 
     It should be recognized that the voltage splitter  31  described above may not be necessary in configurations wherein the magnetostrictive transducer outputs voltage values that are acceptable to the data logger and that alternative voltage splitter configurations may be necessary so as to accommodate various data loggers. 
     Referring to FIG. 4, a rod cover  36  includes a generally cylindrical pipe  34  having a conical top  38  and is hollow so as to fit over the magnetostrictive rod  18 . The diameter of the cover  36  is sufficiently large so as to fit over the float  20 . The cover  36  is particularly useful during deep snowfall events, where a danger exists that the float  20  could become covered by snow, thereby preventing an accurate response, which could render the precipitation gage  10  inoperative for a substantial period of time. The cover  36  further includes a base plate  40  to provide support to the cover when it is mounted within the catch tube  12 . One or more holes  42  extending through the pipe  34  near the bottom so as to permit precipitation entering the catch tube  12  to travel within the pipe, thereby activating the floater  20 . 
     Referring now to FIG. 6, an evaporation sensor  44  includes an evaporation pan  46  that is in fluid communication with a fluid reservoir  48 . Specifically, an elongated pipe  50  extends from the base of the evaporation pan  46  to the base of the fluid reservoir  48  and allows fluid within the fluid reservoir  48  to travel into the evaporation pan  46 . In operation, therefore, a known relationship exists between a decrease in fluid level  52  within evaporation pan  46 , and the corresponding decrease of the fluid level  54  within fluid reservoir  48 . The relationship depends largely on the diameter of the evaporation pan  46  with respect to that of the fluid reservoir  48 , as is understood to one having ordinary skill in the art. The fluid reservoir  48  operates in a similar manner with the precipitation gage as described in FIG.  1 . However, the rod  56  is suspended from the top of the catch tube  58  and has a float  60  that will lower as the fluid level  54  lowers, thereby providing a relationship between the evaporation rate and the fluid level  52 . Accordingly, the data logger  26  will provide data relating to the evaporation rate over a given period of time. 
     Referring now to FIGS. 7-9, a precipitation gage  110  in accordance with another embodiment is illustrated having reference numerals corresponding to similar parts of the precipitation gage  10  of FIGS. 1-3 incremented by one hundred. In particular, the precipitation gage  110  includes an elongated cylindrical magnetostrictive tube  141  disposed adjacent and connected to the catch tube  112  by one of any known suitable methods. A magnetostrictive transducer head  124  is disposed on top of the tube  141 , and is connected to a magnetostrictive rod  118  that extends downwardly therefrom and includes a float  120 , which operates as described above. An aperture  142  exists at the bottom between the tubes  112  and  141  to permit fluid entering the catch tube to flow into the magnetostrictive tube  141  to facilitate measurement of the fluid level  122 . The magnetostrictive tube  141  may be clear with having a fluid level sight gage to allow a user to obtain visual readings of the fluid level  122 . 
     The embodiment illustrated in FIGS. 7-9 allows increased ease of maintenance by allowing access to the precipitation gage  110  from above the fluid level  122 , thereby eliminating the need to drain the gage prior to maintenance. A stop may exist on the bottom of the rod to allow retrieval of the float  120  when the rod  118  is removed during, for example, rod replacement. It is furthermore recognized that the accuracy of the precipitation measurements is increased as the opening  116  of the precipitation gage  110  approaches ground level. Accordingly it is desirable to bury a significant portion of the precipitation gage  110 . Because the magnetostrictive head  124  is positioned on top of the tube  141 , the gage  110  may be buried while allowing access to the electronics for maintenance purposes. It should be appreciated, in this embodiment, that the diameter of the magnetostrictive tube  141  is preferably minimized to increase accuracy the correlation between the fluid level  122  detected in the magnetostrictive tube  141  and that in the catch tube. 
     The invention has been described in connection with what are presently considered to be the most practical and preferred embodiments. However, the present invention has been presented by way of illustration and is not intended to be limited to the disclosed embodiments. Accordingly, those skilled in the art will realize that the invention is intended to encompass all modifications and alternative arrangements included within the spirit and scope of the invention, as set forth by the appended claims.