Abstract:
A system for estimating a flowable substrate level in a storage unit is disclosed. In one embodiment, the system includes a transmitter and a conductor that extend downwardly into a grain storage bin, which cycles through a range of frequencies in order to determine the resonant frequency of the conductor which changes depending on the amount of grain in the bin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 62/033,040, filed Aug. 4, 2014, entitled “System for Sensing Flowable Substrate Levels in a Storage Unit,” which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Compartments such as bins, tanks, elevators, terminals, and silos are commonly used to hold bulk materials such as grains, woodchips, coal, etc. for storage. For example, in the agricultural context, grain storage units, commonly called “grain elevators,” “grain bins,” or “grain terminals” are used to store various forms of flowable substrates such as wheat, rice, corn, etc. For simplicity, the term grain is used herein to refer to any type of flowable substrate. Likewise, the term grain bin is used herein to refer to all structures for storing flowable substrates. 
     It is very important to the grain, feed, seed, and ethanol industries to be able to ascertain the correct amount of grain housed in grain bins. Knowing the correct inventory is essential to the production of goods and therefore to the financial performance of the business. Getting an accurate measurement, however, can be very difficult. Grain is generally deposited into a grain bin from one location near the top of the container, but for various reasons, however, the grain inside the grain bins may come to rest in uneven, non-uniform levels. This uneven surface makes it very difficult for workers to safely assess accurate volumes. 
     Manual measurements of grain levels can be dangerous. For example, bins can develop hazardous atmospheres, which can limit the amount of oxygen available for breathing. In addition, grain can clump together from moisture or mold, which creates an empty space beneath the grain as it is removed from the bin. The “bridging” effect that forms from this circumstance can prove to be deadly to a worker who stands on the clumped grain. If the clumped grain collapses into the open area below, a worker standing on the collapsing grain could fall victim to an avalanching effect, which has the potential to burying the worker. 
     Systems for determining grain levels in grain bins without human interaction have been described in prior art. Single point measurements using technology such as bobs, guided wave radar, open air radar, and ultrasonic have been used to increase the accuracy of grain measurements. Multiple point measurements that implement technology such as 3D level scanners and bob systems are able to measure the level of grain at multiple points in the bin. Multiple point measurement systems that can scan the surface of the grain are able to take multiple measurements at once to better account for variations in the topography of the grain. Single and multiple point measurement systems, however, require new, expensive scanning hardware to be mounted to one or more points on each grain bin. The technologies used to measure the grain must be designed to not generate sparks that could ignite flammable suspended particulate matter in the grain bin. 
     It is thus desirable to provide a system for accurately measuring the amount of grain housed within a grain bin in real time safely and efficiently. 
     SUMMARY 
     In general terms, this disclosure is directed to estimating the level of flowable substrate in a storage unit. In one possible configuration and by non-limiting example, the present disclosure describes a system for estimating the amount of a flowable substrate in a storage unit comprising: a transmission line configured to extend from a top portion of a storage unit to a bottom portion of the storage unit, a transmitter electrically connected to the transmission line at a lower end portion of the transmission line; a conductor extending from a top portion of a storage unit to a bottom portion of the storage unit; a receiver positioned at a top portion of the conductor; a microprocessor configured to cycle through frequencies to be transmitted by the transmitter and identify the frequency that corresponds to the resonant frequency of the conductor; and wherein the resonant frequency of the conductor changes and is correlated to the length of the conductor that extends above the surface level of the flowable substrate in the storage unit. 
     In another embodiment, a system for estimating the amount of a flowable substrate in a storage unit is comprised of a transmission line configured to extend from a top portion of a storage unit to a bottom portion of the storage unit; a wire electrically connected to the transmission line, the wire configured to extend from a top portion of the storage unit to a bottom portion of the storage unit; electrical components arranged in series along the wire; a receiver located at the top portion of the wire; and wherein at least one characteristic of the signal transmission between the transmission line and the receiver is correlated to length of the wire that extends above the surface of the flowable substrate in the storage unit. 
     In another embodiment, a method of measuring a flowable substrate within a storage unit comprises the steps of: sending a radio signal from a first wire to a second wire, and analyzing the signal received via the second wire to estimate the amount of grain in the storage unit. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustrative embodiment of a storage unit containing two cables, surrounded by flowable substrate, for signal transmission and reception; 
         FIG. 2  is an illustrative embodiment of the storage unit shown in  FIG. 1  without flowable substrate therein; 
         FIG. 3  is a cable schematic of a transmission line connected to a plurality of serially connected inductors; 
         FIG. 4  is a cable schematic of a transmission line connected to a copper wire; 
         FIG. 5  is a cable schematic of a transmission line connected to a plurality of serially connected resistors; 
         FIG. 6  is a cable schematic of a transmission line connected to a plurality of serially connected capacitors; 
         FIG. 7  is a cable schematic of a transmission line connected to a plurality of serially connected resistors, inductors, and capacitors; 
         FIG. 8  is an illustrative embodiment of a storage unit comprising one cable connected to an antenna; and 
         FIG. 9  is a cross-section and front illustration of the contents of an example cable assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. The example embodiments set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the appended claims. 
       FIG. 1  is an illustrative embodiment of a storage unit  100  partially filled with a flowable substrate  120 . In the depicted embodiment, the system for estimating the amount of a flowable substrate  120  in a storage unit  100  is comprised of a transmission line  130  configured to extend from a top portion  140  of a storage unit  100  to a bottom portion  150  of the storage unit  100 ; a transmitter  160  electrically connected to a transmission line  130  at a bottom portion  150  of the transmission line  130 ; a conductor  170  acting as an antenna and extending from a top portion  140  of a storage unit  100  to a bottom portion  150  of the storage unit  100 ; a receiver  180  positioned at a top portion of the conductor  170 ; and a microprocessor  195  configured to cycle through frequencies  190  to be transmitted by the transmitter  160  to identify the frequency  190  that corresponds to the resonant frequency of the conductor  170 .  FIG. 2  is an illustrative embodiment of the storage unit  100  shown in  FIG. 1 , but with no flowable substrate  120 .  FIG. 2  illustrates the basic concept for determining the substrate level  110  of  FIG. 1 . 
     In the depicted embodiment dedicated microprocessor  195  is located within the storage unit  100  adjacent a bottom portion  150  of the transmission line  130 . In other embodiments the microprocessor  195  is located outside of the storage unit  100 . In an alternative embodiment a wire extends up alongside of the transmission line and out of the storage unit to a microprocessor that is capable of other function such as temperature monitoring. An example of such a microprocessor is Extron&#39;s BusMux Pro HD multiplexer. 
     As illustrated in  FIG. 1  and  FIG. 2 , a transmission line  130 , for example a coaxial cable, extends vertically from a top portion  140  of the storage unit  100  to a bottom portion  150  of the storage unit  140 . In one embodiment of the present disclosure, a transmitter  160  is attached to the transmission line  130  at some lower end portion of the transmission line  130 . Using a device containing a microprocessor  195 , the frequency  190  transmitted by the transmitter  160  is able to be tuned to a range of frequencies  190  to determine the resonant frequency  190  of the antenna. In one embodiment, the antenna is comprised of a conductor  170  such that when an electromagnetic wave is incident upon the conductor  170 , the conductor  170  intercepts some of the power contained in the electromagnetic wave. The incident electromagnetic wave produces a voltage at the antenna terminals, which is then analyzed by the receiver  180 . 
     In  FIG. 2 , the length of the conductor  170  (antenna) is known. The resonant frequency  190  of the antenna can be determined based on the known length of the conductor  170 . The transmitter  160  can be configured to transmit the resonant frequency  190  of the antenna. The radio signal transmitted at resonant frequency  190  in  FIG. 2  is received by the receiver  180  and read with almost no attenuation because there is a negligible amount of flowable substrate  120  in the storage unit  100  surrounding the conductor  170  to attenuate the radio signal. This resonant frequency  190  serves as a base value because at that frequency  190 , the entire length of the conductor  170  extends above the surface of a negligible to nonexistent surface level of flowable substrate  120 . Thus, a conductor  170  (antenna) of maximum length in the storage unit  100  represents a negligible flowable substrate level  110  at that point of measurement. 
     Referring back to  FIG. 1 , a storage unit  100  is filled with a flowable substrate  120 , but the exact substrate surface level  110  in the storage unit  100  is unknown. To determine the level of the flowable substrate  120 , the length of a conductor  170  (antenna) that extends above the substrate surface level  110  is needed. In one embodiment of the present disclosure, a transmitter  160  employing a microprocessor- 195  based system is configured to systematically transmit discrete frequencies  190  in a range of frequencies  190  until one of those frequencies  190  is read without attenuation by the receiver  180 . This cyclical process can be repeated automatically as many times and as often as needed by the operator. A flowable substrate  120  such as corn, for example, contains water molecules, which can attenuate the signal transmitted from the transmitter  160  at various frequencies high enough to be attenuated at a certain emitted power level. This attenuation in turn affects the resonant frequency  190  of the conductor  170  (antenna). 
     Once the transmitter  160  transmits a frequency  190  that is able to be read un-attenuated by the receiver  180 , the length of the conductor  170  that extends above the surface level  110  of the flowable substrate  120  in the storage unit  100  can be calculated. The receiver  180  communicates the un-attenuated signal frequency  190  to a set of electronics that then computes the length of the conductor  170  and then the surface level  110  of flowable substrate  120  in the storage unit  100 . 
       FIG. 3  is another embodiment of the present disclosure. A transmission line  310  is configured to extend from a top portion  140  of a storage unit  100  to a bottom portion  150  of a storage unit  100 . A wire consisting of inductors  340  connected in series extends from a top portion  140  to a bottom portion  150  of a storage unit  100  where it is electrically connected to a transmission line  310 . An antenna  350  located at a top portion  140  of a storage unit receives a signal where it is then processed by a receiver  330  to determine the flowable substrate level  110 . In an embodiment illustrated in  FIG. 3 , a signal of fixed frequency  190  is sent through the transmission line  310 . The signal then passes through one or more of the inductors  340  before it is received by the antenna  350  and receiver  330 . When a flowable substrate  120  is present, the signal must pass through the series-connected inductors  340  that are submerged in the flowable substrate  120 . The more flowable substrate present in a storage unit  100 , the more inductors  340  the signal must pass through before the signal can be read by the antenna  350  and receiver  330 . The receiver  330  measures the lag experienced by the signal as it passes through the inductors  340  submerged in flowable substrate  120 . The lag, or time deviation, experienced by the signal is interpreted by the receiver  330  and the flowable substrate surface level  110  is determined from the results. It should be appreciated that although the embodiment in  FIG. 3  uses inductors  340  connected in series, the present disclosure is not limited to only the use of inductors  340  as electrical components. 
     Referring to  FIGS. 4-7 , alternative configurations of the wire of  FIG. 3  are shown. In  FIG. 4 , a conductor, such as a copper wire  440  is used to determine the flowable substrate surface level  110  present in a storage unit  100 . In  FIG. 5 , resistors  540  connected in series along a wire are used to determine the flowable substrate surface level  110  present in a storage unit  100 . In  FIG. 6 , capacitors  640  connected in series along a wire are used to determine the flowable substrate surface level  110  present in a storage unit  100 . In  FIG. 7 , a combination of at least resistors  540 , capacitors  640 , and inductors  340 , all connected in series along a wire, are used to determine the flowable substrate surface level  110  present in a storage unit  100 . 
       FIG. 8  depicts another embodiment of the present disclosure, in which a single cable is used to determine the flowable substrate  120  surface level  110 . A frequency  190  signal is sent down the transmission line  130 , and a transmitter  160  transmits a frequency  190  signal inside the storage unit  100 . As the frequency  190  is tuned by the transmitter  160 , it is attenuated by the flowable substrate  120  in the storage unit  100 . At a specific resonant frequency  190  the signal is able to be recorded after the top of the flowable substrate surface level  110  without interference. An antenna  800  receives the signal with little interference, and a receiver  180  electrically connected to the antenna  800  interprets the signal to determine the substrate surface level  110 . 
       FIG. 9  depicts an example cable assembly  900  system that can be used for the aforementioned embodiments of the present disclosure. In the example illustrated by  FIG. 9 , a cable assembly  900  consists of a molding/sheathing  910  used to contain one or more cables or wires within the cable assembly  900 ; a cable rope  920  used for structural support within the storage unit  100 ; a transmission line  130  such as a coaxial cable  930 ; a grain level sensor  940 , and a thermocouple wire  950 . A thermocouple wire may be used in one or more of the previous embodiments as part of the present disclosure to measure a flowable substrate  120  level. Thermocouple wires  950  are used in prior art to determine the temperature at various locations along a y-axis orientation of a storage unit  100 . In some embodiments, a coaxial cable  930  and a grain level sensor  940  are connected using a splice  960  or other means to ensure the information contained transmitted signals is accurately relayed to a grain level sensor  940 . 
     The various embodiments described above are provided by way of illustration only and should not be construed to limit the claims attached hereto. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the following claims.