Abstract:
A condition sensing system for a grain drying system can include a cable assembly and at least one sensor. The cable assembly can include a support cable and a data-conveying member. The sensor can detect in-grain humidity and/or temperature. The sensor can be coupled to the cable assembly between first and second ends of the assembly. A protective enclosure can enclose the sensor and a respective portion of the cable assembly. Further, in-grain humidity and/or temperature data can be transmitted from the condition sensing system to the grain drying system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/391,906, filed Feb. 24, 2009, the entirety of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    An important need exists to dry grain quickly and effectively after harvest to retain maximum quality, to attain a moisture content sufficiently low to minimize infestation by insects and microorganisms (e.g., bacteria, fungi, etc.), to prevent germination and to maximize consumer acceptability of appearance and other organoleptic properties. 
         [0003]    Grains are hygroscopic and will lose or gain moisture until equilibrium is reached with the surrounding air. Grains will dry until they reach their equilibrium moisture content (EMC). The EMC is dependent on the relative humidity and the temperature of the air. The relationship between EMC, relative humidity and temperature for many grains has been modeled by researchers: the results have been summarized in Brooker et al. (1974), Drying Cereal Grains, Westport: The Avi Publishing Company, Inc., 265 pp. For instance, EMC&#39;s for certain grains are shown in the chart immediately below. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Relative Humidity (%) 
               
             
          
           
               
                   
                 30 
                 40 
                 50 
                 60 
                 70 
                 80 
                 90 
                 100 
               
             
          
           
               
                 Grain 
                 Equilibrium Moisture Content (% wb*) at 25° C. 
               
               
                   
               
             
          
           
               
                 Barley 
                 8.5  
                 9.7 
                 10.8 
                 12.1 
                 13.5 
                 15.8 
                 19.5 
                 26.8 
               
               
                 Shelled Maize 
                 8.3  
                 9.8 
                 11.2  
                 12.9 
                 14.0  
                 15.6 
                 19.6 
                 23.8 
               
               
                 Paddy 
                 7.9  
                 9.4 
                 10.8  
                 12.2  
                 13.4 
                 14.8 
                 16.7 
                 — 
               
               
                 Milled Rice 
                 9.0 
                 10.3 
                 11.5 
                 12.6  
                 12.8 
                 15.4  
                 18.1 
                 23.6 
               
               
                 Sorghum 
                 8.6  
                 9.8 
                 11.0  
                 12.0  
                 13.8 
                 15.8 
                 18.8 
                 21.9 
               
               
                 Wheat 
                 8.6  
                 9.7 
                 10.9 
                 11.9 
                 13.6  
                 15.7  
                 19.7 
                 25.6 
               
               
                   
               
               
                 *wet basis 
               
               
                 Source: Brooker et al. (1974) 
               
             
          
         
       
     
         [0004]    There are two basic mechanisms involved in the drying process: the migration of moisture from the interior of an individual grain to the surface and the evaporation of moisture from the surface to the surrounding air. The rate of drying is determined by the moisture content and the temperature of the grain and the temperature, the relative humidity and the velocity of the air in contact with the grain. In general, higher airflow rates, higher air temperatures and lower relative humidities increase drying speed. The rate of moisture movement from high moisture grain to low relative humidity air is rapid. However, the moisture movement from wet grain to moist air may be very small or nonexistent. Also, higher airflow rates generally result in higher drying rates. 
         [0005]    Traditionally, grain crops were harvested during a dry period or season and simple drying methods such as sun drying were used. However, maturity of the crop does not always coincide with a suitably dry period. Furthermore, the introduction of high-yielding varieties, irrigation, and improved farming practices has led to the need for alternative drying practices to cope with the increased production, and grain harvested during the wet season as a result of multi-cropping. 
         [0006]    Among other techniques, in-line dryers have been used for drying the grain. However, these use high amounts of fuel and the dryers act like an oven and tend to cook out all of the moisture and over dry and crack the grain. As a result, it has become common for grain to be stored in bins and dried by mechanically moving air over and through the grain. This method is referred to as the “in-bin natural air drying” technique. 
         [0007]    The in-bin natural air drying technique has several advantages. It can increase the quality of the harvested grain by reducing crop exposure to weather and reduce harvesting losses, including head shattering and cracked kernels. It also reduces the dependency on weather conditions for harvest and allows more time for post-harvest field work. 
         [0008]    However, current in-bin natural air drying systems have several disadvantages. Grains can only be stored without significant deterioration for a period of time depending on the storage conditions, such as temperature and relative humidity. Thus, the EMC must be attainable within that period of time and thereafter maintainable. Drying fans are costly to operate: they should operate when the relative humidity level is low and temperature levels are generally warm. For instance, it is useless to run fans if it is raining. Also, hot spots, i.e., grain degradation, in the grain are difficult to prevent. Sensors for determining the condition of the grain placed throughout the bin help prevent hot spots. Also, it is preferable for the drying system to be centrally controlled, with remote access. 
       SUMMARY 
       [0009]    The improved grain drying system includes a master control unit external to the grain storage bin, which is preprogrammed with a desirable grain moisture content or EMC. Condition sensor assemblies mounted within the grain bin, and extending into the mass of stored grain, determine the relative humidity and the temperature of the grain within the grain bin. Also, sensors mounted in the bin&#39;s plenum determine temperature, relative humidity and air pressure. A weather station mounted externally of the grain bin determines the outside air temperature and relative humidity. Depending on the temperature and relative humidity of the atmospheric air and the temperature and relative humidity of the air in the mass of grain to be dried as determined by the sensor assemblies and the weather station, the master control unit selectively activates the grain bin&#39;s drying fan when needed and when it is efficient and effective to do so to achieve relatively efficient drying of the grain. A radio or cellular modem allows for communication of the grain&#39;s condition to a user&#39;s personal computer or a remote data center. 
         [0010]    The internal sensor assemblies are preferably secured to flexible cables hung or suspended within the grain bin at different levels at which the sensor assemblies will be surrounded by grain stored in the bin. The cable and rigid rod-like members support the sensors. The sensors may be secured in a spaced relationship along the cable so that the grain condition can be determined throughout the grain bin. Preferably, one cable&#39;s sensors all determine the relative humidity and at least one cable&#39;s sensors determine the temperature of the grain throughout the bin. The use of multiple cables with multiple sensors aids in accurately determining the grain&#39;s condition throughout the bin. 
         [0011]    A protective covering extends around each cable and the sensors mounted thereon. With a relative humidity sensor, the protective covering includes an opening that is substantially aligned with the sensor to facilitate the sensor&#39;s determination of the relative humidity. A filter member is sandwiched between each of the humidity sensors and the protective covering openings, to protect the sensors from particulate matter. A second protective covering extends around each of the sensing cables between adjacent sensors, with the lower end of the first protective covering extending over the upper end of the second protective covering and the lower end of the second protective covering extending over the upper end of the first protective covering, to further protect the sensor from grain particulate. 
         [0012]    Various objects and advantages of this invention will become apparent from the following description taken in relation to the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
         [0013]    The drawings constitute a part of this specification, include exemplary embodiments of the present invention, and illustrate various objects and features thereof 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective of a cluster of grain storage bins interconnected in accordance with the grain drying system of the present invention, with the remote, off-site communication shown diagrammatically; 
           [0015]      FIG. 2  is an enlarged, perspective view of one of the grain bins of  FIG. 1 , broken away to show the temperature and moisture cables of the grain drying system therein and with the grain removed for clarity; 
           [0016]      FIG. 3  is an enlarged, partial section of one of one of the grain bins of  FIG. 1  with the components of the grain drying system external thereto removed for clarity, showing the cables and the grain stored therein; 
           [0017]      FIG. 4  is a flow chart showing the grain drying system&#39;s control processing; 
           [0018]      FIG. 5  is a front diagrammatic view of the master control unit of the grain drying system; 
           [0019]      FIG. 6  is a front diagrammatic view of a distributed control unit of the grain drying system; 
           [0020]      FIG. 7  is a fragmentary front plan view of a relative humidity cable of the grain drying system with portions broken away to show a relative humidity sensor and the cable construction; 
           [0021]      FIG. 8  is an enlarged, and fragmentary side view of the relative humidity cable of  FIG. 7 , with portions broken away to show a relative humidity sensor; 
           [0022]      FIG. 9  is a cross-sectional view taken at detail  9 - 9  of  FIG. 8 , with the humidity sensor board shown in full for clarity; 
           [0023]      FIG. 10  is a fragmentary, front plan view of a temperature cable of the grain drying system with portions broken away to show a temperature sensor and cable construction; 
           [0024]      FIG. 11  is a front sectional view of a plenum sensor of the grain drying system mounted in the grain bin; 
           [0025]      FIG. 12  is a front view of a weather station of the grain drying system partially broken away to show the weather sensor therein; 
           [0026]      FIG. 13  is a top view of a temperature sensor board of the grain drying system; 
           [0027]      FIG. 14  is a top view of a moisture sensor board of the grain drying system; and 
           [0028]      FIG. 15  is a flow chart showing the fan control processing of the grain drying system. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
         [0030]    Now, referring to the drawings and specifically  FIGS. 1-3 , conventional grain bins  10  for storing harvested grain  11  are shown which have been modified to include a grain drying control system  20  of the present invention. Each bin  10  has a side wall  12 , a roof  13  and a plenum chamber  14  formed at the bottom of the bin  10 , covered by a perforated floor  15 . One or more fans  16  (and/or an optional heater(s), not shown) are installed outside each grain bin  10  adjacent the plenum chamber  14  to blow atmospheric or ambient air into the chamber  14  through the perforated floor  15  to dry or aerate the grain  11 . As the grain  11  dries, it forms zones, represented diagrammatically by zones  17 ,  18  and  19  as shown in  FIG. 3 . The dry grain  17  extends upwardly from the floor  15 , the wet grain  19  has been most recently harvested and is nearest to the top of the bin  10 , and the drying grain  18  is sandwiched between the dry grain  17  and the wet grain  19 . 
         [0031]    As shown in  FIGS. 1 and 2 , the in-bin natural or atmospheric air grain drying system  20  of the present invention includes a master control unit  22 , distributed control units  24 ,  25  and  26 , a relative humidity sensor cable or cable assembly  28 , temperature sensor cables or cable assemblies  30 , a plenum condition sensor assembly  32 , a weather station  34 , a radio or cellular modem  36  and a remote user interface  38 . Additionally, as shown in  FIGS. 7 and 10 , in-grain condition sensor assemblies  40  and  42  are secured along the respective cables  28  and  30 . Sensor assemblies  40  determine the relative humidity and the temperature of the grain  11  by measuring the temperature and the relative humidity of the air surrounding the individual granules of grain within the stored mass. Sensor assemblies  42  determine the temperature of the grain  11  again by measuring the temperature of the air surrounding the grain within the stored mass.  FIG. 1  shows a group of nearby bins  10 , each with the drying system  20  installed thereon, forming a cluster  21  of bins  10 . 
         [0032]    Each distributed control unit  24 ,  25  and  26  communicates with the master control unit  22 . Depending on the conditions detected by the sensor assemblies  32 ,  40  and  42  and the weather station  34 , and communicated to the master control unit  22 , the master control unit  22  selectively activates the drying fan  16  when it is efficient and effective to do so to achieve and maintain the grain&#39;s selected EMC based upon a comparison of the detected conditions relating to external temperature and humidity and the temperature and humidity within the mass of grain to be dried. The measured temperature and humidity within the plenum  14  may also be factors used to determine fan operation. Generally, if the external relative humidity is lower than the relative humidity within the mass of grain and the external temperature relatively high, the master control unit  22  will activate the fan  16 . The system  20  dries the grain  11  throughout the grain bin  10  to its selected EMC quickly and efficiently to help prevent over-drying or other grain degradation and allows for communication between the system  20  and the user with regard to the grain&#39;s condition. 
         [0033]    As shown in  FIG. 2 , the master control unit  22  is mounted on the exterior of the bin&#39;s side wall  12  near the fan  16  and at an easily accessible height from the ground. As shown schematically in  FIG. 5 , the master control unit  22  includes power circuitry  46 , isolation circuitry  48 , a real-time-clock  50 , non-volatile memory  52 , a power supply  53 , a microprocessor and firmware  54 , relays  56 , switches  58  and a terminal block  60 . The memory  52  stores the grain type and corresponding selected or desired EMC among other information as well as the time and date during periods when the system&#39;s input power supply  53  is off The microprocessor and firmware  54  run the software instructions required for the fan processing. The isolation circuitry  48  extends between the power circuitry  46  and the clock  50 , the memory  52  and the processor  54  to prevent damage to the connected devices in the case of an electrical surge. The relays  56  and switches  58  automatically activate the fan  16  through a pair of wires  62  that run between the master control unit&#39;s terminal block  60  and the fan  16 . 
         [0034]    The distributed control unit  24  is mounted on the roof of the grain bin  10  near the ends of the humidity and temperature cable assemblies  28  and  30 . It controls the sensor assemblies  40  and  42  on up to eight cable assemblies  28  and  30  for determining the in-bin grain conditions. Distributed control unit  25  is mounted on the side wall of the grain bin  10  near the plenum sensor  32  for controlling the plenum sensor assembly  32  and the weather station  34  and determining the out-of-grain environment condition. The distributed control unit  26  is preferably mounted on the roof of the grain bin  10  near the radio/modem  36  and controls the local communication between bins  10  and the remote communication with the remote interface  38 . 
         [0035]    As shown schematically in  FIG. 6 , each distributed controller  24 ,  25  and  26  includes power circuitry  66 , a microprocessor  68 , an input/output interface with sensor or cell modem/radio circuitry  70  and isolation circuitry  72 . Similar to the isolation circuitry  48  of the master control unit  22 , the isolation circuitry  72  extends between the power circuitry  66 , and the processor  68  and the I/O interface  70  to prevent damage to the connected devices in the case of an electrical surge. The distributed control units  24 ,  25  and  26  communicate with the master controller  22  via a pair of RS-485 communication wires  74 . 
         [0036]    As seen in  FIG. 2 , the wire pair  74  preferably connects the master control unit  22  and each of the distributed control units  24 ,  25  and  26  together in a daisy chain. The communication protocol parameters are: RS-485 for electrical signal levels; asynchronous 8-bit characters at 9600 baud with one start bit, one stop bit and no parity; and poll/response messaging where the master control unit  22  polls a specific distributed control unit  24 ,  25  or  26  for information and the distributed control unit  24 ,  25  or  26  sends a response. Each distributed control unit  24 ,  25  and  26  has an address assignment, so that each polling message contains an address field for the destination address, and each response contains an address field for the source address. 
         [0037]    As seen in  FIGS. 2 and 7 , a wire pair  75  is secured along the cables  28  and  30  to communicate the grain conditions from the sensor assemblies  40  and  42  back to the controller  24 . Similarly, the wires  75  interconnect the plenum sensor assembly  32  and the weather station  34  with the controller  25 . 
         [0038]    The sensor cables  28  and  30  include an upper end  76  and a lower end  77 . The upper end  76  of the cables  28  and  30  is secured to and hangs vertically from the roof of the grain bin  10 , with the lower ends  77  being spaced just above the perforated floor  15 . The upper end  76  of the cables  28  and  30  is secured to an eyebolt  78 . The eyebolt  78  is mounted through neoprene washers  80  and secured to the exterior side of the bin&#39;s roof  13  by a steel hanger  81  (only one shown in  FIG. 2 ). 
         [0039]    The cables  28  and  30  can be any desired length to fit within any grain bin  10 . As shown, one relative humidity cable  28  hangs from near the center of the roof  13 , with four temperature cables  30  spaced radially around the bin  10 , between the relative humidity cable  28  and the wall of the bin  10 . However, any number of cables  28  and  30  can be used and mounted in any configuration, as desired. 
         [0040]    As seen in  FIGS. 7 through 10 , the cable assemblies  28  and  30  are similarly constructed in many respects. They each include the communication wires  75  mounted to extend along the length of a main support cable  82 , with a group or string of sensor assemblies  40  or  42  secured in a spaced relationship along the wires  75  and the cable  82  as desired. However, it is preferable for the sensor assemblies  40  and  42  to be spaced approximately four feet apart along the cable&#39;s length. The cable  82  is preferably formed of a flexible, galvanized steel cable to provide each sensor cable assembly  28  and  30  sufficient strength. This is especially important when the grain  11  is added or removed from within the bin  10  which places the cables  28  and  30  under tremendous strain due to the pull on the cables  28  and  30 . 
         [0041]    The cables  28  and  30  are wrapped in protective tubing  92  and  93 . The protective tubing  92  covers the sensor assemblies  40  and  42  and each assembly&#39;s corresponding length of the wires  75  and the cable  82 , and the protective tubing  93  covers the length of the wires  75  and the cable  82  between adjacent sensor assemblies  40  and  42 . The tubing  92  and  93  is preferably polyvinyl chloride (PVC) shrink tubing, with tubing  92  having a ½″ diameter and tubing  93  having a ⅜″ diameter. 
         [0042]    Each segment of the tubing  92  has an upper end  94  and a lower end  96 . Similarly, each segment of the tubing  93  has an upper end  98  and a lower end  100 . The cable assemblies  28  and  30  are preferably constructed from their lower end  77  to their upper end  76 , with the upper ends  98  of the tubing segments  93  being overlapped by the lower ends  96  of the tubing segments  92  and the upper ends  94  of the tubing segments  92  being overlapped by the lower ends  100  of the tubing segments  93 . This construction prevents any grain  12  from becoming lodged in the cables  28  and  30  as it is deposited or removed from the bin  10 . 
         [0043]    The sensor assemblies  40  and  42  do differ from one another. The sensor assemblies  40  are mounted along the relative humidity cable  28  and include a sensor circuit board  84  having both a relative humidity (or moisture level) sensor  86  and a temperature sensor  87  thereon, whereas the sensor assemblies  42  are mounted along the temperature cables  30  and include a sensor circuit board  85  having a temperature sensor  87  thereon but no relative humidity sensor  86 . The circuit boards  84  and  85  are shown in  FIGS. 14 and 13  respectively. Up to thirty sensors  86  and  87  can be attached to the same cable assembly  28  or  30 . Thus, as shown in  FIG. 2 , the center relative humidity cable  28  detects moisture and moisture differences between vertical layers of the grain  11  in the bin  10 , and all of the cables  28  and  30  detect temperature and are useful in finding hot spots or areas in which the grain  11  may be undergoing a chemical change or degradation. 
         [0044]    Referring to  FIG. 8 , each relative humidity sensor  86  is covered with a mesh filter  110 . The filter  110  overlays the sensor  86 . The filter  110  helps prevent dust or grain particulate from damaging the sensor  86  and is preferably a very thin, fine polypropylene mesh material. 
         [0045]    Each sensor assembly  40  and  42  overlays a steel rod or nail  88  secured in place by two pieces of shrink tubing  90 . As best seen in  FIG. 9 , the sensor circuit boards  84  or  85  lay over the steel cable  82  and the rod  88 , which provide parallel supports for the circuit board  84  or  85 . The combined diameters of the cable  82  and the rod  88  are preferably substantially equal to the width of the circuit boards  84  or  85 . The wires  75  are secured by crimping them to the circuit boards  84  and  85  with fasteners  89 . This also aids in securing the circuit boards  84  and  85  in place. With the relative humidity sensor assembly  40 , the wires  75  lie along opposite sides of the relative humidity sensor  86  and over the mesh filter  110 , thereby securing the mesh filter  110  in place and providing protection to the sensor  86 . 
         [0046]    The rod  88  is preferably steel and three inches in length. It lies along and parallel to the cable  82  below the circuit board  84  or  85  and thereby provides rigidity to the cable assembly  28  or  30  where the sensor circuit board  84  or  85  lays so that the board  84  or  85  bears little, if any, shear force when the sensor cable assembly  28  or  30  is moved or rolled prior to installation or when jarred by grain  11  as the bin  10  is filled or emptied. Although nails are readily available, any rigid rod-like member may be substituted or utilized. 
         [0047]    The tubing pieces  90  secure the wires  75  and each end of the rod  88  to the cable  82  adjacent the ends of the sensor circuit board  84  or  85 , sandwiching the circuit boards  84  or  85  therebetween. Polyolefin shrink tubing is preferred because it has an integral adhesive that melts into the braiding of the steel cable  82  to secure and affix the wires  75 , the cable  82  and the rod  88  together. 
         [0048]    The shrink tubing  92  secures the circuit boards  84  or  85  to the cable  82 . The tubing  92  extends around the cable  82 , the circuit board  84  or  85 , the wires  75 , the rod  88  and the polyolefin shrink tubing  90  to secure these elements together and provide abrasion resistance. As best seen in  FIG. 8 , with the relative humidity sensor assembly  40 , the tubing  92  has apertures  112  therethrough. These apertures  112  are aligned over the relative humidity sensor  86  to allow air and moisture to exchange and equalize through the mesh filter  110  and the apertures  112 , between the sensor  86  and the grain  11 . As shown in  FIG. 8 , the tubing  92  includes three small apertures  112 ; however, the number of apertures may be varied. 
         [0049]    As generally shown in  FIGS. 2 , the cable assemblies  28  and  30  with sensor assemblies  40  or  42  mounted thereon are suspended from the ceiling of the bin  10  and extend toward the floor  15  prior to filling the bin  10  with grain  11 . The bin  10  is then filled with grain  11  so that the cable assemblies  28  and  30  with sensor assemblies  40  and  42  mounted thereon extend into the mass of the stored grain  11 . Air voids are formed between the individual seeds or grains  11 , and it is the relative humidity and temperature of the air in the voids that is measured by the sensor assemblies  40  and  42  to determine the moisture content of the grain  11 . 
         [0050]    As seen in  FIGS. 2 and 11 , the plenum sensor assembly  32  is mounted in and extends through the side wall  12  of the grain bin  10  into the plenum chamber  14 . The plenum sensor assembly  32  includes a breathable plastic tube  116  with both relative humidity and temperature sensors  118  and  120  mounted therein to measure the temperature and the moisture content of the air being pushed into the grain  11  by the fan  16 . The plenum sensor assembly  32  also includes an air pressure tube  122  for conducting the air pressure within the plenum chamber  14  to the distributed control unit  25  where it is measured. This allows the system to determine if the fan  16  is running Also, if the grain  11  within the bin  10  is very wet, the air pressure increases. 
         [0051]    The weather station  34  is shown in  FIGS. 1 ,  2  and  12 . The weather station  34  includes a pair of sensor boards (not shown) for measuring the relative humidity and air temperature outside the grain bin  10 . The sensor boards are mounted within a breathable plastic tube  130  and a vented radiation shield  132  to protect them from the environment. Preferably, the weather station  34  is colored white to reflect the sun&#39;s rays and is mounted to the exterior side wall  12  of the grain bin  10  away from the fan  16  to obtain the most accurate readings. 
         [0052]    It is most preferable for the system  20  to include both the plenum sensor  32  and the weather station  34  as described to obtain the most accurate measurements for optimum drying. For instance, the measurements taken by the plenum sensor  32  and the weather station  34  may differ given the heat added to the air in the plenum chamber  14  as a result of the air movement through the fan  16 , the increased pressure in the plenum chamber  14  and the heat given up or absorbed by the ground that forms nearly half of the plenum chamber  14  surface area. However, one weather station  34  may be adequate for a cluster  21  of nearby bins  10 . 
         [0053]    The cellular modem or low power local radio  36  is preferably mounted on the bin&#39;s roof  13  for the most effective signal transmission. If a cellular modem  36  is included, then its antenna  134  is mounted nearby. As shown in  FIG. 2 , the antenna  134  is mounted on the roof  13  of the grain bin  10 . For cost savings, one cellular modem  36  and weather station  34  may be shared among a cluster  21  of bins  10 , with each of the other systems  20  on nearby bins  10  using a low power radio  36 , to provide the local communication between the bins  10  and the cellular modem providing the remote communication from the cluster  21 . 
       Operation 
       [0054]    The master control unit  22  controls the operation of the bin&#39;s fan  16  (and heater, if installed) using the closed loop control system shown in  FIG. 4 . The system&#39;s input  138  is the grain type and the desired or selected EMC and temperature. These are entered by the user at the master control unit  22  or through the remote user interface or computer  38 . These settings  138  may be determined and set once per season or updated frequently. The settings  138  are stored in the master control unit&#39;s non-volatile memory  52  so that the system  20  can operate without continual intervention or even a connection to a user or outside computer. The system&#39;s output  140  is the actual EMC and temperature. 
         [0055]    The sensor processing  142  and  146  is partially performed in the distributed control units  24  and  25  before being passed to the master control unit  22  for completion. The distances between the sensor assemblies  32 ,  34 ,  40 , and  42  and the distributed control units  24  and  25  are made relatively short to reduce the susceptibility of the electrical signals between them to electromagnetic interference. Accordingly, in the preferred embodiment, some of the sensor processing is done at the distributed control units  24  and  25  which are mounted around the exterior of the grain bin  10  in relatively close proximity to the sensor assemblies  32 ,  34 ,  40  and  42 . That part of the sensor processing  142  and  146  that is done in distributed control units  24  and  25  is to verify the integrity of the sensor data, to perform averaging, and to convert it to a form that can be used by the master control unit  22 . 
         [0056]    The cable assemblies  28  and  30  are powered by the distributed control unit  24  one at a time. The control unit  24  sends commands to the circuit board  84  or  85  on the powered cable  28  or  30  by switching off and on the power on that cable  28  or  30 . Switching between the two states, on and off, provides the digital communication. Each circuit board  84  or  85  contains an address that is also a relative location of the circuit board  84  or  85  on the cable assembly  28  or  30 . For example, the circuit board  84  or  85  farthest from the distributed control unit  24  has an address of “1”. The circuit board  84  or  85  next closest to the distributed control unit  24  has an address of “2” and so on. The addresses differentiate one circuit board  84  or  85  from another on the same cable assembly  28  or  30 . 
         [0057]    The messages communicated from the distributed control unit  24  to the sensors  86  and  87  are called commands and every command contains the address of the destination sensor  86  or  87 . Every message from circuit board  84  or  85  to the distributed control unit  24  is a response, and every response contains the source address of the circuit board  84  or  85 . The circuit board  84  or  85  creates a response by switching a load on and off while the distributed control unit  24  has the voltage at its high level. Thus, the current changes between a low current and a high current and is detected by a current circuit of the distributed control unit  24 . 
         [0058]    When the distributed control unit  24  is not communicating with a particular string of sensor assemblies  40  or  42  on a cable assembly  28  or  30 , it leaves the power off on that cable  28  or  30 . Thus, the sensors&#39; microprocessors are reset each time the power is applied before another measurement and communication event. While the distributed control unit  24  transmits by switching power off for brief periods, capacitors on the sensor boards  84  or  85  keep the sensors&#39; circuitry active. 
         [0059]    Both local communication between systems  20  on nearby bins  10  and remote communication with a remote user interface  38  are coordinated through the distributed control unit  26 . This distributed control unit  26  communicates with the system&#39;s low power local radio or cellular modem  36 . 
         [0060]    Remote communication includes communication from the system  20  to the remote user interface  38  as well as communication from the remote user interface  38  to the system  20 . For instance, daily status reports containing the hourly temperature and moisture content, the time the fan  16  has operated and other data that is of interest to a user who may be monitoring system performance is transmitted from the system  20 . Remote communication also includes the transmission of alarm conditions, which can be displayed through the browser and/or communicated to the user via text message, telephone or e-mail. Lastly, remote communication includes incoming messages from the remote user interface  38  for purposes of changing system inputs  138 , such as the grain or commodity type, desired temperature and desired EMC. 
         [0061]    Local communication includes collecting and distributing remote communication when only one cell modem  36  is installed in a cluster  21  of nearby bins  10 . It also includes the distribution of information from the weather station  34  when one weather station  34  is installed in a cluster  21  of bins  10 .