Abstract:
A power control system for automatically and proportionately metering power to a heating device used to create a warm microenvironment conducive to the health and growth of an animal during a predetermined incubation period is herein disclosed. The power control system transmits proportionally more power to a heating device where an ambient room temperature measured outside of the microenvironment is nearer a predetermined lower limit, and proportionately less power when the ambient room temperature measured outside of the microenvironment is nearer a predetermined upper limit. A method of providing a heated microenvironment within a larger environment also is disclosed.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a Continuation Application of U.S. application Ser. No. 10/426,672, filed 30 Apr. 2003, entitled “Electronic Control for Heating Apparatus”, which claims the benefit of U.S. Provisional Application No. 60/376,981 filed 30 Apr. 2002, entitled “Electronic Control for Heating Apparatus.” 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to an electronic control device for automatically adjusting the power supplied to one or more heating devices so as to maintain a heated microenvironment within the larger environment of an animal confinement building.  
       BACKGROUND OF THE INVENTION  
       [0003]     Infrared heat lamps and/or electric heat mats are often used by swine producers to provide supplemental heat to young and newly born piglets. Supplemental heat is required for young piglets because they lack the necessary thermal insulation and the ability to manage their body temperature. Without supplemental heat, the piglets would obtain the necessary warmth from the sow. However, because sows can often trample or lay upon piglets, it is desirable to provide the supplemental needed to warm the piglets using artificial heating devices.  
         [0004]     The supplementary heat is localized to a small area, thereby creating for the piglets a comfortable microenvironment within a larger farrowing room. Providing localized heat is preferred over large area heating because of the reduction in energy consumption, improved air quality, and ability to maintain a cooler room temperature, which is more appropriate for the lactating sows.  
         [0005]     As newborn piglets grow their need for supplemental heat is reduced, allowing for the gradual reduction of supplemental heat during the first 2-3 weeks following birth. Various manual and semiautomatic methods have been devised for reducing this heat, including: raising up the heat lamps by means of a chain, a rheostat control for manual power adjustment, on/off thermostats, timers, high/low power switches, unplugging the heat lamp and using circuit breakers or toggle switches for manual on/off control. There are also a number of electronic controls having variable output power capability that can, to a limited degree, and at considerable expense, provide a means to automatically adjust the heat output to match the needs of the piglet.  
         [0006]     Thermostats, timers and various other types of on/off switching devices lack the ability to modulate the power to the heating device, often resulting in a too hot or too cold condition that causes discomfort to the piglet, affecting the health of the animal, and it&#39;s ability to efficiently convert feed to weight gain.  
         [0007]     Rheostats and similar manually adjusted devices lack the ability to dynamically adjust the heater&#39;s output in response to changing room temperatures and the reduced heat requirement of a growing piglet. Again, this often results in a too little or too much heat being applied to the microenvironment as the room temperature fluctuates due to seasonal and weather conditions beyond the producer&#39;s control. For example, a hot summer day can result in a gradual heating of the room to the extent that supplemental heat is not required for the young piglets. But as the nighttime air cools the room, the need for supplemental heat is again required. Attempting to manually adjust the supplemental heat to match the changing conditions becomes a 24-hour a day management problem.  
         [0008]     Some of the current generation of sophisticated electronic controls, do have the capability of adjusting the output of heating devices based on temperature and animal age. These controls measure the temperature within the microenvironment near the heating device and regulate the output thereof based on a desired microenvironment temperature, using a closed loop control algorithm. However, from a practical standpoint, these controls are not able to reliably control the large number of heating devices found in a typical animal confinement building. These controls have failed to achieve widespread appeal and success due in part to their high purchase and installation costs. In addition, the skill required to properly setup, operate, maintain, and troubleshoot these complex controls is also a major factor. Other, simpler and less expensive controls have sprung up to compete with their relatively more complex brethren, but are also limited by their limited capability and high installation costs.  
         [0009]     The present invention is therefore directed to the following objectives: to provide energy savings through automatic reduction of the heating power applied to heating devices as piglets age; to provide energy savings through the automatic reduction of heating power applied to heating devices as the temperature of the farrowing room where the piglets are kept rises; to obviate the need to manually adjust lamp heights or to manually reduce power; to create an improved heated microenvironment for the piglets to result in healthier and more productive piglets; to reduce potential for heat stress to the sows by minimizing the heat added to the larger environment of the farrowing room; to extend the useful life of the heating devices used by providing a soft start feature; to eliminate lamp inrush current so that lamps run cooler at reduced power levels; to reduce peak demand from backup generators or power utilities; and, to reduce piglet mortality due to crushing by maintaining a comfortable microenvironment that allows young piglets to keep away from the sow. In addition to its use in farrowing operations, it is to be understood that the present invention is susceptible of use in agricultural, zoological and home settings with myriad animals, including but not limited to, birds such as chickens and turkeys, dogs, and cats.  
         [0010]     These and other objectives and advantages of the invention will appear more fully from the following description, made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     The objects of the present invention are realized in a method of controlling the heat applied to a microenvironment in such a manner as to promote the health, well-being, and growth of a young animal present within the microenvironment. This method begins with the step of providing a heating device that is constructed and arranged to create the heated microenvironment within a larger environment. Next, a low temperature limit at and below which the heating device will operate at substantially 100% of its rated power is chosen, as is a high temperature limit at which the heating device will be caused to operate at substantially 0% of its rated power. The temperature of the larger environment outside of the microenvironment is then measured and power is applied the heating device based on this measurement. Where the temperature of the larger environment is below the high temperature limit, the heating device will be activated to create the heated microenvironment. The power that is applied to the heating device is varied with the temperature of the larger environment so as to maintain a continuous heat output from the heating device. The power applied to the heating device ranges from 0%-100% of the rated power for the heating device and is applied over that range of temperatures defined by the upper and lower temperature limits. The power applied to the heating device is set to 100% of rated power when the temperature of the larger environment is at or below the lower temperature limit and is set to 0% when the temperature of the larger environment is above the upper temperature limit.  
         [0012]     Power may be applied to the heating device in a linear or non-linear manner and may be varied discontinuously or continuously. In a preferred embodiment of the present invention, power is applied to the heating device so as to obtain a linear output from the heating device.  
         [0013]     A preferred embodiment of a control mechanism for controlling the power applied to a heating device comprises a data processor that is operatively coupled to a memory device, to an operator control input/output device, and to a temperature sensor for sensing a temperature of larger environment inside which is created the heated microenvironment. The temperature sensor provides control data to the microprocessor. The control mechanism is also provided with a variable power switch that is coupled between a power input and a power output. The variable power switch communicates with and is controlled by the data processor according to the temperature sensed by the temperature sensor. The power output of the control mechanism is in turn coupled to a heating device whose output creates the heated microenvironment within the larger environment. The variable power switch preferably comprises a switching mechanism that can be one of a rheostat, a triac, or one or more thyristors.  
         [0014]     The power control mechanism preferably also comprises a fault checking circuit for determining whether a fault condition is present. This fault checking is coupled to the microprocessor, which is programmed to open the variable power switch if a fault condition is sensed. The fault checking circuit preferably shares an induction coil with a low pass filter. The low pass filter acts to prevent electromagnetic noise that can disrupt electronic equipment in the area adjacent the power control mechanism.  
         [0015]     A power control algorithm, embodied in the appropriate computer coding, is recorded on the memory device. The power control algorithm defines a high temperature limit above which power to the heating device is cut off and a low temperature limit at and below which power applied to the heating device is set to 100% of the rated power of the heating device. The power control algorithm varies the power applied to the heating device based on the output of the temperature sensor so as to vary the heat output of the heating device, preferably in a continuous manner.  
         [0016]     The power control algorithm controls the variable power switch through the data processor. Power is provided at levels between 0-100% of the rated power of the heating device for temperatures in the larger environment defined by the high and low temperature limits. The power control algorithm is constructed and arranged to supply power through the variable power switch such that a heat output of the heating device is linear over an operational range that is defined by high and low temperature limits.  
         [0017]     In one embodiment of the present invention, all of the components of the power control mechanism are located together within a single, sealed enclosure. However, in some applications, the present invention may distribute the components of the power control to remote locations. In one such embodiment, the data processor, the memory device, the operator control input/output device, and the temperature sensor are positioned outside of the microenvironment and remotely from the variable power switch. In a distributed embodiment of the power control mechanism, the data processor may be coupled to a plurality of variable power switches, each of the plurality of variable power switches being constructed and arranged to control power output to a heating device positioned within a single microenvironment or to multiple heating devices in one or more microenvironments.  
         [0018]     The present invention may also be described as a power control for metering the power transmitted to a heating device having a rated power capacity that is constructed and arranged to create a warm microenvironment conducive to the health and growth of an animal. The percentage of the rated power capacity applied to the heating device by the power control is related to an ambient room temperature and the age of the animal.  
         [0019]     The power control device sets a high and a low limit that are related to an ambient temperature outside of the microenvironment. The power control transmits proportionately more power to the heating device where the ambient temperature is nearer the lower limit and proportionately less power where the ambient temperature is nearer the high limit. These high and low temperature limits may be modified to adjust the output of the heating devices. For example, the power control may periodically lower the high and/or low temperature limits over a predetermined elapsed time period. One example of the present invention lowers the high temperature limit one degree per day for 25 days.  
         [0020]     Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention, which may be embodied in other specific structure. While the preferred embodiments have been described, the details may be changed without departing from the invention, which is defined by the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a table setting forth the algorithm whereby power settings are modified to maintain a suitable microenvironment while simultaneously reducing power consumption;  
         [0022]      FIG. 2   a  is a perspective view of the present invention illustrating a portable embodiment of the present invention having built in power receptacles;  
         [0023]      FIG. 2   b  is a perspective view of the present invention illustrating a portable embodiment of the present invention having an output power cord with a receptacle at the end thereof;  
         [0024]      FIG. 3  is a schematic of one embodiment of a circuit that enables the present invention;  
         [0025]      FIG. 4  is a schematic view of the power control illustrated in  FIGS. 2   a  and  2   b  in use in a farrowing operation;  
         [0026]      FIG. 5  is a schematic view of a distributed power control of the present invention;  
         [0027]      FIG. 6  is an exploded perspective view of a master control of the power control illustrated in  FIG. 5 ;  
         [0028]      FIG. 7  is an exploded perspective view of a slave switch of the power control illustrated in  FIG. 5 ;  
         [0029]      FIG. 8  is a graph of typical power output in (% of rated power) of a heating element for a given power input (in volts); and,  
         [0030]      FIG. 9  is a schematic illustration of a distributed power control system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     The power control of the present invention may be embodied in a stand-alone device such as that pictured in  FIGS. 2   a  and  2   b  or in a hard-wired version such as that pictured in  FIGS. 6-7 . Referring first to  FIGS. 2   a ,  2   b , and  4 , a portable embodiment of the power control  10  can be seen to comprise a small watertight enclosure  12  with an input power cord  14  having a suitable and standard male or female coupling  16 , and an external temperature sensor  22 . The portable embodiment of the power control  10  may further comprise one or more built in receptacles  21  that are built into the housing  12  (see  FIG. 2   a ) or an output power cord  18  with one or more standard receptacles  20  (see  FIG. 2   b ). The input power cord  14 , output power cord  18  (where present), and the temperature sensor  22  preferably enter the enclosure through liquid tight strain relief connectors  24 , though it is to be understood that any suitable connection mechanism may be utilized.  
         [0032]     Referring next to  FIG. 4 , the power control  10  may be used advantageously in a farrowing operation to promote the health and efficient growth of piglets. Note that though the power control  10  as described herein is used in a farrowing operation, the power control  10  may be reconfigured without exceeding the broad scope of the present invention to be used in aviaries, zoos, or in the home for the care of household pets. The power controls  10  of the present invention are situated within a farrowing room  40 . Within the farrowing room  40  there are placed one or more farrowing crates  42  in which are confined the sows (not shown). The farrowing crates  42  are provided with mechanisms for cleaning and feeding the sow and typically have sides that allow the piglets (not shown) to move freely from the farrowing crate  42  to a heated microenvironment  44 . Note that the microenvironment  44  is immediately adjacent to the farrowing crate  42  and is accessible to the piglets. Note also that the farrowing crate  42  and the microenvironment are fenced to prevent the piglets from escaping to the larger environment of the farrowing room  40  in general.  
         [0033]     While  FIG. 4  illustrates only two farrowing crates  42 , microenvironments  44 , and associated power controls  10 , it is to be understood that a farrowing room  40  may contain any number of farrowing crates  42 . In addition, while  FIG. 4  illustrates only a single heating device  30  in use with each of the respective power controls  10 , it is to be understood that a single power control  10  may be used to control multiple heating devices  30 .  
         [0034]     Heating devices  30  are arranged with respect to the microenvironments  44  so as to provide heat thereto. While the heating devices pictured in  FIGS. 4 and 5  are schematic illustrations of infrared lamps of one type or another, it is to be understood that the power controls  10  of the present invention may be readily adapted for use with virtually any electrically powered heating device, including but not limited to, heat lamps and heating pads. In addition, with the provision of a suitable control valve (not shown), the power controls  10  could be adapted to operate gas or oil fired heating devices (not shown).  
         [0035]     A heating device  30  is installed in its predetermined position in or adjacent the microenvironment  44  such that heat energy  36  is directed into the microenvironment  44 . Where the heating device  30  is a lamp, heat energy  36  will be radiated into the microenvironment  44  via infrared radiation. Where the heating device  30  is a heat mat, the heat energy  36  is generally transmitted into the microenvironment  44  by thermal conduction. Installation of the embodiments of the power control  10  shown in  FIGS. 2-4  comprises plugging a heating device  30  into the power control  10  output receptacle  20  or  21  as the case may be. The power control  10  power cord  14  is then connected using plug  16  to a standard electrical outlet (not shown). While the enclosure  12  of the power control  10  may simply rest on the floor of the farrowing room  40 , it is preferred to hang or mount the enclosure  12  off the floor to avoid damage thereto. The power control  10  may be provided with elongate power cords  14 ,  18  of a length that would allow for the mounting of the enclosure  12  in a desired location. As the power control  10  operates on an open loop basis, the temperature sensor  22  must be mounted outside of the microenvironment  44  and otherwise away from the heating devices  30 . The temperature sensed by the sensor  22  will accordingly be the temperature of the larger environment of the farrowing room  40  rather than that of the microenvironment(s)  44 . In general, as the temperature of the farrowing room  40  goes up, the power applied to the heating devices  30  is reduced and vice versa.  
         [0036]     The power control  10  modifies the output of the heating devices  30  by modulating the input power (voltage) to the heating devices  30  over an adjustable range of between 0% and 100%. The power input range is determined by the rated power output of the power control  10 . Where the power control  10  is rated at a maximum output of 120 volts, the adjustable range of power input to the heating device will vary between 0 volts (0%) to 120 volts (100%). Similarly, where the power control  10  is rated for a maximum output of 240 volts, the adjustable range of power input to the heating device will vary between 0 volts (0%) to 240 volts (100%). Note that the power control may be adapted to control any suitable power range. The range typically being determined by the nature of the heating devices  30  themselves as heating devices  30  rated at 120 volts will require a power control rated at 120 volts and heating devices rated at 240 volts will require a power control rated at 240 volts. The power input to the heating devices  30  is managed by correlating the measured room temperature outside of the microenvironment  44  and the time elapsed since the heating device  30  was activated to create the heated microenvironment  44 .  
         [0037]     The power control band is based on a LOW temperature setting corresponding to the desired temperature for minimum heat output (0% power) and a HIGH temperature setting corresponding to the desired temperature for maximum heat output (100% power). When the measured room temperature is between the HIGH and LOW settings, the power output to the heating devices  30  will be modulated to proportionate with respect to the temperature and where it falls on the control band.  
         [0038]     In one preferred embodiment, the power output to the heat devices  30  by the power control  10  may be modulated as shown in  FIG. 1 . In this embodiment the control band is set to a HIGH limit of 90° F. and a LOW limit of 70° F. such that where the temperature of the farrowing room  40  as determined by temperature sensor  22  is 90° F., the power output to the heating device  30  will be set at 0%. Similarly, where the temperature of the farrowing room  40  as determined by temperature sensor  22  is 70° F., the power output to the heating device  30  will be set at 100%. In general, where the temperature of the farrowing room  40  is below the LOW temperature limit, the power output to the heating devices  30  will be set to 100% and will remain there until such time as the room temperature increases to above the LOW temperature limit. This is to provide heat to the microenvironment  44  on colds days where the temperature of the farrowing room  40  never reaches the LOW temperature limit.  
         [0039]     In the control algorithm embodied in the chart of  FIG. 1 , the power setting of the power control  10  varies linearly over the control band defined by the LOW and HIGH temperature limits by 5% for each degree of change in the room temperature. For a control device rated at 120 volts, for each degree change, the power output of the power control  10  will vary by 6 volts. Accordingly, on day  1  of operation and where the temperature of the farrowing room  40  is 85° F., the power output setting of the power control  10  will be 25% of rated power.  
         [0040]     As the requirements of the piglets for supplementary heat during their first weeks of life gradually diminish, the power output settings of the power control  10  will be revised downward. In the embodiment shown in  FIG. 1 , the microenvironment  44  is heated for the first 25 days of the piglets&#39; lives, with the output of the power control  10  being lowered each day. Note that this period may be varied from zero on up according to the needs of the particular application to which the power control  10  is adapted. Note also that the time period over which the power control  10  is used may be measured in any useful time measure, from seconds to years. The drop in the output of the power control  10  over a period of time is in the embodiment of  FIG. 1  determined by dropping the LOW and HIGH temperature limits by one degree Fahrenheit each day over the selected 25-day period. This has the practical effect of lower the range of power outputs available to the power control  10  by 5% per day over the given period.  
         [0041]     It is to be understood however, that the power output of the power control  10  may be modulated in a non-linear and/or discontinuous fashion over a given control band and over a selected period of time. Because the output of many heating devices  30  is not linear and may even be discontinuous with respect to the voltage applied thereto, modulating the power output of the power control  10  in a linear fashion will result in non-linear or discontinuous output from the heating device  30 . As it is desirable to provide at least a continuous heat output from the heating devices  30 , the control algorithm whereby the power control  10  modulates the power output therefrom may be adapted to provide electrical power to the heating devices in a non-linear and/or discontinuous manner.  
         [0042]     As can be seen in  FIG. 8 , heating devices  30  such as a heat lamp will, for a given applied voltage, yield a power output that is non-linear with respect to the power (voltage) input to the heating device  30 . Note that the output of a typical heating device  30  is shown in the Figure as line  31   b . Accordingly, where it is desirable to ensure that the output of the heating devices  30  be linear as shown by line  31   a  which represents an ideal linear power output, the voltage applied to the heating devices  30  by the power control  10  will be varied non-linearly over the control band in order to drive a linear output for the heating devices  30 . It is to be understood that the function used to calculate the percent power output of the power control  10  would be specific to each heating device  30 . Resistive heating devices  30  such as heat pads are more generally linear in their response and accordingly the function used to calculate the power to be applied to a heat pad would be linear in nature. As heat lamps vary in their output as shown in  FIG. 8 , the function used to determine the output of the power control  10  would more closely approximate a homolog of the curve shown in the Figure. Again, it is desirable to provide a continuous heat output from the heating devices  30  in order to increase the comfort and productivity of the piglets. Accordingly, it is preferred to utilize an algorithm for determining the power output of the power control  10  that results in a continuous power output from the heating devices  30 . The preferred continuity would apply to both the output of the heating devices  30  over the control band temperatures and over time. Note that both the control band HIGH/LOW temperature limits and the period over which the HIGH/LOW temperature limits are reduced may be preset for a particular operation, in the present case a farrowing operation, or may be modified directly by the user of the power control. In either case, the user may override the preset control band and the time period over which the power control is used, or the rate at which the control band is modified by direct input of information into the power control  10 .  
         [0043]      FIG. 3  represents one embodiment of the circuitry of a power control  10  of the present invention. The power control  10  comprises a microprocessor  50 . One suitable microprocessor  50  includes integrated memory but may instead be coupled to a suitable RAM and/or ROM memory device. The microprocessor  50  is programmed with an object code that manages the overall operation of the power control  10 , as described above.  
         [0044]     The power control  10  implements a unique open loop process for proportionally controlling the power (voltage) applied to a plurality of heating devices  30  based on the temperature of a larger environment and elapsed time or animal age for the purpose of achieving an optimized thermal microenvironment. The power control is capable of operating in Celsius or Fahrenheit modes using a 50/60-Hertz power source.  
         [0045]     A user interface  52  is built into the enclosure  12  and preferably consists of a 3-digit numeric display  54  and a number of pushbutton switches  56 , preferably four, along with the related microprocessor interface components including display driver transistors  60 , diodes  62 , resistor arrays  64  and the necessary electrical connectors that are constructed and arranged as shown in  FIG. 3 . Note that the user interface  52  may comprise any useful combination of input mechanisms and display devices known to those skilled in the art. The user interface  52  may be used to start the operation of the power control  10 , set the appropriate time period over which the control band temperatures will be modified, to input the control band temperatures or virtually any other datum needed to implement the algorithm set forth hereinabove. In some embodiments, the user interface  52  may be used to “lock” the power control  10  in order to prevent accidental data entry, i.e. to prevent accidental entry of erroneous commands or data.  
         [0046]     An internal temperature sensor  58  measures the temperature within the enclosure  12  and communicates its readings to the microprocessor  50 . The object code with which the microprocessor  50  is programmed includes instructions that will temporarily shutdown the power control  10  if the internal temperature rises above approximately 150° F.-160° F. Note that the shutdown temperature is variable depending on the nature of the components that make up the circuitry and the setting in which the power control  10  is used.  
         [0047]     The external temperature sensor  22  is electrically connected to the microprocessor  50  through respective male and female coupling halves  68  and  70 , though the sensor  22  may be permanently connected as by soldering. As indicated above, these coupling halves  68 ,  70  preferably make up a liquid tight strain connectors  24 . The sensor  22  measures the room temperature and communicates its readings to the microprocessor  50 . A nonvolatile memory chip  66  is electrically coupled to the microprocessor  50  and is used to store various parameters and operating information such as the temperature readings from the sensor  22 . The nonvolatile memory chip  66  also retains all power control operational settings in the event of a power failure.  
         [0048]     The power supply  71  translates the nominal 120 VAC (or with ready modification 240 VAC) received through power cord  14  conductors  72  to approximately 4.5. VDC for proper operation of the aforementioned low voltage circuitry. Resistors  74  couple the line voltage frequency into the microprocessor  50  to provide a suitable synchronization signal, in this case at 50/60 Hertz. Microprocessor  50  controls the power supply  71  so as to apply power to the heating devices  30  in a gradual manner generally known as a “soft start”. The soft start application of voltage to the heating devices  30  prevents voltage surges from damaging the heating devices  30  by limiting the power applied to, for example, a heat lamp. Because heat lamps have a low resistance when they are cold and are first powered up, the application of full power to a cold lamp will result in momentary high inrush currents that can damage the lamp.  
         [0049]     A solid-state power switch known as a triac  76  directly controls the voltage applied to the heating devices  30  through conductors  73  and is itself controlled by signals received from transistor  78 . Resistor  80  and capacitor  82  form a snubber circuit, along with a varistor  84 , protect the triac  76  from voltage surges. Filter coil  86  and capacitor  88  form a low pass filter for minimizing generated electromagnetic noise.  
         [0050]     Filter coil  86  in this embodiment, doubles as part of a fault detection circuit that also includes switch  90 . Switch  90  is a magnetic switch that is magnetically coupled to filter coil  86  such that the switch  90  closes when a magnetic field produced by current flowing through the filter coil  86  reaches a predetermined strength that is associated with a short circuit condition. The microprocessor  50  periodically checks the open/close status of switch  90  to determine if a short circuit condition has been detected. Upon detecting a closed switch condition, the microprocessor  50  cuts power to the heating devices  30  for approximately 5 seconds and then slowly reapplies it. If the short circuit condition remains, the power is again cut for 5 seconds, and again slowly reapplied. In a preferred embodiment, this cycle will repeat for as long as the short circuit condition exists. However, it is to be understood that switch  90  may also remain open until manually reset.  
         [0051]     The snubber filter defined by resistor  80 , capacitor  82  and varistor  84 , along with the low pass filter defined by filter coil  86  and capacitor  88 , prevent the triac  76  from being inadvertently opened during power failures and brownouts or when the power control  10  is subjected to the presence of nearby electrical noise. The power control  10  may also include software and/or additional circuit mechanisms that protect the triac  76  from voltage fluctuations and spikes.  
         [0052]     Microprocessor  50  controls the power supply  71  so as to apply power to the heating devices  30  in a gradual manner generally known as a “soft start”. The soft start application of voltage to the heating devices  30  prevents voltage surges from damaging the heating devices  30  and especially the bulbs of a heating lamp.  
         [0053]     A preferred embodiment of the present invention comprises a distributed power control system for controlling a plurality of heating devices  30  used to create a microenvironment  44  within a larger environment as described above in conjunction with  FIG. 4 . See  FIG. 5 . Each of the microenvironments  44  are heated by one or more heating devices  30 . The heating devices  30  pictured in  FIG. 5  are heating lamps, though it is to be understood that other heating devices such as heating mats, quartz radiant heaters, or standard resistant wire electric heaters may be used as well. The heating devices  30  are connected to one or more sources of electrical power  100  by conductors  101  that are coupled to the heating devices  30  in a hard connection or a removable plug as shown schematically at  103 . The provision of electric power from the power source  100  to which each of the heating devices  30  are connected is controlled by a number of slave switches  102 . Each of the slave switches  102  is in turn electrically coupled to a master control  104  by a communications means  108 , which may be an electrically conductive cable, a wireless transmitter, or a communications cable such as a telephone cable or fiber optic cable. The master control  104  has an external temperature sensor  106  attached thereto for sensing the temperature within the farrowing room  40  in the same manner as temperature sensor  22  described hereinabove. The temperature sensor  106  of the master control  104  is therefore constructed and arranged to sense the ambient temperature within the farrowing room  40  and to provide this data to a microprocessor (not shown) that directs the plurality of slave switches  102  to allow a predetermined quantity of electrical power to flow from the power source  100  to the heating device  30 .  
         [0054]     The distributed power control  10  described above is illustrated schematically in  FIG. 9 . The master control  104  is connected to the slave switch  102  by a communications means that in this embodiment is a serial communication cable  108 . The temperature sensor  106  is operatively coupled to the microprocessor  150  of the master control  104 . The microprocessor  150  also has a numeric display  152 , a RAM and/or ROM memory device  154 , an input device  156  such as a keypad or the like, an internal temperature sensor  158 , and a power supply  160  that provides the necessary power for controlling the microprocessor  150  and its attached devices.  
         [0055]      FIG. 9  also illustrates schematically the slave switch  102 . The slave switch  102  is typically distant to the master control  104  and therefore includes its own microprocessor  162 . The microprocessor  162  of the slave switch  102  is coupled to the master control  104  by communications means  108 . The microprocessor  162  has coupled thereto an output device  164  such as a status LED or a numeric display, a RAM and/or ROM memory device  166 , an input device  168  that allows for local control of the slave switch  102 , a fault control circuit  170 , and a power supply  172 . The power supply  172  receives power from a power source  100  such as a breaker panel and provides the power to operate the microprocessor  162  and its attendant devices and also provides power to a power control switch  174 . The power control switch  174  is also coupled to and controlled by the microprocessor  162  and regulates power that is applied to a heating device  30 . The power control switch  174  also includes an RCL filter for preventing electromagnetic interference. The inductor of the RCL filter of the power control switch  174  is magnetically coupled to the fault control circuit  170  such that where the magnetic field present in the inductor of the RCL filter exceeds a predetermined set point, the fault control circuit  170  will cut power to the heating device  30  as the presence of large magnetic fields in the inductor of the RCL filter is indicative of a fault condition in the power control  10 . Note that magnetically coupling the inductor of the RCL filter to the fault control circuit  170  requires only a single inductor in the power control switch  174 .  
         [0056]     The distributed embodiment of the power control  10  illustrated in  FIGS. 5-7  operates in the same manner as does the embodiments described in conjunction with  FIGS. 2-4  above. However, the manner in which the slave switches  102  are arranged with respect to the master control  104  may vary from application to application.  
         [0057]     A preferred embodiment of the distributed power control  10  involves providing a single power source  100  for a plurality of microenvironments. The slave switch  102  is coupled between the single power source  100  and the heating devices  30  used to create the plurality of microenvironments  44 . Note that each microenvironment  44  may require more than one heating device. Accordingly, a single slave switch  102  may be used to control multiple heating devices  30  in multiple microenvironments  44 . Because of the distributed nature of the embodiment of the power control  10  illustrated in  FIGS. 5-7 , a single master control  104  may control the microenvironments  44  for a large number of farrowing sows at a given time. Note that where a single master control  104  is used, it may be necessary to ensure that farrowing sows are brought into estrus and inseminated on an identical schedule so as to ensure that the resulting piglets are all of substantially the same age.  
         [0058]     Another embodiment of the distributed power control  10  involves providing a single slave switch  102  for each microenvironment and coupling the slave switches  102  to the master control  104  using communication means  108 . In this embodiment, the slave switches  102  many be operated identically by the master control  104  or may be operated independent of one another such that each microenvironment  44  in a farrowing room  40  might have a different temperature at a given time. In these cases, it is preferable to provide a master control  104  that comprises a programmable logic controller (PLC) or, more preferably, a remotely located personal computer or other computing device having a processing power sufficient to track independently each of the farrowing rooms  40 , farrowing crates  42 , and microenvironments  44  associated therewith. With this embodiment of the distributed power control  10 , for example, a sow two weeks out of cycle with the remainder of the impregnated sows may be accommodated without undue effort. By using a distributed system of this type a single computer/master control  104  could be used to control hundreds or even thousands of microenvironments  44  all on different schedules without regard to the development rate of the piglets involved.  
         [0059]     In operation, the master control  104  utilizes the temperature sensor  106  to sense the ambient temperature within the farrowing room  40 . The master control  104  then checks to see where the sensed temperature falls with respect to a specified control band as described hereinabove. A microprocessor within master control  104  then selects an appropriate power setting that is transmitted from the master control  104  to the slave switches  102 . The slave switches  102  then adjust the power flowing from the source  100  to the heating devices  30 . The slave switches  102  comprise a power supply that receives power from power source  100  and a switching mechanism that may include a triac as described hereinabove in conjunction with  FIG. 3 . Another embodiment of the switching mechanism may comprise a pair of thyristors and an associated circuit that controls them. The switching mechanism is coupled to the master control  104  via communications means  108  and receives instructions therefore regarding the amount of power that is to be applied to the heating devices  30 . In addition, it is desirable to provide the slave switches  102  with the fault detection and filter mechanisms described in conjunction with  FIG. 3  above to ensure the safe and reliable operation of the distributed power control  10 .  
         [0060]     The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.