Abstract:
A snow melting system including a controller, a first heater supplying heat under the control of the controller, the first heater supplying heat at a power density, a moisture detection apparatus located apart from the first heater, the moisture detection apparatus communicatively coupled to the controller and a second heater located proximate to the moisture detection apparatus, the controller directing power to the second heater at an other power density, the other power density substantially the same as the power density.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a continuation-in-part of U.S. patent application Ser. No. 10/607,237, entitled “APPARATUS AND METHOD FOR MONITORING OF AN AUTOMATIC DEICING CONTROLLER”, filed Jun. 26, 2003. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to deicing equipment, and, more particularly, to automatic controls for deicing equipment used to melt and remove snow and ice from pavement, roofs, gutters, downspouts and the like. 
   2. Description of the Related Art 
   Electric and hydronic heaters are commonly used to melt ice and snow. Applications include pavement and similar structures, but also include roofs, downspouts and gutters. Pavement applications include sidewalks, driveways, stairs, drive through window areas, building portals, loading docks, bridge decks, parking garages and off ramps, etc. 
   Typically, automatic controls are utilized to sense ambient temperature and moisture to control ice removal heating equipment. Heater elements may include hydronic tubing installed under or proximate to areas in which the removal of ice or snow is desirable. Hydronic systems include an interface with a heating system that provides energy for the removal of ice and snow. Electrical heating cables may also be employed that consist of stranded copper wires separated by a semi-conductor polymer enclosed in one or more layers of organic insulating material, this type of electrical cable is often referred to as self-limiting or self-regulating heating cable. Additionally, an insulated resistant wire may be used, which maintains a relatively constant resistance as it dissipates heat. The insulation may consist of magnesium oxide or various polymeric materials. 
   The status of, and functioning of, the automatic control can be determined by way of a visual indicator on the control or an electrical interface to which an electrical device can be connected to analyze the functioning of the control. The visual indicator thereon may indicate the sensed temperature, the presence of electrical power and whether moisture is detected. Additionally, the automatic control can be checked if the temperature and moisture are controlled to a point of causing the controller to energize the heating system to thereby verify operation of the control system. 
   The power density used for the melting of snow on pavement varies between 30 and 60 Watts/ft 2 , with 45–50 Watts/ft 2  being typical. In comparison, the heaters used to melt snow and ice on a precipitation sensor has typically been at least 380 Watts/ft 2 . This power density is more than eight times greater than that of the pavement heaters which are typically controlled by the controller. The higher power density has been utilized by controllers to determine the amount of frozen precipitation so that the time in which the precipitation stopped can be determined and to burn through any accumulated snow on the sensor. This prior art approach results in a guess as to when the precipitation on the pavement will be dissipated. It is a guess because the precipitation on the sensor is typically dissipated before the moisture on the pavement is melted. To compensate for the unknown the heater is held on for a predetermined time to ensure the melting of the ground precipitation. The typical heater hold-on time is usually 2½ to 10 hours. 
   What is needed in the art is an automatic heater controller that tracks the melting of the precipitation on the pavement or walkway by way of a remotely mounted sensor. 
   SUMMARY OF THE INVENTION 
   The present invention provides a monitoring method and apparatus having a sensor that tracks the melting of the precipitation on the heated pavement. 
   The invention comprises common in one form thereof, a snow melting system including a controller, a first heater supplying heat under the control of the controller, the first heater supplying heat at a power density, a moisture detection apparatus located apart from the first heater, the moisture detection apparatus communicatively coupled to the controller and a second heater located proximate to the moisture detection apparatus, the controller directing power to the second heater at an other power density, the other power density substantially the same as the power density. 
   An advantage of the present invention is that a shorter hold-on time for the heater in the pavement can be utilized. 
   Another advantage is that the controller accurately determine&#39;s the completion of the moisture dissipation on a pavement by melting the frozen precipitation on the sensor at the same rate as that utilized in the heating element associated with the pavement. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is combination perspective view of an embodiment of a heater control of the present invention and a schematical form of typical external circuitry attached thereto; 
       FIG. 2  is a schematic diagram of a heater control of  FIG. 1 ; 
       FIG. 3  is a block diagram of a method used by the heater controller of  FIGS. 1 and 2 ; and 
       FIG. 4  is a block diagram of another method used by the heater controller of  FIGS. 1 and 2 . 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , there is shown one embodiment of a deicing control system  10  of the present invention. System  10  includes power system  12  and control system  14 . 
   Power system  12  includes power conductors  16  and  18 , control conductor  20 , relay coil  22 , relay contact  24  and heater system  26 . Power conductors  16  and  18  are connected to electrical power such as a 120 volt circuit. Power conductors  16  and  18  also provide power to control system  14 . Control conductor  20  receives a signal from control system  14  that drives relay coil  22  causing a controllable connection of relay contact  24  thereby allowing power to flow from power conductor  16  through heater system  26  to power conductor  18 . Heater system  26  can be the controlling pump of a hydronic heating system  26  or an electrical heating element  26 . 
   Now, additionally referring to  FIG. 2 , there is shown a control circuit  30 , which is part of control system  14 . Control system  14  also includes moisture detector  32  and temperature detector  34 . Moisture detector  32  includes a moisture grid that is a spaced apart interdigitated set of conductors exposed on the top of control system  14 . Moisture, in the form of water, ice, snow and/or sleet on the surface of moisture detector  32  is detected by a current flow between fingers of the interdigitated conductors. 
   Prior moisture detectors measured the conductivity between the interdigitated conductors using an uninterrupted supply of a DC voltage. This causes electrochemical problems including polarization and copper electroplating that reduces the life expectancy and reliability of the sensor. Polarization occurs when DC current flows through the grid when wet. The water from melted snow and ice becomes an electrolyte due to atmospheric contamination and the ions therefrom are positioned, due to the constant electro-potential on the interdigitated fingers. However, the circuit and method employed by the present invention reduces this problem to a negligible proportion by employing an active sensing technique that reduces the current through the moisture detection grid by more than an order of magnitude. Further, the circuit detects moisture on the sensing grid in the form of ice, in any form, without the need for heating the sensor to turn the ice into water. An advantage of this approach is that heat is not dissipated in the moisture sensor at a higher rate than that utilized in the pavement, or other application areas, where the heating element is distributing the heat. The advantage of this is that the moisture on the moisture detector will dissipate at the same rate as the moisture on the ground or other area under the control of control system  14 . The selection of the power density that is applied to the moisture sensor to melt the snow and ice on the conductive grid is such that it operates to allow the snow and ice to be removed at approximately the same rate as that on the ground. This advantageously permits a shorter hold-on time of the heating system thereby saving energy. The hold-on time, of approximately one hour, ensures complete melting of the moisture and the evaporation of any standing melt water. 
   Now, additionally referring to  FIG. 4 , there is illustrate a method  200  that is utilized to determine when moisture detector  32  is energized and when heater elements  26  located in pavement or walkway  27  are energized. Method  200  starts at step  202  and continues to step  204 , where the temperature of the air is determined to be above or below a predetermined value such as 38° F. If temperature sensor  34  detects a temperature equal to or above the predetermined value then method  200  returns to step  204 . 
   If temperature sensor  34  detects an air temperature below the predetermined value, then method  200  proceeds to step  206 . At step  206 , moisture sensor  32  is turned on by controller  36 . 
   At step  208 , if moisture is detected by moisture sensor  32 , method  200  proceeds to step  212 . If moisture sensor  32  does not detect moisture then method  200  proceeds to step  210 . 
   At step  212 , heating element  26  is turned on, thereby providing heat to pavement  27 . When the heat is turned on at step  212 , controller  36  additionally activates heaters  42 . Heaters  42  are sized to provide the same or substantially the same power density as that being applied to heater element  26  is pavement  27 . 
   At step  214 , method  200  de-energizes moister sensor  32  for a predetermined time, such as ten minutes. After the completion of the predetermined time period, moisture sensor  32  is reenergized and method  200  proceeds to step  208 . 
   If no moisture is then detected at step  208 , method  200  proceeds to step  210 . At step  210 , power to heaters  42  is removed and heat to heating element  26  is held on for a predetermined time, such as one hour, and then automatically heating element  26  is de-energized. Method  200  then proceeds back to step  204 . Advantageously, since the melting of precipitation on moisture detector  32  approximates the rate of the melting of precipitation on pavement  27 , a relatively short hold-on time can be used, thereby reducing energy costs. 
   Power to the moisture sensor is turned off at temperatures above 38° F. At lower temperatures excitation of moisture detector  32  is continuous until precipitation is detected. Thereafter, moisture detector  32  is electrically activated at predetermined intervals, such as every six minutes, for a few seconds to check for the presence of moisture. If moisture had been previously detected, then the detection of a lack of moisture marks the beginning of the heater hold-on time interval. This modulating of the DC voltage on moisture detector  32  advantageously reduces the average current flowing through moisture detector  32  thereby prolonging its life. 
   Alternatively, at step  212 , when energy is applied to heating element  26 , the energy supplied to resistors  42  may be modulated by controller  36  to thereby provide a power density to moisture detector  42  that matches the power density of heating element  26  in pavement  27 . This advantageously allows a standard heating element  42  to be utilized with the power density being under the control of controller  36 . The selection of the power density to be applied to moisture detector  32  by way of heating elements  42  can be predetermined or selected at the time of installation. 
   Additionally, another technique in detecting moisture involves the measurement of AC conductivity of the moisture-sensing grid of moisture detector  32 . Low frequency AC excitation reduces the electrochemical deterioration of the surface of the moisture sensing grid when it is exposed to precipitation in any form, since the average current is zero. Further, the measurement of the AC capacitance of the moisture-sensing grid of moisture detector  32  may be used to detect moisture. 
   Control circuit  30  incorporates a negative temperature coefficient precision thermistor  34  to convert the ambient temperature into a voltage value using half of a DC excited Wheatstone bridge. The other half of the bridge is supplied by a successive approximation routine that utilizes an analog-to-digital converter in microcontroller  36 . Since both halves of the Wheatstone bridge are excited by supply voltage V + , the encoded temperature value is essentially independent of variations in V + . 
   Control circuit  30  includes microcontroller  36 , relay  38 , field effect transistor (FET)  40 , heater elements  42 , FET  44 , FET  46 ; capacitor  48  and resistor  50 . Controller  36  is interconnected with temperature detector  34 , FETs  40 ,  44  and  46 . FET  40  controls the driving power to relay  38 , thereby providing an electrical connection between power line  16  and control line  20 . This places microcontroller  36  in control of the power supplied to heating element  26 . FET  44  is connected to resistive elements  42  that are proximate to and/or integrated with moisture detector  32 . Resistors  42  provide heat to moisture detector  32  when energized by FET  44 . FET  46  functions as an operational amplifier having a feedback capacitor  48  and a feedback resistor  50 . Feedback capacitor  48  serves to integrate current conducted from moisture detector  32 . Feedback resistor  50  provides a leak off of the integrated value otherwise integrated by FET  46 , capacitor  48  and current from moisture detective  32 . 
   Conductors  52 ,  54 ,  56 ,  58  and  60  electrically interconnect microcontroller  36  with elements of control circuit  30 . Conductor  52  connects controller  36  with FET  40  thereby allowing controller  36  to turn power on to heater element  26  in a controllable manner. Conductor  54  is interconnected with controller  36  and FET  44  thereby controlling power to heating elements  42  that heat moisture detector  32 . The control of heat to moisture detector  32  is selected such that the power density applied thereto matches the power density in the deicing area. Microcontroller  36  advantageously controls the power supplied to heater elements  42 , in a programmed manner, to substantially match the heat density applied to moisture detector  32  to that supplied to the deicing area by way of heating element  26 . Conductor  56  provides a voltage level from thermistor  34  that corresponds with the external temperature. The voltage level is utilized by controller  36  to determine the ambient temperature and decide when to activate FETs  40 ,  44  and  46 . For example, if the temperature detected from thermistor  34  is above 38°, FETs  40 ,  44  and  46  will not be activated. When the temperature detected is below 38° F. moisture detector  32 , by way of conductors  58  and  60 , is activated to determine if any moisture is present on moisture detector  32 . If moisture is detected on moisture detector  32 , then conductor  52  is energized thereby causing FET  40  to be conductive causing the contact in relay  38  to close, thereby providing power to relay coil  20 , causing relay contact  24  to close, thereby directing electrical power to heating element  26 . FET  44  is modulated according to a prescribed power density to approximate the power density of heater element  26 . Once moisture is detected from moisture detector  32 , conductor  60  is de-energized for a predetermined amount of time. After the predetermined amount of time conductor  60  is re-energized to again detect the presence or absence of moisture on moisture detector  32 . Conductor line  58  serves as a sensor input to microcontroller  36  and conductor  60  supplies power to moisture detector  32 . Microcontroller  36  is a microprocessor driven controller and in the preferred embodiment a microchip 12C672 8-bit Harvard Architecture device is utilized. Microcontroller  36  advantageously has analog input and digital input/output ports, which are correspondingly interconnected to conductors  52 ,  54 ,  56 ,  58  and  60 . 
   Now, additionally referring to  FIG. 3 , there is shown a method  100  that is executed by microcontroller  36 . Method  100  is initiated at step  102 , upon power on of control system  14  or upon a manual initiation, for example, by the pressing of a button not shown. Upon initiation, method  100  proceeds to step  104  in which controller  36  obtains the operational status of control system  14 . Operational status includes a test of moisture detector  32 , a reading of temperature reported by detector  34  and the status of power applied to FETS  40 ,  44  and  46 . Status information thus obtained at step  104  is then available for transmittal at step  106 . 
   At step  106 , status information about control system  14  is directed to heater element  26  by way of relay  38  and relay elements  22  and  24 . The information is conveyed by a predetermined pulsing of relay  38  causing the current flowing through heating element  26  to be turned on and off in a predetermined pattern. The pulsing of the current through the heater element  26  can be detected by an operator having placed a clamp-on amp meter around conductor  28  to thereby detect the pattern being pulsed from control system  14 . The information passed to heater element  26  includes the current temperature detected by temperature detector  34  and whether or not moisture detector  32  is detecting any moisture. Additionally, status regarding microcontroller  36  and the status of relay  38  upon turn on may be directed to heater element  26 . 
   Method  100  proceeds to step  108  wherein controller  36  reads a memory contained within microcontroller  36  that contains historical operating information. The historical operating information may include performance in a previous time period such as the last time controller  36  energized heater element  26  and the duration thereof. 
   At step  110 , microcontroller  36  sends the historical data to heater element  26  again by a predetermined pulsing pattern of power under the control of FET  40 , relay  38  and relay elements  22  and  24 . The information sent to heater element  26  is thereby interpreted by an operator observing a voltmeter detecting the application of voltage to heater element  26  or by way of an amp meter detecting the current through conductor  28 . Alternatively, if relay elements  22  and  24  include a light circuit, the operator can detect the pulse pattern by observing the light on the relay or listen to the relay closures. Advantageously, the present invention conveys information regarding control system  14  to a user by way of a pulse pattern to the heating element, thereby allowing control system  14  to provide operating information without the need of applying a controlled temperature and moisture environment to temperature detector  34  and moisture detector  32  to thereby test the operation of control system  14 . 
   The information provided from control system  14  to heater element  26  and conductor  28  may be in the form of pulsing steps, which include varying the time duration of pulses or the frequency of pulses in the pattern. The pattern of pulses is completed in a relatively short period of time upon turn power-up of control system  14 . The relatively short period of time may be less than one minute in duration and more specifically less than 30 seconds. Additionally, the pulse pattern may be delayed for a short period of time allowing an operator to move from a power on switch to the amp meter to thereby detect the information. The delay in operation may be a predetermined time such as 2 minutes. 
   While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.