Apparatus and method for monitoring of an automatic deicing controller

An ice and snow melting heater control assembly including at least one sensor, at least one heater element and a controller communicatively coupled with the at least one sensor and the at least one heater element, the controller directing status information about at least one sensor to the at least one heater element.

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.

What is needed in the art is an automatic heater controller that can convey its status without the need for, and the cost of, a display or an electrical interface on the controller or the need to physically simulate an environment in which to turn on the heating system.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and monitoring method in which the heater control can be monitored.

The invention comprises common in one form thereof, an ice and snow melting heater control assembly including at least one sensor, at least one heater element and a controller communicatively coupled with the at least one sensor and the at least one heater element, the controller directing status information about at least one sensor to the at least one heater element.

An advantage of the present invention is that a controller can be checked for operation without simulating an environment therefore.

Another advantage is that the heater controller of the present invention can provide status information to a technician.

Yet another advantage is that the control circuit can be manufactured without the need to include visual indicators or readouts on the control circuit itself.

Yet still another advantage is that the present invention allows the status of the automatic controller to be determined without the additional cost of any additional parts.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, there is shown one embodiment of a deicing control system10of the present invention. System10includes power system12and control system14.

Power system12includes power conductors16and18, control conductor20, relay coil22, relay contact24and heater system26. Power conductors16and18are connected to electrical power such as a 120 volt circuit. Power conductors16and18also provide power to control system14. Control conductor20receives a signal from control system14that drives relay coil22causing a controllable connection of relay contact24thereby allowing power to flow from power conductor16through heater system26to power conductor18. Heater system26can be the controlling pump of a hydronic heating system26or an electrical heating element26.

Now, additionally referring toFIG. 2, there is shown a control circuit30, which is part of control system14. Control system14also includes moisture detector32and temperature detector34. Moisture detector32includes a moisture grid that is a spaced apart interdigitated set of conductors exposed on the top of control system14. Moisture, in the form of water, ice, snow and/or sleet on the surface of moisture detector32is 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 system14. 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 ensures complete melting of the moisture and the evaporation of any standing melt water. Power to the moisture sensor is turned off at temperatures above 38° F. At lower temperatures excitation of moisture detector32is continuous until precipitation is detected. Thereafter, moisture detector32is 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 detector32advantageously reduces the average current flowing through moisture detector32thereby prolonging its life.

Additionally, another technique in detecting moisture involves the measurement of AC conductivity of the moisture-sensing grid of moisture detector32. 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 detector32may be used to detect moisture.

Control circuit30incorporates a negative temperature coefficient precision thermistor34to 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 microcontroller36. 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 circuit30includes microcontroller36, relay38, field effect transistor (FET)40, heater elements42, FET44, FET46, capacitor48and resistor50. Controller36is interconnected with temperature detector34, FETs40,44and46. FET40controls the driving power to relay38, thereby providing an electrical connection between power line16and control line20. This places microcontroller36in control of the power supplied to heating element26. FET44is connected to resistive elements42that are proximate to and/or integrated with moisture detector32. Resistors42provide heat to moisture detector32when energized by FET44. FET46functions as an operational amplifier having a feedback capacitor48and a feedback resistor50. Feedback capacitor48serves to integrate current conducted from moisture detector32. Feedback resistor50provides a leak off of the integrated value otherwise integrated by FET46, capacitor48and current from moisture detective32.

Conductors52,54,56,58and60electrically interconnect microcontroller36with elements of control circuit30. Conductor52connects controller36with FET40thereby allowing controller36to turn power on to heater element26in a controllable manner. Conductor54is interconnected with controller36and FET44thereby controlling power to heating elements42that heat moisture detector32. The control of heat to moisture detector32is selected such that the power density applied thereto matches the power density in the deicing area. Microcontroller36advantageously controls the power supplied to heater elements42, in a programmed manner, to substantially match the heat density applied to moisture detector32to that supplied to the deicing area by way of heating element26. Conductor56provides a voltage level from thermistor34that corresponds with the external temperature. The voltage level is utilized by controller36to determine the ambient temperature and decide when to activate FETs40,44and46. For example, if the temperature detected from thermistor34is above 38°, FETs40,44and46will not be activated. When the temperature detected is below 38° F. moisture detector32, by way of conductors58and60, is activated to determine if any moisture is present on moisture detector32. If moisture is detected on moisture detector32, then conductor52is energized thereby causing FET40to be conductive causing the contact in relay38to close, thereby providing power to relay coil20, causing relay contact24to close, thereby directing electrical power to heating element26. FET44is modulated according to a prescribed power density to approximate the power density of heater element26. Once moisture is detected from moisture detector32, conductor60is de-energized for a predetermined amount of time. After the predetermined amount of time conductor60is re-energized to again detect the presence or absence of moisture on moisture detector32. Conductor line58serves as a sensor input to microcontroller36and conductor60supplies power to moisture detector32. Microcontroller36is a microprocessor driven controller and in the preferred embodiment a microchip 12C672 8-bit Harvard Architecture device is utilized. Microcontroller36advantageously has analog input and digital input/output ports, which are correspondingly interconnected to conductors52,54,56,58and60.

Now, additionally referring toFIG. 3, there is shown a method100that is executed by microcontroller36. Method100is initiated at step102, upon power on of control system14or upon a manual initiation, for example, by the pressing of a button not shown. Upon initiation, method100proceeds to step104in which controller36obtains the operational status of control system14. Operational status includes a test of moisture detector32, a reading of temperature reported by detector34and the status of power applied to FETS40,44and46. Status information thus obtained at step104is then available for transmittal at step106.

At step106, status information about control system14is directed to heater element26by way of relay38and relay elements22and24. The information is conveyed by a predetermined pulsing of relay38causing the current flowing through heating element26to be turned on and off in a predetermined pattern. The pulsing of the current through the heater element26can be detected by an operator having placed a clamp-on amp meter around conductor28to thereby detect the pattern being pulsed from control system14. The information passed to heater element26includes the current temperature detected by temperature detector34and whether or not moisture detector32is detecting any moisture. Additionally, status regarding microcontroller36and the status of relay38upon turn on may be directed to heater element26.

Method100proceeds to step108wherein controller36reads a memory contained within microcontroller36that contains historical operating information. The historical operating information may include performance in a previous time period such as the last time controller36energized heater element26and the duration thereof.

At step110, microcontroller36sends the historical data to heater element26again by a predetermined pulsing pattern of power under the control of FET40, relay38and relay elements22and24. The information sent to heater element26is thereby interpreted by an operator observing a voltmeter detecting the application of voltage to heater element26or by way of an amp meter detecting the current through conductor28. Alternatively, if relay elements22and24include 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 system14to a user by way of a pulse pattern to the heating element, thereby allowing control system14to provide operating information without the need of applying a controlled temperature and moisture environment to temperature detector34and moisture detector32to thereby test the operation of control system14.

The information provided from control system14to heater element26and conductor28may 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 system14. 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.