Abstract:
An electronic control circuit for intelligently controlling a gas discharge lamp associated with an HVAC system. The circuit includes a microcontroller having a memory containing instructions executable by the microcontroller to process a plurality of dynamic lamp state signals and dynamically generate control signals in at least partial dependence on a plurality of pre-established control parameters to maintain the gas discharge lamp in a minimum operable state defined by the pre-established control parameters. The gas discharge lamp is coupled to an electronic ballast circuit configured to dynamically control a current flow through the gas discharge lamp in dependence on the dynamically generated control signals sent by the microcontroller. The executable instructions cause the microcontroller to iteratively determine the minimum operable state of the gas discharge tube in at least partial dependence on a voltage excursion included as one of the plurality of dynamic lamp state signals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
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   FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
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   REFERENCE TO A MICROFICHE APPENDIX 
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   COPYRIGHT NOTICE 
   A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
   RELEVANT FIELD 
   A electronic control circuit is described for implementation in a heating, ventilating, and air conditioning (HVAC) system; and more specifically, an electronic control circuit for intelligently controlling a plurality of gas discharge lamps used in the environmental and biocidal treatment of air. 
   BACKGROUND 
   Electronic ballasts have significant advantages over inductive type ballasts known in the relevant art; including greater energy efficiency, smaller size, lower cost and lower component and maintenance costs. Many of the electronic ballasts allow for electrical programming of the lamp&#39;s various operating parameters by selecting components that provide an RC time constant of a proper frequency for the various types of the gas discharge lamps to be connected to the electronic ballasts. 
   The selected components are then hardwired to the electronic ballasts and are not changed for the life of the electronic ballast circuits. The criteria for selecting the proper resistors and capacitors are based on the lamp&#39;s manufacturer recommendations. The operating characteristics of the gas discharge lamps used in selecting the components are optimized by the manufactures for maximum energy efficiency for a new or “typical” lamp. 
   However, the operating characteristics for a given type of gas discharge lamp may vary among manufacturers, change over time as the lamps are used and vary according to their environmental conditions. A selected operating program for a new or “typical” gas discharge lamp may be deleterious to a lamp after a given amount of operating time which adversely impacts the life of the lamp, increases maintenance costs and downtime, and may increase hazardous waste generation as many gas discharge lamps contain sufficient quantities of mercury to require disposal as hazardous waste or otherwise require special handling for recycling purposes. Therefore, a simple mechanism to intelligently control the operating characteristics of a gas discharge lamp over time would be advantageous. 
   SUMMARY 
   This disclosure addresses the deficiencies of the relevant art and provides in various embodiments an electronic control circuit for intelligently controlling a gas discharge lamp associated with an HVAC system. 
   In a first main exemplary embodiment, the electronic control circuit comprises a microcontroller operatively coupled to a memory. The memory includes instructions executable by the microcontroller to process a plurality of dynamic lamp state signals and dynamically generate control signals in at least partial dependence on a plurality of pre-established control parameters. The pre-established control parameters facilitate the maintenance of the gas discharge lamp in a minimum operable state defined by the pre-established control parameters under dynamically varying environmental conditions. An electronic ballast circuit is used to dynamically control a current flow through the gas discharge lamp in dependence on the dynamically generated control signals. The microcontroller iteratively determines the minimum operable state of the gas discharge tube in at least partial dependence on a voltage excursion included as one of the plurality of dynamic lamp state signals. 
   In a first related exemplary embodiment, an airflow sensor is operatively coupled to the microcontroller and configured to provide airflow state signals to the microcontroller based on airflow detected in the HVAC system. 
   In a second related embodiment, the airflow sensor is configurable to control one of: the biocide lamp, ozone generation lamp and any combination thereof in dependence on various airflow thresholds to compensate for dynamic air flow variations. 
   In a third related exemplary embodiment, an ozone sensor is operatively coupled to the microcontroller. The ozone sensor provides ozone sensor signals to the microcontroller in based on detected ozone concentrations in the HVAC system. 
   In a fourth related exemplary embodiment, a power supply configured to provide sufficient electrical power to the microcontroller, electronic ballast circuit and the gas discharge lamp in an isolated ground arrangement such that voltage measurements are relative to a negative portion of an input power sine wave. 
   In a fifth related exemplary embodiment, a user interface is operatively coupled to the microcontroller. The user interface is configured to receive user inputs which allow a user to manually override the microcontroller. In addition, the user interface displays a state of the airflow sensor, the gas discharge lamp, the ozone sensor, the power supply and a current control mode. 
   In a sixth related exemplary embodiment, the dynamic control signals may include an IN/OUT signal, a pulse width modulation output signal, an output intensity signal, a user interface signal, a current sense signal and a voltage sense signal. 
   In a seventh related exemplary embodiment, the plurality of dynamic states of the gas discharge lamp may include an ON state, an OFF state, a preheat state, an ignition state, and a dimmed state. 
   In an eighth exemplary related embodiment, the dynamic lamp state signals are 0-5 volt signals measured relative to a negative portion of an input power sine wave and an isolated ground. 
   In a ninth exemplary related embodiment, the plurality of pre-established control parameters may include operating cycle time(s), an output intensity level, a low ozone setpoint, a scheduled service interval, and a high ozone setpoint. 
   In a tenth related exemplary embodiment, the low and high setpoints may include a voltage, a current, an ozone concentration and a pulse width modulation frequency. 
   In a twelfth eleventh related exemplary embodiment, the voltage excursion is measured relative to a negative portion of an input power sine wave and an isolated ground. 
   In a thirteenth related exemplary embodiment, the output intensity level may controlled to about a 25 percent output intensity with a 50% duty cycle of the gas discharge tube in a low mode, about 50 percent output intensity in a medium mode mode, 75 percent output intensity in a high mode and 100 percent output intensity in a boost mode. 
   In a fourteenth related exemplary embodiment, the ozone sensor signals may include a 4-20 ma current signal, 0-5V voltage signal and an ON/OFF state signal. 
   In a fifteenth related exemplary embodiment, the output intensity may be dynamically controlled at 256 discrete levels in a range corresponding to 50% to 100%. 
   In a sixteenth related exemplary embodiment, the output intensity may be dynamically controlled at output levels below 50% by pulsing of the gas discharge lamp. 
   In a seventh related exemplary embodiment, the instructions executable by the microcontroller further includes executable instructions to adjust a voltage excursion detection sensitivity in at least partial dependence one or more of the plurality of pre-established control parameters. 
   In a second main exemplary embodiment, an electronic control circuit for intelligently controlling a pair of gas discharge lamps associated with an HVAC system is provided. This second exemplary embodiment comprises a microcontroller including a memory having instructions executable by the microcontroller to dynamically generate control signals in at least partial dependence on a plurality of optically isolated sensor signals and voltage input signals. 
   The microcontroller also has functionally coupled to it, first and second electronic ballasts. The first ballast is configured to control a first current flow through an ozone generation lamp in dependence on a portion of the dynamically generated control signals. The second ballast is configured to control a second current flow through a biocide lamp in dependence on another portion of the dynamically generated control signals. 
   In a first related exemplary embodiment, the plurality of input signals includes a voltage signal derived from an operational state dependent voltage applied to the ozone generation lamp. 
   In a second related exemplary embodiment, the plurality of input signals includes a voltage signal derived from an operational state dependent of the biocide lamp. In a third related exemplary embodiment, the plurality of optically isolated input signals includes user interface signals and sensor signals. 
   In a fourth related exemplary embodiment, the airflow sensor is configurable to control one of, the biocide lamp, ozone generation lamp and any combination thereof in dependence on various airflow thresholds included in one or more of the plurality of pre-established control parameters to compensate for dynamic air flow variations. 
   In a third main exemplary embodiment, an electronic control circuit for controlling a pair of disparate gas discharge lamps associated with an HVAC system is provided. This third main exemplary embodiment comprises a microcontroller including a memory having instructions executable by the microcontroller to process a plurality of input signals and dynamically generate control signals for each of the gas discharge lamps in at least partial dependence on a plurality of pre-established control parameters. 
   The pre-established control parameters facilitate the maintenance of the gas discharge lamps in states defined by the pre-established control parameters. A first electronic ballast circuit is operatively coupled to the microcontroller and configured to control a current flow through either an ozone generation lamp or a first biocide lamp in at least partial dependence on voltage dependent control signals received from the microcontroller. A second electronic ballast circuit is likewise operatively coupled to the microcontroller and configured to control a current flow through a second biocide lamp in at least partial dependence on voltage dependent control signals received from the microcontroller. 
   In a first related exemplary embodiment, the plurality of input signals includes airflow state signals, ozone sensor signals, current signals, voltage signals and ON/OFF state signals. 
   In a second related exemplary embodiment, the dynamically generated control signals associated with the ozone generation lamp is generally dependent on the ozone sensor signals. 
   In a third related exemplary embodiment, the voltage dependent control signals comprises a ground isolated 0-5V signal measured relative to a negative portion of an input power sine wave and the isolated ground. 
   In a fourth related exemplary embodiment, the dynamically generated control signals derived from the airflow state signals controls both the ozone generation lamp and the biocide lamp. 
   In a fifth related exemplary embodiment, the ON/OFF state signals is associated with one of, a relay state, electrical power state and a user interface switch. 
   In a sixth related exemplary embodiment, the ozone generation lamp is iteratively controlled by the microcontroller to maintain operation at a lowest possible operating intensity in at least partial dependence on the plurality of input signals. 
   In a seventh related exemplary embodiment, the microcontroller ignites the biocide lamp only after a sufficient warm-up period is confirmed by a significant increase in resistance is detected across a filament associated with the biocide lamp and using an electronic ballast circuit lacking an internal dimming circuit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. Where possible, the same reference numerals and characters are used to denote like features, elements, components or portions. It is intended that changes and modifications can be made to the described exemplary embodiments without departing from the true scope and spirit of the subject invention. 
     FIG.  1 —depicts a generalized and exemplary block diagram of an intelligent electronic control circuit as described in the various exemplary embodiments. 
     FIG.  2 —depicts an exemplary flow chart of a process for intelligently controlling the operation of an ozone generation lamp. 
     FIG.  3 —depicts a continuation of the exemplary process for intelligently controlling the operation of the ozone generation lamp. 
     FIG.  4 —depicts an exemplary flow chart of a process for intelligently controlling the operation of a biocide lamp. 
   

   DETAILED DESCRIPTION 
   An electronic control circuit is described in various embodiments which utilizes a microcontroller under programmatic control to receive and process a plurality of sensor signals derived from electronic ballast circuits, determine the appropriate operational state(s) for one or more gas discharge lamps in dependence on a plurality of pre-established control parameters and the processed sensor signals. 
     FIG. 1  provides a generalized and exemplary block diagram of an intelligent electronic control circuit as is described in the various exemplary embodiments. The intelligent electronic control circuit includes a microcontroller  100 , a pair of electronic ballast circuits  105 ,  120 , and a three part voltage power supply  30 A, B, C. Each electronic ballast circuit  105 ,  120 , is designed to power a different type of ultraviolet lamps  110 ,  115  under the programmatic control of the microcontroller  100 . In an embodiment, the electronic ballast circuit  120  is disposed in a modular plug in form factor which allows for the operation of an ozone generation lamp  110  and biocide lamp  115  or two biocide lamps  115 ′. The electronic ballast circuit  105  for the ozone lamp  110  an internal dimming circuit. The electronic ballast circuit  120  for the biocide lamp  115  does not use an internal dimming circuit which provides additional cost savings over the more expensive internally dimmable electronic ballast circuit  105 . 
   One portion of the power supply  30 A provides a highly regulated and power factor corrected output to power the majority of the electronic circuits at approximately 400 VDC relative to the negative portion of the alternating current sine wave  65  and is utilizes an isolated ground  80 . The second portion of the power supply  30 B utilizes the same isolated (i.e., floating) ground  80  arrangement and provides a 12VDC output relative to the negative portion of the alternating current sine wave  65 . The third portion of the power supply  30 C provides an 18 VDC output relative to common ground  75  to safely power the remote user interface  45 B without electrical shock potential. 
   The microcontroller  100  is operated using the isolated ground system  80  which allows the microcontroller  100  to simply and directly measure relative voltage changes induced by changes in the operating state (i.e., OFF, PREHEAT, IGNITION, ON) of the ozone generation lamp  110 . The isolated ground arrangement  80  places the microcontroller at the same voltage potential as the gas discharge lamps  110 ,  115  which allows for relative voltage changes to be accurately measured by the microcontroller  100 . 
   The power supply  30 A includes circuits to provide for power factor correction and optionally electromagnetic interference attenuation (EMI.) 
   The microcontroller  100  receives signals to determine the lamp configuration mode of the system (ozone and biocide lamps or two biocide lamps); a current signal from the biocide lamp  115  indicating that the biocide lamp  115  is actually in an ON state; a voltage signal proportional to the ozone generation lamp voltage; user interface  45 A, B pushbutton  47 ,  49  signals; a signal from the ozone sensor  125 , a signal from the ground isolated low voltage power supply  30 B indicative of a power failure, and a signal from the airflow sensor  130 . In an alternate embodiment, the microcontroller  100  determines if an ozone sensor  125  is connected to the microcontroller, and if so, the type ozone sensor  125  (not shown.) 
   The microcontroller  100  utilizes one or more of these input signals to programmatically control the operation of the two lamps  110 ,  115 . The microcontroller  100  under programmatic control output signals to turn the two lamps  110 ,  115  ON or OFF; display the operational mode of the control system on the user interface(s)  45 A,  45 B; and a pulse width modulated (PWM) signal  50  to set the output intensity level of the ozone generation lamp  110 . The PWM signal is conditioned back to a 0-5VDC signal to directly interface with the electronic ballast circuits  105 ,  120 . 
   The microcontroller  100  includes a processor  5 , a memory  10 , a timing circuit  15 , and an I/O interface  35 . A suitable microcontroller  100  is available from Microchip Technology, Inc., www.microchip.com, number PIC16F690. The microcontroller  100  is a highly integrated device which incorporates into a single package analog-to-digital conversion circuitry, timing circuitry, communications circuitry, comparator circuitry, multiplexer circuitry, and flash memory circuitry. Information concerning the PIC 16F690 is provided in Microchip Technology, Inc. specification sheet, entitled “PIC 16F685/687/689/690, Data Sheet, 20-Pin Flash-Based, 8-Bit, CMOS Microcontrollers with nanoWatt Technology,” 2005, which is herein incorporated by reference. 
   The microcontroller  100  includes a communications infrastructure  90  used to transfer data, memory addresses where data items are to be found and control signals  50  among the various components and subsystems associated with or coupled to the microcontroller  100 . The processor  5  is provided to interpret and execute logical instructions stored in the memory  10 . 
   The memory  10  is the primary general purpose storage area for instructions and data to be processed by the processor  5 . The term memory  10  is used in its broadest sense and includes RAM, EEPROM and ROM. The memory  10  maintains the firmware which is executed by the processor  5 , a set of predetermined control parameters, variables and other data necessary to intelligently control the operation of the two lamps  110 ,  115 . 
   A timing circuit  15  is provided to coordinate activities within the processor  5  in near real time and may be used to make time-based assessments of signals received by an I/O interface sensor interface  35 . 
   The I/O interface  35  receives signals from a variety of external electronic circuits including a set of optoisolators  60 , a sensor interface  25  and a remote interface  20 . The flexible nature of the microcontroller  100  allows the I/O interface  35  to utilize signals provided in a variety of forms including analog, 4-20 milliamps (ma), 0-5 volts (V); pulse width modulation (PWM); transistor to transistor logic (TTL), binary or state, (0/1 and ON/OFF); and serial communications formats. The optoisolators  60  electrically isolate the remote user interface  45 B, ozone sensor  125  (if installed) and associated interface circuitry  20 ,  25  from voltages apparent on the microcontroller  100  due to the isolated ground arrangement. The sensor signals  50  are conditioned backed from PWM signals used to traverse the optoisolators  60  to 0-4.3 VDC signals rather than to 0-5 VDC to protect the microcontroller  100  from over-voltages. 
   The remote interface circuit  20  is provided to drive a user interface UI  45 B which includes a display  40 B and a least one pushbutton  47 . In its simplest embodiment, the display  40 B consists of one or more light emitting diodes (LED). The display  40 B and user interface  45 B may be integrated into a common housing which allows remote operation of the control system. A local user interface UI  45 A is provided for operating the control system at the microcontroller panel, generally during servicing of the control system. The local user interface may include a simple display  40 A and one or more pushbuttons  49  analogous to the remote user interface  45 B. 
   The user interfaces  45 A, B allow for manually controlling the microcontroller  100  and/or displaying the operating mode of the control system, generally using LEDs  40 A, B. The LEDs also provide an indication of the operating status of the various external devices  30 ,  105 ,  120 ,  125 ,  130  and low voltage power supply  30 B. In another embodiment, the displays  40 A, B and user interfaces  45 A, B may be integrated into a touch sensitive liquid crystal display (LCD) screen. The user interface  45 A, B provides the means for a user to control and interact with the microcontroller  100 . The user interface  45 A, B provides interrupt signals to the processor  5  that may be used to interpret user interactions with the microcontroller  100  and are electrically coupled to the communications infrastructure  90  via the I/O interface  35  incorporated into the microcontroller  100 . User input signals  55  to the microcontroller  100  are sent through optoisolators  60  to isolate the input signals from the microcontroller&#39;s voltage which is relative to the negative portion of the AC input power voltage. The sensor interface  25  includes circuitry to convert the 0-5 VDC or 4-20 mA continuous signals into a Pulse Width Modulated (PWM) signal that passes through the optoisolators  60  and is conditioned back into the 0-4.3V for protection from analog device signal over-voltages. 
   The remote user interface UI  45 B may be hardwired to the remote interface circuit  20  using standard eight wire network cable (e.g., CAT 5.) In an alternate embodiment, a wireless arrangement based on BlueTooth (TM) or the various IEEE standards 802.11x, where x denotes the various present and evolving wireless computing standards may be used to connect the remote user interface UI  45 B to the microcontroller  100 . The optoisolators  60  ensure that only low voltage DC is provided to the remote interface unit  45 B as a user electrical shock prevention safety feature. 
   The various external devices  30 A,B,C  105 ,  120 ,  125 ,  130  include in one embodiment, first and second electronic ballast circuits  105 ,  110  which are coupled to first and second gas discharge lamps  110 ,  115 . The first and second electronic ballast circuits  105 ,  120  utilize commercially supplied electronic ballast chips available from a variety of manufacturers. For example, suitable electronic ballast chips are available from International Rectifier, Inc.; www.irf.com, nos. IR2156 and IR21593. Information concerning the IR2156 electronic ballast chip is provided in International Rectifier&#39;s Data Sheet No. PD60182-I entitled, “IR2156(S) &amp; (PbF) Ballast Control IC,” which is herein incorporated by reference. Information concerning the IR21593 electronic ballast chip is provided in International Rectifier&#39;s Data Sheet No. PD60194_A “IR21593 Dimming Ballast Control IC.” 
   These electronic ballast chips are electrically programmable to control a wide variety of operating characteristics of the gas discharge lamps  110 ,  115 . For example, the dead-time, run frequency, preheat frequency, preheat time, ignition current and related programmable parameters may be incorporated into the electronic ballast circuits  105 ,  120  by judiciously selecting the proper capacitances required to obtain the necessary RC time constants to suit a particular gas discharge lamp. 
   In an embodiment, the first gas discharge lamp  110  is a 185 nanometer ozone generation lamp. The ozone generation lamp  110  is a hot filament type lamp which is configured to maximize ozone generation is electrically dimmable with a 0-5V control signal  50  sent by the microcontroller  100  to the first electronic ballast circuit  105 . 
   In an embodiment, the second gas discharge lamp  115  is an ultraviolet biocide lamp  115 . The biocide lamp  115  is likewise a hot filament type lamp which is configured to irradiate a recirculated air volume sufficiently to destroy airborne pathogens. The biocide lamp  115  provides an output flux of about 300 microwatts per square centimeter when measured at one meter from the lamp. The biocide lamp(s)  115  are generally operated in an ON/OFF mode (state) and is controlled by the microcontroller  100  in dependence on detected airflow signals received by the airflow sensor  130 . 
   The ground isolated direct voltage and current data are directly related to the operational state of the gas discharge lamps  110 ,  115 . In the case of the ozone generation lamp  110 , the voltage across the entire ozone generation lamp  110  (i.e., filaments as well as an ignition arch length) is used to produce a dynamic voltage signal  55  which is directly proportional to the ozone generation lamp&#39;s voltage. 
   As the ozone generation lamp  110  is dimmed, the vapor inside the ozone generation lamp  110  cools causing the lamp&#39;s internal resistance to increase. The increase in the lamp&#39;s internal resistance causes a directly proportional increase in the lamp&#39;s voltage in accordance with Ohms Law. This voltage signal  55  is measured by the microcontroller  100  to determine and control the operational state of the ozone generation lamp  110  allowing the microcontroller  100  to dim the ozone generation lamp  110  safely over a wide range of ozone demands, dynamic environmental conditions and lamp operating ages. 
   The microcontroller  100  controls the ozone generation lamp  110  to protect the filaments while allowing the ozone generation lamp  110  to be dimmable in conjunction with a dimmable electronic ballast circuit  105 . At initial startup, the ozone generation lamp  110  is provided with a sufficient filament preheat time (controlled by the electronic ballast circuit  105 ) then set to full (100%) output by the microcontroller  100  for approximately thirty seconds to allow the ozone generation lamp  110  time to come up to full operating temperature before it is dimmed by the microcontroller  100 . The voltage across the entire ozone generation lamp  110  is monitored continuously as the ozone generation lamp  110  is slowly dimmed to its lowest sustainable output level. 
   If a voltage reading is detected which is significantly higher (i.e., a voltage excursion) than two previous voltage readings, the microcontroller  100  determines that the ozone generation lamp  110  is about to go out and sends a signal to the electronic ballast circuit  105  to turn the ozone generation lamp  110  on at full (100%) output. The voltage excursion readings decrease over time due to aging effects of the lamp&#39;s filaments. In practice, the voltage changes become less prominent when compared to a newer lamp. In an embodiment, the microcontroller is programmed to compensate for the decreased voltage signal based on the run time of each lamp. 
   The microcontroller  100  then sends a signal to the electronic ballast circuit  105  to begin dimming the ozone generation lamp  110  once again, while increasing the lowest dimmable setting. In this manner, over many cycles, the microcontroller  100  increases the lowest dimmable setting until the lowest possible output intensity has been determined for the given air temperature and air flow. Since air temperature and air flow change continuously, the dim point is cleared and found again every fifteen minutes. Dimming of the ozone generation lamp  110  is accomplished by the microcontroller  100  sending a 0-5V signal to the first electronic ballast circuit  105 . 
   In an embodiment, the ozone generation lamp  110  may be operated in a continuous ozone concentration monitoring mode. In this mode, the microcontroller  100  receives an analog 4-20 mA signal or a 0-5V signal from the ozone sensor  125 . In this continuous ozone concentration monitoring mode is initiated by a user pressing a pushbutton  47  on the remote user interface  45 B. A low ozone concentration corresponds to 0.03 parts per million (PPM), a medium ozone concentration corresponds to 0.05 PPM and a high corresponds to 0.08 PPM. These ozone setpoints are included as part of the predetermined control parameters used by the microcontroller  100  to control the ozone generation lamp  110 . 
   In this embodiment, the microcontroller  100  receives the ozone concentrations and averages the current ozone concentration with the previous two readings to calculate how much of an increase or decrease in the ozone generation lamp intensity is required to maintain the desired ozone level. In the event that the ozone generation lamp  110  has been dimmed as much as possible to maintain an operational state, and after three consecutive readings where the measured ozone output is still above the desired level setpoint, the microcontroller  100  sends a signal to the electronic ballast circuit  105  to turn off the ozone generation lamp  110  until the measured ozone concentrations falls below the desired concentration. 
   In an embodiment, the ozone generation lamp  110  may be operated in a manual mode. The manual mode bypasses signals from the ozone sensor  125  if installed. In this mode, the user presses a button  47 ,  49  to set the ozone generation lamp  110  into a low, medium, high or boost level. The low level corresponds to an average lamp output level of approximately 25%. The 25% average output level is maintained by the microcontroller  100  by cycling the ozone generation lamp  110  on and off every few minutes at a 50% output intensity; the lowest possible dim state that the ozone generation lamp  110  can be safely dimmed without risking possible damage to the lamp. 
   The medium level corresponds to an output level of approximately 50%. When dimming to about the 50% intensity level, the microcontroller  100  programmatically controls the lamp output intensity so that the minimum lamp output level stays above the voltage excursion point described above. When dimming to about the 75% intensity level, the microcontroller  100  first determines where the approximate 50% intensity level is situated, given the current air flow, air temperature and lamp age. Once the voltage excursion threshold has been determined, the microcontroller calculates the required dimming level to achieve the 75% intensity level. The boost mode corresponds to a 100% output intensity and is achieved by the user continuously depressing the pushbutton  47  on the user interface  45 B for a few seconds, at which point the ozone generation lamp  110  is set at 100% output for 30 minutes before it returns to the previous setting. 
   In an embodiment, the ozone generation lamp  110  may be operated in relay signal monitor mode. In this mode, the microcontroller  100  receives a switch (state) signal from the ozone sensor  125 . In this embodiment, the desired ozone concentration setpoint is set on the ozone sensor. When the ozone concentration rises above the desired ozone concentration level the switch opens, or alternately, when the ozone concentration falls below the desired concentration level the switch closes. 
   In this embodiment, the microcontroller  100  programmatically seeks the closed state. When the microcontroller  100  senses that the switch is closed, the microcontroller  100  slowly increases the ozone generation lamp  110  output level until the switch opens. Upon detecting the change in the switch state, the microcontroller  100  slowly decreases the ozone output level. As discussed above, if the ozone generation lamp  110  is dimmed to the minimum sustainable operational level and the switch is still open, then the microcontroller  100  will turn the ozone generation lamp  100  off until the switch opens. 
   The ozone generation lamp  110  is controlled by the microcontroller  100  to minimize the number of cold restarts which deteriorates the filaments within the lamp. The prolonged life of the ozone generation lamp  110  reduces maintenances costs and minimizes hazardous waste generation. 
   In the case of the biocide lamp  115 , the electronic ballast circuit  120  monitors the voltage across a bottom filament of the biocide lamp  115 . In a preheat mode, the amount of current passing through the lamp&#39;s filaments are fixed, thus allowing the voltage across the filament to be directly proportional to its resistance. The lamp&#39;s filament resistances are a function of their temperatures. As such, the biocide lamp  115  is allowed a sufficient amount of time to warm up and only ignite the lamp when the lamp&#39;s filaments have reached their ideal operating temperatures as recommended by the lamp&#39;s manufacturers. The microcontroller  100  determines the operating state of the biocide lamp  115  by measuring changes in voltage which are directly proportional to the filament&#39;s resistance. As the lamp&#39;s filament&#39;s warm up, the filament&#39;s resistance increases dramatically, approximately three fold, allowing the microcontroller  100  to measure the proper point in which to ignite the lamp. This ability to minimize the impact of cold starts on the lamp&#39;s filaments and ensuring that the lamp&#39;s filaments are not under or overheated regardless of the dynamic environmental conditions, thus prolonging the biocide lamp&#39;s  115  operational life, reducing maintenances costs and minimizing hazardous waste generation. 
   An ozone sensor  125  is provided to measure the ambient ozone concentration contained in the recirculated air volume. The microcontroller  100  may be configured to receive three different types of signals from the ozone sensor  125  including continuous analog signals (0-5V, 4-20 mA) or binary relay state signals (ON/OFF). The ability to utilize several different signal types provides greater flexibility in the number and types of ozone sensors  125 . 
   An airflow sensor  130  is provided to detect the presence of air flow in the HVAC system. The microcontroller  100  is programmed to turn off the ozone and biocide lamps  110 ,  115  if the air flow falls below a predetermined setpoint indicative of the HVAC system being turned off. This feature minimizes electrical power usage and prolongs the operational life of the two lamps  110 ,  115 . The airflow sensor may be adjusted to control a gas discharge lamp at various thresholds to compensate for variations in HVAC systems or dynamic variations in airflow within the HVAC system. 
   Referring to  FIG. 2 , an exemplary flow chart of a programmatic process for intelligently controlling the operation of an ozone generation lamp  110  is depicted. Where necessary, the firmware programs, applications, algorithms and routines may be programmed in a high level language, for example JAVA (TM), C++, C#, or BASIC. Alternately, assembly language specific to the microcontroller may be used. An exemplary computer code provided in a version of BASIC is provided in Appendix 1 to this specification. Appendix 1 is hereby incorporated by reference in its entity as if fully set forth herein. 
   The process is initiated  200  by loading the control parameters  204  from memory followed by a system calibration  208 . The microcontroller then checks the power status of the power supply  210 . If the power state is abnormal (i.e., and undervoltage state or a failed state)  218 , the microcontroller goes into fault mode where it saves the critical data in non-volatile memory  212 . If the power state is normal  218 , the microcontroller checks whether there is airflow in the HVAC system  214 . 
   If a low airflow or no air flow state is determined from the airflow sensor  222 , the microcontroller sends a signal to the electronic ballast circuit  1  and electronic ballast circuit  2  to turn off the ozone generation lamp and the biocide lamp  226  and indicates a no airflow state on the display LED  228 . 
   If the airflow is determined to be normal  222 , the microcontroller checks the operational status of the ozone generation lamp  234 . If the ozone generation lamp is programmatically permitted to be on  238  (i.e., the ozone concentrations have not been determined to be too high) and the ozone generation lamp is indeed on  242 , then the display LED will indicate that the ozone generation lamp is on  246 . If the ozone generation lamp is programmatically permitted to be on  238  and the ozone generation lamp is off  242 , then the display LED will indicate that the ozone generation lamp is off  254 . If the ozone generation lamp is not programmatically permitted to be on  238 , and there is airflow  250  then the display LED indicates that the ozone generation lamp is shutoff programmatically by pulsing the ozone generation lamp LED  258 . If the ozone generation lamp is not programmatically permitted to be on  238 , and there is no airflow  250  then the display LED indicates that the ozone generation lamp is off  254 . 
   The microcontroller then checks the user interface button  266 . If the button has been pushed  258 , the unit&#39;s operating mode is cycled  262 . The microcontroller then sets the ozone concentration threshold to what the ozone sensor should ideally read for the current operating mode  270 . 
   In an alternate exemplary embodiment, the microcontroller does not read a signal from the ozone analyzer. In this embodiment, the ozone generation lamp may be cycled on and off at approximately 50% output to produce a 25% output low level, set to 50% output for medium level, set to 75% for a high level, and 100% for boost level  264 . In this embodiment, the user selects the ozone level by pressing the button the user interface  266  to set the appropriate operating mode. 
   The 75% level is found by first searching for the 50% level given the particular environmental conditions, then calculating the appropriate 75% output level as is described below in the process for intelligently controlling the dimming of the ozone generation lamp  332  ( FIG. 3 ). 
   The process continues at A  300  of  FIG. 3 . Continuing at A  300  of  FIG. 3 , the microcontroller reads the current ozone level from the ozone sensor  304  and averages the current ozone concentration reading with the two previous readings. The microcontroller then compares the current average to the ideal ozone concentration threshold previously set  308 . 
   If the current average does not equal the ideal ozone concentration threshold  312 , the ozone output goal is adjusted up or down  316  as appropriate by the microcontroller to return the ozone concentration to an operating band defined by the preestablished control parameters. 
   If the microcontroller has dimmed the ozone generation lamp as far as it can safely be dimmed (approximately 50%) and the last three ozone measurements  320  were above the desired operating band  324  for the given mode, the microcontroller turns the ozone generation lamp off and prevents the lamp from turning on until the ozone measurement drops below the operating band for the given mode  328 . 
   The microcontroller begins a process for intelligently restarting and controlling the dimming of the ozone generation lamp. The microcontroller reads the current lamp voltage  332 , stores the current voltage reading in memory and determines whether the age  333  of the ozone generation lamp exceeds one or more of the predetermined control parameters  204  ( FIG. 2 .) The microcontroller is programmed to compensate for aging of the ozone generation lamp by keeping track of the hours of operation, essentially by a counter, for example, the service counter  380 . 
   If the age of the ozone generation lamp  333  exceeds the one or more predetermined control parameters  204 , the voltage detection sensitivity is increased  335  to allow the microcontroller to detect a smaller voltage excursion  334  as is discussed below. The microcontroller continuously monitors the voltage across the lamp&#39;s filaments until a voltage excursion is detected  334  as is discussed below. Such an excursion is indicative of the ozone generation lamp about to go out. The microcontroller uses the current voltage reading and two previous readings to determine if there has been an excursion. 
   If a voltage excursion has occurred, the ozone generation lamp is turned on and the output control signal is increased by a step  336 . The microcontroller then compares the control signal to the output goal  338 . If the goal is larger than the control signal  340  then the control signal is set equal to the goal  360  and the microcontroller exits the current loop and proceeds to determine if the ozone generation lamp has just turned on  372  as is described below. 
   If the goal is less than the control signal  340  then the microcontroller compares the control signal to the minimum allowable control value  348 . If the control signal is greater than the minimum allowable control value  348  then the control signal is decreased by a step. Each control step is determined by the number of bits available to the processor. In this exemplary embodiment, an 8 bit processor is employed; therefore a total of 256 voltage steps are available. In this exemplary embodiment, each step corresponds to +/−0.02V (0-5V control signal range/256 bits.) Then the microcontroller exits the current loop and proceeds to determine if the ozone generation lamp has just turned on  372  as is described below. 
   If the microcontroller determines that the ozone lamp has just turned on  372 , the microcontroller sends a signal to the electronic ballast circuit to set the output to 100% for thirty seconds to allow the ozone generation lamp to fully warm up  376 . The microcontroller then increments the service timer  380  and returns to the beginning of the loop at B  382  of  FIG. 2 . 
   Referring to  FIG. 4 , an exemplary flow chart of a programmatic process for intelligently controlling the operation of the biocide lamp is depicted. Unlike the ozone generation lamp, the biocide lamp is generally operated in a continuous full power mode except during initial startup, maintenance, power failures and HVAC airflow loss. 
   The process is initiated  400  by loading the control parameters  404  from memory followed by a system calibration  408 . The microcontroller then checks the power status of the power supply  410 . If the power state is abnormal (i.e., an undervoltage state or a failed state)  414 , the microcontroller goes into fault mode where it saves the critical data in non-volatile memory  412 . If the power state is normal  414 , the microcontroller checks whether there is airflow in the HVAC system  416 . 
   If a low airflow or no air flow state is determined from the airflow sensor  418 , the microcontroller sends a signal to the electronic ballast circuit  1  and ballast circuit  2  to turn off both the ozone generation lamp and the biocide lamp  226  and indicates a no airflow state on the display LED  228 . 
   If the airflow is determined to be normal  418 , the microcontroller checks the operational status of the biocide lamp  422 . If the biocide lamp is actually on  424 , the biocide lamp LED is turned on  436  and the process repeats in a loop  410  by repeatedly checking the power state  410 , HVAC airflow  416  and biocide lamp state  418 . 
   If the biocide lamp is not turned on  424 , the biocide lamp LED is turned off  426 , the microcontroller signals the electronic ballast circuit for the biocide lamp to turn on the lamp while maintaining a constant current across the lamp&#39;s filaments  428  during the preheating of the biocide lamp  430 . The microcontroller continuously monitors the voltage across the biocide lamps&#39; filaments until the biocide lamp has obtained a sufficient operating temperature to ignite the vapor within the lamp  438 . Once the biocide lamp is ignited, the process repeats in the loop  410  by repeatedly checking the power state  410 , HVAC airflow  416  and biocide lamp state  418  as previously described. 
   The various exemplary embodiments described herein are merely illustrative of the principles underlying an inventive concept. It is therefore contemplated that various modifications of the disclosed exemplary embodiments will, without departing from the spirit and scope of the various exemplary inventive embodiments will be apparent to persons of ordinary skill in the art. In particular, it is contemplated that functional implementation of the various exemplary embodiments described herein may be implemented equivalently in hardware, software, firmware, and/or other available functional components or building blocks. No specific limitation is intended to a particular method, system or process sequence. Other variations and exemplary embodiments are possible in light of above teachings, and it is not intended that this Detailed Description limit the scope of invention, but rather by the Claims following herein.