Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2002-11-26
2004-11-16
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S313000
Reexamination Certificate
active
06819060
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to lamp control, and more particularly to a system and method for controlling lamp operation, such as ultraviolet (UV) and fluorescent lamp operation, in brownout and other substandard source voltage conditions.
BACKGROUND OF THE INVENTION
Increased consumer power, deregulation laws, and other factors have imposed additional physical and economic stresses on utility organizations, thereby threatening record occurrences of power line phase droop and interruption events characteristic of poor transmission line regulation. In some cases, it is estimated that power line transmission losses will triple for utility companies.
Low line voltage or “sag” can have a significant impact on electrical equipment and products. For example, power supplies in some electronic equipment may fall out of regulation, motors can overheat or slow down, electrical interference may increase, etc. One product category that is significantly impacted by poor power line regulation includes ultraviolet/fluorescent lamps, that can flicker extensively under brownout conditions. In addition to the potentially undesirable visual effects, this flickering can damage the filaments of the lamp and cause premature lamp mortality. Lamps that would otherwise likely meet expected warranty periods or other commercial expectations can thus fail due to brownout conditions that are beyond the control of lamp manufacturers, product developers, and consumers.
Premature lamp mortality occurs in brownout or other low line voltage conditions as a result of the physics underlying ultraviolet (UV) lamp technology. In UV and fluorescent lamps, a sealed glass tube generally includes a small amount of mercury and an inert gas. The tube generally includes two electrodes or “filaments,” one at each end of the tube, which are wired to an electrical circuit coupled to an alternating current (AC) power source. When the lamp is initially turned on, electricity heats up the filaments, which boils off electrons from the metal surface into the gas tube, which in turn ionizes the gas and creates an electrically conductive medium. At this point, the lamp's ballast provides the voltage kick across the filaments to establish an electrical arc through the gas. The resulting collision of free electrons with atoms releases other electrons, which creates ions, and ultimately plasma which establishes a path for an electrical current. Electrons migrating through the tube provide energy that causes some of the mercury to change to a gaseous state, which collides with the electrons and charged atoms. These collisions excite the atoms and bumps the electrons to higher energy levels, and when the electrons return to their original level, light photons are released.
When AC power is diminished due to brownout or other low voltage conditions, enough voltage may still be provided to create the arc through the gas, but not enough voltage to sustain the arc and resulting current through the lamp. In such a case, arcing occurs repeatedly, which causes the flickering effect. When the lamp flickers in this manner, the filaments are continually called upon to boil off electrons from its metal surface to ionize the gas and establish the arc. This degenerates the integrity of the filament, and ultimately causes lamp failure. More particularly, when the lamp is subject to low line conditions, the operating lamp's cathode glowing layers cover only part of the cathode. When this occurs, the glow moves around, causing the flickering effect. If the available current is enough to cause the cathode to be covered with glow, the voltage drop of the cathode will be higher than what is expected under normal operation, causing ions to bombard the cathode with increased force and accelerating the sputtering of cathode material atoms. This sputtering effect essentially “evaporates” the cathode material, causing uneven discharge, and leaving the filament thinner in some areas. The weakened area of the filament becomes hotter, which leads to even faster evaporation, thereby causing the filament to burn back and the lamp to burn out. Some lamps may burn out the instant they are turned on, because a thinned filament in a cold state cannot withstand the inrush surge of energy.
UV lamps are commonly used in the context of fluorescent lighting, where the inside surface of the UV lamp is coated with a phosphor that gives off a white light when exposed to UV light. However, UV lamps are used in a wide variety of other contexts. For example, UV lamps can be used to kill airborne bacteria and surface mold in air treatment systems. One such UV air treatment system is available under the trade name “Enviracaire Elite™,” provided by Honeywell Inc., Golden Valley, Minn., U.S.A. The lamp life of UV lamps used in these and other UV lamp applications can be significantly diminished as a result of brownouts and other low line voltage conditions.
Accordingly, there is a need for a system and method for increasing lamp life that otherwise could be degraded due to poor power line regulation. The present invention fulfills these and other needs, and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the invention, a control system is provided for controlling operation of at least one lamp powered by a power source. The control system includes a monitor circuit to monitor at least one power characteristic of the power source, and to provide a signal indicative of the monitored power characteristic in response. A controller is coupled to the monitor circuit to receive the signal, and to interrupt power supplied by the power source to the lamp, when the signal indicates that a voltage of the power source is less than a voltage threshold.
In more particular embodiments of such a control system, the power characteristic being monitored may be the current through the lamp, which may become erratic under low voltage conditions. In this case, the monitor circuit includes a current monitor to monitor the current through the lamp, and to provide a signal indicative of the state of current flow through the lamp. The controller is coupled to the current monitor to receive this signal, and to interrupt power supplied by the power source to the lamp when the signal indicates an erratic state of current flow through the lamp as a result of the voltage being less than the voltage threshold.
In other particular embodiments of such a control system, the power characteristic being monitored may be the voltage itself provided by the power source. In this case, the monitor circuit includes a voltage monitor to monitor the voltage provided by the power source, and to provide a signal indicative of the voltage provided by the power source. The controller is coupled to the voltage monitor to receive this signal, and to interrupt power supplied by the power source when the signal indicates that the voltage is less than the voltage threshold. Any aspect of the voltage may be monitored, such as peak voltage, RMS voltage, etc.
In other particular embodiments of such a control system, a controllable switch is provided between the power source and the lamp. This controllable switch may be provided at any location between the power source and the lamp within the circuit path, such as on either the supply or return side of the lamp. Further, the controllable switch may be a discrete switch(s), or may be a switch associated with another component such as a ballast that includes an input(s) to control the ballast switch. In one embodiment of the invention, the controller interrupts power supplied by the power source to the lamp by automatically opening the controllable switch in response to the signal indicating that the voltage of the power source is less than the voltage threshold.
In still other particular embodiments of such a control system, the controller is further configured to restore power supplied by the power source to the lamp in response to at least one predetermined event. The predetermined event(s)
Lentz Tracy L.
Readio Philip O.
Dinh Trinh Vo
Honeywell International , Inc.
Wong Don
LandOfFree
Power line monitor and interrupt arrangement for averting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power line monitor and interrupt arrangement for averting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power line monitor and interrupt arrangement for averting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3355384