Electric lamps, particularly incandescent halogen lamps of the type employed for automotive applications, have experienced premature failures in service; and, it has been quite difficult to determine whether the failure was due to faulty lamp construction or intervals of exposure to excessive supply voltage to the lamp. Excessive supply voltage, even for a relatively limited interval, can cause the lamp to operate at above-normal temperatures which results in shortening the expected life of the lamp as expected with the nominal supply voltage. Where the lamp is exposed to excessive supply voltages for such limited periods, it is virtually impossible to detect such occurrences by visual examination of the lamp until failure occurs.
Thus, it has been long desired to provide a way or means of determining whether an electric lamp has been exposed to over voltage in service resulting in excessive temperatures of the lamp. It has been desired to provide such a determination of excessive voltage in a manner which is readily detectable by the user during service and by the manufacturer after the lamp has failed.
In addition, when the lamp is put into service with insufficient air circulation thereabout, even at nominal operating voltage, the lamp can experience excessive temperatures resulting in premature failure.
The present disclosure describes a technique for providing visual indication on a an electric lamp of the thermal dosage the lamp has been exposed to during service, and particularly thermal dosage resulting in temperatures considered to be excessive in terms of the normal expected operating voltage for the lamp. In one version, thermally responsive coating is applied to a selected spot on the lamp or its base. The coating is responsive to exhibit different colors based upon the temperature to which the coating has been exposed and the time that the lamp was exposed to such excessive temperature which together provide an indication of a thermal dosage. This information may then be used to determine the reduction in the expected service life of the lamp. In another version, a semiconductor element is attached to a designated portion of the exterior surface of the lamp or either one of the interior or exterior of its base and the electrical properties found in the semiconductor are monitored during service. From a look-up table of electrical properties as a function of temperature, it can be determined what temperatures the lamp has experienced during sensing of the certain electrical properties. In another version, a cell of carbon material of predetermined dimensions is disposed in a designated area of the surface of the lamp or its base and; upon operation of the lamp the dimensions of the carbon may be measured at intervals. From a look-up table of changes in the dimensions as a function of thermal dosage, it can be determined what temperatures the lamp has experienced during the intervals. From this information the reduction in normal service life due to exposure to the high temperatures for a particular interval can be estimated. Carbonaceous material may also be employed as a cell of predetermined dimensions.
The disclosure describes a way or means to determine the operating temperature exposure and cumulative time of operation of the lamp; and, from the combination of these two, the cumulative thermal dosage is determined.
Referring
A spot of thermally responsive coating 28 is provided on a designated region of portion of the base 14; and, the coating 28 is formed of suitable materials such as acrylate/resin and changes color as the coating is exposed to elevated temperatures for various time intervals. The coating may alternatively be provided on a designated region of an internal surface portion of the base 14.
Referring
From
In the present practice, it has been found satisfactory to employ a material for the coating 28 of the version of
Alternatively, the thermally responsive coating 28 may be replaced by a temperature indicating semiconductor which is electrically connected to circuitry for monitoring the electrical properties of the semiconductor. In this version, the change in electrical properties of the semiconductor may be compared with a look-up table (not shown) of values of temperature as a function of the electrical properties such as drain current change; and, thus the temperature exposure of the lamp determined by the change in electrical properties.
Referring to
With continued reference to
Alternatively, the cell 40 may be formed of suitable carbonaceous material which exhibits the properties of sublimation at temperature as does the carbon material cell.
The present disclosure thus describes a technique for providing an indication in real time of the thermal dosage or time at temperature exposure of an electric lamp in service, particularly to excessive temperatures such as would be caused by excessive voltage applied to the lamp. In one version, a coating applied to a designated region of the lamp undergoes different color changes when exposed to different combinations of temperature of specified intervals. In another version, a semiconductor is monitored for changes in its electrical properties to give an indication of the thermal exposure of the semiconductor on the lamp. In another version, carbon or carbonaceous material in the form of a cell of specified dimensions is applied to the surface of the lamp; and, changes in the dimension of the cell leads to sublimation from temperature exposure employed to determine the degree of thermal dosage to which the cell has been exposed. The technique of the present disclosure thus provides the unique and simple way of determining whether an electric lamp has been exposed to excessive thermal dosage or high temperatures for specified intervals of time which would result in a reduction in the normal expected life.
The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations and is limited only by the following claims.