Note: Descriptions are shown in the official language in which they were submitted.
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83-1-066 -AL-
BrMETAL CIRCUIT BREAKER WITH LEG PORTIONS OF UNEQUAL LENGTH
TECHNICAL FIELD
This invention relates to rapids art type fluorescent
lamps and more particularly Jo rapid-start type fluorescent
lamps having a thermally sensitive bimetal circuit breaker
thereon of U-shaped configuration and uneven length
portions.
BACKGROUND ART
generally, the most commonly encountered fluorescent
lamps are the so-called "preheat" and "rapid-startl' types
of fluorescent lamps. In the "preheat" type of lamp,
heater current flows through the lamp electrode during lamp
ignition. Thereafter, an external voltage sensitive
starter opens the electrical circuit to the lamp electrode
and heater current flow is discontinued. The "rapid-start
type of fluorescent lamp normally ha a constant flow ox
heater current through each electrode not only during
ignition but also during operation of the lamp. However,
heater current flow during operation, as in the
rapid start lamp, is lost power which undesirably reduces
the operational efficiency of the lamp.
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Numerous suggestions have been made for enhancing the
efficiency of "rapid-start" type fluorescent lamps. For
example, US. Patent Nos. 4,052,687: 4,0g7,779; ,968;
4,156,831 and 4,171,519 which are all assigned to the
Assignee of the present application, provide numerous
configuration for enhanced operation of "rapid-start" type
fluorescent lamps. Primarily, each provides a thermally
responsive circuit breaker suitable for discontinuing
heater current during operation of the fluorescent lamp.
Although the above-described fluorescent lamp and
circuit breaker structures have numerous advantages, it ha
been found that there are problems with the known
configurations. More specifically. the known rapid start
fluorescent lamp utilizing a circuit breaker therein
normally employ a circuit breaker of the type having a
substantially U-shaped bimetal switch. This U-shaped
thermally responsive bimetal switch includes a pair of leg
portions of substantially uniform length. One ox the leg
portions is welded to an electrical conductor passing
I through the glass envelope of the circuit breaker and the
other leg portion makes contact with another electrical
conductor passing through the glass envelope.
While the above-described circuit breakers having a
U-shaped bimetal switch with a pair of leg portions of
equal length have been an improvement o'er other known
structures, it has been found that the-leg portion which is
attached to one of toe electrical conductors tends to bend,
upon the application of heat thereto, prior to the bimetal
moving away from the other electrical conductor whereat a
switching contact is present. As a result of this
undesired bending of the bimetal, it was determined that
the opening temperature of the bimetal switch vary by
several degrees centigrade depending upon the amount of
flexor occurring along the leg portion fastened to the
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electrical conductor. Moreover, this undesired wending of
the leg portion of the U-shaped bime~al caused a shift in
the location at which the opposite leg portion kinked
the other electrical conductor. This variation in contact
point was also detrimental to a uniform operation of the
switch at a given temperature.
OBJECTS AND SUMMERY OF THE INVENTION
An object of the present invention it to provide an
enhanced rapid star fluorescent lamp. Another object of
the invention is to improve the operation of a circuit
breaker suitable for use in a rapid-start fluorescent
lamp. A further object of the present invention is to
improve the consistency and repeatability of toe switching
operation of a circuit breaker usable in a rapid-start
fluorescent lamp.
These and other objects, advantages and capabilities
are achieved in one aspect of the invention by a
rapid-start fluorescent lamp having a circuit breaker
therein with a thermally sensitive bimetal switch having a
substantially U-shaped configuration and a pair of leg
portions of different lengths.
BRIEF DESCRIPTION OF TOE DRAWINGS
.
FIG. 1 is an elevation Al view, partly in section, on
one end of a rapid-start fluorescent lamp having a circuit
breaker therein: and
FIG. 2 it a cross-sectional view of the circuit breaker
of FIG. 1 illustrating the configuration of the invention.
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BEST MOD OR CARRYING OUT THE INVENTION
For a better understanding of the present invention,
together with other and further objects Advent and
capabilities thereof, reference is made to the following
disclosure and appended claims in conjunction with the
accompanying drawings.
Referring to FIG. 1 of the drawings, a rapid-start
fluorescent lamp includes an elongated glass envelope 5
having a coating of phosphors 7 on the inner wall surface
of the envelope 5. A glass stem member 9 is sealed into
the end of the envelope 5 and includes a pair of electrical
leads 11 and 13 sealed therein and passing there through.
An end cap 15 is telescoped over and attached to the end of
the glass envelope S and include a pair of pins 17 and 19
electrically connected to a portion of the electrical leads
11 and 13 and formed to provide electrical connection to an
external source (not shown). Moreover, the envelope 5 has
a gas fill therein selected from the group consisting of
argon, krypton, neon, helium and combinations thereof.
I An electrode 21 is located within the envelope 5 and
connected at opposite ends to the electrical leads 11 and
13. Thus the longitudinal axis of the electrode 21 is in
a direction substantially normal to the direction of the
electrical leads 11 and 13. Moreover, this electrode 21,
which it frequently referred to as a filament or cathode,
is of a well known type use in rapid start fluorescent
lamps and usually include a tungsten coil having a coating
thereon in the form of alkaline earth oxides which were
applied in the form of carbonates and processed Jo provide
toe oxides.
Disposed within the envelope 5 is a circuit breaker
z3. The circuit breaker 23 is preferably in the form of a
glass bottle 25 having a press seal at one end thereof. A
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pair of electrical conductor 27 and 29 are sealed into and
pa through the press seal of the glass bottle 25. Also,
a thermally-sen~itive metal 31 is positioned within the
glass bottle 25 with one end thereof attached to one of the
electrical conductor 27 and the opposite end of the
bimetal 31 contacting the other electrical conductor 29.
Further, a conductive by-pass element 33, which is meltable
in response to a short duration high voltage pulse
potential shunts the bimetal 31 and is electrically
connected to the electrical conductor 27 and 29.
moreover, toe electrical conductors 27 and 29 extending
outwardly of the glass bottle 25 are connected to the pass
pin 17 and to the electrical lead 11 respectively with the
electrical lead 11 also connected to one end of the
15 electrode 21.
Referring to the enlarged illustration of the circuit
breaker (FIG.. 2), it can readily be seen that the bimetal
31 is of a substantially U-shaped configuration having a
first leg portion 35 which is attached to one of the
20 electrical conductor 29. A second leg portion 37 it in
contact with the other one of the electrical conductor
27. As can readily be seen, the first and second leg
portions 35 and 37 are of unequal length. Also, the first
leg portion 35 which it affixed to the one electrical
conductor 29, as by welding for instance, is not as great
in length a the second leg portion 37 which contacts the
other electrical conductor 27.
Additionally, it can readily be seen that a shorter
first leg portion I tends to virtually eliminate any
flexor along the length thereof. Also, the reduced length
of the first leg portion 35 permits a shortening of the
contact area of the second leg portion 37 and second
electrical conductor 27 since the effective length of the
bimetal 35 and consequently, the amount of change of length
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due to heaving, has been reduced. Moreover, the total
length of bimetal material has been reduced which also
reduces the amount and cost of bimetal material. As a
result of this reduction in bimetal material, reduction in
flexor of the bimetal by reduction of the length of the
first leg portion and reduced amount of movement between
bimetal leg portion 3J and electrical conductor Z7,
uniformity and consistency of operating temperature of the
bimetal switch 35 has been improved.
While there has been shown and descried what is at
present considered the preferred embodiments of the
invention, it will be obvious to those skilled in the art
that various modifications and changes may be made therein
without departing from the invention as defined by the
appended claims
