Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: SWITCH COVER PLATE PROVIDING AUTOMATIC EMERGENCY LIGHTING
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION:
This invention relates generally to emergency lighting devices such as standby
automatic
lamps, and more particularly to such an emergency lighting device assembled
into a
common switch cover plate and providing an illumination source and a sensor
for
1 o determining when AC power has been Lost to the electrical switch covered
by the plate.
DESCRIPTION OF RELATED ART:
The following art defines the present state of this field:
Nicholl et al., U. S. 4, I 77,500 describes a power failure light for
monitoring a power line
and for illumination upon the interruption of power. This invention includes a
Iight
bulb, a rechargeable battery, a power supply providing charging current for
the battery, a
pair of diodes connecting the battery across the power supply, a pair of
cascaded
2o transistors connecting the bulb across the battery with base-emitter
junctions
Chiu, U. S. 4,461,974 describes a multiple Lamp system for use with fiber
optic light
guide for automatically switching from a main lamp to a standby Lamp, upon
failure of
the former. A solenoid is employed with the inductor in the circuit of the
main lamp to
overcome the bias of the switch in the standby lamp circuit to keep the former
open.
When the main lamp fails causing the interruption of current flow, the switch
closes
thereby permitting energization of the standby lamp. An indicator is provided
to show
which lamp is functioning.
3ester, U. S. 4,514,789 describes a light switch plate having a rearwardly
opening
housing for removably holding an AA battery. This invention is detachably
mountable
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over a conventional wall mounted 110 volt AC light switch. An LED mounted on
the
front of the housing is connected to the battery through an integrated circuit
oscillator,
which flashes the LED.
McCue et al., U. S. 4,631,649 describes an emergency light fixture that is
permanently
mountable in a conventional power outlet box having, in fixed relation, a
threaded bore
for accommodating a screw for a face plate and slots for accommodating an
electric plug.
The emergency light fixture includes a housing, an electric plug extending
from the rear
wall of the housing, a battery, a battery charger, and a lamp mounted in the
housing and
to wired to provide illumination during a power outage.
Bavaro et al., U. S. 4,977,351 describes an emergency lighting system which
permits at
least one gas discharge lamp to be operated from an AC power source when AC
current
is present and form a battery when AC signal is not present. The circuit also
provides the
capability for turning the lamp on under other selected emergency conditions
such as in
response to an intruder detection, or in response to detection of smoke, heat,
water, or
some other emergency.
Waiters et al., U. S. 5,132,596 describes an outdoor lighting control that
includes a
2o photosensor responsive to ambient outdoor light and an alternating current
relay with a
pair of contacts movable between make and break positions. The relay includes
a contact
actuating arrangement that responds to the photosensor and alternating current
bias the
contact into a make position and move the contacts electromagnetically into a
break
position. The contact actuating arrangement is sufficiently stiff and
responsive to the
2s alternating current to limit chatter in the contact during passage from
make to break to
fifteen milliseconds when the photosensor senses a transition between dark and
daylight.
Preferably, the chatter is limited between l and 10 mill-seconds.
Li, U. S. 5,336,977 describes an emergency lighting device that includes a
hollow casing,
3o a magnetic field detecting unit, a lamp unit and a driving unit. The casing
is positioned
adjacent to an electric outlet. The magnetic field detecting unit is disposed
inside the
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casing and detects the absence of a magnetic field from the electric outlet.
The lamp unit
is mounted operatively on the casing. The driving unit is disposed inside the
casing and
is connected electrically to the lamp unit and to the detecting unit. The
driving unit
includes a Light-sensitive switch unit and is responsive to the detecting unit
so as to
activated the lamp unit only when the magnetic field from the electric outlet
is absent and
there is weak surrounding light.
Blackman, U. S. 5,473,517 describes a housing for an emergency light source,
which is
electrically connectable to a conventional light switch. The housing replaces
a
conventional switch plate and has at least one opening for receiving the
switch plate and
has at least one opening for receiving the switch actuator of the light
switch. The
replacement housing includes wires for electrical connection to the light
switch and is
divided into upper and lower housing section, wherein the upper section
includes a
battery compartment, a printed circuit board compartment, and an opening to
receive the
switch actuator. The lower housing section includes a compartment for
receiving a
compact fluorescent lamp, reflectors, and a diffuser cover.
The prior art teaches a variety of safety and emergency lighting devices.
Blackman
teaches a replacement switchplate with wired connection to a light switch.
TluS SmtCh
2o plate contains a lighting means. Waiters teaches a lighting control having
photosensor
responsive means. Jester teaches a lighted switch plate. Li teaches a magnetic
field
sensor responsive to an absence of power at a nearby AC outlet, such a sensor
being
unable to operate in conjunction with a switch since without current flow a
magnetic
field is not produced. However, the prior art does not teach a switch plate of
compact
size and proportions having field sensing capability so as to avoid the
necessity of hard
wiring and which provides an exit marker and illumination. The present
invention fulfills
these needs and provides further related advantages as described in the
following
summary.
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SUMMARY OF THE INVENTION
The present invention teaches certain benefits in construction and use which
give rise to
the objectives described below.
The present invention provides a wall mounted plate which includes an
electrical circuit
capable of sensing the electrostatic field associated with an electrical
circuit within, or
behind the wall. The electrical circuit uses an antenna for sensing the loss
of field energy
and then enables a lighting circuit in order to provide emergency exit
lighting.
A primary objective of the present invention is to provide a proximity circuit
capable of
providing emergency lighting when a power failure occurs, such circuit having
advantages not taught by the prior art.
Another objective is provide such a circuit within a switch plate that is
mounted over a
switch box by the typical screw-on method used for common switch plates.
2o A further objective is to provide such a circuit which has the advantage of
being operated
over Iong periods of time by a small battery source and therefore does not
require the use
of household current.
A still further objective is to provide such a switch plate embodied in a
relatively flat and
compact size so as to give the appearance of an ordinary switch plate, yet
which provides
the advantages of emergency lighting and automatic functioning upon power
failure.
A still further objective is to provide such a wall plate embodied in a
relatively flat and
compact size so as to give the appearance of an ordinary AC outlet cover, yet
which
3o provides the advantages of emergency lighting and automatic functioning
upon power
failure.
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A still further objective is to provide such a wall plate embodied in a
relatively flat and
compact size so as to give the appearance of an ordinary wall cover plate, yet
which
provides the advantages of emergency lighting and automatic functioning upon
power
s failure.
Other features and advantages of the present invention will become apparent
from the
following more detailed description, taken in conjunction with the
accompanying
drawings, which illustrate, by way of example, the principles of the
invention.
to
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawings illustrate the present invention. In such drawings:
1 s FIGURE 1 is a front elevational view of a first embodiment of the present
invention,
a wall switch cover plate;
FIGURE 2 is a sectional side elevational view thereof taken along cutting line
2-2 in
Fig. l and showing a switch box and wall switch;
FIGURE 3 is a block diagram of an electrical circuit of the invention;
FIGURE 4 is a perspective view of the embodiment of Fig. 1; and
FIGURE 5 is a perspective view of a second embodiment of the invention, a
power
outlet cover plate.
DETAILED DESCRIPTION OF THE INVENTION
3o The above described drawing figures illustrate the invention an emergency
lighting
device generating illumination in closed spaces when a general power failure
occures. A
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first embodiment of the invention, an emergency lighting device for covering a
wall
switch electrical box 10, which is mounted in or behind a wall 20 is
illustrated in Figs. 1-
4. The electrical box 10 contains an electrical wall switch 30 having a switch
arm 32
extending outwardly from the wall 20 so as to be manually adjusted for turning
room
s lights on and off.
The invention includes a switch plate 40, one version of which is illustrated
in Figs. 1, 2
and 4, for covering the wall switch electrical box 10, the switch plate
providing an
electrical circuit mounting surface 42, a switch plate mounting means 44,
typically a pair
of spaced apart holes, and a switch arm engaging means 46, typically a
rectangular hole.
Preferably, the switch plate 40 provides a central portion 40A including the
switch plate
mounting means 44 and the switch arm engaging means 46. The central portion
40A is
preferably planar, so as to lie in contact with the wall surface. The switch
plate 40
further includes a peripheral portion 40B providing an enclosure means 40C for
enclosing an electrical circuit 50. The enclosure means 40C provides a space
for
containing the components of the electrical circuit 50. This space is enclosed
between
the wall 20 and the switch plate 40 so that the electrical circuit components
and their
supporting elements are not visible from the front of the switch plate 40. The
central
portion 40A cooperates with the wall switch 30, and the peripheral portion 40B
2o cooperates with the central portion and the surrounding wall to enclose the
electrical
circuit 50. This is considered a key inventive aspect of the present invention
in that the
device, as a whole takes on the appearance of a simple, common wall switch
cover, and
provides, a close-to-the wall portion (40A) for engaging the switch arm 32
(also
commonly refered to as a "bat" or "toggle"), and a peripheral enclosure
portion (40B)
providing a means for circuit housing within the electrostatic filed of the
wall switch, or
as described below, any other electrostatic field generating electrical
device.
The electrical circuit 50, is illustrated in Fig. 3. In this circuit, an
antenna 80 is exposed
to the local electrostatic field produced by the building AC wiring or other
electrostatic
3o field generating means such as the wall switch 30. The combination of
electrostatic field
strength, the coupling capacitance created by the antenna 80, the ground
return, and the
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input impedance of an amplifier 82 all determine the level of signal voltage
developed by
the antenna 80. U.L. safety requirements demand that two large value safety
resistors 84
be inserted in series with the antenna 80 to limit current flow should an
electrical short
occur between the antenna 80 and the building AC power wiring. Since, in the
present
s invention there is no way for these two elements to come into contact, this
occurance
would be unlikely.
The amplifier 80 boosts the detected signal voltage for driving a peak
detector circuit 86
and a steering logic circuit 88 as shown in Fig. 3. The peak detector circuit
86 produces
to a DC voltage which is proportional to the amplified antenna voltage once it
exceeds a
first threshold. Beyond a second threshold the peak detector circuit 86
saturates,
providing no additional DC voltage boost although the AC field strength may
increase
further. Rapid charge and slow discharge characteristics are appropriately
selected to
avoid both false triggering of a bank of LED's 90 and any unnecessary delay in
i s operation.
The steering logic circuit 88 accepts inputs from both the peak detector
circuit 86 and a
test/reset means 87, described herein also as a button. Both inputs are
condtioned in the
steering logic circuit 88 by schmiddt triggers to produce clean logic
transitions. The
2o steering logic circuit 88 makes decisions about whether the LED's 90 will
be on or off
depending on the following conditions, where it is understood that AC power is
considered equivalent to the presence of the above described electrostatic
field and loss
of AC power is equivalent to the loss of the electrostatic field:
2s I ) With AC power present with sufficient field strength the LED's 90 will
be held
off. Momentary activation of the test/reset button 87 will in turn momentarily
activate the LED's 90. When the test/reset button 87 is released the LED's 90
automatically turn back off to avoid accidental and unnecessary draining of a
battery 58 (see Fig. 2).
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2) With AC power suddenly vanishing the LED's 90 will be latched in the on
state
until one of three things occurs:
a) The battery 58 is discharged to an unuseable level.
b) AC power is restored.
c) The test/reset button 87 is momentarily pushed to reset the LED's 90 to an
off state.
Subsequent cycling of the test/reset button 87 with AC power not present will
cause
1 o alternate latching 'ON' and unlatching 'OFF' of the LED's 90. An LED
driver circuit 89
senses the logic level produced by the steering logic circuit 88 and provides
suffient
current to drive the LED's 90 when it is commanded to do so. The LED's 90 are
preferably super high flux types which can provide adequate lighting in a
small room
during AC power emergency conditions to facilitate personnel orientation. The
test/reset
means 87 and the steering logic circuit 88 is adapted for automatically
placing the
invention in an active state following a loss of the electrostatic field of
the electrostatic
field generating means (wall switch, etc.) and a manual shutdown of the
illumination
means 56, such that a subsequent return of the electrostatic field and a
subsequent second
loss of the electrostatic field provides a further ignition of the
illumination means 56
2o without human intervention.
A low battery test circuit 92 senses when the battery 58 is discharged below a
level that
is necessary for providing sustained emergency lighting. It then flashes one
of the LED's
90A with a repeated low duty cycle pulse to provide a visual warning. The low
battery
test circuit 92 is designed to test the battery 58 while minimizing battery
current drain
during the test. A pulse generator circuit 94 operates at a very low duty
cycle providing
battery power to a comparator circuit 96. Both the comparator circuit 96 and a
voltage
reference circuit 98 are momentarily turned on during each cycle of the pulse
generator
circuit 94. A sample of the battery voltage is compared to the voltage
reference of the
3o voltage reference circuit 98. The comparator circuit 96 then momentarily
fires the LED
driver 89B if the sampled battery voltage is too low. It should be clear from
the
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description of the operation of each of the individual circuit elements
described above
that one of skill in the electrical engineering art will know how to build and
operate each
of these circuit elements. The purpose of the above circuit description and
Fig. 3 is
merely for enablement of the present invention and to identify how such well-
known
elements may be assembled and interconnected to make a working device capable
of
achieving the objectives of the present invention.
The switch plate 40 further provides an illumination means viewing means 48.
The
illumination means viewing means 48 may include at least one aperture 48A in
the
1 o switch plate 40, the apertures) 48A being positioned and engaged with the
illumination
means 56 for direct viewing of the illumination means 56. Therefore, as shown
in Fig. 1,
aperture 48A is one or more rectangular holes in switch plate 40 through which
elements
of illumination means 56 may protrude or be visible. Alternately, the
illumination means
viewing means 48 may include at least one light transmissive portion 48B on
the switch
is plate 40, where, the at least one light transmissive portion 48B is
positioned and engaged
with at least one element of the illumination means 56 for indirect viewing of
the
illumination means 56, i.e., by viewing the light from the illumination means
56 without
viewing the illumination means 56 itself. Such an alternate viewing means 48B
may be a
clear or a colored portion of switch plate 40 which, as shown in Fig. 1 may
Iay over an
2o illumination element part of illumination means 56.
In a second embodiment of the invention, as shown in Fig. 6, the electrical
apparatus
covered by the switch plate is an electical outlet means such as a duplex
socket of the
type well known in most households (not shown). Such a device has an
electrical socket
25 means accessable to the invention. In this case the electrical box engaging
means is an
electrical plug means 70, such as the dual plugs shown in the figure, for
engaging the
electrical socket means of the electrical apparatus. Therefore in this
embodiment, the
invention is mounted over a wall outlet box and is in close proximity thereto.
Further the
invention, in this embodiment provides a duplex socket 72 for accepting plugs
that would
30 otherwise be inserted into the socket of the electrical outlet means. This
embodiment
shows that the present invention may be used with an electical socket outlet
as well as a
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wall switch for the same intended purpose. Obviously, the present invention
may be
applied to other applications beside wall switches and AC outlets. Any
situation wherein
an AC voltage change is occuring, with, or without current flow, within a few
centimeters of the surface of a wall is appropriate for the mounting of the
present
invention onto the exterior wall surface in order to indicate that the AC
voltage is no
longer present and to provide emergency illumination. One important
application is in
the interior of elevators in order to provide emergency lighting in case of a
power failure.
It is clear that in many applications of the present invention no physical or
electrical
interconnection between the invention and the AC device or wiring that is
being
t o monitored by the invention is necessary. In such cases, the enclosure
means 40 may be a
smooth plate with mounting means. Such mounting means may be an adhesive
backing
or a magnet or other well known possibilities.
While the invention has been described with reference to at least one
preferred
embodiment, it is to be clearly understood by those skilled in the art that
the invention is
not limited thereto. Rather, the scope of the invention is to be interpreted
only in
conjunction with the appended claims.
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