Abstrict An emergency exit sign auxiliary lamp flashing system operates
from self-contained rechargeable batteries upon failure of the electrical
power from the AC power mains supplying power to the exit sign,
including a charging circuit for recharging the batteries, with
provisions for preventing overcharging and for disconnecting the
load from the batteries before the battery voltage drops to a level
which would impair its service life. Included is a solid state circuit
which provides for automatically exercising and self-testing the
proper functioning of the system to ensure its being serviceable
when called upon to function during a power failure by periodically
simulating the effect of a failure of AC power and verifying that
the battery, lamp and flashing circuit operate normally or signalling
a visual and/or audible alarm if they fail to operate properly.
Claims What is claimed is:
1. An emergency exit sign auxiliary lamp illumination system operative
in response to the failure of electrical power mains voltage, the
improvement including:
(a) switch means to interrupt electrical power to a portion of
said system and activating said switch means automatically at periodic
intervals by included timing means;
(b) alarm means including visual and/or audible signal indications,
said alarm means operative upon interruption of electrical power
mains voltage to actuate said portion of said exit sign auxiliary
lamp illumination system;
(c) detection means including filtering means for delaying response
of said detection means, said detection means responsive to normal
operation of said exit sign auxiliary lamp illumination system;
(d) means for automatically exercising and self-testing the proper
functioning of said system to insure the system's being in a serviceable
condition when called upon to function during power failure;
(e) circuit means utilizing a pulsating DC voltage to determine
a sufficiently depleted battery so that current drain from the battery
ceases and is not continued beyond a determined limit, the pulsating
DC voltage sent across a transistor coupled to a capacitor, thence
through a diode, the ceasing being with a DC voltage insufficient
to maintain appreciable base current to an associated transistor,
and
(f) restoring means to restore power to said portion of said auxiliary
lamp illumination system, said restoring means operative upon detection
of normal auxiliary lamp operation by said detection means.
2. An emergency exit sign auxiliary lamp illumination system improvement
in accordance with claim 1 wherein
both said switch interrupting and restoring means consist of a
solid state semiconductor.
3. An emergency exit sign auxiliary lamp illumination system improvement
in accordance with claim 1 wherein
said visual indicator includes an incandescent lamp with filament
of low thermal inertia.
4. An amergency exit sign auxiliary lamp illumination system improvement
in accordance with claim 1 wherein there is provided in said circuit
means a timing means to establish a rate and cause the visual indication
to blink at said timing rate.
5. An emergency exit sign auxiliary lamp illumination system improvement
in accordance with claim 4 wherein the blinking indication is provided
by an LED indictor energized through a resistor to cause blinking
at said timing rate.
Description SUMMARY OF THE INVENTION
The present invention relates to emergency exit signs operating
from standby rechargeable batteries upon failure of electrical power
from the AC power mains, and means to automatically verify periodically
that the equipment will operate properly when called upon to do
so in a real power failure. More specifically, it relates to emergency
exit signs provided with an auxiliary lamp flashing system operated
from rechargeable batteries charged from the rectified current from
the AC power mains and capable of providing several hours of flashing
operation of the exit sign illumination in the event of a power
failure. While describing the system primarily in terms of flashing
auxiliary lamp illumination, the principle is equally applicable
to non-flashing illumination by simple modifications described.
Often, particularly when an emergency standby battery system has
been inactive for long periods of time, a failure of some component
of the emergency system will preclude its proper operation at the
time when emergency use is required, thereby vitiating its whole
intent and purpose. Periodic servicing, verifying proper operation
by "exercising" the system and making any necessary repairs
should all be properly done at the time when the emergency system
is not needed, but until there is a power failure, little incentive
exists to check such systems and so they are frequently left unchecked
to deteriorate and be inoperative at the time needed.
It is therefore the primary object of the present invention to
provide an automatic system for checking that the emergency battery
powered equipment will function properly should it be called upon
to do so, by periodically (say, once per day or once per week or
at such interval as deemed appropriate) simulating the effect of
an interruption of AC mains power and verifying that the emergency
battery powered equipment indeed operates as required.
It is a further object of the present invention to provide a visual
and/or audible alarm in the event that the emergency system would
have failed to function properly at that time should a real power
failure have occurred, by performing simulated power failure tests
periodically and signalling such alarm upon malfunction.
The above and other objects of the present invention are realized
in a specific illustrative embodiment thereof wherein a rechargeable
battery is maintained at full or near full capacity by float charging
from the rectified AC power mains current and arranged to provide
power to an auxiliary lamp flashing circuit upon failure of the
AC mains power with means to disconnect the battery from its load
before it becomes excessively depleted and timing means to interrupt
the charging current to the battery, thereby simulating a condition
which occurs upon failure of the AC power. Simultaneously a visual
and/or audible alarm becomes activated and is then deactivated by
circuit means upon evidence that the emergency flashing lamps have
operated properly through the generation of a resetting signal which
removes the simulated power failure and reinitiates the timing mechanism
to begin timing again toward the next periodic failure simulation
and test. In the event that such resetting signal derived only from
proper operation of the lamp flashing system is not obtained, signifying
some malfunction of the battery, charger, lamp or flashing circuit,
the visual and/or audible alarm does not become inactivated and
being energized from a source separate from the rechargeable battery
system, namely the AC power mains, continues to operate until AC
power is disconnected or the cause of the circuit malfunction is
corrected. Provision is included to shorten the periodic verification
period, which may be as often as every day or extended to once per
week or once per month or whatever test schedule is deemed appropriate,
to once every few minutes for purposes of "fast testing"
the system during servicing and bench testing without the need to
wait for the daily, weekly, monthly or other normal timing cycle.
A further purpose of the invention is to "exercise" the
emergency lamp flashing system in a manner similar to that which
it would be called upon to do should an actual power failure occur
and by so "exercising" the system, to stress its components
under normal operation thereby disclosing faults which might not
be uncovered with other checking systems which might only measure
battery voltage or charging corrent, or lamp continuity. Consequently,
failure of any part of the battery charging system, for example,
will, through this periodic "exercising" of the entire
flashing system, gradually result in depletion of the battery to
such a point that it will not be capable of providing normal flashing
and the resetting signal and only then signalling a failure when
tested even though immediately upon failure of the battery charging
system and for a short time afterwards while the batteries still
hold a sufficient charge, the periodic test would not have indicated
the circuit malfunction because enough charge would have been retained
to activate the emergency lamp flashing system normally for a limited
period of time after this failure in the battery charging system.
The invention further includes means to visually indicate that
charge current is flowing and that timing is in progress through
miniature Light Emitting Diode illumination.
The above and other objects, features and advantages of the present
invention will become more apparent from the following detailed
description of a specific embodiment thereof presented herein below
in conjunction with the accompanying drawings which schematically
depict the charger-flasher circuit incorporating automatic self-checking
provisions in accordance with the principles of the present invention
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall block diagram of the charger-flasher system
incorporating self-testing provisions.
FIG. 2 is an overall detailed schematic of a circuit diagram of
a circuit embodying the invention.
FIG. 3 is a detailed schematic circuit diagram of the alarm indicator
giving either or both visual and audible alarm indication upon failure
of the charger-flasher during periodic test.
FIG. 4 is a detailed schematic circuit diagram of the emergency
battery operated lamp flashing system and charger including provisions
for preventing overcharging of the rechargeable battery and means
to disconnect the battery from its load prior to excessive depletion
which might result in diminished battery life.
FIG. 5 is a logic diagram of the periodic timing circuit of the
charger-flasher system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 there is shown a block diagram of the charger-flasher
system with self-testing capability which includes a rectifying
circuit 1 operating directly from the AC power mains to provide
rectified and filtered DC, 77 and 78 to a failure indicating alarm
circuit 2 and through switch means 3 shown here schematically and
blocking diodes 5 6 7 to rechargeable battery 8 there being some
circuit elements common to the FIG. 1 subportions. Connected in
parallel circuit arrangement with battery 8 is a Zener diode 9 which
prevents application of excessive voltage to battery 8 by shunting
a current which, in conjunction with the self-resistance of rectifying
circuit 1 is sufficient to maintain the voltage applied to battery
8 at a value not exceeding the manufacturer's recommendations. Flashing
and switching means 10 connects battery 8 with a load 11 consisting
of one or more incandescent lamps or such other load which it is
desirous of energizing upon failure of AC power, in series with
a transistor switch 36 shown schematically in FIG. 1 for sake of
simplification. Triggering means 14 is connected to actuate flashing
and switching means 10 from the junction between blocking diodes
5 and 6 the voltage at said junction being close to the positive
voltage of battery 8 when diodes 5 and 6 are conducting charging
current to battery 8 and falling closer to the potential of the
negative terminal of battery 8 when charging current ceases to flow,
said change of voltage operating flashing and switching means 10
to energize load 11 when charging current to battery 8 ceases. Sensing
and filtering circuit 12 is connected at the output of flashing
and switching means 10 in a series circuit configuration with load
11 to provide a resetting command signal 15 to timing means 4. Timing
means 4 operates to close switch means 3 by means of a logic 1 signal
output permitting the normal flow of charging current to battery
8. At the end of a timing period which may be one day or one week
or any desired interval, timing means 4 "times out", changing
its output from a logic 1 to a logic 10 which serves to open switch
means 3 stopping the flow of charging current to battery 8 and
through triggering means 14 activating flashing and switching means
10 causing load 11 shown here as an incandescent lamp, to alternately
flash on and off. This opening of switch means 3 stimulates the
kind of response of flashing and switching means 10 in conjunction
with lamp 11 as would occur upon failure of AC power from the power
mains. The failure indicating alarm circuit 2 is connected across
the output of rectifying circuit 1 and upon removal of the load
from this rectifying circuit, as occurs when switching means 3 opens,
its output voltage measured between leads 77 and 78 rises sharply.
Said rise in output voltage is sufficient to activate a flashing
visual alarm indicator 26 and, if desired, an audible indicator
63 in parallel configuration therewith. Should the emergency flashing
lamp load 11 operate properly, sensing and filtering circuit 12
will generate a resetting command signal 15 restoring the output
of timing means 4 to a logic 1 closing switch means 3 thereby restoring
normal charging current to battery 8. This application of a load
to rectifying circuit 1 reduces its output voltage as measured between
77 and 78 disabling failure indicating alarm circuit 2. If for
any reason no resetting signal 15 is obtained, for example, as would
occur upon failure of battery 8 or non-continuity of load 11 or
malfunction of flashing and switching means 10 or sensing and filtering
circuit 12 or malfunction of rectifying circuit 1 (which would result
in gradual depletion of voltage of battery 8) or such other circuit
malfunction which inhibits obtaining of resetting signal 15 switch
means 3 will not become closed since no resetting signal 15 had
obtained and failure indicating alarm circuit 2 will continue to
give its failure indication, drawing the attention of appropriate
service personnel.
Since periodic self-testing may be scheduled by adjusting timing
means 4 for some long interval, say, once per day or once per week,
switch means 13 is provided to shorten the time cycle so that bench
testing and servicing can be done in a reasonably short period of
time.
Referring to FIG. 2 an overall detailed schematic circuit diagram
embodying the invention is shown. AC power is applied through a
current limiting capacitor 17 to a bridge rectifier 18. Resistor
16 is connected in series configuration with capacitor 17 and bridge
rectifier 18 and serves to discharge capacitor 17 when AC power
is disconnected. The rectified DC output of rectifier 18 is filtered
by capacitor 19 and applied to the failure indicating alarm circuit
consisting of transistors 21 and 23 in circuit combination with
resistors 20 22 25 and capacitor 24. At sufficiently high DC voltage
across capacitor 19 the failure indicating alarm circuit operates
to periodically trigger a flashing visual alarm indicator 26 and/or
audible indicator 63. The rectified output current is also applied
through transistor 3 when suitably biased, LED indicator 29 across
a shunt resistor 28 and through blocking diodes 5 6 7 to the parallel
combination of zener diode 9 and rechargeable battery 8 in a direction
to charge battery 8. Base voltage of transistor 39 is maintained
close to the voltage of its emitter by the current flowing through
diode 6 which blocks current flow through transistor 39. When current
through this diode ceases, such as would occur on failure of AC
power or cutoff of transistor 3 current through transistor 39 will
be caused to flow, momentarily energizing flashing circuit consisting
of transistors 32 34 and 36 with their associated resistors 30
31 35 and capacitor 33 to cause lamp 11 and, if desireable, parallel
lamp 27 to flash intermittently, said flashing from the alternate
conduction and cutoff of transistor 36 generating a pulsating DC
voltage at the collector of transistor 36 which is coupled to filter
capacitor 43 through blocking diode 42 thereby providing base current
to transistor 39 through resistor 41 and zener diode 40. When continued
flashing of lamps 11 and 27 have sufficiently depleted battery 8
the pulsating DC voltage across transistor 36 coupled to capacitor
43 through diode 42 will be insufficient to maintain appreciable
base current in transistor 39 and said flashing circuit consisting
of transistors 32 34 and 36 with their associated circuit components
will cease to flash. This then removes all base current from transistor
39 which cuts off current in transistor 36 thereby cutting off further
current drain from battery 8.
Referring now to timing circuit 59 energized by the rectified output
from rectifier 18 through zener arrangement consisting of 55 and
57 shunt resistor 56 across zener 55 and filter capacitor 58 is
shown RC timing interval components consisting of resistors 53 and
54 and capacitors 51 and 52 with switch means 13 across capacitor
51 so that the timing interval is shortened when switch means 13
is open, effectively decreasing the circuit capacity by adding a
capacitor in series with capacitor 52. LED indicator 61 is energized
through resistor 60 to give visual blinking indication of timing
rate. The output of timing circuit 59 applied through resistor 62
to the base of transistor 3 is normally a logic 1 serving to provide
base current to transistor 3 and maintaining it in conduction and
then switching to a logic 0 at the end of its timing interval, cutting
off the base current of transistor 3 and thereby switching it to
its open or non-conducting state. Said non-conduction of transistor
3 has an equivalent affect on flashing circuit consisting primarily
of transistors 32 34 36 battery 8 and lamps 11 and 27 and their
associated circuits as would occur upon failure of AC power from
the power mains, namely, activating this circuit and causing lamps
11 and 27 to flash intermittently. As aforementioned, a pulsating
DC voltage is generated at the collector of transistor 36 which
voltage is coupled to rectifiers 37 and 38 through coupling capacitor
44 filtered by capacitor 45 and coupled as a negative voltage to
the base of transistor 48 some short time interval after pulsating
DC appears at the collector of transistor 36 said time interval
being determined primarily by the value of filter components 44
45 46 47 and the input resistance of the base circuit of transistor
48. This short time interval is incorporated to ensure that at least
several pulsations of voltage across transistor 36 are required
before reset of timing circuit 59 occurs. Said negative voltage
serves to cut off transistor 48 providing a positive pulse at its
collector which, when applied to timing circuit 59 resets its output
to a logic 1 restoring normal current flow through transistor 3.
It is apparent that where non-flashing operation of the emergency
exit sign auxiliary lamp is desired, diode 38 may be eliminated
and by replacing diode 37 by a short circuit and disabling flashing
operation through elimination of capacitor 33 steady auxiliary lamp
illumination is obtained while preserving all other exercising and
self-testing features. Filter capacitor 50 is connected across the
collector curcuit of transistor 48 to prevent spikes or other surges
from false triggering and resetting of timing circuit 59 except
from a proper reset signal derived from operation of lamp loads
11 and 27. Failure of such proper reset signal to appear as would
be occasioned by the circuit malfunctions aforementioned would leave
timing circuit 59 latched in its timed out condition, i.e., output
a logic 0 cutting off transistor switch means 3 and, by virtue
of removal of load from rectifying circuit 18 raising its output
voltage sufficiently high to activate the failure indicating alarm
circuit consisting of transistors 21 and 23 and their associated
components providing visual and/or audible alarm indication through
indicators 26 and 63 as aforementioned and thereby drawing attention
to the existence of some malfunction of the emergency auxiliary
lamp system.
In order to provide a failure alarm indication, circuit 2 described
more fully in the detailed schematic circuit diagram FIG. 3 utilizes
the sharp increase in voltage between leads 77 and 78 occasioned
by the removal of load upon opening of switch means 3 during the
periodic test interval to initate free running multivibrator action
of transistors 21 and 23 with their associated circuit components
consisting of resistors 20 22 and 25 capacitor 24 and incandescent
lamp load 26 and optional audible alarm 63 connected in parallel
configuration with lamp 26. Detailed description of operation of
this circuit will refer to FIG. 3.
Upon increase of voltage at 77 with respect to 78 when load is
romoved on opening of switch means 3 shown here schematically,
current through transistor 21 increases due to the increase of its
base current bias. This causes a corresponding increase of bias
current in transistor 23 through limiting resistor 22. The resulting
collector current of transistor 23 flows through the parallel combination
of resistors 25 lamp 26 and optional audible alarm 63 if used.
I have discovered that when an incandescent lamp of low thermal
inertia 26 is used, its positive temperature coefficient of resistance
vs. current will result in a rapid increase in voltage at the collector
of transistor 23 which, when coupled to the base of transistor 21
through capacitor 24 serves to regenerate and increase the current
through 21 and 23 which quickly reach saturation. When capacitor
24 has charged sufficiently, current through 21 decreases rapidly
cutting off current through 23 and thereby current through lamp
26 provided that the shunting effect of resistor 25 and audible
alarm indicator 63 if incorporated, is not too great. This cutoff
of current through resistor 23 extinguishes lamp 26 and the voltage
across it drops close to zero. This voltage change is again coupled
to the base of transistor 21 reinforcing cutoff of current through
it. The cycle is repeated as 24 charges and discharges, so sustaining
regenerative action at a rate determined primarily by the value
of resistor 20 capacitor 24 and the thermal time constant of lamp
26 neglecting the minor shunting effects of 25 and 63 as aforementioned.
By effectively including lamp 26 in the feedback configuration of
the circuit its sharp resistance versus current characteristic is
utilized to permit sustained regeneration only at voltages measured
between 77 and 78 significantly higher than occur when the overall
charger-flasher circuit shown in FIG. 2 operates normally and as
do in fact occur when rectifier circuit 1 is unloaded through the
opening of switch means 3 during periodic test.
Shown in FIG. 4 is the detailed schematic circuit diagram of the
battery operated lamp flashing system and charger. DC voltage between
leads 79 and 80 cause a charging current to flow through diodes
5 6 into chargeable battery 8. Zener diode 9 is connected in parallel
circuit configuration with battery 8 to prevent excessively high
voltages between 79 and 80 from being applied to battery 8 through
diodes 5 6 with consequent damage to it. The charging current flowing
through diodes 5 and 6 cause a low voltage to exist between base
and emitter of transistor 39 effectively cutting off current flow
through this transistor and maintaining the voltage on capacitor
43 that is at lead 82 close to the voltage of battery 8 less the
base emitter voltage of transistor 39 less the voltage of zener
diode 40. When charging current through diodes 5 and 6 and into
battery 8 ceases, as occurs upon failure of the AC power mains voltage
or during periodic self-test of the charger-flasher by the opening
of switch means 3 simulating the effect of an AC power mains failure,
voltage between base and emitter of transistor 39 is no longer held
low by the current through diode 6 and transistor 39 begins to conduct
current from battery 8. The base voltage of transistor 32 initially
close to the potential of lead 80 allows emitter current to flow
in transistor 32 as soon as current through transistor 39 is initiated.
A corresponding increase of base current in transistor 34 causes
the voltage at the collector of transistor 34 to rise, initiating
current through transistor 36. This current flowing from battery
8 through lamp load consisting of 11 and 27 illuminates them and
the resulting decrease in voltage at the collector of transistor
36 is coupled to capacitor 43 through blocking diode 42. This partially
discharges capacitor 43 reducing the voltage at the base of transistor
39 as coupled through resistor 41 and zener diode 40 until transistor
39 is cut off. Cutoff of this current also cuts off the current
through transistor 34 and consequently transistor 36 thereby extinguishing
lamps 11 and 27. The voltage across capacitor 43 then rises again,
initiating current through transistor 39 and the cycle repeats causing
a flashing action of lamps 11 and 27 at a rate determined primarily
by capacitors 33 and 43 with their associated resistive time constants.
When continued flashing of the lamps 11 and 27 have sufficiently
depleted battery 8 the pulsating current flowing through resistor
41 and zener diode 40 is insufficient to gate the current in transistor
39 alternately on and off until current through transistor 39 becomes
substantially zero, stopping the regenerative action of the circuit
and leaving transistor 36 in the cutoff state and so effectively
removing all load from battery 8 whose voltage has now dropped to
a significantly lower value than that of zener diode 9 so that an
insignificantly small or effectively zero battery current flows
through it or back biased diode 6. From this description it can
be seen that a pulsating DC voltage appears between leads 81 and
82 only when the battery operated lamp flashing circuit is operative
and this, when applied to the sensing and filtering circuit 12 of
FIG. 1 comprising blocking capacitor 44 diode rectifiers 37 and
38 and filter elements 45 46 and 47 of FIG. 2 produces a negative
voltage at the gate of transistor 48 which generates a positive
resetting command at the collector of transistor 48 to reset timing
circuit 59 closing switch means 3 reinitiating charging current
into battery 8 and simultaneously disabling the flashing of lamps
11 and 27 as well as the failure indicating alarm circuit 2. Should
no pulsating DC voltage appear between leads 81 and 82 due to a
malfunction indicative of one or more of the aforementioned possible
failures, no resetting of timing means 59 will occur, leaving switch
means 3 in the open state and failure indicating alarm circuit 2
in its flashing condition, calling attention to the malfunction
in the battery operated flashing lamp system.
The timing circuit 59 is described more fully in FIG. 5 a logic
diagram of the periodic timing circuit of the charger-flasher system.
Counting is initiated by application of a logic 1 to either input
port of gate 75. This can be obtained as a reset signal applied
to port E or at the initial application of power through operation
of one shot pulse generator 76. The output of gate 75 then initiates
gates 64 counter 69 latch 70 71 and gate 72. An RC oscillator
comprised of amplifier inverters 63 65 66 67 68 and gate 64
has its frequency determined by resistor 53 and capacitance 52 when
switch 13 is in the closed condition or the equivalent series capacitance
of capacitors 51 and 52 when switch 13 is open. Feedback applied
to input port A through resistor 54 closes the loop and sustained
oscillations result. The output of inverting amplifier 66 is applied
to the input of counter 69 and at the end of its countdown causes
switching and latching through operation of gates 70 and 71. This
change of state is coupled to output port D through gates 72 73
and 74. The second input of exclusive or gate 73 left unused is
available for inversion purposes in another application of this
circuit not applicable to this invention disclosure.
At time out the output at port D changes from a logic 1 to a logic
0 which opens switch means 3 as previously described and this output
remains in this state through latching action of 70 and 71 until
a reset signal is received at port E or through power initiation
and operation of pulse generator 76. Also, it is clear that the
length of time till time out can be altered by varying the number
of binary counter stages in 69 or by varying the frequency determining
components of the RC oscillator. This latter provides a simple means
for altering the length of time to timeout under normal conditions
of operation, say 24 hours, with switch 13 closed, to as short a
time as five minutes or less with switch 13 open, as would be useful
during test or troubleshooting of the overall system.
The self-testing cmergency exit sign auxiliary lamp flashing system
may be provided on a printed circuit board in accordance with present
day practice mounted within the emergency exit sign with the LED
lamps 29 and 61 also being mounted on the board and, if desired,
adjacent to apertures permitting them to be seen from outside the
exit sign without need to disassemble the exit sign itself.
The above discussion of the emergency exit sign charging-flashing
system including means for periodic exercising and self-testing
for proper functioning has therefore demonstrated that the circuit
of FIG. 2 operates in a reliable and secure manner to provide a
visual and, if desired, audible alarm upon malfunction of any of
the critical components of the system.
The foregoing discussion is merely illustrative of the principles
of the present invention and there are many modifications, changes
and adaptions thereof which will be readily apparent to those skilled
in the art without departure from the spirit and scope of the present
invention and while it has been described chiefly with reference
to an emergency exit sign charger-flasher system, it is readily
adaptable to other applications utilizing standby batteries which
must be activated upon failure of power from the AC power mains
and where it is desireable to periodically "exercise"
and verify for proper operation of the standby system to ensure
that it be properly functional when called upon to operate during
an emergency. |