Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2001-12-11
2003-11-04
Wu, Daniel J. (Department: 2832)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S629000, C340S634000, C340S636150, C340S514000, C340S515000, C340S516000, C340S517000, C340S506000, C340S521000, C340S527000
Reexamination Certificate
active
06642849
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hush mode disabling circuit for a self contained smoke alarm that is connected to a remote fire alarm system.
BACKGROUND OF THE INVENTION
Smoke alarms often experience false alarms as a result of smoke produced from cooking, smoking and other non-threatening situations. Thus, it is desirable to be able to temporarily disable or desensitize a smoke alarm under such false-alarm conditions.
For this purpose, many modern smoke alarms include what is referred to as a silencing feature or hush mode. Typically, smoke alarms include a test button to allow a user to initiate a self-test function to assure the smoke alarm is working properly. In order to simplify smoke alarm construction and operation, many manufacturers have incorporated the hush mode into the test button. As such, when the test button is depressed, the smoke alarm will go into a silent or decreased sensitivity mode for a predetermined period of time, after which the smoke alarm will rearm itself in its normal operating mode.
FIG. 1
shows a typical photoelectric smoke alarm chip
100
, Model No. A5358CA or A5366CA manufactured by Allegro Microsystems, Inc., connected to external circuitry with which it would normally be used. The entire circuit is contained within a smoke alarm enclosure
102
. A power source
104
is provided to provide V
DD
and V
SS
(ground) for the circuit and the chip
100
.
The enclosure
102
is provided with a smoke chamber
106
in which a infrared emitting diode
108
and an infrared photo diode
110
are contained. The emitting diode
108
is connected between pin
6
of the chip
100
and V
DD
of the circuit. The emitting diode
108
is driven by a oscillator and timing circuit
112
provided on the chip
100
. The detecting diode
110
is connected between pin
3
of the chip
100
and V
DD
of the circuit. The output of the detecting diode
110
is amplified by a photoelectric amplifier
114
provided on the chip
100
. The output of the photo amp
114
is fed to a logic circuit
116
provided to the chip
100
.
When smoke particles enter the smoke chamber
106
, the particles cause the light emitted by the emitting diode
108
to be diffracted before it is received by the detecting diode
110
. The logic circuit
116
of the chip
100
detects this diffraction and, when appropriate, causes a horn driver
118
provided on the chip
100
to drive an external horn
120
which generates and audible alarm.
A momentary push button
122
connected between V
DD
and pin
16
of the chip
100
, when pressed, causes the chip
100
to test the smoke alarm circuit and drive the horn
120
if the circuit is functioning properly.
To avoid false alarms, a hush mode is provided to the chip
100
. To utilize the hush mode, a voltage divider VD comprising two resistors R
1
, R
2
is connected between the power source
104
and pin
4
of the chip
100
. A ratio of the voltage provided by the voltage divider VD and V
DD
sets a decreased sensitivity level of the smoke alarm circuit when hush mode is active. Whenever the push-button
122
is pressed, hush mode is activated for a predetermined period of time. To disable the hush mode entirely, the voltage VD provided to pin
15
of the chip
100
must be set to V
SS
. In this way, the hush mode is either permanently enabled or permanently disabled, depending upon the circuit configuration.
In recent years, there has been a need to provide inexpensive centralized fire alarm systems. In order to do this, many manufacturers have taken inexpensive individual smoke alarms and linked them together to form a centralized system. One of the features of these systems is the ability to perform a self-test of all of the smoke alarms in the system simultaneously from a centralized or remote location.
However, when smoke alarms having the hush mode described above enabled are used in such a network system, the activation of a remote self-test will engage the hush mode. As a result, all of the smoke alarms will be silenced or have reduced sensitivity for a period of time. During this time period, the areas protected by the smoke alarms will be at an increased risk of an undetected fire hazard. Further, the occupants of the individual areas may not be aware of the reduced sensitivity of the smoke alarm. Thus, it would be desirable to provide a means for selectively disabling and enabling the hush mode of this type of smoke alarm.
BRIEF SUMMARY OF THE INVENTION
To overcome the disadvantages of the prior described above, the present invention provides a circuit for disabling the hush mode of a smoke alarm during a remote test. According to an aspect of the present invention, a hush mode disabling device for a smoke alarm having a self-test function, a hush mode that engages upon activation of the self-test function to silence or desensitize the smoke alarm for a predetermined period of time, and a remote self-test controller is provided. An improvement comprises a hush mode disabler for determining whether the self-test function has presently been activated by the remote self-test controller and for disabling the hush mode only if the self-test function has presently been activated by the remote self-test controller.
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Maple Chase Company
Nguyen Tai T.
Wu Daniel J.
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