Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-08-11
2004-06-22
Lieu, Julie (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S629000, C340S630000, C340S514000, C340S632000
Reexamination Certificate
active
06753786
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the hazardous condition detectors, and more specifically to the hush feature of such detectors.
BACKGROUND OF THE INVENTION
In the past, many people died in their sleep because there was no warning system to awaken them during the early stages of a dwelling fire. Likewise, without a system that could detect the presence of a fire early in its development, many people were trapped in burning buildings once the fire escalated to a point that became easily detectable. Luckily, smoke detectors have been developed which reliably provide an early warning to individuals that a fire may be present. These smoke detectors are so effective in saving lives that they have been mandated as required appliances in many types of dwellings. Current smoke detectors utilize an Application-Specific Integrated Circuit (ASIC), such as the Motorola MC 14467. These ASIC's and their corresponding analog circuitry allow for long battery life, reliable operation, and relatively low cost for these smoke detectors.
It goes without saying that to be effective a smoke detector must be operational. However, since smoke detectors are typically silent, consumers may not know whether or not their detector is operational. While many manufacturers include a feature that provides a periodic chirp as the battery is running low, many individuals desire the capability to affirmatively test the operability of their smoke detector. As such, modern smoke detectors include a push button that, when held in its actuated position, will place the smoke detector in a test mode of operation. This test mode will typically sound the smoke detector alarm after the test button is held for a period of two to three seconds.
While the alarm from a smoke detector is quite effective at warning occupants that smoke has been detected, such smoke does not always mean that a fire exists in the dwelling. Instead, the source of the detected smoke may be under the control of the occupant as, for example, in the situation where the occupant may be cooking in the kitchen. Occasionally, such cooking activities result in the generation of smoke to such a degree that the smoke detector is triggered. In such and other situations the sounding of the smoke detector alarm becomes more of an annoyance than a help.
To accommodate consumer desires to silence the alarm in such situations, while at the same time maintaining functionality of the smoke detector, a hush feature was introduced into conventional smoke detector design. Such a hush feature operates in conventional ASIC-based smoke detectors to reduce the sensitivity of the smoke detectors so that the smoke resulting from consumer-controlled conditions do not result in the sounding of the smoke detector alarm. In such a reduced sensitivity mode of operation, the conventional ASIC-based smoke detectors will sound an alarm if a level of smoke sensed continues to increase beyond the reduced sensitivity level. In this way, the consumers will again be provided with an audible warning indicating that the level of smoke within their dwelling has continued to increase since the hush feature was initiated.
While both the hush feature and the test feature satisfied consumer demands, many smoke detectors provided separate push-button switches to initiate these different modes of operation. Unfortunately, it was found that many consumers were inadvertently actuating the wrong push-button switch and, as a result, were confused by the subsequent operation of their smoke detector. As an example, if the hush button were actuated when the consumer actually wished to determine operability of the smoke detector by entering the test mode of operation, the alarm would not sound, possibly causing the consumer to believe that smoke detector is defective. Likewise, in the situation where the source of smoke is a known consumer-controlled event, actuation of the test button will not silence the smoke detector alarm as desired by the consumer. Such may result in the consumer believing that a larger problem exists within his dwelling, or that the smoke detector is malfunctioning. These problems in selecting the wrong switch are exacerbated by the fact that most smoke detectors are located on or near the ceiling where it is difficult to read the labeling provided for each of these two switches.
In an attempt to provide the desired functionality of both the test mode of operation and the hush mode of operation, many modern smoke detectors are beginning to utilize a single push-button switch, which is capable of actuating both the test mode and the hush modes of operation. One such detector having a hush feature is described in U.S. Pat. No. Re. 33,920 for a SMOKE DETECTOR HAVING VARIABLE LEVEL SENSITIVITY, issued to Tanguay et al. (hereinafter the Tanguay et al. '920 patent). The Tanguay, et al. '920 patent describes an application specific integrated circuit (ASIC) based analog smoke detector circuit having variable level sensitivity for allowing operation exclusively in a normal mode or in a hush mode, and having a test mode, both operable via a single switch.
The Tanguay, et al. '920 patent utilizes a conventional smoke detector ASIC such as the Motorola MC14467. As is conventional with such a smoke detector ASIC, a reference voltage is supplied to pin P
13
of the chip. This voltage input is coupled to an input of an analog voltage comparator within the ASIC, and establishes the alarm threshold value against which the output analog voltage from the smoke chamber
30
will be compared. The output voltage from a conventional ionization chamber is coupled to pin P
15
, which is the other input to the analog voltage comparator within the smoke detector ASIC. As is conventional with this type of device, when the voltage on pin P
15
drops below the voltage on pin P
13
the ASIC generates an output alarm signal to sound an audible alarm and to light a visible LED.
The smoke detector of the Tanguay, et al. '920 patent also includes a user-actuated switch that initiates both a test mode and a hush mode of operation. Unfortunately, both modes of operation are always entered when the user-actuated switch is activated. That is to say, that hush mode of operation is actuated even if the smoke detector is not currently in an alarm condition and the user solely wishes to check the operability of the detector. In accordance with the teachings of Tanguay, et al. '920, the detector test is initiated by contact of the user-actuated switch to the container of the ionization chamber. As described, this reduces the voltage supplied to the ionization chamber, resulting in a reduced output voltage therefrom. This reduced output voltage is sufficient for the smoke detector ASIC to generate an output alarm signal.
At the same time that the output from the ionization chamber is reduced due to the user-actuated switch completing a circuit to ground from the ionization chamber thereby reducing its input voltage, a test switch sensor circuit conducts current flow to an inhibit control circuit and a time constant circuit. These elements control the hush mode of operation once the user-actuated switch is released. Specifically, during actuation of the switch current flows into the time constant circuit to charge a capacitor through the test switch sensor transistor and a diode. Once the user releases the switch, the time constant circuit now begins operation by draining off the charge of the capacitor through the resistor divider network of R
12
and R
13
. The voltage generated through this resistor divider network is sufficient to turn on the Darlington configured transistor, which reduces the voltage at pin P
13
. The level to which the voltage on pin P
13
is lowered may be adjusted through the proper selection of resistors R
15
and R
16
and the transistor. These three elements form what is termed a sensitivity control means in the specification of Tanguay, et al. '920. The Darlington configured transistor is referred to in the specification as a diminis
Andres John J.
Apperson Michael W.
DeLuca Joseph G
Gilbert Chris R.
Ratzlaff Larry
Lieu Julie
Merchant & Gould P.C.
Walter Kidde Portable Equipment Inc.
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