Apparatus and method for providing alarm synchronization among multiple alarm devices

A method and apparatus for synchronizing a series of interconnected alarm devices. The alarm device detecting an alarm condition produces a signal having a distinct rising edge which is detected at each of the remaining alarm devices. A pulsed alarm signal having a fixed number of pulses is generated at each remaining device in response to the rising edge. A reset signal from the alarm device detecting the alarm condition resets each of the remaining alarm devices after each fixed number of pulses is produced so that each of said devices has a pulsed alarm signal which begins and ends at substantially the same time.

BACKGROUND OF THE INVENTION

The present invention relates to residential alarm systems for detecting dangerous conditions in multiple locations within a building. Specifically, a method and system for synchronizing audible warning appliances which are distributed throughout a home or other facility is described.

Alarm systems which detect dangerous conditions in a home, such as the presence of smoke, or carbon dioxide, are extensively used to prevent death or injury. In recent years, it has been the practice to interconnect different alarm units which are located in different rooms of a person's home. Specifically, smoke detecting systems for warning inhabitants of a fire have been installed in individual rooms of a home and interconnected so that all alarms will sound if one alarm detects any combustion products produced by a fire. In this way, individuals located away from the source of combustion products are alerted to the danger of fire, as well as those in closer proximity to the fire. In accordance with various safety codes, these devices are equipped with a light-emitting source, so that the alarm which detects the smoke or other dangerous condition will provide a visual indication of the source of the dangerous conditions. In this way, it is possible for responding fire personnel to determine which of the units is sensing the alarm condition while the remaining devices distributed throughout the home provide an audible alarm.

The system interconnecting the various alarm units in a dwelling relies upon the sensing alarm to apply a voltage to a common conductor interconnecting each of the distributed alarm units. When the applied voltage is detected to be above a threshold value, typically three volts, the remaining alarms begin sounding their audible signaling horn. The common conductor carries a signaling voltage from the sensing alarm to each of the remaining alarms for triggering the audible responses from the remaining remote alarm devices.

The input/output connection to the common conductor is equipped with a filter to minimize the possibility of the random triggering of the alarm by voltages induced on the common conductor, as well as to minimize the effects of voltage spikes on the neutral of the power line which may inadvertently signal connected smoke detectors into an alarm condition.

The prior art interconnected smoke detector alarms included a test capability at each alarm. When an individual in a room having a smoke alarm activates the test feature, an audible signal is produced from the smoke alarm being tested. As long as the user releases the test switch within a brief period of time, the other units throughout the facility are not activated. However, the presence of the input filter of each smoke alarm connected to the common conductor resulted in a latent electrical charge being maintained on the filter capacitor which required several seconds to discharge. Following a test, or actual alarm condition which is transmitted on the common conductor, the input filters may remain charged to the point where each remote alarm unit can remain in a temporary alarm condition resulting in an objectionable false alarm.

The foregoing problem has been addressed in the prior art by applying a momentary low impedance from the common conductor to circuit ground following the generation of an alarm signal on the common conductor, quickly discharging the filter capacitors, avoiding the consequence of an inadvertent false alarm due to the stored charge.

The detected alarm condition in future alarm systems may represent one of several types of alarms. For instance, the danger of fire may be sensed with a smoke detector, and the danger from carbon monoxide poisoning may be sensed with a gas detector. Various authorities having jurisdiction have required manufacturers to generate different audible signaling patterns so that people hearing the respective alarms can distinguish between the different sensed dangers.

Using signaling formats of specific temporal patterns is made difficult if all detectors are not synchronized to produce the same audible pattern of warning signals. The unsynchronized alarms produce a cacophony of sounds which make discerning any particular pattern difficult.

The effectiveness of the connected alarm devices could, therefore, be enhanced by synchronizing the audible responses provided by each alarm device when responding to a remote unit which is detecting an alarm condition. The foregoing features which permit self tests to be made at each alarm, and which discharge each of the filter capacitors of the connected alarms following a test, provide the basis for a circuit which can be modified to permit synchronous signaling by each of the connected alarms.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an ability to synchronize the audible alarm sounds of interconnected alarm devices to more clearly distinguish the alarm as being either a smoke condition, or a carbon monoxide condition, or any other alarm condition which may be sensed at a given location, avoiding the cacophony of unsynchronized audible signals which obscure the nature of the detected condition.

An alarm device for responding to a locally generated alarm condition, which also responds to a remotely detected alarm condition, is provided by the invention. The alarm device includes a sensor which detects a local alarm condition such as smoke, carbon monoxide, explosive gas mixtures, etc., and sounds an audible, pulsed alarm when a dangerous condition is sensed. Each alarm device is equipped with a signal detector connected to a common conductor which detects an alarm voltage on the common conductor generated by a remote alarm device detecting an alarm condition. A transmitter circuit at the remote alarm device sends a pulsed signal to each connected alarm device, which is time synchronous with the audible alarm being generated by the remote alarm device, initiating a pulsed audible signal at each of the alarm devices. By generating a synchronized audible signal at each location, the homeowner, resident or the responding emergency personnel can quickly and correctly identify the specific alarm condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 , a facility 1 is shown having a plurality of levels 2 , 3 and 4 with rooms on each level. Remote sensing devices 13 - 18 are located in each room of the facility 1 , and are interconnected by a common conductor 12 . It is understood that each of the units 13 - 18 have a common connection, through either the neutral of the facility power supply, or by a second conductor (not shown).

Each of the alarm devices 13 - 18 detect a dangerous condition, such as smoke being generated from a fire. The alarm devices 13 - 18 produce a pulsed audible sound which may be heard within the room in which the device is located. When an alarm condition is detected by one of the devices (the alarm sensing device), the remaining alarm devices (remote alarm devices) also produce, at the same pulse width and pulse period, an audible alarm signal synchronized with the remaining alarm signals so that an occupant of any room may clearly determine the nature of the alarm.

The effect of not synchronizing the audible alarm signals can be shown with reference to FIGS. 2A , 2 B and 2 C. In accordance with a standard format for generating audible alarm signals in a smoke detector, three pulses having an on time of 0.5 seconds separated by an off time of 0.5 seconds are generated in response to the detected alarm condition. The temporal signal shown in FIG. 2A has an off period following the third pulse which is approximately 1.5 seconds. If the alarm condition persists, either in response to the actual detection of an alarm condition, or when the self-test feature is invoked by the user, additional groups of pulsed signals of the format shown in FIG. 2A are subsequently produced on the common conductor 12 .

FIG. 2B illustrates the generation of the same audible signal by a remote alarm device which receives an alarm signal on common conductor 12 . The alarm device responds by producing the same pattern of audible pulses. Under current interconnect practices, the remote alarm devices are turned on, and not synchronized with respect to the initiating alarm device audible signals. Accordingly, to the occupant, depending on his location within the facility, the unsynchronized signals from the alarm devices, shown in FIG. 2 A and FIG. 2B , can vary from an in phase to an out of phase condition. To the occupant, only a continuous audible signal is generated as shown in FIG. 2C when the two alarm devices are producing out of phase audible signals at the listener's location, rather than individual pulses of a regular pulsed frequency, obscuring the nature of the alarm condition. Once the initiating alarm device ceases sending the alarm signal on conductor 12 , a charge dump signal is applied to conductor 12 , to remove all of the latent charge which has accumulated on each remote alarm device input filter capacitor.

The present invention synchronizes each of the audible signals produced from each alarm device so that, to an occupant, it is clear what the nature of the alarm condition is.

In accordance with the present invention, the nature of the signal on common conductor 12 is shown in FIG. 3B , with respect to the pulsed audible alarm signal shown in FIG. 3A produced by the originating alarm device sensing a dangerous condition. FIG. 3C shows two, four second intervals of pulsed audible signals generated when the remote alarm device detects the positive rising pulse 6 shown in FIG. 3B on the common conductor 12 . The remote sensing device generates the rising edge of pulse 6 substantially coincident with the edge of the first pulse of the second group of pulses 7 of FIG. 3 A. The pulse 6 is not applied to the common conductor 12 until the second group of audible pulses 7 are generated by the sensing alarm device. In this way, remote alarm devices are not enabled to transmit the alarm signal if a brief self-test occurs at one of the alarm devices. Only if an alarm device is indicating an alarm for more than one full period of pulsed alarm pulses shown in FIG. 3A will the signal on common conductor 12 rise above three volts.

FIG. 3B illustrates voltage 6 on conductor 12 rising in synchronism with the second group of audible pulses of FIG. 3A , and each group of audible pulses 9 produced from the remotely connected alarm device. Following the first group of alarm pulses 9 , produced by the remote alarm device, the voltage on conductor 12 applied by the sensing alarm device, undergoes a negatively going transition 6 A for discharging the filter capacitors of each of the remote devices, and the remote devices are reset and cease signaling an alarm after providing one complete 4 second group of audible pulses. Since the conductor 12 voltage returns to above three volts, to produce a second detectable rising edge, representing a continuous alarm condition at the sensing alarm device, a second group of pulsed audible signals 10 is produced by the remote device. When the alarm condition ceases at the sensing alarm, the negative going transition of conductor 12 maintains the remote alarm devices in the reset state. Thus, the remote devices' audible pulses are effectively generated in synchronization with the sensing alarm audible pulses.

The relationship between the second group of audible pulses 7 produced by the sensing alarm and the voltage on conductor 12 , represented by the circle 11 , is shown more particularly in FIG. 3 D. The leading pulse 8 of each remote alarm device pulsed audible alarm signal substantially coincides with the positive going edge following the negative going capacitor discharge portion of voltage 6 A on the common conductor 12 . As will be evident from a description of the preferred embodiment, circuitry within each of the remote alarm devices determines that the voltage level 6 is above the voltage threshold for at least a predetermined period of time t, selected in a preferred embodiment to be approximately 250 milliseconds. When this condition is satisfied, a second group of temporal pulses 10 is generated.

If the alarm condition sensed by the sensing alarm device ceases, control voltage 6 negatively transitions to produce a charge dump on the remote alarm device to its stand-by level of less than three volts, and typically zero volts, and no additional series of pulsed audible alarm signals are generated at each remote device.

FIG. 4 illustrates an alarm device, in accordance with a preferred embodiment of the invention, in block diagram form, for implementing the foregoing feature. The alarm device can either originate an alarm signal on conductor 12 , or receive an alarm signal on conductor 12 . A local sensor 20 , which in the case of a smoke detector, detects smoke particles in the air, provides a signal for activating an alarm status detector 22 . If a local alarm condition has been detected, status detector 22 pulses LED 30 , as well as energizes the pulsed audible signal generator 29 . Pulsed audible signal generator 29 has a transducer for producing a loud audio signal comprising bursts of audible frequency signals which occur within the temporal signal format shown in FIG. 3 A. As long as the local sensor 20 detects the alarm condition, a series of the pulsed audible signals will be produced from signal generator 29 . Additionally, the alarm status detector 22 enables a transmit signal generator 23 to apply a voltage greater than three volts to the common conductor 12 . The transmit signal generator 23 produces a voltage 6 on conductor 12 which transitions above the threshold level of three volts in synchronism and in anticipation of the leading edge of the first pulse of the second temporal pulse sequence produced from signal generator 29 and transitions negatively at substantially 50% of the alarm signal period. The voltage level is applied through a diplexer 34 , and filter 35 to conductor 12 . Filter 35 as explained previously in accordance with the prior art, filters any transient voltage signals which might inadvertently be coupled to conductor 12 . Filter 35 includes a capacitor 37 , series resistor 38 , and an over voltage protection zener diode 36 .

A test capability is provided through a switch 21 connected to the alarm local sensor 20 . If a user entering a room in which the alarm device is located desires to test the alarm device, he may close switch 21 which will generate an alarm signal from signal generator 29 , comprising the temporal pulsed audible signal of FIG. 3 A. If he releases his switch 21 before a full period of temporal pulses is produced, transmit signal generator 23 will not generate a rising voltage 6 on conductor 12 for initiating alarm signals at the remote alarm devices.

In the case where the alarm device of FIG. 4 does not detect a local alarm condition, but instead receives a voltage 6 on conductor 12 indicating an alarm condition has been sensed at another alarm device, edge detector 25 will detect the leading edge of voltage 6 which is synchronized to a pulsed alarm signal generated at the sensing alarm device. Level detector 26 will determine whether the level has exceeded a threshold value, for a minimum of two sampling periods (40 ms) for the time t shown in FIG. 3 D. If the condition is satisfied, a remote alarm status circuit 28 will initiate a single group of temporal pulsed audible signals from signal generator 29 , which as described earlier, are in synchronism with the pulsed alarm signal produced by the alarm device sensing the alarm condition.

When the edge detector 25 and level detector 26 detect the negative going, discharge portion of voltage 6 , which occurs at substantially 50% of the period of the temporal alarm signal, the input filter capacitor 37 is discharged back through the originating transmit signal generator 23 of the sensing device originating the voltage on conductor 12 , and signal generator 29 is reset. When the control voltage 6 applied to the common conductor 12 rises again in response to an alarm condition at the sensing alarm device, an additional group of audible signals will be produced by the remote alarm device.

The alarm device FIG. 4 includes a bus arbitration circuit 27 . Bus arbitration circuit 27 is provided, so that in the event a connected alarm device senses the same alarm condition, only one alarm device will be able to provide a transmit signal 6 through the common conductor 12 . In this way, two alarm devices are kept from competing to establish synchronization among the remaining alarm devices.

The foregoing embodiment of the invention contemplates synchronizing the interconnecting alarm devices using the charge dump reset feature of the prior art. As a further design enhancement of the invention, the alarm device can be configured to initiate a transmit signal from transmit signal generator 23 which has the pattern corresponding to the temporal audible signal pattern issued by signal generator 29 to directly drive each of the interconnected alarm devices, generating an alarm pulse coincidental with each transmit signal pulse on the conductor 12 .

In this embodiment of the invention, each rising edge would be detected on the conductor 12 by detector 25 , and signal generator 29 would generate an audible signal temporal pulse pattern in response to each of the rising edge detections.

As a further enhancement of the device, the device could be configured so that it operates with so-called legacy alarm devices. The prior art legacy alarm devices issue a continuous DC voltage to any interconnected remote devices, thus generating asynchronous audible warning signals. In the event that a new synchronous alarm device in accordance with the foregoing embodiment was installed in such a location, for instance an additional unit necessary for a new room in a house remodeling project the level detector 26 could be set to initiate an alarm condition based on the detection of a first rising edge of voltage 6 which would then remain at a high level for the duration of the sense alarm condition. While the result would not be an alarm signal synchronous with the initiating alarm signal, it will at least provide a warning to occupants of a facility.