Communications: electrical – Condition responsive indicating system – With particular system function
Reexamination Certificate
1999-04-19
2001-05-08
Crosland, Donnie L. (Department: 2632)
Communications: electrical
Condition responsive indicating system
With particular system function
C340S510000, C340S511000, C340S588000, C340S522000, C340S628000, C340S577000
Reexamination Certificate
active
06229439
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to ambient condition detectors. More particularly, the invention pertains to such detectors which incorporate variable smoothing of signals indicative of an ambient condition.
BACKGROUND OF THE INVENTION
Distributed fire alarm systems which incorporate a plurality of ambient condition detectors, such as smoke, heat or gas detectors, are often installed in business or commercial buildings. Such systems often have a common control unit which can be in either unidirectional or bidirectional communication with multiple, spatially separated, ambient condition detectors.
One of the problems associated with transmission of information to or from such detectors is the presence of uncorrelated noise. Noise is uncorrelated wherein it is not related to a selected parameter or parameters which is/are being monitored.
In the event that the parameter being monitored is a level of ambient smoke, an ambient temperature, or a level of an ambient gas, the signals of interest are those which have a high correlation to the particular ambient condition being detected. Other signals, due to electrical or thermal noise which are not correlated to the ambient condition being detected, and which may in fact be random, are undesirable. Various techniques have been used in the past to minimize the effects of such uncorrelated noise signals.
One known type processing or filtering involves sampling the signals from at least one of the ambient condition detectors and calculating a running average based on a predetermined number of prior sample values, such as 6 or 8 or 10, along with the latest sample value. As each new sample value is received, the running average is updated. This technique provides a vehicle for minimizing or suppressing the effects of uncorrelated noise. This process can also be carried out continuously using analog circuits.
Filters can be implemented using analog or digital hardware. Alternately, they can be implemented digitally in software. One such system is described in U.S. Pat. No. 5,612,674 entitled High Sensitivity Apparatus and Method With Dynamic Adjustment for Noise assigned to the Assignee hereof and incorporated by reference herein.
While known approaches do provide a vehicle for suppressing or reducing uncorrelated noise in signals from ambient condition detectors, they also introduce delays. In the event that the parameter of interest, such as level of smoke or ambient temperature, does start to increase, the increases are attenuated and only appear in the output filtered signals after a delay interval which is characteristic of the type of averaging or filtering which is used.
As disclosed and claimed in the parent hereto, hereby incorporated by reference, a smoothing or filtering function can be altered in the presence of a fire indicating profile. It would be desirable to be able to start to adjust the degree of smoothing or filtering even before a fire indicating profile can be detected.
SUMMARY OF THE INVENTION
An apparatus in accordance with the present invention incorporates at least first and second ambient condition sensors. For example, and without limitation, a first sensor can be responsive to ambient smoke while a second sensor can be responsive to gas such as carbon monoxide or carbon dioxide or other hydrocarbons. The second sensor could alternately be responsive to temperature.
Control circuitry processes an output from the first sensor by filtering or smoothing same to reduce transients and or noise therein not correlated with the ambient condition to which the first sensor responds. The smoothing or filtering characteristics are then altered in response to an output from the second sensor. The control circuitry can be located adjacent to the sensors. Alternately, the control circuitry can, in part, be adjacent to the sensors and, in part, remote therefrom.
If both sensors are fire sensors, then one fire sensor could be used to control the response of the other fire sensor. Alternately, they effectively can interact by setting smoothing coefficients of each other.
If one sensor is a fire sensor and another is a non-fire sensor, then the non-fire sensor can be used to control the response of the fire sensor by slowing down its response. For example, the fire sensor may be responding to a false condition such as dust or humidity. Hence, if the first sensor responds to smoke (ion or photo-type sensor), the second could respond to gas, dust, temperature or humidity.
This is a combination detector where two or more sensors are logically combined in a detector to determine if a specific ambient condition exists. This ambient condition may be a fire, for example.
By controlling the smoothing coefficient, the detector is not prevented from alarming if a condition prevails long enough. It tends to be fail safe. The smoothing coefficient simply controls the rate of response and the development of a condition profile at any time will immediately increase the response from a non-profile condition because the detector stays active.
A method in accordance with the invention uses one or more of the sensors to establish at least one smoothing coefficient for another one or more of the sensors. The multiple sensors are used to improve the recognition of a condition or the absence of that condition in order to provide a faster response to the condition or a slower response to false conditions to prevent unwanted alarms.
Filter altering outputs from the respective sensors can be evaluated by amplitude, rate-of-change, or other means to determine if the condition is present. Processing can be carried out locally at the respective detector or remotely at a common control unit. In the latter instance, the coefficient(s) could be downloaded after having been modified if filtering is to be carried out at the detector.
The indication of a fire can be categorized or continuously based upon the sensor output values and evaluation of the values. For example, the indications can be categorized into:
No indication (there is no pattern or trend);
Slight indication (there is no pattern but a trend is started or there is a sharp increase to saturation);
Moderate indication (there is a pattern but significant doubt still exists about the condition); and
Strong indication (there is a specific pattern and little doubt exists about the condition).
Multiple sensors provide additional information beyond that available from a single sensor. As a result, a condition signature can be established to increase confidence that an actual fire condition is developing. This method is not limited to two sensors but can also include three or more.
Various types of filtering can be used and modified without departing from the spirit and scope of the present invention. For example, running averages can be used and dynamically modified in response to the output of the appropriate sensor.
The entire process can be carried out locally at each respective detector. Alternately, part of the processing can be carried out at the detector and part at a common control unit.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.
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Crosland Donnie L.
Pittway Corporation
Rockey Milnamow & Katz Ltd.
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