Abstract:
A multi-function detector has at least two different sensors coupled to a control circuit. In a normal operating mode the control circuit, which could include a programmed processor, processes outputs from both sensors to evaluate if a predetermined condition is present in the environment adjacent to the detector. In this mode the detector exhibits a predetermined sensitivity. In response to a failure of one of the sensors, the control circuit processes the output of the remaining operational sensor or sensors so that the detector will continue to evaluate the condition of the environment with substantially the same sensitivity.

Description:
FIELD OF THE INVENTION 
     The invention pertains to ambient condition detectors. More particularly, the invention pertains to such detectors which incorporate multiple sensors and processing circuitry and which exhibit improved operational characteristics in the presence of sensor failure. 
     BACKGROUND OF THE INVENTION 
     Known ambient condition detectors include one or more condition sensors. Representative sensors include smoke, heat and gas sensors. 
     In some detectors outputs from the respective sensors are processed substantially independently for purposes of determining if a predetermined condition, to which a respective sensor is responding, meets a selected alarm criteria. In other detectors, outputs from multiple sensors are taken into account in alarm determination processing. 
     In those detectors where alarm determinations are made in response to single sensor processing, a failure of one sensor will not necessarily affect processing of output signals from the other sensor. On the other hand, while multi-sensor processing can potentially provide the benefit of more complex, multi-input processing, loss of the output from one of the sensors, in known detectors, may result in a loss of sensitivity. 
     Known prior art detectors that process sensor outputs in parallel and independently may have several software routines operating in parallel, one of which is a safety or bypass routine if a sensor fails. The first routine to determine an alarm condition generates an alarm indicating output. These routines are fixed and operate without change. They do not adjust themselves to compensate for the loss of a sensor. More specifically, these routines do not make automatic adjustments to maintain sensitivity when a sensor fails but rather have failure mode sensitivities less sensitive than the normal mode sensitivities. A trouble indication is given by these detectors whenever a sensor fails so the less sensitive operating mode during trouble is tolerated. However, in many cases, this trouble mode may not be serviced in a timely manner and the fire protection is not optimum during the time frame between failure and servicing. 
     There are also prior art detectors that have more than one sensor and provide different audible sounds as a local warning. For example, some devices combine a smoke detector and a CO detector and give separate sounds locally at the device indicative of the type of detector responding. However, these devices do not transmit that information into a system and use this information for controlling other processes or functions such as ventilation, lighting, heating, security, etc. 
     It would be desirable if the advantages of multi-sensor processing could be provided with minimal sensitivity losses due to sensor failure. Preferably, substantially constant sensitivity could be provided even where a sensor fails. It would be most desirable if such functionality could be provided without significantly increasing detector complexity or cost. 
     SUMMARY OF THE INVENTION 
     An ambient condition detector includes two or more sensors. Each sensor is coupled to a control circuit. The control circuit could, in one embodiment, be implement, at least in part, using integrated circuits including a programmed processor. 
     In one aspect of the invention, the sensors could respond to indicia of fire such as smoke, heat or gas, such as carbon monoxide. The control circuit processes the sensors&#39; outputs to evaluate if a fire condition exists. Depending on the type of sensors used, other conditions can be sensed and evaluated. The selected sensors in combination with the processing result in a detector that has a characteristic sensitivity. 
     In yet another aspect of the invention, the characteristic sensitivity can be substantially maintained even if one of the sensors ceases functioning properly. In this embodiment, in response to a sensor failure the control circuitry processes the outputs from the remaining sensors so as to continue to maintain the same sensitivity. 
     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. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 illustrates a block diagram of a multiple sensor detector in accordance with the present invention; 
     FIG. 2 illustrates the detector of FIG. 1 configured with selected sensors; 
     FIG. 3 is a flow diagram of several different processing routines executable by the detector of FIG. 2; 
     FIG. 4 illustrates a flow diagram of alternate processing that takes into account a failure of a sensor; 
     FIG. 5 illustrates processing routines executable by the detector of FIG. 1; and 
     FIG. 6 illustrates alternate processing routines executable by the detector of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     FIG. 1 illustrates an ambient condition detector  10  that incorporates multiple sensors S 1 , S 2 , S 3 , through SN. Outputs from one or more of these sensors can be processed by control circuitry  12  to produce one or more processed outputs indicative of the one or more ambient conditions to be detected. These outputs  14  can be transmitted to a remote processor via a communications medium  16 . Medium  16  can be hardwired or wireless. 
     The control circuitry may incorporate a plurality of processing routines and may be constructed with discrete circuitry, custom integrated circuits, processors, or the like. As illustrated in FIG. 2, one or more of the sensors S 1 , S 2  . . . Sn can be selected depending on each different ambient condition desired to be detected. When different sensors are selected, then such as S 1 , S 3 , respective processing routines are also selected and executed. 
     Sensor selection can be implemented locally at the detector  10  at installation or when convenient. Selection can be by hardwired circuitry at the detector  10  or via software pre-loaded into the control circuitry  12 . Alternately, commands and/or selection programs can be downloaded from a remote processor via the medium  16 . 
     The sensors can include without limitation smoke, particle, gas, temperature, light, sound, security, or other sensors of an ambient condition. They can be combined in a multi-sensor detector, such as detector  10  to detect the desired ambient condition(s). 
     Examples of types of gas sensors includes optical, NDIR, photo-acoustic NDIR, polymers, or other like sensors that give a signal when selected gases are present in the environment. Gas sensors can include CO, CO2, H2, and H2O [humidity] sensors as well as sensors of other gases indicative of an environmental condition to be detected. 
     Optical sensors can respond to any light frequency including infrared and ultraviolet. They can be used to sense passive infrared, day/night or flames. 
     Smoke sensors can be implemented as scattering, obscuration or ionization type sensors. Particle sensors can include particle counters which may or may not measure the size of particles in the environment. 
     Temperature sensors can include thermistors or junction temperature sensing devices. Audio sensors can include microphones, crystals, or other devices sensitive to sound waves or vibration sources. Security sensors can include passive infrared or other types of motion or occupancy sensors. 
     An example of a multi-sensor detector  10  includes a combination of 1) smoke, 2) CO2, and 3) temperature sensors. Another example includes a combination of 1) smoke, 2) CO, and 3) temperature sensors or alternatively 1) CO and 2) temperature sensors. 
     FIG. 3 illustrates three different processing routines which are available at detector  10  for selection in detecting an ambient condition when sensors S 1  and S 3  are selected. Processing routine ( 1 ) of FIG,  3  is used if both sensors S 1  and S 3  are operational. The routine of FIG. 3 illustrates summing of smoothed sensor values. 
     Other processing routines can be used for any or all of the sensors without departing from the scope of this invention. The processing routines can use neural network routines, algorithms, fuzzy logic, weighed summing of sensors and the like without limitation. 
     If sensor S 3  becomes non-operational by failing or by a command directing it to not contribute to the processed output  14 , then the processing routine ( 2 ) of FIG. 3 is selected and executed. Routine ( 2 ) could be implemented using rate of change processing in addition to the smoothing, change in weighing values, and the like to compensate for the fact that sensor S 3  is no longer contributing to the output processed value  14 . 
     If sensor S 1  becomes non-operational by failing or by a command directing it to not contribute to the processed output value  14 , then the processing routine ( 3 ) of FIG. 3 is selected. Likewise, other routines can be selected other than those illustrated in FIG.  3 . 
     In addition to selecting different routines, the operating routines can be altered during the failure of a sensor by automatically changing coefficients or weighing values. Alternately, gain or thresholds can be adjusted to facilitate using the responses of the remaining sensors to maintain sensitivity to the desired ambient condition(s). 
     Alteration of the processing routines may include assigning an operating sensor value to that of a non-operating sensor value. For example, if a detector contains three sensors [S 1 , S 2 , S 3 ] and S 2  becomes non-operational, and S 3  is preferred over S 1  in sensing the environmental condition, then the values of S 3  could be assigned to S 2  since S 2  is non-operational. Outside of this alteration, the processing method could be otherwise unchanged. The detector will now determine the environmental condition only using sensors S 1  and S 3  but maintain a sensitivity that is close to its normal sensitivity. This process could be automatic and predetermined or executed after a command is received via the medium  16  directing the detector to make this substitution in sensor values. 
     FIG. 4 illustrates an example of a detector changing an alarm threshold when a sensor fails. The purpose is to adjust the sensitivity back toward the normal operating sensitivity. 
     In FIG. 4 the alarm threshold is reduced by 50% since the sensors were simply summed together with equal contribution in this example. If more complex or less complex processing were used, the alteration in the alarm threshold due to sensor failure could be more complex to maintain the desired sensitivity to the environmental condition. 
     The processing routines may be different if the selected sensors were S 1  and S 2  or if the selected sensors were S 2  and SN. This functionality enables the detector to reconfigure itself by command for several different ambient conditions to be detected using an associated set of routines. In one example, the detector may be configured to detect a fire in a hallway. In another case, the detector may be configured to detect a fire in a bedroom. Also, the detector can be configured to detect a concentration of CO and/or CO2 in the desired area using different routines. 
     FIG. 5 illustrates an example where the detector contains four sensors. S 1  and S 2  and S 3  are used to detect fire as the ambient condition. S 1  and S 3  are used to detect hazardous gas as the ambient condition. The respective detector can be commanded to switch or can automatically switch between programs to detect either ambient condition or both ambient conditions relatively simultaneously. 
     To detect both ambient conditions, the two different processing routines are included in the detector. One processing routine uses signals from sensors S 1  and S 2  and S 3 . The second processing routine uses signals from sensors S 1  and S 3 . It is possible that the same sensors could be included in both the first processing and the second processing and the different environmental conditions determined by differences in the first and second processing methods. It is also possible that the output from a single sensor could be used as an input to two processing methods. These could output two different signals indicative of two associated environmental conditions. 
     FIG. 6 illustrates an example of processing where a multi-sensor detector incorporates three selected sensors and detects two environmental conditions. Outputs from the three sensors are combined to determine the presence of a fire condition using Smoke, CO2 (air quality), and T (temperature). Sensor S 2  is used to detect an air quality environmental condition based on the degree of sensed CO2. 
     The different environmental conditions use different processing routines. If a sensor S 1  or S 2  or S 3  fails, then the processing routines are altered or changed to different processing routines for the detection of the environmental conditions. 
     Various sensors can be incorporated into a single detector and used to detect different environmental conditions and to output signals used to control various functions associated with these various environmental conditions. In some cases, the sensors are located within the same detector but some of the processing is accomplished at another device or control unit(s) external from the detector. The environmental information is communicated to other devices or control unit(s) over the communication medium  16 . This communication medium could be hardwired, wireless such as RF, light paths, or other mediums. The environmental information is used to control functions associated with the environmental conditions such as ventilation control, door lock control, heating control, lighting control, access control, or other controls designed into a system. 
     These multi-sensor detectors can incorporate compensation circuitry to adjust parameters internal to the processing to compensate for changes in the sensor&#39;s sensitivity or drift of signal values over time. The processing routines can use rates of change in sensor values, absolute sensor values, change in sensor values from longer term averages of sensor values, differentiation or integration of sensor values, algorithms, neural networks, fuzzy logic and many other processing methods to determine the environmental condition. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.