Testing photoelectric smoke detectors

Abstract: A photoelectric smoke detector (10) has test circuitry (34; 26a) for testing the detector (10) by increasing the sensitivity thereof. The sensitivity is increased by either altering a bias condition of a photosensor (30) or by altering a gain parameter of the detector (10). The detector (10) returns to a quiescent state when the sensor (30) returns to its original bias condition or when the gain parameter returns to its quiescent value.

Description: The invention pertains to smoke detectors. More particularly, the invention pertains to photoelectric-type smoke detectors which incorporate a test feature. Smoke detectors have been recognized as important safety devices which can be used to provide an early alarm indication in the event that the level of smoke in the ambient atmosphere exceeds a predefined threshold. Both ionization-type and photoelectric-type detectors are known and have been used in both residential and commercial applications. One aspect of smoke detector-type products is that they do not normally go into an alarm condition and are silent until the level of smoke in the ambient atmosphere exceeds the predetermined value. As a result, the great majority of time the detector is in a non-alarmed state and is not emitting an alarm indication. Test circuits have, as a result, been developed for the purpose of temporarily placing detectors into an alarmed state to establish whether or not the unit is functioning properly. One such circuit is disclosed in Mallory et al. U.S. Patent 4,321,466. In battery powered photoelectric detectors where the test circuitry increases the radiant energy output of the light source, the batteries are subjected to an increased current draining during the test interval. It is particularly important in battery powered detectors to minimize current draining so as to maximize long-term battery life. Hence, it would be desirable to provide test circuitry which does not increase the radiant energy output of the light source of a photoelectric detector, so as to enhance and extend battery life by minimizing current draw while in a test condition. According to a first aspect of the present invention there is provided a photoelectric smoke detector comprising: a source of radiant energy; a sensor of radiant energy; and control circuitry coupled to said sensor for determining when an output from said sensor indicates an alarm condition, wherein said circuitry has a quiescent state and an alarm state; characterised by test circuitry for increasing the sensitivity of the detector, said test circuitry including a manually-operable switch, having a normal state and a test state, in combination with one of a gain altering circuit, for altering the gain of the said control circuitry, or a bias altering circuit, for altering the bias of the said sensor, whereby, if the said detector is functioning correctly, said control circuitry enters the alarm state from the quiescent state in response to said switch being placed in the test state and enters the quiescent state from the alarm state in response to said switch being placed in the normal state. A photoelectric smoke detector embodying the present invention includes a source of radiant energy and a sensor of radiant energy. The source and sensor are positioned in a smoke chamber. Control circuitry is coupled to the sensor for determining when an output from said sensor indicates a smoke condition. The sensor is biased to provide a first, quiescent level of sensitivity in a non-alarm state. A test circuit includes a manually operable switch in combination with a bias altering circuit. When the switch is closed, the test circuit alters the bias condition of the sensor, thereby increasing the sensitivity of the detector. The control circuitry then enters an alarm state in response to the increased sensitivity. Alternatively, a gain parameter of the detector can be increased in the test condition. According to a second aspect of the present invention there is provided a method of testing a photoelectric smoke detector, which detector is a detector in accordance with the first aspect of the present invention operable to: generate a beam of radiant energy; detect a scattered portion of the beam; establish a non-alarm condition based on a first level of detected scattered energy; and establish an alarm condition based on a second level of detected scattered energy being indicative of a predetermined level of combustion; which testing method is characterised by manually altering one of a bias condition of the sensor of the detector or a gain condition of the control circuitry of the detector, whereby the detector establishes an alarm state during the test, without altering the radiant energy beam, if the detector is functioning correctly. Reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a block diagram of a photoelectric detector embodying the present invention; and Fig. 2 is a schematic diagram of the detector of Fig. 1. While this invention is susceptible of embodiment in many different forms, there is 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. Figure 1 illustrates a block diagram of a detector 10 which embodies the present invention. The detector 10 includes an integrated circuit 12 which provides control functions. The integrated circuit 12 could be, for example, a Motorola type MC145011 which is publicly available and used for photoelectric-type smoke detectors. It will be understood that other integrated circuits might be usable. The particular integrated circuit that might be chosen is not a limitation of the present invention. The integrated circuit 12 includes an output driving port 12a for intermittently energizing a light source 14. The output of the source 14 can initially be adjusted during manufacture by a sensitivity adjustment circuit 16. The source 14 emits radiant energy R into a smoke chamber, not illustrated. The integrated circuit 12 also includes an alarm indication output port 12b which is coupled to a horn driving circuit 20. One type of horn that could be used is a piezoelectric horn used with smoke detectors. Timing for the integrated circuit 12 is provided at an input port 12c from timing circuitry 22. A DC supply 24, which could be a 9 volt battery, provides a source of electrical energy for the detector 10. The integrated circuit 12 contains an amplifier for which the gain can be set, via an input port 12d, in a gain circuit 26. Coupled to an input port 12e of the integrated circuit 12 is a radiant energy receiver or sensor 30. Radiant energy R emitted from light source 14 is scattered by particulate matter in the ambient air in the smoke chamber and a portion R S of the scattered ambient radiant energy is incident upon the receiver 30. As the particulate matter in the atmosphere increases, due to the presence of products of combustion, the degree of scattered radiant energy R S increases thereby providing, when amplified within the integrated circuit 12, an indicium of the presence of combustion. The radiant energy receiver or sensor 30 is biased under normal conditions by a bias circuit 32. In this condition, the detector has a sensitivity level set in part by the bias condition and partly by the gain of the detector. A bias altering, sensitivity test circuit 34 can be coupled to the receiver 30 by means of a manually operable test switch 36. When the test switch 36 is closed, the bias altering circuit 34 alters the bias of the sensor or receiver 30 and increases the sensitivity of the detector. This bias alteration is such that an output is produced in response to a quiescent, non-alarm level of incident radiation R S . This output is sufficient to cause the integrated circuit 12 to enter an alarm state and energize the horn circuit 20 producing an audible test output in a response to closure of the switch 36. Thus, when the switch 36 is closed, the sensitivity of the receiver or sensor 30 is increased so that a smoke indicating signal is provided to the integrated circuit 12 thus placing it into an alarm state. Alternately, instead of altering the bias of the sensor receiver 30, the gain circuit 26 can be altered to provide increased gain in the integrated circuit 12 thereby generating a smoke condition and placing the integrated circuit into an alarm state. Figure 2 illustrates portions of the detector 10 in more detail. The same identification numerals are used in Figure 2 for corresponding circuitry as was discussed above with respect to Figure 1. In the embodiment illustrated in Figure 2, the normal receiver or sensor biasinq circuitry is indicated generally at 32, and includes resistors 34a, 34b. Bias altering circuitry 34, coupled to a manually operable test switch 36, comprises resistor 34'. When the switch 36 is closed, the resistor 34' is coupled in parallel across the resistor 34a thereby increasing the sensitivity of the detector 10 and driving the integrated circuit 12 into an alarm state. When the switch 36 is released, the receiver or sensor 30 returns to its normal level of sensitivity and exits the alarm state. Alternatively, the gain of the integrated circuit 12 can be increased by coupling a capacitor 26a, illustrated in phantom, across a gain setting capacitor 26b in the gain circuit 26. Increasing the capacitance results in increased gain in the integrated circuit 12, thereby causing the detector 10 to go into an alarm state. The bias point of the sensor or receiver 30 can also be shifted by increasing the resistance of the resistor 34b such as by switching an additional resistance 34c, indicated in phantom, in series therewith. This will also increase the sensitivity of the receiver or sensor 30. Thus, according to an embodiment of the present invention, the sensitivity of a sensor or receiver element of a photoelectric smoke detector can be increased thereby placing the detector into an alarm state, for test purposes. When the test switch is released, the unit returns to its normal level of sensitivity. The sensitivity can be increased by increasing the gain of amplifier circuitry in the detector. Alternately, the bias point of the sensor or receiver can be altered so as to produce a smoke condition signal which is coupled to the integrated circuit control circuitry thereby placing that circuitry into an alarm state. From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the 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.

Claims: A photoelectric smoke detector (10) comprising: a source (14) of radiant energy; a sensor (30) of radiant energy; and control circuitry (12) coupled to said sensor (30) for determining when an output from said sensor (30) indicates an alarm condition, wherein said circuitry (12) has a quiescent state and an alarm state; characterised by test circuitry (34; 26a) for increasing the sensitivity of the detector (10), said test circuitry (34, 26a) including a manually-operable switch, having a normal state and a test state, in combination with one of a gain altering circuit (26), for altering the gain of the said control circuitry (12), or a bias altering circuit (34), for altering the bias of the said sensor (30), whereby, if the said detector (10) is functioning correctly, said control circuitry (12) enters the alarm state from the quiescent state in response to said switch being placed in the test state and enters the quiescent state from the alarm state in response to said switch being placed in the normal state. A detector (10) as claimed in claim 1, wherein the said output of the sensor (30) is indicative of the amount of smoke particles present in the vicinity of the sensor (30), the said control circuitry (12) determining when that output indicates the presence of an amount of smoke particles which exceeds a preset level and placing the detector (10) in an alarm condition in accordance therewith, the said test circuitry (34; 26a) being operable such that when the said switch is placed in the test state the amount of smoke particles present in the vicinity of the sensor (30) is sufficient to cause the detector (10) to be placed in an alarm condition, regardless of whether that amount exceeds said preset level, if the detector (10) is functioning correctly. A detector as claimed in claim 1 or 2, wherein said bias altering circuit (34) includes a resistor (34; 34c) couplable to a resistor (34a; 34b) which establishes, at least in part, a quiescent bias condition. A detector as claimed in claim 1 or 2, wherein said gain altering circuit (26) includes a capacitor (26a) couplable to a capacitor (26b) which, at least in part, establishes a quiescent gain condition. A method of testing a photoelectric smoke detector, which detector is a detector (10) as claimed in any one of claims 1 to 4 operable to: generate a beam of radiant energy; detect a scattered portion of the beam; establish a non-alarm condition based on a first level of detected scattered energy; and establish an alarm condition based on a second level of detected scattered energy being indicative of a predetermined level of combustion; which testing method is characterised by manually altering one of a bias condition of the sensor (30) of the detector (10) or a gain condition of the control circuitry (12) of the detector (10), whereby the detector (10) establishes an alarm state during the test, without altering the radiant energy beam, if the detector (10) is functioning correctly.

Inventors: MINNIS DAVID A, MINNIS, DAVID A
Applicants: BRK BRANDS INC, BRK BRANDS, INC.
Application year: 1995
Main classification: G08B29
IPC codes: G08B21, G08B29, G01N21