LIGHT EXTINCTION SMOKE DETECTOR

Abstract: A light extinction type smoke detector which uses simple pulse light or modulation pulse light to reduce energy consumption, and precisely discriminates smoke generated by fire from interruption of the light beam from the light source to the photoelectric element to prevent a false alarm.

Description: Light Extinction Smoke Detector Technical Field The invention relates to a light extinction smoke detector comprising a light source emitting pulse light and a light receiver disposed outside the path of light from the source so as to receive radiation scattered from smoke particles in the path of the light. Such smoke detectors are used e.g. as fire alarms. Background Art In general the light extinction type smoke detector produces a fire signal upon detecting the extent to which the output of a photoelectric element receiving light from a light source that is spaced across the passageway for smoke, is reduced by the smoke of a fire. Therefore, it has the dis¬ advantage that the interception of a light path extending from the light source to the photoelectric element, attribu¬ ted to the shift of the light path or the like, might reduce the output of the photoelectric element, to provide a false alarm. The known means for eliminating this disadvantage is as stated below. On the output side of the photoelectric element which receives the light from the light source that is spaced across a smoke passageway, there are connected a first level discriminator which detects the reduction in the output level of the photoelectric element ascribable to the smoke of the fire, and a second level discriminator which detects a rapid reduction in the output level of the photoelectric element SUBSTITUTE SKEETi ascribable to the interception of the light path extending from the light source to the photoelectric element or which detects the rate of variation of the output level. The output of the first level discriminator enters one of the input ter¬ minals of a logical product circuit through a delay circuit, and the fire signal is provided from the output terminal of the said logical product circuit. The output of the second level discriminator enters the set input terminal of an R/S flip-flop circuit, the set output of which enters the other input terminal of the said logical product circuit through a "not" circuit and is also used as a light path interception signal. Such means has no problem in a case where the received light output of the photoelectric element decreases slowly due to the smoke of the fire but does not fall below the second level. However, in a case where high density smoke first enters the light path, the output photoelectric element be¬ comes lower than the second level and subsequently when low density smoke enters rendering the output of the photoelec¬ tric element to become a value somewhere between the first and second levels, the output of the second level discrimina¬ tor enters the input terminal of the logical product circuit through both the R/S flip-flop circuit and the "not" circuit, to inhibit the logical product circuit in providing the fire signal and simultaneously provides the light path intercep¬ tion signal. In addition, when low density smoke and high smoke density- enter the light path alternately, the fire sig¬ nal is provided if the output of the photoelectric element is above the second level. However, when the above output becomes lower than the second level, the second level discri¬ minator produces an output, which inhibits the continuous provision of the fire signal and provides the light path in¬ terception signal. Furtheremore, in this case, it is SUBSTITUTESHEET inevitable that the light path interception signal is pro¬ duced without the provision of the fire signal, if the delay time of the delay circuit connected to the first level dis¬ criminator is longer than the period of time during which the smoke density changes. Disclosure of Invention The invention aims at obtaining a smoke detector which uses a simple pulse light or modulated pulse light as light source instead of continuous light to save energy consumed, and which is capable of avoiding false alarm by correctly discriminating and detecting smoke generated by fire and in¬ terception of the light path extending from the light source to the photoelectric element to receive the light. The accompanying drawings, which are incorporated in and con ¬ stitute a part of this specification, illustrate two embodi¬ ments of the present invention and, together with the speci¬ fication, serve to explain the principles of the invention. Brief Description of the Drawings Figure 1 is a circuit diagram of a first embodiment of the invention . Figures 2 and 3 are time charts showing the operating states of various portions of the embodiment shown in Figure 1. Figures 4 and 5 are time charts showing the operating states of various parts in the cases where the interception of the light path has occured. Figure 6 is a circuit diagram of the essential portions of a second embodiment of the invention. Figures 7 and 8 are time charts corresponding to Figures 2 and 4 and showing the operating states of various parts of the embodiment shown in Figure 6. • - SUBSTITUTE SHEET Modes for Carrying Out the Invention Figure 1 is a circuit diagram of a first embodiment of the invention. Numeral 1 designates a generator for a simple pulse voltage, numeral 2 a light emitting element, such as a light emitting diode, which emits pulse light with the out¬ put of the generator 1, numeral 3 a space through which smoke from a fire passes, numeral 4 a photoelectric element, such as a solar cell, which receives the pulse light emitted by the element 2 across the space 3 intervening therebet¬ ween, and numeral 5 an amplifier for the pulse voltage de¬ veloped in element 4. Numeral 6 indicates a circuit for holding the peak value of the pulse voltage, constructed of a circuit which charges a capacitor C, with the output vol¬ tage of the amplifier 5 through a resistor R. as well as through diode D , and a circuit which differentiates the out¬ put voltage of the amplifier 5 through a series circuit con¬ sisting of a diode D„, a capacitor C_ and a resistor R_ and turns "on" a transistor T. owing to a voltage drop having developed across the resistor R_, so as to discharge the charge of the capacitor C through a resistor R as well as the transistor T. , and which includes a discharging resistor R__ for the capacitor C_; and a source follower of a field- effect transistor T whose conduction is controlled by the voltage of the capacitor C and which includes an output re¬ sistor R.. Numeral 7 indicates a fire discriminating circuit which provides a fire signal when the source voltage of the field-effect transistor T of the peak value holding circuit 6 has reached a predetermined proportion of a reference vol¬ tage. It includes a comparator CM, which has an inverting input terminal (-) supplied with the source voltage of the transistor T , and which has a noninverting input terminal (+) supplied with the reference voltage appearing at the SUBSTITUTE SHEET i K AT OMPI /.. WIPO intermediate point of the output resistor R, and R of a source follower of a field-effect transistor T , the conduc¬ tion of which is controlled by the voltage of a capacitor C that is charged with the source voltage of the transistor T through a diode D_ as well as a resistor R,.. An output from the comparator CM., turns "on" transistor T. with the delay of a predetermined time τ, through a delay circuit 8 for preventing any erroneous operation due to noise. The delay circuit 8 is constructed of a capacitor C. which is charged with the aforementioned output through a resistor Ro, and a comparator CM 2_. which has a noninverting input terminal (+) supplied with the voltage of the capacitor C and which has an inverting input terminal (-) supplied with a reference voltage at the intermediate point of resistor y and R_L Λ U that are connected to a power source E in a receiver Re in series with each other. Thus, the delayed out¬ put energizes a relay Y. so as to close its contact y 1 , whereupon the fire signal is sent to a zone relay N in the receiver Re so as to operate it. On the other hand, numeral 9 indicates a light path interception-discriminating cir¬ cuit. It includes a comparator CM whose inverting input ter¬ minal (-) is supplied as a reference voltage with the voltage of the intermediate point of resistors R_._. and 17 that are connected to the power source E in the receiver Re in series with each other, and whose noninverting input terminal (+) is supplied with the voltage of a capacitor C^ that is char¬ ged through a resistor R. _ by the power source E; and a tran¬ sistor T for discharging the capacitor C_, which is connec¬ ted in parallel with the capacitor C ς and which is turned "on" through resistors R.. and R by the output voltage of the amplifier 5. Normally, the transistor T 5 is conductive, so that the voltage of the capacitor C is null. However, when the light path has been intercepted to drastically lower OMPI . UBS7 TUTΞSHEET ™ the output of the amplifier 5 and to render the transistor T nonconductive, the capacitor C is charged. When, after lapse of a predetermined time τ_, the voltage of the capa¬ citor C_ has exceeded the reference voltage of the compa¬ rator CM-, this comparator CM produces an output. When the comparator CM produces the output, a transistor T turns "on" to make null the voltage of the noninverting input ter¬ minal (+) of the comparator CM., in the fire discriminating circuit 7, and the operation of the circuit 7 is inhibited. At the same time, a transistor To 0 turns "on", and a relay Y_ is energized to close its contact y and to send the light path interception signal, which operates a light path interception-indicating relay T in the receiver Re. Con¬ versely, when the comparator CM has produced its output, a transistor Tb _. which has a resistor R1,./ connected across the base and emitter thereof is turned "on" after lapse of a predetermined time T through a delay circuit 10, which is constructed of a capacitor C_. that is charged with the o output voltage of the comparator CM J_. through a resistor Rl.b and a Zener diode ZD that is turned "on" by the voltage of the capacitor C fi . Thus, the voltage of the noninverting in¬ put terminal (+) of the comparator CM is made null, and the operation of the light path interception-discriminating circuit 9 is interdicted. Figures 2 and 3 are time charts showing the operating states of various parts in the cases where smoke has entered the light path at points of time indicated by arrows Sm in the normal states as shown at (0), respectively. In the former case, the density of the smoke has changed slowly as indi¬ cated by a solid line, while in the latter case, the high density smoke equal to or above a light path interception SUBSTITUTESHEET OMPI VIPO level has entered initially, followed by the low density smoke equal to or above a fire level. Figures 4 and 5 are time charts showing the operating states of various parts in the cases where the interception of the light path has occurred at points of time indicated by arrows lc in the normal states, respectively. In the time charts of Figures 2 to 5, (0) illustrates the density variation of the smoke in the light path, (1) the pulse light emission output of the light emitting element 2 having a period t., (2) the out¬ put of the amplifier 5 obtained by amplifying the light re¬ ception output voltage of the photoelectric element 4, (3) the voltage obtained by differentiating the output voltage of the amplifier 5, the illustrated voltage appearing across the resistor R„ of the peak value holding circuit 6, (4) the peak voltage held in the capacitor C. , (5) the maximum value of the output voltage of the amplifier 5, the illus¬ trated value being stored in the capacitor C_ of the fire discriminating circuit 7, (6) the output of the comparator CM , (7) the voltage of the capacitor C . of the delay cir¬ cuit 8, (8) the output of the comparator CM , (9) the voltage of the capacitor C fi of the delay circuit 10, (10) the operating state of the transistor T g , (11) the operating state of the transistor T ς of the light path interception- discriminating circuit 9, (12) the voltage of the capacitor C_, (13) the output of the comparator CM_, and (14) the operating state of the transistor T_. Symbol L.. at (0), (2) and (4) in Figures 2 to 5 denotes the level which is to be determined the fire, symbol L at (0) and (2) denotes the level which is to be determined the light path interception, symbol L_ at (3) denotes that level of the base-emitter voltage of the transistor which is necessary for the con¬ duction of this transistor, symbol L at (5) denotes the SUBSTITUTE SHEET OMPI -/>,__. WIPO level of the reference voltage which is applied to the non¬ inverting input terminal (+) of the comparator CM and which corresponds to the fire level _.. at (2) and (4), symbol ς at (7) denotes the level of the reference voltage which is applied to the inverting input terminal (-) of the com¬ parator CM_, symbol L, at (9) denotes the level of the Zener voltage of the Zener diode ZD, and symbol L_ at (12) denotes the level of the reference voltage which is applied to the inverting input terminal (-) of the comparator CM . Referring to Figures 2 to 5, while there is not any smoke in the smoke passage 3 and the light path is not inter¬ cepted, either, the differentiated voltage of the output voltage of the amplifier 5 as shown at (3) appears across the resistor R_ each time the amplifier output voltage shown at (2) develops, so that the transistor T. turns "on" to discharge the charges of the capacitor C_ through the re¬ sistor R- as shown at (4). However, when the above differen¬ tiated voltage comes below the level L_, the transistor T. turns "off", so that the capacitor C_ is recharged with the output voltage of the amplifier 5 and holds the peak value thereof. The held voltage is applied to the inverting input terminal (-) of the comparator CM, of the fire discriminat¬ ing circuit 7. This voltage held by the capacitor C. becomes lower than the fire level L. , as accordingly does the lever L. of the reference voltage of the noninverting input ter¬ minal (+) of the comparator CM-, of the fire discriminating circuit 7 as shown at (5), for a moment when the transistor has turned "on". Therefore, the comparator CM_^ produces its output as shown at (6), and the capacitors C. and C fi are charged with the output of the comparator CM, as shown at (7) and (9) respectively. However, since, the output of the comparator CM 1 ceases immediately, the voltages of the capacitors C. and C, do not reach the level L,- of the refer¬ ence voltage of the comparator CM 2_. and level " b, of the Zener voltage of the Zener diode ZD respectively, so that the charges of these capacitors C. and C, are discharged through the comparator C . On the other hand, the capacitor C of the light path interception-discriminating circuit 9 is charged through the resistor £■,-■ > • However, each time the output of the amplifier 5 exceeds the light path intercep¬ tion level L_ as shown at (2), the transistor Tb c turns "on" as εhwon at (11), and the charges of the capacitor C c are discharged through the transistor T as εhwon at (12), so that the voltage of the capacitor C-. does not reach the level \_ of the reference voltage applied to the inverting input terminal (-) of the comparator CM_. When, as illustrated at (0) in Figure 2, the smoke has started entering the light path at the point of time indicated by the arrow Sm and the density of the smoke slowly changes as indicated by the solid line, the output voltage of the amplifier 5 falls gradually with increase in the density of the smoke as shown at (2), and the differ¬ entiated voltage thereof shown at (3) falls gradually accor¬ dingly. Each time the differentiated voltage exceeds the level L_, the transistor T. turns "on" to discharge the charges of the capacitor C. as shown at (4), and the dis¬ charged capacitor C. is recharged up to the peak value of the lowered output voltage of the amplifier 5, but as the output voltage of the amplifier 5 has become lower than the level L, at (2), the voltage held by the capacitor C.. be¬ comes lower than the level L , and the input of the in¬ verting input terminal (-) of the comparator CM becomes lower than the reference voltage L. of the noninverting in¬ put terminal (+), so that the comparator CM-, continues to SUESTITUTE SHEET ( A* W OM 1P P O I provide its output as shown at (6). As a result, the capaci¬ tors C and C fi are respectively charged with the output of the comparator C through the resistors R 0 and R. _ as shown x o lb at (7) and (9). On the other hand, the capacitor C - c _> is charged through the resistor R. _ as shown at (12), just as in a normal state. However, since the output of the am¬ plifier 5 is greater than the light path interception level L_ as shown at (2), the transistor T ς turns "on" as shown at (11) and discharges the charge of the capacitor C_ each time the amplifier 5 provides its output. As shown at (9), the voltage of the capacitor Cb c increases and exceeds the level L, indicative of the Zener voltage of the Zener diode ZD after lapse of the predetermined time τ Then, the tran¬ sistor Tb,. turns "on" as shown at (10) and inhibits the com- parator C to provide the output. Subsequently, the voltage of the capacitor C. increases as shown at (7) and exceeds the level of the reference voltage of the inverting input terminal (-) of the comparator CM after a lapse of the pre- determined time τ . Then, the comparator CM provides its output as shown at (8), the transistor T. is turned "on", and the relay Y, operates to close its contact y. , so that the fire signal is provided. Next, when as illustrated at (0) in Figure 3, the smoke has started entering the light path at the point of time indica¬ ted by the arrow Sm and high density smoke equal to or above the light path interception level L has entered at first as indicated by the solid line, the output of the amplifier 5 immediately falls below the light path interception level L„ as shown at (2), and the transistor T of the light path interception-discriminating circuit 9 does not turn "on" as shown at (11), so that the capacitor C,. continues to be charged as shown at (12). However, when low density smoke SUBSTITUTESHEET -. O IP P O I - in between the fire level L and the light path interception level L subsequently enters, the output of the amplifier 5 becomes a value somewhere between the levels L. and L-, as shown at (2), and the transistor T-. turns "on" again as shown at (11), so that the capacitor C_ has its charge dis¬ charges as shown at (12). Therefore, in a case where the output of the amplifier 5 has fallen below the light path interception level L» for a short time, the comparator CM 3 of the light path interception-discriminating circuit 9 does not provide its output as illustrated at (13). As shown at (7) and (9), the respective capacitors C. and C, of the delay circuits 8 and 10 start being charged with the output of the comparator CM of the fire discriminating circuit 7 illustrated at (6), at the time of which the output of the amplifier 5 has fallen below the fire level L, as shown at (2). When, as illustrated at (9), the voltage of the capacitor C r has reached the level , of the Zener voltage b b of the Zener diode ZD after a lapse of the predetermined time τ_, the transistor T_. turns "on" as shown at (10), to j b inhibit the operation of the light path interception-dis¬ criminating circuit 9. When, as illustrated at (7), the voltage of the capacitor C has exceeded the level L of the reference voltage applied to the inverting input ter¬ minal (-) of the comparator CM 2 of the delay circuit 8, after a lapse of the predetermined time τ,, the comparator CM provides its output as shown at (8), the transistor T turns 2 "on",. and the relay Y. operates to close its contact y 1 , so that the fire signal is provided. As can be seen from such operating states, according to the invention, in both cases where smoke of a higher density than the light path interception level has entered the light path at first and then smoke of a density somewhere between SUBSTITUTE SHEET J ΓRE-A O OMMPPII IPO the fire level _ and the light path interception level I__ has entered, and where smoke of such high and low densities has entered laternately, the capacitor C of the light path interception-discriminating circuit 9 has its charge dis¬ charged as shown at (12) , when thin smoke somewhere between the levels L. and L has entered. Therefore, the comparator CM does not provide its output. Figure 4 illustrates the operating states of the various parts in the case where the light path has been intercepted in the quiescent period of the light emission of the light emitting element 2. The arrow lc denotes the point of time at which the interception has occurred. Notwithstanding that the light emitting element 2 is continuing the pulse light emission as shown at (1), the amplifier 5 produces no output as shown at (2) from the point of time indicated by the arrow lc, because the photoelectric element 4 receives no light. As a result, the differentiated voltage of the ampli¬ fier output does not appear across the resistor R_, and the capacitor C continues to hold the peak voltage of the last output of the amplifier 5 as shown at (4) . Since the com¬ parator CM, does not produce its output as shown at (6) either, the capacitors C. and C fi are no longer charged as shown at (7) and (9), respectively. On the other hand, the capacitor C_ of the .light path interception-dicriminating circuit 9 is charged through the resistor R 1 _ as shown at (12). Herein, since the transistor has turned "off" due to the null output of the amplifier 5, the capacitor C continues to be charged. After a lapse of the period of time τ_, the charged voltage of the capacitor C exceeds the level L_ of the reference voltage of the inverting input terminal (-) of the comparator CM_, and this comparator CM provides its output as shwon at (13). Therefore, the tran- INSTITUTE SHEET} IPO sistor T turns "on" as shown at (14) and makes null the level L of the reference voltage of the noninverting input terminal (+) of the comparator CM., as shown at (5), so as to inhibit the comparator CM, from providing its output. Simultaneously, the transistor To Q turns "on" to energize the relay Y so as to close the contact y thereof and to provide the light path interception signal. Figure 5 illustrates the operating states of the various parts in the case where the light path has been intercepted at the point of time indicated by the arrow lc, during the light emission of the light emitting element 2. At this time, the period of time during which the photoelectric el¬ ement receives the light is short on account of the inter¬ ception of the light path. The width of the output voltage of the amplifier 5 narrows as shown at (2), the differen¬ tiated voltage of the amplifier output appearing across the resistor R_ is sharp, and the conduction period of time of the transistor T is short as compared with that in the normal state. In the short period, the charges of the ca¬ pacitor C- are discharged, and the charged voltage thereof falls below the fire level L, of the comparator CM. as shown at (4). Herein the capacitor C. , after the discharge, can scarcely be charged with such a narrow puls width voltage of the amplifier 5. Since the lowered voltage held by the capacitor C. has become below the level L. of the reference voltage of the noninverting input terminal (+) of the com¬ parator CM. corresponding to the fire level L , the com¬ parator CM., produces its output as shown at (6) , and the capacitors C . and C, are charged with this output as shown at (7) and (9) respectively. On the other hand, since the pulse width of the output voltage of the amplifier 5 is so nar¬ row that the transistor T_ turns on for a short time as SUBSTITUTESHEET OMH /_. IPO shown at (11), whereby the charge of the capacitor C_ is discharged as shown at (12). Immediately after completion of the discharge, the capacitor C,. begins to be charged. When after a lapse of the period of time τ , the voltage of the capacitor C has exceeded the level L_ of the refer¬ ence voltage applied to the inverting input terminal (-) of the comparator CM , this comparator CM_ produces its out¬ put as shown at (14). Then, the level L of the reference voltage of the noninverting input terminal (+) of the com¬ parator CM., becomes null as shown at (5), and the output of the comparator CM., becomes null as shown at (6), so that the charges of the capacitors C. and C, are discharged through the comparator CM as shown at (7) and (9) re¬ spectively. At the same time, the output of the comparator CMo_ turns "on" the transistor To Q , which energizes the relay Y ' to close the contact y_, so that the light path intercep¬ tion signal is provided. The relationships of the magnitudes of the periods of time τ . , τ_ and τ_ may be selected as the following inequalities where t denotes the conduction time of the transistor T^ corresponding to the pulse width of the pulse output shown at (2) and obtained by amplifying the recieved light output of the photoelectric element 4: - t 2' τ 3 ^ τ l The reasons therefor are as stated below. When the inter¬ ception of the light path has occurred during the light emission of the light emitting element 2 as illustrated at (1) in Figure 5, the comparator CM., of the fire discriminat¬ ing circuit 7 produces its output continuously from the point of time of the initiation of the light emission as seen from (6), and the capacitors C. and C_ b- begin to SUBSTITUTE SHEET charged as shown at (7) and (9) respectively. In addition, as seen from (12), the capacitor C_. having begun to be charged since the point of time of the light path inter¬ ception, this point of time being later than the point of time of the initiation of the charging of the capacitors C . and C fi equal to the conduction time t of the transistor T , continues to be charged as it is. Therefore τ_ must be shorter than the period of time obtained by subtracting t from τ or τ , in order that the light path interception signal may be provided before the generation-of the fire signal and the inhibition of the operation of the light path interception-discriminating circuit. Moreover, the light path interception signal must not be provided before the fire signal is produced. Therefore, τ-, must not be longer than τ.. Figure 6 is a circuit diagram of the essential portions of a second embodiment of the invention which employs modula¬ ted pulse light shown at (1) in Figure 7 that is a time chart coresponding to Figure 2. As compared with the first embodiment of the invention shown in Figure 1, the second embodiment of the invention differs only in that a generator 1' for the modulated pulse voltage is employed instead of the generator 1 for the simple pulse voltage, that a band¬ pass filter 11 which passes only current of a modulation pulse frequency based on a mudulated pulse voltage having developed in " the photoelectric element 4 for receiving the light, and a half-wave rectifier circuit 12 which rectifies the output of the amplifier 5, are respectively disposed before and after the amplifier 5 for the output voltage of the element 4, and that a peak value holding circuit 6' is employed instead of the peak value holding circuit 6. The same portions on the right side as in Figure 1 have been SUBSTITUTE SHEET omitted for want of space. More specifically, in the circuit 6, the output voltage of the amplifier 5 is differentiated through the series circuit consisting of the diode D , ca¬ pacitor C and resistor R , and the transistor T is turned "on" by the voltage drop having appeared across the resistor R^. In contrast, the circuit 6 * includes a waveshaping cir¬ cuit 13 wherein the output voltage of the half-wave rec¬ tifier circuit 12 shown at (2) in Figure 7 is applied through a resistor 1R to the noninverting input terminal (+) of a comparator CM., to the inverting input terminal (-) of which is coupled the intermediate point of resistors R. q and R_ n connected in series to the same power source as that E in the receiver Re shown in Figure 1, and wherein the aforementioned output voltage is waveεhaped through the com¬ parator CM. as shown at (2_.) in Figure 7; and a charge-and- diεcharge circuit 14 for the output of the circuit 13, wherein as shown at (2_) in Figure 7, a capacitor C_ iε once charged with the output of the circuit 13 through a reεistor' R- . as well as a diode D_, and the charges of the capacitor C are discharged through a discharge resistor before the circuit 13 provides the next output thereof. The output voltage of the circuit 14, namely, the voltage of the capaci¬ tor C_ shown at (2_) in Figure 7 is differentiated through the series circuit consiεting of the capacitor C_ and the resistor R ? , as shown at (3) in Figure 7, and the transistor T-. is turned "on" by the voltage drop appearing across the resistor R_. Both the embodiments agree in the point that the conduction of the transiεtor T_ of the light path inter¬ ception-discriminating circuit is controlled by the voltage of the input side of the differentiation circuit which has the capacitor C_ and the resistor R_ connected in series. SUBSTITUTE SHEET - tEAT OMPI Figures 7 and 8 are time charts corresponding to Figures 2 and 4 and showing the operating states of various parts as to the embodiment shown in Figure 6, in the case where smoke has entered the light path in the normal state at a point of time indicated by arrow Sm and where the smoke density has changed slowly, and in the case where the interception of the light path has occurred in the normal state at a point of time indicated by arrow lc, respectively. In these time charts, (O) illustrates the density variation of the smoke in the light path, (1) the modulated pulse light emisεion of the light emitting element 2 having a period ;t, (2) the output voltage obtained from the received light out¬ put of the photoelectric element 4 passing through the band— pass filter 11, amplifier 5 and half-wave rectifier circuit 12, (2.) the output voltage of the waveshaping circuit 13 in the peak value holding circuit 6', (2_) the output voltage of the charge-and-discharge circuit 14 in the same 6', (3) the voltage appearing across the resistor R_ of the circuit- 6' i.e. a result of the differentiation of the output voltage of the circuit 14, (4) the peak voltage of each pulse train of the half-wave rectifier circuit 12, this peak voltage being held in the capacitor C , (5) the maximum value in the output voltages of the circuit 12, this value being stored in the capacitor C_ of the fire discriminating circuit 7, (6) the output of the comparator CM. , (7) the voltage of the capacitor C. of the delay circuit 8 shown in Figure 1 and connected on- the output side of the comparator CM., (8) the output of the comparator C of the same circuit as the cir¬ cuit 8 shown in Figure 1, (9) the voltage of the capacitor C fi of the delay circuit 10, (10) the operating state of the transistor T_b-, (11) the operating state of the transistor TD c of the light path interception-discriminating circuit 9, (12) the voltage of the capacitor C , (13) the output of the com- SUBSTITUTE SHEET parator CM_, and (14) the operating state of transistor T . Symbol L at (0), (2) and (4) denotes the level which is to be determined a fire, symbol L_ at (2) denotes the level which is to be determined light path interception, the levels indicated by L_ - L_ at (3) - (12) are the same as those shown in Figures 2 and 4, and symbol L„ at (2_) denotes the voltage level which is required for the conduction of the transistor T of the light path interception-discriminating circuit 9. In this manner, in the embodiment shown in Figure 6, the modulated pulse light of high frequency is used instead of the simple pulse light, and the output voltage of the light receiving photoelectric element 4 is pasεed through the band¬ pass filter 11, amplified by the amplifier 5 and rectified by the half-wave rectifier circuit 12. Therefore, due to in¬ ductance, resistance etc. in the filter 11 and the amplifier 5, the amplitude of the rectified output voltage becomes smaller at the end parts thereof as seen at (2) and in Fi¬ gures 7 and 8, and there is a fear that the smoke detector might operate erroneously, (refer to the specification and drawings of Japanese Utility Model Application No. 56-139190 filed by the same Applicant). For this reason, the output waveform is shaped as shown at (2..) by means of the wave- shaping circuit 13 in the peak value holding circuit 6*. The capacitor C_ of the charge-and-discharge circuit 14 is charged with the shaped output voltage through the resistor R . and the diode D_ as illustrated at (2 ). Each time a charging current flows through the capacitor C_, the voltage shown at (3) develops which is the differentiated voltage of the capacitor C_ across the resistor R_ through the ca¬ pacitor C_. Only when the peak value of the voltage has exceeded the level L , the transistor T. turns "on" to diε- SUBSTITUTE SHEET ' - OMPI / j ._ WIPO charge the charges of the capacitor C as shown at (4). After the end of the discharge, the capacitor C is recharged with the output voltage of the half-wave rectifier circuit 12 shown at (2), until the voltage of this capacitor reaches the peak value of the output voltage shown at (2) of each figure. Except for these points, the operating states do not differ from those of the various portions of the embodiment of Figure 1 as illustrated in Figures 2 and 4. In addition, the operating states of the various portions of the embodi¬ ment of Figure 6, corresponding to those in the embodiment of Figure 1, in the case shown in Figure 3 where high density smoke equal to or above the light path interception level has entered the light path at first and where low density smoke equal to or above the fire level has subsequently entered and in the case shown in Figure 5 where the inter¬ ception of the light path has occurred at a point of time indicated by the arrow lc during the light emisεion of the light emitting element 2, can be readily conjectured from the operating states of the various portions shown in Figures 7 and 8 because the parts (2„) of Figures 7 and 8 correspond to the parts (2) of Figures 2 - 5. Regarding the relation¬ ships of length among the periods of time i , i. and τ.., the embodiment of Figure 6 is the same as that of Figure 1, except in the point that t denotes the conduction time of the transistor T c which is determined by the waveform of the output voltage of the charge-and-discharge circuit 14 shown at (2_), corresponding to the width of the pulse train equal to or above the level L_ of the half-wave rectified output shown at (2) of Figure 7 or Figure 8, instead of the width of the pulse output shown at (2) of each of Figures 2 - 5. SUBSTITUTE SHEET As set forth above, a light extinction type smoke detector employing pulse light according to each of the two inventions produces, owing to a simple and appropriate arrangement, the effect that energy consumption is reduced by employing simple pulse light or modulated pulse light in place of con¬ tinuous lighting and that smoke due to a fire and the inter¬ ception of a light path which extends from a light source to a photoelectric element receiving the light of the light source are correctly discriminated and detected, so that a false alarm can be prevented. ^ es i iTUT£ SHE£ ζ JfcEA OMPI .

Claims: Claims A light extinction type smoke detector using pulse light characterized in that, on an output side of a photoelec¬ tric element which receives the light of a pulse light emitting element that is spaced on the other side of the passageway for the smoke of a fire, a fire discrimina¬ ting circuit is connected through a peak value holding circuit, while a light path interception-discriminating circuit is directly connected by which, only when inter¬ ception of a light path extending from said light emitting element to said photoelectric element has occurred and continued for at least a predetermined period of time τ_, the light path interception is discriminated after a delay of the time period τ_ from the time of the occurrence thereof; so that when εaid fire discriminating circuit has provided an output, the operation of said light path interception-discriminating circuit is inhibited after the lapse of a predetermined period of time τ , while a fire signal is provided after a delay of a predetermined period of time τ_. , and that when said light path interception-discriminating circuit has provided an output, the operation of said fire dis¬ criminating circuit is immediately inhibited, and a light path interception signal is εimultaneaously pro¬ vided; lengths of the periods of time τ , τ and τ being so related that while τ_ is not longer than T , the light path interception signal is set so as to be provided before the provision of the fire signal and the inhibition of the operation of said light path inter¬ ception-discriminating circuit. SUBSTITUTE SHEET 2. A light extinction type smoke detector using pulse light characterized in that, on an output side of photoelec¬ tric element which receives the light of modulated pulse light emitting element that is spaced on the other side of a passageway for the smoke of a fire, a fire discrimi¬ nating circuit is connected through a peak value holding circuit, while a light path interception-discriminating circuit by which, only when interception of a light path extending from said light emitting element to said photo¬ electric element has occurred and continued for at least a predetermined period of time τ , the light path inter¬ ception is discriminated after delay of the time period τ from the time of the occurrence thereof is connected through an output waveεhaping circuit and charge-and-diε- charge circuit for the output of εaid waveshaping cir¬ cuit; so that when said fire discriminating circuit haε provided an output, the operation of εaid light path in- terception-diεcriminating circuit is interdicted after the lapse of a predetermined period of time τ while a fire signal is provided after a delay of a predetermi¬ ned period of time τ , and that when said light path in¬ terception-discriminating circuit haε provided an output, the operation of said fire discriminating circuit iε im¬ mediately inhibited, and a light path interception, signal is simultaneously provided; lengths of the periods of time τ , τ and τ being so related that, while τ is not longer than τ , the light path interception signal is set so as to be provided before the proviεion of the fire signal and the inhibition of the operation of said light path interception-discriminating circuit. C _m_ £*

Inventors: ISHII KENJI, YASUKAWA MAKOTO, ISHII, KENJI, YASUKAWA, MAKOTO
Applicants: CERBERUS AG, NOHMI BOSAI KOGYO CO LTD, NOHMI BOSAI KOGYO CO., LTD.
Application year: 1982
Main classification: G08B17
IPC codes: G01N21, G01N33, G08B17, G08B29