Ionization Smoke Detector Co-Used to Issue Fire Alarm and Detect Ambient Atmosphere

The present invention comprises an auxiliary circuit to co-use an ionization smoke detector included in a fire alarm circuit, for a purpose of detecting ambient atmosphere in which the detector is placed. The ionization smoke detector is used itself by the auxiliary circuit to detect the probability of issuing a false warning and to determine its cause without any influence to the normal function of the fire alarm circuit including the detector.

A fire alarm circuit, for instance, is disclosed in U.S. Pat. No. 3,521,263. This circuit comprises, as shown in FIG. 2, a comparison chamber of the accompanying drawings 100 and a measuring chamber 101 connected in series, a field effect transistor 102 having a gate connected to a common electrode of the two chambers, the rectifier 103 controlled by the transistor, and a relay 104 energized by ignition of the rectifier.

From the standpoint of human life and property, a fire alarm is charged with an important mission, and its action is required to be reliable and prompt. An ionization smoke detector is very effective for finding the fire at an early stage because the smoke generated from the fire can be detected by the smoke detector, and a warning may be issued at the early stage of the fire. However, in certain cases, an ionization smoke detector may issue false warnings of fire. Such cases are as follows:

1. When the detector is mounted at a place where a strong air current blows as, for example, at the outlet of an air conditioner, or the like;

2. When the detector is mounted at a place where a large quantity of dust and steam exist;

3. When its cause stems from elements in the detector circuit itself as, for example, a break-down of the ionization chamber, or a short circuit; and

4. When the detector is set to a critically high sensitivity and is mounted in an environment which includes particles cutting off some ionic current in the normal operation.

Cases (1) and (2) above involve problems concerning the suitability of the surroundings for locating the detector, they affect the detector for the following reasons: In case (1), the strong air current blows off the ionic current by bridging between electrodes so as to cut off the ionic current between electrodes. Accordingly, the detector is apt to issue a false warning under a small shock such as noise.

In case (2), dusts or steam enter an outer ionization chamber where the outer air flows relatively easily, and brings about malfunctioning of the detector by the adherance of dust on the electrodes in the ionization chamber, thereby preventing the flow of the ionic current and breaking the insulation therebetween.

In case (3), the cause pertains to the detector itself and therefore proper functioning of the detector ceases.

In case (4), there are problems of the environment in which the detector is placed and the mounting of the detector. Corpuscles cut-off some ionic current under normal condition when entering the outer ionization chamber. Thus, when the detector is placed in such environment and set to a high sensitivity point, it is apt to issue false warnings resulting from noise.

These and other causes occur individually or in combination, and accordingly, it is difficult to ascertain which detectors issue false warnings, or what the cause is. According to the prior art, when a false warning is issued from a smoke detector, a plurality of densitometers having the same construction and shape as the smoke detector, arranged in parallel to the smoke detector deemed as the one issuing the false warning. In particular, the ion densitometers are arranged adjacent to respective smoke detectors connected in parallel to the circuit which issued the false warning, or the ion densitometer is placed adjacent to the group of the smoke detector after a serviceman dismounted it from the mounting place and brought it back for repair. Thus, issuance and cause of false warnings have been investigated by measuring the response of the ion densitometer placed in the same environment. However, in the former, it is impossible to place the smoke detector and the ion densitometer in the same environment, and there are various difficulties in matching the ion densitometer. Furthermore, it has the disadvantage that a precise value cannot be obtained in spite of applying much time and effort to measuring the instruments. In the latter case, also, the work efficiency of the measuring instrument is low because the instrument does not quickly measure the condition at the installation point, and the cause of issuing a false warning due to the environment wherein the detector is mounted is difficult to determine since it is difficult to obtain the same environment as at the installation point.

Accordingly, an object of the present invention is to provide a new detecting method and apparatus in which an ionization type smoke detector having an ionization chamber is installed, so as to permit the outer air to flow therein and an ionic current to continuously change from smoke entering the chamber. The current is detected, visually indicated, and compared with a standard value of the ionic current whereby the functional operation of the detector can be easily judged in situ at the installation. Thus, according to the present invention, the cause of issuing a false warning can be rapidly and firmly determined by easily investigating whether the environment in which the detector is mounted, is suitable or not for accurate operation of the detector, or whether something is wrong with the detector itself.

The ceiling fixtures to be tested are provided with auxiliary circuits adapted to produce an auxiliary output signal the amplitude of which varies in accordance with the ambient atmosphere of the corresponding fixture while the ionization smoke detector thereof is on duty and in situ. In such case the ionization smoke detector is subject to existing actual environmental conditions which might cause the smoke detector to issue a false alarm signal during the testing period. Such auxiliary output signal is applied to the female terminal of a wall receptacle carried by each fixture. Thus, it is only mecessary to mate the corresponding male terminals of the plug of the auxiliary indicating circuit with such receptacle female terminals of a selected fixture. The ammeter therefore automatically provides a visual indication of the amplitude of the auxiliary signal substantially instantaneously; while the recorder makes a continuous trace synchronized with time, during the entire time the smoke detector on duty is being monitored by the auxiliary signal indicator. By comparing the type of pattern traced at the time, the cause of any possible false alarm signals of the smoke detector under test can easily be determined, and corrected.

The invention will be better understood, and objects will become apparent, when consideration is given to the following detailed description thereof which makes reference to the annexed drawings wherein:

FIG. 1 is the diagram of a circuit co-using an ionization smoke detector to issue a fire alarm and to detect ambient atmosphere;

FIG. 2 is a circuit diagram of a known fire alarm system;

FIG. 3 is a diagram of a fire alarm system comprising a multiple locations of ionization smoke detectors;

FIG. 4 is a view, partly in elevation and partly in section of an installation illustrative of the invention co-using a smoke detector by connecting to the detector the common plug of measuring devices;

FIG. 5a is a view in elevation of a ceiling fixture showing a plug connection to an adaptor fixed to a case including an ionization smoke detector;

FIG. 5b is a similar view of a plug/case connection;

FIG. 5c is a similar view of a plug connection to a socket holding a case of the detector;

FIG. 6 is a sectional view of the fixture including an ionization smoke detector in combination with a block circuit diagram of the electric components associated therewith;

FIG. 7 is a circuit diagram of an ionization smoke detector connected with a circuit for detecting ambient atmosphere and also a circuit for issuing a fire alarm;

FIG. 8 is a circuit diagram of a modification of the invention another circuits for co-using the detector;

FIG. 9 is a circuit diagram of still another modification co-using the ionization smoke detector;

FIGS. 10a through 10c are graphs which illustrate typical pattern recorded in response to various changes of ambient atmosphere to which an ionization smoke detector is exposed.

Refering to FIG. 1, a line L + having a positive polarity is a power supply line to a detector and also a signal transmitting path. A line L - having a negative polarity comprises the power supply line to the detector body, and is also a signal transmitting path. The voltage between lines L + and L - is, for example, 24 volts D.C. The lines L + and L - connect the detector body to an alarm signal receiver FR through a socket (not shown). The detector body includes an adaptor comprising a full-wave rectifier bridge Rec. The adaptor converts the applied A.C. into D.C., and the porality of the detector body is kept unchangeable at ground, i.e., negative by the rectifier bridge even when the A.C. power source is be reversely connected with respect to the normally grounded line thereof.

The detector body comprises an outer ionization chamber OC having an outer electrode 1, an intermediate electrode 2, and an inner ionization chamber IC comprising the intermediate electrode 2 and an inner electrode 3. A field effect transistor FET1 is adapted to change state according to the potential of the intermediate electrode 2. An amplifying and switching device SA is controlled by the transistor FET1 for short-circuiting the lines L + and L -. These constitute a known construction of detector, the operation of which is similar to known detectors as previously state. That is, air is ionized by radiation sources 4 and 5, and an ionic current always flows in the inner and outer ionization chamber IC and OC to which are applied voltage. The lines L + and L -, and also the intermediate electrode 2 are at predetermined potential differences. In this condition, when smoke enters into the outer ionization chamber OC through a hole of the outer electrode 1, the ionic current circulating in the chambers is reduced and thereby increases the impedance. As a result, the relative potential of the intermediate electrode 2 drops. Accordingly, the field effect transistor FET1 becomes " ON" and the switching device SA becomes ON to short-circuit the lines L + and L - and thus issues a warning signal. This warning signal may be issued, for instance, to actuate a relay included into the lines L + and L - when D.C. current of the lines increases due to short-circuiting.

The above mentioned description relates to the operation in case of detecting a fire. The following description, however, relates to a method and apparatus for detecting non-fire warning according to the invention in which an auxiliary circuit detects existence of the non-fire warning of the smoke detector in situ without damaging the smoke detecting function thereof.

In the preferred embodiment there is provided an amplifier which proportionally changes in conductivity according to the ionic current. In this case, the amplifier comprises preferably a field effect transistor FET2. The transistor FET2 is provided with a gate electrode G, a base electrode D and a source electrode S. The gate electrode is connected to the intermediate electrode 2. The line L - is connected to L to the base electrode D, and a detector terminal to its source electrode S. A visual indicating device 6 for ionic current is connected with such detector terminal directly or through the terminal of an adaptor. An ionic current indicator is preferred for this indicator. A registor 9 is located in the circuit connected to the source electrode S of the transistor FET2, and a pen recorder PR is connected to the terminals of the registor 9. An ammeter 8 is located in the circuit connected to the electrode D of the transistor FET2 through the line L -. A rectifier 7 is included to the visual indicating device 6 and a voltage between electrodes S and D of the transistor FET2 is applied by the rectifier 7. Although the visual indicating device 6 and the amplifier FET2 form a non-fire warning detector circuit, this amplifier FET2 may be incorporated in an adaptor and also in the visual indicating device 6. However, it is preferred that the amplifier FET2 be located near the ionization chamber of the detector so as to shorten the lead wire as much as possible, since it is not desirable that the lead wire from the intermediate electrode of the ionization chamber be a high impedance circuit by being long. When this device is used as a portable separate detector an outer amplifier employing a cell and the visual indicating device must be constructed as a unit independently of the detector. Now, when the outer ionization chamber OC of the detector is in the normal operating condition in which corpuscles of smoke, dust or the like are not entering, staying and stored in the chamber, because the intermediate electrode 2 is at its predetermined potential, a certain minute current flows between the source S and the base D of the field effect transistor FET2, and the ammeter A indicates such current. Secondly, if smoke flows in the outer ionization chamber OC and the dist adheres thereon, the ionic current flowing in the outer ionization chamber is reduced, and since the intermediate electrode 2 becomes less than the predetermined voltage, the conductivity between the source and base electrodes of the field effect transistor FET2 increases. Accordingly the current in the circuit 9, transistor FET2 and meter 8 increases to cause a wide deflection of the latter. From such deflection, it can be detected when the smoke detector generates a false warning signal and the cause thereof.

That is, when the cause of the false warning happens in case (1) above, the current of the ion stream in the outer ionization chamber OC is removed by the strong air current. As a result, the ionic current decreases and the intermediate electrode 2 potential becomes less than its predetermined voltage, and the ammeter 8 indicates such reduction of ionic current. The indication, moreover, changes according to variation in intensity of the air current. If this indication reaches the value corresponding to the signal operating point of the smoke detector, the testing smoke detector issues a signal corresponding to a false warning, and it may be presumed that the cause is case (1). Further, the air current from an air conditioner is largely changed by changing the vane angle of an outlet, and the strength and direction of the air current in the chamber are remarkably changed by the opening and closing condition of a door, window or the like. When the long time record of the ionic current is taken by a recording meter as, for example, the pen recorder PR connected to the visual indicating device 6, the air current which was not present in existence when the inspector was present, and occurrence of a false warning therefrom can easily be ascertained. Also, when the cause of the false warning is case (2), the state of the outer ionization chamber is presumed by the indication of the ammeter 8, since the ionic current is regularly decreased when compared to the stndard value of the ionic current by the entrance and accumulation of the dusts within the outer ionization chamber. When the indication of the ammeter 8 exceeds the predetermined critical value or is near it, the cause of the occurrence of the false warning is presumed to be case (2). Further, when the cause of the false warning is case (3) it may be presumed, for example, that the ionic current is caused by mal-function of the set-up per se, and when the cause is case (4) it may be presumed by inspecting the reduction of the ionic current indicated, that the critically high sensitivity of the smoke detector is responsible.

FIGS. 10a, 10b and 10c illustrate, by way of a example, various graph patterns in response to the above-mentioned cases. When a strong air current happens in ambient atmosphere, a pattern II is usually recorded as impedance quickly increases. A pattern III is recorded when an air current becomes gradually feeble. When the ambient atmosphere is stable, recording pattern I is near a standard level set for to the ionization smoke detector. A level to issue alarm can trigger a switching-amplifier circuit which is included in the fire alarm circuit.

When an ionization smoke detector is affected by dust, the impedance thereof gradually increases according to the gradual accumulation of dust in the ionization chamber. This cause traces a pattern IV in FIG. 10b and does not reduce the increased impedance, because dust deposited in the chamber remains therein.

When steam may affects the detector, patterns IV and V are recorded, since a water drop is so produced between encountering electrodes of the ionization chamber as to increase impedance thereof. The function of ionizing the air becomes depressed. The pattern V may also happen when the temperature of the ambient atmosphere changes so greatly as to produce a water drop on the electrodes of the ionization chamber.

Pattern VI is recorded when static electricity, either negative or positive, is accumulated and discharges in the ionization chamber. The change of impedance is radical.

When combustion products from cooking and the like mix with the air, pattern VII is recorded, as shown in FIG. 10c, because such combustion products include various particles of such as nagative, positive electric, vapourized and so on. The ionization function of the chamber can be directly changed by entrance of ionized, or wet particles which render unstable the impedance thereof.

Referring to FIGS. 6 and 7, an ionization smoke detector electrically shown in FIG. 7 is incorporated in a case shown in FIG. 6. A circuit of a visual indicating device is also shown in FIG. 7. A power source of 100 V is reduced to 24 V by a transformer T31, and such transformed voltage, which is controlled by a constant voltage circuit comprising a transistor Tr31 and a zener diode ZD31, is applied to a pen recorder FR. A resister R33 functions as the resister 9 shown in FIG. 1. This pen recorder writes a pattern in response to change of a voltage which is applied to gate electrode of FET22, when a potential of the intermediate electrode of the ionization chambers OC and IC is changed owing to a change happened in the ambient atmosphere. If a great change of the potential happens over a level set for the issuance of an alarm signal, the output from the ionization smoke detector increases by making a short-circuit due to amplification of a transistor Tr21 triggering a thyrister SCR1, and the output thus increased, operates a relay L included in a receiver circuit to energize a lamp P11 and a bell B11 by closing three open-switches 1. In FIG. 7, an adaptor is connected to the ionization smoke detector circuit and a pair of terminals t1 and t2 which are provided with the adaptor shown in FIG. 6 connect with the visual indicating device.

FIG. 6 illustrates a fixture comprising the ionization smoke detector, to which the visual indicating device and receiver are connected. According to this embodiment, co-use of a inoization smoke detector is performed to detect a condition or state of ambient atmosphere which might issue a false alarm signal without a fire. There is provided, in the ionization smoke detector circuit, a power switch SW11, a reset switch SW12, fuse F11, a power lamp NL11, a power transformer T11, constant voltage circuit comprising a transistor Tr22, a resistor R25, a zener diode ZD21 and a condenser C21, an amplifying transistor Tr21 for triggering a thyrister SCR and a variable resister VR21 for adjusting a potential of a source electrode of the FET21 so as to control a conduction condition of the FET21 in response to impedance change of the ionization chamber OC. In the visual indicating device circuit, a transistor Tr33 is used to lower a base potential thereof through the FET22 in response to increase of the impedance of the chamber OC. Another transistor Tr32 is used to energize a partial circuit comprising Tr32-R33-VR32-Ammeter A-Tr33 according to decrease of emitter potential of Tr33 while the base potential of the Tr33 becomes lower. A voltage which appears at the resister R33 is recorded by the pen recorder. When there occurs no change in ambient atmosphere, there flows no current at the resister R33, because electric balance is kept between the emitter potentials of Tr32 and Tr33 in which the emitter potential of Tr32 is designed by VR31, R32 and Tr32 and the emitter potential of Tr33 is also designed by FET22, R35 and Tr33. There is further provided a constant voltage circuit comprising a transistor Tr31, a resister R31, a zener diode ZD31 and a condenser C31, a variable resister VR31 for balancing the potential between Tr32 and Tr33, and also the variable resister VR32 for controlling a magnitude of the recording graph.

In FIG. 8, an adaptor is omitted from the ionization smoke detector circuit and a pair of terminals t1 and t2 which are included in the detector circuit permit a plug connection of the visual indicating device. A thyrister SCR21 triggered by increasing voltage at a resister R23 after a zener diode ZD22 conducts under operation of the field effect transistor FET21. A lamp P21 radiates, and a current between line CL1 and CL2 increases at instant. voltage drop which, thus after, appeared at a resistor R12 become lower than zener voltage peculiar to a zener diode ZD12 and a transistor Tr13 may conduct to operate a relay L. After the ionization smoke detector circuit, shown in FIG. 8, makes a short-circuit in order to operate a receiver, a required voltage is still applied to the ionization chambers OC and IC in the presence of resisters R24, R25, and R21 and a zener diode ZD21 so that the visual indicating device circuit continues to operate while a receiver issues alarms. This feature is very desirable. There is also provided a constant voltage circuit comprising a transistor Tr11, a resistor R11, a zener diode ZD11 and a condenser C11 as shown in a diagram of a receiver circuit.

In FIG. 9, impedance change in the chamber OC is picked up by means of a resistor R21 which is connected in a source electrode line of the field effect transistor FET21. The pair of terminals t1 and t2 to which the visual indicating device circuit is connected by a plug thereof, are provided at the both ends of the resistor R21. When conduction of the FET21 changes under the influence of ambient atmosphere to the chamber OC, a voltage drop at the resister R21 changes concurrently and further a conduction of the FET31 changes in response to the change of voltage drop in which the resister R21 and the gate electrode of the FET31 is connected through the terminal. The gate of FET31 is guarded by a condenser C32 and a zener diode ZD32 from the visual indicating device circuit. In response to conduction change of FET31 a current which flows in a line of a resister R32 - FET31 - ammeter A indicates in proportion to impedance changes of the chamber OC. There is also provided a constant voltage circuit comprising a condenser C31, a resister R31, a transister Tr31 and a zener diode ZD31.

According to the invention, dual-use of the ionization smoke detector is instantly performed by simply connecting a plug of the visual indicting device either to the adaptor fixed between the socket and the case of including the detector, FIG. 5a; the case including the detector, FIG. 5f; or the socket fixed with the case including the detector, FIG. 5c. Further, a network a fire alarm system network is schematically illustrated in FIG. 3, comprising a plurality of ionization smoke detectors. Each ionization smoke detector connects the plug of the auxiliary testing circuit of the invention for continuously indicating and recording the signal output of the selected detector for determining the cause of possible, as well as actual false alarm signals while the detector is in use for such function.