US3812362A

US3812362A - Smoke detector circuit

Info

Publication number: US3812362A
Application number: US00376011A
Authority: US
Inventors: L Larsen; E Kobek
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1973-07-02
Filing date: 1973-07-02
Publication date: 1974-05-21
Anticipated expiration: 1991-05-21
Also published as: DE2430809C2; CH566603A5; DE2430809A1; CA1015071A

Abstract

A combustion products detector system of the type having at least one ionization chamber, the combustion products sensing ionization chamber being open or accessible to the surrounding air. The output signal voltage from the chamber is connected through an FET to a four terminal voltage comparator switch, which four terminal switch has an easily adjustable threshold voltage.

Description

United States Patent [191 Larsen et al.

[ SMOKE DETECTOR CIRCUIT [75] Inventors: Larry D. Larsen, Palatine; Edward F. Kobek, Chicago, both of Ill.

[73] Assignee: Honeywell Inc., Minneapolis, Minn. [22] Filed: July 2, 1973 [21] App]. No.: 376,011

[52] U.S. Cl. 250/370, 250/390, 340/237 S, 307/252 G [51] Int. Cl. Golt 1/24 Field of Search 250/390, 385, 370; 340/237 S; 307/252 G [56] References Cited UNITED STATES PATENTS 2/l97l Walthard 340/237 S 4/1942 Evans 340/237 S [451 May21, 1974 Abe 340/237 S Walthard 340/237 S Primary Examiner-Archie R. Borchelt Assislant ExaminerHarold A. Dixon Attorney, Agent, or FirmLamont B. Koontz; Omund R. Dahle [57] ABSTRACT 9 Claims, 2 Drawing Figures SMOKE DETECTOR CIRCUIT SUMMARY OF THE INVENTION A unique portion of the system is in the provision of a four terminal voltage comparator switch means which has a continuously adjustable threshold switching level. One terminal of the switch which may be termed the reference terminal or threshold terminal is connected to an adjustable reference voltage source, which in the specific embodiment shown is the wiper of a potentiometer in a voltage divider network. The arrangement of the circuit provides for a switched output signal in response to smoke as well as an analogue output signal the magnitude of which is a function of smoke density.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is a schematic representation of a preferred embodiment of the invention, and

FIG. 2 is a variation of a portion of the circuit of FIG. 1.

DESCRIPTION Referring now to FIG. 1 there is generally shown at an ionization smoke detector circuit having a plurality of output terminals which are wired to a common or central station 11. The smoke detector circuit discloses a pair of series connected ionization chambers including a closed or nearly sealed reference chamber 12 and a smoke sensing chamber 13 which has louvers to allow a free exchange of air in and out of the chamber so that the appearance of products of combustion or smoke in the surrounding air is quickly sensed. Reference chamber 12 has

electrodes

14 and 15 and the sensing chamber 13 has electrodes 16 and 17. The electrodes 14 and 17 are connected across the supply voltage on

conductors

20 and 21, and the

intermediate electrodes

15 and 16 are electrically connected together and provide an analogue signal output at conductor 22. Although the impedance 12 has been specifically described as a reference chamber it is not a necessary part of the invention and may be in the form of any suitable resistor or impedance means.

The conductor 22 is connected to the gate G of a field effect transistor 23, which is shown as being an nchannel device of the junction-gate type connected in a source follower configuration. The drain electrode D of PET 23 is directly connected to the positive supply conductor 20 and the source electrode S is connected by a junction 24 and a resistor 25 to the negative conductor 21. The junction 24 is also connected by a resistor 26 to the input terminal 30 of a four-terminal comparator switching means 31.

The four-terminal comparator switching means 31 is shown as comprising a PNP and an NPN transistor in I a positive feedback configuration. Input terminal 30 connects to the emitter electrode of the PNP transistor. The PNP base electrode is directly connected to the NPN transistor collector electrode and to a reference terminal 32. The PNP collector electrode is directly connected to the NPN transistor base electrode and to a third terminal 33. The NPN transistor emitter electrode is directly connected to an output terminal 34 and terminal 34 is further connected through a resistor 35 to negative conductor 21. The reference terminal 32 is directly connected to the adjustable wiper of a setpoint potentiometer 36. Potentiometer 36 is part of a resistive voltage divider connected across

supply conductors

20 and 21 and adjustment of the wiper permits a selection of a desired reference or set-point voltage at terminal 32. The third terminal 33 is connected to the negative conductor 21 by a delay circuit comprising a capacitor 40 paralleled by a resistor 41.

' Output terminal 34 of the comparator or threshold switching circuit 31 is directly connected to the input of a further transistor 42. The collector load circuit for transistor 42 is a light emitting diode LED and a resistor 43. An output terminal 5 is also connected to the collector electrode of transistor 42. Several other exterior terminals of the ionization smoke detector circuit 10 are tied to various parts of the circuit just described, including terminal 1 which is connected by a resistor 44 to the electrode 17; terminal 2 connected to conductor 20; terminal 3 connected to terminal 32; terminal 6 connected to junction 24' and terminal 7 connected to conductor 21.

Two or more of the exterior terminals of the smoke detector 10 are connected to the common or central panel 11. Terminals 2 and 7 are connected by conductors 50 and 51, respectively to a suitable source of DC potential in panel 11. If desired a relay coil or coils 52 may be in series with one of these conductors to sense changes in current magnitude as is well known in the art. There may be a normally energized or actuated supervisory relay to detect a current reduction and a normally not actuated marginal relay to indicate a current increase by pulling in. The switching output terminal 5 may be connected through an alarm relay coil 53 to the positive supply line. The exterior terminal 6 may be connected to a voltmeter 54 to provide an indication of the analogue voltage at junction 24 with respect to the negative source lead 51 and in addition to indication this voltage may be used in a control system. The exterior terminal 3 may be connected to a voltmeter 55 to provide an indication of the differential voltage between the set point voltage of point 32 and the analogue voltage at junction 24, or the meter 55 may have one terminal connected to conductor 51 to indicate the set point voltage. A normally open Test switch in the central panel, when operated, connects a positive potential to the exterior terminal 1 to cause the detector circuit 10 to go into alarm.

FIG. 2 shows a variation of a portion of the circuit of FIG. 1, namely that the four terminal comparator switching means 31 is shown in the form of a silicon controlled switch (SCS). In this connection, the anode is the input terminal 30, the anode gate is the reference terminal 32, the cathode gate is the third terminal 33, and the cathode the output terminal 34.

OPERATION OF FIG. 1

In the normal standby condition in which there is little or no smoke in the air being sensed by the sensing chamber 13, the effective impedance of the two chambers l2 and 13 is approximately the same and therefore about half of the supply potential on conductor 20 appears on conductor 22 to gate electrode G. The F ET 23 is connected as a source follower circuit and conducts sufficient current so that the analogue voltage at junction 24 follows the analogue signal voltage at the gate. The standby analogue voltage at junction 24 is coupled through resistor 26 to input electrode 30 of the comparator switch circuit 31. The position of the wiper of set point potentiometer 36 adjusts the clean air operating differential voltage. and the position is selected to be higher in voltage than the standby voltage of terminal 30 so that the circuit 31 is non-conductive; thus there is no voltage at output terminal 34 and transistor 42 is also non-conductive. In this operating condition the comparator switch 31 is stable, and due to the delay circuit connected toterminal 33 of switch 31, even the occurrence of a voltage transient tending to momentarily increase the potential of terminal 32, will not turn on switch 31. The potentiometer 36 makes it possible to adjust the clean air operating differential as desired at any time during the life of the device, and it may be desirable at specific intervals of time over the years to check the differential and to adjust as necessary.

Upon the occurrence of smoke at sensor 13, the potential at the gate electrode G increases above its clean air magnitude resulting in an increased potential at terminal 30. The voltage magnitude is a function of the 1 density of smoke. An analogue voltage exists at sensor 13, and this analogue voltage may be measured at exterior terminal 6 with respect to terminal 7, by a measuring and/or. control system which in most elementary form is shown as voltmeter 54. As the potential at terminal 30 begins to exceed the reference voltage at terminal 32 due to smoke at sensor 13, the switch 31 begins to turn on. A delay in the switching occurs as the delay network comprising capacitor 40 charges. This delay prevents transient voltages from turning on the switch. As the switching is completed a positive voltage developed across resistor 35 appears at output terminal 34 and biases on transistor 42. The collector current flowing in transistor 42 turns on the LED indicator and also provides a low impedance path from output terminal tothe negative supply conductor 21. The relay 53 in the common panel 11 is energized. Subsequent to the switching on of comparator switch 31, the supply potential on conductors and 21 remains substantially constant and the analogue voltage at terminal 24 continues to indicate the density of smoke at sensor 13.

If it'is 'desired'to-test the system from the common panel 11 and cause the detector to go into alarm, the Test switch is closed applying a positive voltage through resistor 4410 electrode 17 thereby raising the potential at conductor 22. The switch 56 in the positive supply conductor can be opened briefly to reset, or the exterior terminal 3 can be briefly connected to the positive conductor to reset switch 31. In operation the switch of FIG. 2 may be explained in the same manner as has been explained for FIG. 1.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. In an ionization type products-of-combustion detector, an improved circuit for providing an analogue output signal voltage indicative of the sensed condition as well as providing a switched output indicative of the sensed condition exceeding a set point, the improved circuit comprising in combination;

first and second power input terminals to be energized from a dc. source;

impedance means and an ionization sensing chamber 6 analogue output signal voltage indicative of the sensed condition exists at said signal terminal;

a four-terminal semiconductor switch having as terminals an input terminal, a reference terminal, a third terminal, and an output terminal, said switch switching from an off to an on condition when the voltage at the input terminal exceeds the voltage at the reference terminal;

a source of adjustable set-point voltage connected to said reference terminal;

means connected to said switch input terminal and to said chamber signal terminal and providing a signal to said input terminal which is a function of said analogue voltage;

delay circuit means connected to said third terminal;

and output circuit means connecting the output terminal to said second power input terminal, said switch providing a switched output at said output terminal.

2. The invention of claim 1. in which said fourterminal semiconductor switch comprises two transistors, one an NPN transistor and the other a PNP transistor, the base electrode of the PNP transistor being directly connected to the collector electrode of the NPN transistor and also to said reference terminal, the base electrode of the NPN transistor being directly connected to the collector electrode of the PNP transistor and also to said third terminal, the emitter electrode of said PNP and NPN transistors comprising said input terminal and output terminal, respectively.

3. The invention. of claim 1 in which said fourterminal semiconductor switch is a four-terminal SCS (silicon controlled switch) having an anode, an anode gate, a cathode gate and a cathode as the input terminal, reference terminal, third terminal and output terminal, respectively.

4. The invention of claim 1 in which said delay circuit means comprises capacitive means.

5. The invention of claim 1 in which said delay circuit means comprises a capacitor and resistive means in parallel connecting said third terminal to said second power input terminal.

6. The invention of claim 1 in which said impedance means is a reference ionization chamber in series with the ionization sensing chamber. 7

7. The invention of claim 1 in which said means connected to said switching means input terminal and to said chamber signal terminal comprises a field effect transistor circuit.

v8. The invention of claim 1 and further comprising:

circuit means connecting said analogue output signal voltage to an external connection point where it can be adapted for use in control and indication.

9. In an ionization type smoke detector, an improved first and second power input terminals to be energized from a dc. source;

a reference chamber and a smoke sensing chamber serially connected across said terminals and having a signal terminal connected intermediate said chambers;

impedance means connecting one of the current carinput terminal, the gate electrode thereof being connected to said signal terminal, so that in operation an analogue output signal voltage indicative of the sensed condition exists at a terminal connected to said one current carrying electrode;

four-terminal semiconductor switch having as terminals an input terminal, a reference terminal, a third terminal, and an output terminal in which said four-terminal switch comprises two transistors, one an NPN transistor and the other a PNP transistor, the base electrode of the PNP transistor being directly connected to the collector electrode of the NPN transistor and also to said reference terminal, the base electrode of the NPN transistor being directly connected to the collector electrode of the PNP transistor and also to said third terminal, the emitter electrode of said PNP and NPN transistors comprising said input terminal and output terminal, respectively, said switching means switching from an off to an on condition when the voltage at the input terminal exceeds the voltage at the reference terminal;

a source of adjustable set-point voltage connected to said reference terminal and to an output signal terminal for providing an analogue output signal voltage indicative of the set-point;

resistive means connecting the input terminal to said one current carrying electrode;

capacitive delay circuit means connected to said third terminal;

Claims

1. In an ionization type products-of-combustion detector, an improved circuit for providing an analogue output signal voltage indicative of the sensed condition as well as providing a switched output indicative of the sensed condition exceeding a set point, the improved circuit comprising in combination; first and second power input terminals to be energized from a d.c. source; impedance means and an ionization sensing chamber serially connected across said terminals and having a signal terminal connected intermediate said means and said chamber, so that in operation an analogue output signal voltage indicative of the sensed condition exists at said signal terminal; a four-terminal semiconductor switch having as terminals an input terminal, a reference terminal, a third terminal, and an output terminal, said switch switching from an off to an on condition when the voltage at the input terminal exceeds the voltage at the reference terminal; a source of adjustable set-point voltage connected to said reference terminal; means connected to said switch input terminal and to said chamber signal terminal and providing a signal to said input terminal which is a function of said analogue voltage; delay circuit means connected to said third terminal; and output circuit means connecting the output terminal to said second power input terminal, said switch providing a switched output at said output terminal.

2. The invention of claim 1 in which said four-terminal semiconductor switch comprises two transisTors, one an NPN transistor and the other a PNP transistor, the base electrode of the PNP transistor being directly connected to the collector electrode of the NPN transistor and also to said reference terminal, the base electrode of the NPN transistor being directly connected to the collector electrode of the PNP transistor and also to said third terminal, the emitter electrode of said PNP and NPN transistors comprising said input terminal and output terminal, respectively.

3. The invention of claim 1 in which said four-terminal semiconductor switch is a four-terminal SCS (silicon controlled switch) having an anode, an anode gate, a cathode gate and a cathode as the input terminal, reference terminal, third terminal and output terminal, respectively.

6. The invention of claim 1 in which said impedance means is a reference ionization chamber in series with the ionization sensing chamber.

8. The invention of claim 1 and further comprising: circuit means connecting said analogue output signal voltage to an external connection point where it can be adapted for use in control and indication.

9. In an ionization type smoke detector, an improved circuit for providing analogue output signal voltages indicative of a) the sensed condition and b) the set point, as well as providing a switched output signal voltage indicative of the sensed condition exceeding a set point, the improved circuit comprising in combination; first and second power input terminals to be energized from a d.c. source; a reference chamber and a smoke sensing chamber serially connected across said terminals and having a signal terminal connected intermediate said chambers; impedance means connecting one of the current carrying electrodes of a field effect transistor to said second power input terminal, the other current carrying electrode being connected to the first power input terminal, the gate electrode thereof being connected to said signal terminal, so that in operation an analogue output signal voltage indicative of the sensed condition exists at a terminal connected to said one current carrying electrode; a four-terminal semiconductor switch having as terminals an input terminal, a reference terminal, a third terminal, and an output terminal in which said four-terminal switch comprises two transistors, one an NPN transistor and the other a PNP transistor, the base electrode of the PNP transistor being directly connected to the collector electrode of the NPN transistor and also to said reference terminal, the base electrode of the NPN transistor being directly connected to the collector electrode of the PNP transistor and also to said third terminal, the emitter electrode of said PNP and NPN transistors comprising said input terminal and output terminal, respectively, said switching means switching from an off to an on condition when the voltage at the input terminal exceeds the voltage at the reference terminal; a source of adjustable set-point voltage connected to said reference terminal and to an output signal terminal for providing an analogue output signal voltage indicative of the set-point; resistive means connecting the input terminal to said one current carrying electrode; capacitive delay circuit means connected to said third terminal; and output circuit means connecting the output terminal to said second power input terminal, said switch providing a switched output at said output terminal.