Smoke detector circuit

Claim 2

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.

Claim 3

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.

Claim 4

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.

Claim 5

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

Claim 6

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.

Claim 7

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

Claim 8

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.

Claim 9

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.

Claim 10

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.

Claim 11

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.