Gas indicator with semiconductive gas sensor

Claim 2

A gas indicator, comprising a semiconductive body serving as a gas sensor adapted to be thermally activated and having in activated condition the property that the resistivity thereof is substantially reduced upon exposure to a gas, a first electrode incorporated in said body and shaped as a filament for activating the same, an alternating current source, means for connecting said alternating current source across said first electrode, a second electrode incorporated in said body and spaced with respect to said first electrode, a circuit interconnecting the said electrodes and including a direct current source, a current change occurring in the said circuit when the resistivity of said body is reduced, a delay circuit coupled to said direct current source and actuated when the indicator is energized, a first trigger controlled by said delay circuit to change state at the end of a determinable activating time, a second trigger controlled by said current change so as to change state when the resistivity of said body is reduced, a coincidence gate controlled by output signals of the said triggers occurring after their changes of state, and an alarm circuit actuated by the output signal of said coincidence gate, the alternating current source being an oscillator coupled to and energized by said direct-current source.

Claim 3

A gas indicator as claimed in claim 1, further comprising means for supplying the output voltage of said oscillator as a heating voltage to the ends of said first electrode.

Claim 4

A gas indicator as claimed in claim 2, further comprising a piezo-electric sound generator inserted in said alarm circuit, and means for supplying the output voltage of said oscillator as an energizing voltage to said sound generator.

Claim 5

A gas indicator as claimed in claim 3, wherein said coincidence gate has a third input terminal, further comprising means for supplying said oscillator voltage to said third input terminal.

Claim 6

A gas indicator, comprising a semiconductive body serving as a gas sensor, adapted to be thermally activated and having, in activated condition, the property that the resistivity thereof is substantially reduced upon exposure to a gas, a first electrode incorporated in said body and shaped as a filament for activating the same, an alternating current source coupled across said first electrode, a second electrode incorporated in said body and spaced with respect to said first electrode, a circuit interconnecting the said electrodes, a direct current source coupled to said interconnecting circuit such that a current change occurs in the same when the resistivity of said body is reduced, a delay circuit including a first resistor and a condenser in series with said first resistor, a first Schmitt trigger controlled by the voltage across said condenser so as to deliver a 1-signal during the activating time of said body and a 0-signal after expiration of said activating time, a second inverting Schmitt trigger, an inverter controlled by the 0-signal of said first trigger, a nand-gate having at least two input terminals, means for supplying the output signal of said inverter to one of the said input terminals, a second resistor, an emitter follower having a base, an emitter and a collector, means for supplying the output signal of said inverter throught said second resistor to the base of said emitter follower, means connecting one of the said electrodes with the base of said emitter follower, means for grounding the other of the said electrodes, means connecting the emitter of said emitter follower with the input terminal of said second trigger, means connecting the output terminal of said second trigger with a second input terminal of said nand-gate with said alarm circuit, in such manner that the emitter voltage of said emitter follower disappears upon occurrence of a gas after expiration of the activating time of said body, whereby said second trigger delivers a 1-signal, and said hand-gate is operated to deliver a 0-signal for actuating said alarm circuit.

Claim 7

A gas indicator, comprising a semiconductive body serving as a gas sensor, adapted to be thermally activated and having, in activated condition, the property that the resistivity thereof is substantially reduced upon exposure to a gas, a first electrode incorporated in said body and shaped as a filament for activating the same, an alternating current source coupled across said first electrode, a second electrode incorporated in said body and spaced with respect to said first electrode, a circuit interconnecting the said electrodes, a direct current source coupled to said interconnecting circuit such that a current change occurs in the same when the resistivity of said body is reduced, a delay circuit including a first resistor and a condenser in series with said first resistor, a first Schmitt trigger controlled by the voltage across said condenser so as to deliver a 1-signal during the activating time of said body and a 0-signal after expiration of said activating time, a second inverting Schmitt trigger, an inverter controlled by the 0-signal of said first trigger, a nand-gate having at least two input terminals, means for supplying the output signal of said inverter to one of the said input terminals, a second resistor, an emitter follower having a base, an emitter and a collector, means for supplying the output signal of said inverter throught said second resistor to the base of said emitter follower, means connecting one of the said electrodes with the base of said emitter follower, means for grounding the other of the said electrodes, means connecting the emitter of said emitter follower with the input terminal of said second trigger, means connecting the output terminal of said second trigger with a second input terminal of said nand-gate with said alarm circuit, in such manner that the emitter voltage of said emitter follower disappears upon occurrence of a gas after expiration of the activating time of said body, whereby said second trigger delivers a 1-signal, and said hand-gate is operated to deliver a 0-signal for actuating said alarm circuit.

Claim 8

A gas indicator as claimed in claim 5, wherein said inverter is an inverting Schmitt trigger.

Claim 9

A gas indicator as claimed in claim 5, further comprising a second inverter connected with the output terminal of said nand-gate, a second nand-gate having at least two input terminals, means for supplying the output signal of said second inverter to one of the input terminals of said second nand-gate, an oscillator, means for supplying the output voltage of said oscillator to another input terminal of said second nand-gate, a loudspeaker, and means connecting said loudspeaker with the output terminal of said second nand-gate.

Claim 10

A gas indicator as claimed in claim 7, further comprising a relay having a coil and at least one back contact, means for supplying the output signal of said second inverter to one of the ends of said coil, means connecting the other end of said coil with the 1-voltage, and means for removing the dangerous condition due to the presence of a gas, such as an exhauster, actuated by said back contact when said relay is de-energized.