US3887908A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Toxic gas indicator
Assignee: Environmental Metrology Corp
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Filing: 1973-05-07
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Granted: 1975-06-03
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Expires: 1993-05-07
Abstract
Abstract A toxic gas detection and alarm system comprising a variable resistance semiconductor type sensor connected in a bridge circuit and compared to a reference voltage to control a relay circuit for an alarm device. The voltage comparison is carried out by means of an amplifier and switch arrangement having a positive feedback circuit for controlling a ''''hysteresis'''' effect in the overall detector circuit sensitivity. An autotransformer having a tapped primary and a pair of secondary windings is used to energize the sensor and to provide the bridge reference voltage such that turning the alarm device on results in increased sensor energization current. This increase in energization causes a decrease in sensor sensitivity and an automatic purging of the sensor area.
Inventors
- 👤 David L Swigert
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 20:16
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/10; G08B17/117
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
306 words
Apparatus for indicating the presence of a toxic gas comprising, a solid state sensor having a relatively large nominal resistance but being responsive to the presence of said toxic gas to present a substantially reduced electrical resistance characteristic, bridge circuit comprising as a first leg the series combination of said sensor and a variable resistor and as a second leg the series combination of two reference resistors, the first and second legs being connected in parallel, input circuit means including first means connected directly to said sensor for energizing said sensor with electrical energy of a predetermined magnitude for producing an electrical signal quantity related to the resistance characteristic of said sensor, said input circuit means further including second means connected across both of the first and second legs for energizing the bridge circuit and for producing a reference quantity, control circuit means including comparator means having separate inputs connected to the mid-points of said first and second legs for comparing said electrical signal quantity to said reference quantity and for producing an output signal quantity when said electrical signal quantity bears a predetermined relationship to said reference quantity, and indicator means for indicating an alarm condition connected to be controlled by said output signal quantity for indicating the presence of said gas, said input circuit means including a transformer having a tapped primary winding and first and second secondary windings, said tapped primary winding being connected to said indicator means for energizing said indicator means under the control of said output signal quantity, said first secondary winding being connected to energize said sensor, and said second secondary winding being connected by circuit means to said reference resistor to produce said reference quantity, whereby the relative energization of said first and second legs is constant irrespective of variations in the voltage applied to said primary winding.
Claim 2
Dependent Claim
306 words
Apparatus for indicating the presence of a toxic gas comprising, a solid state sensor having a relatively large nominal resistance but being responsive to the presence of said toxic gas to present a substantially reduced electrical resistance characteristic, bridge circuit comprising as a first leg the series combination of said sensor and a variable resistor and as a second leg the series combination of two reference resistors, the first and second legs being connected in parallel, input circuit means including first means connected directly to said sensor for energizing said sensor with electrical energy of a predetermined magnitude for producing an electrical signal quantity related to the resistance characteristic of said sensor, said input circuit means further including second means connected across both of the first and second legs for energizing the bridge circuit and for producing a reference quantity, control circuit means including comparator means having separate inputs connected to the mid-points of said first and second legs for comparing said electrical signal quantity to said reference quantity and for producing an output signal quantity when said electrical signal quantity bears a predetermined relationship to said reference quantity, and indicator means for indicating an alarm condition connected to be controlled by said output signal quantity for indicating the presence of said gas, said input circuit means including a transformer having a tapped primary winding and first and second secondary windings, said tapped primary winding being connected to said indicator means for energizing said indicator means under the control of said output signal quantity, said first secondary winding being connected to energize said sensor, and said second secondary winding being connected by circuit means to said reference resistor to produce said reference quantity, whereby the relative energization of said first and second legs is constant irrespective of variations in the voltage applied to said primary winding.
Claim 3
Dependent Claim
306 words
Apparatus for indicating the presence of a toxic gas comprising, a solid state sensor having a relatively large nominal resistance but being responsive to the presence of said toxic gas to present a substantially reduced electrical resistance characteristic, bridge circuit comprising as a first leg the series combination of said sensor and a variable resistor and as a second leg the series combination of two reference resistors, the first and second legs being connected in parallel, input circuit means including first means connected directly to said sensor for energizing said sensor with electrical energy of a predetermined magnitude for producing an electrical signal quantity related to the resistance characteristic of said sensor, said input circuit means further including second means connected across both of the first and second legs for energizing the bridge circuit and for producing a reference quantity, control circuit means including comparator means having separate inputs connected to the mid-points of said first and second legs for comparing said electrical signal quantity to said reference quantity and for producing an output signal quantity when said electrical signal quantity bears a predetermined relationship to said reference quantity, and indicator means for indicating an alarm condition connected to be controlled by said output signal quantity for indicating the presence of said gas, said input circuit means including a transformer having a tapped primary winding and first and second secondary windings, said tapped primary winding being connected to said indicator means for energizing said indicator means under the control of said output signal quantity, said first secondary winding being connected to energize said sensor, and said second secondary winding being connected by circuit means to said reference resistor to produce said reference quantity, whereby the relative energization of said first and second legs is constant irrespective of variations in the voltage applied to said primary winding.
Claim 4
Dependent Claim
306 words
Apparatus for indicating the presence of a toxic gas comprising, a solid state sensor having a relatively large nominal resistance but being responsive to the presence of said toxic gas to present a substantially reduced electrical resistance characteristic, bridge circuit comprising as a first leg the series combination of said sensor and a variable resistor and as a second leg the series combination of two reference resistors, the first and second legs being connected in parallel, input circuit means including first means connected directly to said sensor for energizing said sensor with electrical energy of a predetermined magnitude for producing an electrical signal quantity related to the resistance characteristic of said sensor, said input circuit means further including second means connected across both of the first and second legs for energizing the bridge circuit and for producing a reference quantity, control circuit means including comparator means having separate inputs connected to the mid-points of said first and second legs for comparing said electrical signal quantity to said reference quantity and for producing an output signal quantity when said electrical signal quantity bears a predetermined relationship to said reference quantity, and indicator means for indicating an alarm condition connected to be controlled by said output signal quantity for indicating the presence of said gas, said input circuit means including a transformer having a tapped primary winding and first and second secondary windings, said tapped primary winding being connected to said indicator means for energizing said indicator means under the control of said output signal quantity, said first secondary winding being connected to energize said sensor, and said second secondary winding being connected by circuit means to said reference resistor to produce said reference quantity, whereby the relative energization of said first and second legs is constant irrespective of variations in the voltage applied to said primary winding.
Claim 5
Dependent Claim
78 words
Apparatus as defined in claim 1 wherein said control circuit means further includes switch means having conductive and nonconductive states and being connected to receive said output signal quantity to be controlled thereby and relay means connected in circuit with said switch means and a source of electrical energy, applied to said sensor said relay means being operatively connected with said indicator means for energizing said indicator means whenever said switch means is in one of said conditions.
Claim 6
Dependent Claim
23 words
Apparatus as defined in claim 2 wherein said relay means energizes said indicator means whenever said switch means is in the nonconductive condition.
Claim 7
Dependent Claim
65 words
Apparatus as defined in claim 1 wherein said sensor is a solid state semiconductor device having a response characteristic to the presence of said toxic gas which is related to the magnitude of the energizing electrical energy applied thereto, said input circuit means including means for increasing the magnitude of said energizing energy applied to said sensor whenever said indicator means indicates an alarm condition.
Claim 8
Dependent Claim
71 words
The apparatus as defined in claim 1 further including feedback means connected between the input to said comparator means connected to said second leg and the output of said control circuit means for automatically varying said predetermined level upon activation of said indicator means when the presence of said gas is detected by said sensor whereby the toxic gas level for terminating the alarm condition is less than said predetermined level.
Claim 9
Dependent Claim
161 words
Apparatus for indicating the presence of a toxic gas comprising, a solid state sensor having a nominal relatively large resistance but being responsive to the presence of said toxic gas to present a substantially reduced electrical resistance characteristic, input circuit means connected to said sensor for energizing said sensor with electrical energy of a predetermined magnitude, control circuit means having an input and output, said input being connected to said sensor for receiving an electrical signal quantity from said sensor related to the resistance characteristic thereof, said control circuit means producing on said output an output signal quantity when said electrical signal quantity on said input reaches a predetermined level, and alarm means for indicating an alarm condition connected to be controlled by said output signal quantity for indicating the presence of said gas, said input circuit means further including means for increasing the magnitude of said energizing energy applied to said sensor whenever said alarm means indicates an alarm condition.
Claim 10
Dependent Claim
161 words
Apparatus for indicating the presence of a toxic gas comprising, a solid state sensor having a nominal relatively large resistance but being responsive to the presence of said toxic gas to present a substantially reduced electrical resistance characteristic, input circuit means connected to said sensor for energizing said sensor with electrical energy of a predetermined magnitude, control circuit means having an input and output, said input being connected to said sensor for receiving an electrical signal quantity from said sensor related to the resistance characteristic thereof, said control circuit means producing on said output an output signal quantity when said electrical signal quantity on said input reaches a predetermined level, and alarm means for indicating an alarm condition connected to be controlled by said output signal quantity for indicating the presence of said gas, said input circuit means further including means for increasing the magnitude of said energizing energy applied to said sensor whenever said alarm means indicates an alarm condition.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-06-02 | 1978-12-02 | 1979-06-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-06-02 | 1982-12-02 | 1983-06-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-06-02 | 1986-12-02 | 1987-06-03 | $7700.00 | Window Closed / Lapsed |