Patent US3821734A successfully refreshed from Google Patents.
US3821734A
Expired / Lapsed
US
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Fire alarm system with remote central station
Assignee: Cerberus AG
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Filing: 1973-06-28
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Granted: 1974-06-28
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Expires: 1993-06-28
Abstract
Abstract To provide unambiguous indication of fire alarm conditions in a central station, in which a plurality of fire alarm sensing lines come together, to which sensors are connected which, in case of fire, have low electrical resistance, the central has a current limiter which limits the current in case an alarm is sensed to a first limited value (Im), the predetermined current being selected with respect to the alarm sensors such that, until the limiting current is reached, the electrical resistance of the sensor is higher than a predetermined value and, when the predetermined current has been reached, the electrical resistance drops below that resistance value; the signal central further having a voltage sensor to sense voltage drop at the connection point of the lines leading to the sensors which, when an excessive voltage drop across a certain line is sensed at the predetermined current value (Im) further causes transmission of a higher current than the predetermined current(Im), at least for a limited period of time, in order to be able to clearly differentiate between alarm conditions, possible line short circuits or interruptions, or non-alarm conditions during line trouble.
Inventors
- 👤 O Herrliberg
- 👤 A Scheidweiler
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 23:07
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/10; G08B17/11
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
247 words
Fire alarm systems having a central sensing station (1; FIG. 5) and at least one remote sensor (F1, F2; FIGS. 3, 4, 7) wherein the sensor has a high electrical resistance under normal, monitoring conditions, and a low electrical resistance under fire sensing alarm conditions; and wherein connecting lines are provided, connecting the central station to the sensors, and the central station supplied electrical power over the lines to the sensors and includes an alarm system to indicate alarm conditions said system comprising means in the central station connected into the lines limiting the current flowing to the sensors to a first predetermined limit value (Im); said sensors have the characteristic that, under alarm conditions, the electrical resistance thereof is a first value which is greater than a predetermined resistance and when current up to said first predetermined limit value (Im) flows to the sensor and, the electrical resistance of the sensor is at a second value which is below said predetermined resistance when current above said first predetermined limit (Im) flows to the sensor; means in said signal central (1) measuring and evaluating the voltage across the lines leading to the sensors; and means in said signal central (1) logically controlled by said voltage measuring means at least temporarily increasing current flow to said lines upon detection of a. a voltage drop across the lines in excess of a predetermined value (US) and b. current flow through the lines approximately at said first limit value (Im).
Claim 2
Dependent Claim
247 words
Fire alarm systems having a central sensing station (1; FIG. 5) and at least one remote sensor (F1, F2; FIGS. 3, 4, 7) wherein the sensor has a high electrical resistance under normal, monitoring conditions, and a low electrical resistance under fire sensing alarm conditions; and wherein connecting lines are provided, connecting the central station to the sensors, and the central station supplied electrical power over the lines to the sensors and includes an alarm system to indicate alarm conditions said system comprising means in the central station connected into the lines limiting the current flowing to the sensors to a first predetermined limit value (Im); said sensors have the characteristic that, under alarm conditions, the electrical resistance thereof is a first value which is greater than a predetermined resistance and when current up to said first predetermined limit value (Im) flows to the sensor and, the electrical resistance of the sensor is at a second value which is below said predetermined resistance when current above said first predetermined limit (Im) flows to the sensor; means in said signal central (1) measuring and evaluating the voltage across the lines leading to the sensors; and means in said signal central (1) logically controlled by said voltage measuring means at least temporarily increasing current flow to said lines upon detection of a. a voltage drop across the lines in excess of a predetermined value (US) and b. current flow through the lines approximately at said first limit value (Im).
Claim 3
Dependent Claim
28 words
System according to claim 1 wherein the sensor has a non-linear voltage-current characteristic which, when the current exceeds a predetermined level therethrough, exhibits voltage saturation (FIG. 2; Da).
Claim 4
Dependent Claim
44 words
System according to claim 1 wherein the sensor comprises fire detection transducer means; and switching means connected to and controlled by said transducer means and connecting a circuit of low electrical resistance to the connection lines connecting the sensor to the signal central (1).
Claim 5
Dependent Claim
36 words
System according to claim 3 wherein the sensor further comprises means sensing current flow through said circuit; alarm indicator means in said circuit, said alarm indicator means being connected into the circuit by said switching means.
Claim 6
Dependent Claim
53 words
System according to claim 3 wherein the transducer means comprises an ion chamber accessible to ambient atmosphere, the resistance of which increases upon presence of smoke or fire aerosols; and said switching means comprises a field effect transistor (FET 15, 34) having an input circuit connected to and controlled by said ion chamber.
Claim 7
Dependent Claim
39 words
System according to claim 5 further comprising an electronic switch controlled by said field effect transistor, establishing an alarm circuit of low electrical resistance in said sensor, said field effect transistor and said controlled switch comprising said switching means.
Claim 8
Dependent Claim
57 words
System according to claim 3 further comprising a transistor connected to sense current flow through said circuit, and indicating means connected in the collector-emitter path of said transistor, to indicate alarm conditions, the transistor being connected to be controlled to become conductive when the current in said circuit of low electrical resistance exeeds a predetermined current value.
Claim 9
Dependent Claim
11 words
System according to claim 7 wherein the indicator comprises a lamp.
Claim 10
Dependent Claim
22 words
System according to claim 2 wherein the sensor includes a ZenEr diode to provide said voltage saturation characteristics, independent of current flow.
Claim 11
Dependent Claim
28 words
System according to claim 1 wherein said voltage measuring and evaluating means comprises means responsive to two or more voltage levels across the lines leading to the sensors.
Claim 12
Dependent Claim
118 words
System according to claim 10 wherein the voltage measuring and evaluation means comprises means sensing a voltage level less than a predetermined threshold level; and said means logically controlled by said voltage measuring means includes the line trouble indicating means and a fire alarm indicating means, the line trouble indicating means being activated when: a. the terminal voltage is less than said threshold level and b. the current flowing through said lines is at least at, or above said first limit current value (Im); and the alarm means is activated when: c. the voltage across the terminals is above said threshold level and d. the current flowing through the lines is approximately at said first limit value (Im).
Claim 13
Dependent Claim
29 words
System according to claim 11 wherein the voltage level of the threshold level is approximately the same voltage as the saturation voltage of the current-voltage characteristic of the sensor.
Claim 14
Dependent Claim
88 words
System according to claim 1 further comprising pulse means (76; FIG. 5) connected to said central station, said pulse means being energized upon detection of an alarm condition comprising detection of a voltage drop across the lines in excess of a predetermined value (US); said pulse source being connectible to said lines and, in pulsed cycles, increasing the current through said lines to provide pulsed power to the sensor which changed to alarm condition to permit flashing, intermittent illumination of a sensor indicator which is in alarm condition.
Claim 15
Dependent Claim
82 words
System according to claim 1 including a terminating element (FIG. 1: E; FIG. 6), said terminating element including variable resistance means cyclically changing between higher and lower resistance values, to provide for flow of an a-c component through said lines; means in said signal central (1) responsive to current flow of said a-c component; and trouble indicator means in said signal central (1) responsive to cessation of said a-c component to indicate an open circuit or break of continuity of said lines.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-06-27 | 1977-12-27 | 1978-06-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-06-27 | 1981-12-27 | 1982-06-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-06-27 | 1985-12-27 | 1986-06-28 | $7700.00 | Window Closed / Lapsed |