US3813655A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Monitoring systems and apparatus therefor
Assignee: Microwave and Electronic Systems Ltd
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Filing: 1972-05-23
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Granted: 1974-05-28
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Expires: 1992-05-23
Abstract
Abstract A central station monitors the condition of a group of remote sensors each of which is connected in a reporter unit which generates a characteristic frequency signal the modulation condition of which is changed when the sensor goes into the alarm condition. The central station scans the characteristic frequencies and detects the nature of the modulation received at each. The absence of a signal at any of these frequencies is also detected. The characteristic frequencies are generated by crystal-controlled oscillators and the central processor includes a digital filter locked to a crystal-controlled reference oscillator to give high immunity to noise. The wanted signals may be deliberately hidden in the signals of a noise or swept frequency source.
Inventors
- 👤 H Allen
- 👤 J Johnston
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 19:38
CPC Classifications
G; G08; G08B; G08B26/00; G08B26/001; G08B26/002
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
229 words
A monitoring system comprising: a plurality of detector units, a like plurality of condition responsive sensors individually associated with each detector unit, each detector unit including means for generating a signal at a frequency individual to and characteristic of that unit, and means for modulating the characteristic frequency Signal produced by said signal generating means, said modulating means being responsive to a change from a first to a second condition of the associated sensor to provide a change from a first to a second modulation condition of said characteristic frequency signal; a signal processing unit, and communication means linking said detector units and said signal processing unit, said signal processing unit including frequency-selective filter means selectively operable at each of a plurality of discrete frequencies corresponding to the characteristic frequencies of said detector units to discriminate between said characteristic frequency signals from said detector units and provide corresponding filtered signals at an output of said filter means, and means connected to the output of said filter means for monitoring the modulation condition of each of said filtered signals and having a plurality of outputs individually associated with said plurality of discrete frequencies and selectable in synchronism with the selection of said discrete filter frequencies, whereby each of said plurality of outputs indicates the modulation condition of the associated filtered signal and thereby the condition of the sensor associated therewith.
Claim 2
Dependent Claim
229 words
A monitoring system comprising: a plurality of detector units, a like plurality of condition responsive sensors individually associated with each detector unit, each detector unit including means for generating a signal at a frequency individual to and characteristic of that unit, and means for modulating the characteristic frequency Signal produced by said signal generating means, said modulating means being responsive to a change from a first to a second condition of the associated sensor to provide a change from a first to a second modulation condition of said characteristic frequency signal; a signal processing unit, and communication means linking said detector units and said signal processing unit, said signal processing unit including frequency-selective filter means selectively operable at each of a plurality of discrete frequencies corresponding to the characteristic frequencies of said detector units to discriminate between said characteristic frequency signals from said detector units and provide corresponding filtered signals at an output of said filter means, and means connected to the output of said filter means for monitoring the modulation condition of each of said filtered signals and having a plurality of outputs individually associated with said plurality of discrete frequencies and selectable in synchronism with the selection of said discrete filter frequencies, whereby each of said plurality of outputs indicates the modulation condition of the associated filtered signal and thereby the condition of the sensor associated therewith.
Claim 3
Dependent Claim
24 words
A system as claimed in claim 1 wherein one of said modulation conditions of each characteristic frequency signal is a condition of no modulation.
Claim 4
Dependent Claim
30 words
A system as claimed in claim 2 wherein in the other of said modulation conditions each of said modulating means causes the associated characteristic frequency signal to be pulse modulated.
Claim 5
Dependent Claim
68 words
A system as claimed in claim 1 wherein each of said detector units further comprises a timing device coupled between said associated sensor and said modulating means responsive to a change from said first to said second condition of said sensor to actuate said modulating means from providing said first to providing said second modulation condition of said characteristic frequency signal for only a predetermined period of time.
Claim 6
Dependent Claim
51 words
A system as claimed in claim 1 wherein said modulation condition monitoring means comprises a bistable circuit associated with each of said detector units operable to adopt a first or a second state in response to the associated characteristic frequency signal being in said first or said second modulation condition, respectively.
Claim 7
Dependent Claim
91 words
A system as claimed in claim 3 wherein said first and second modulation conditions are the conditions of pulsed modulation and of no modulation, respectively, said signal processing unit further comprising a clock source coupled to said frequency-selective filter means to supply signals thereto to cause said filter means to scan said plurality of discrete frequencies in succession, and coupled to said modulation condition monitoring means to supply signals thereto to cause the successive selection of said plurality of outputs in synchronism with the selection of said plurality of discrete frequencies.
Claim 8
Dependent Claim
138 words
A system as claimed in claim 6 wherein said moudlation condition monitoring means includes a pulse-responsive circuit coupled to the output of said filter means to provide a first or a second output signal corresponding to a filtered signal being in the pulse modulated or unmodulated condition, reepectively, a plurality of bistable circuits each associated with a respective one of said detector units and providing said plurality of outputs, and a selector circuit coupled to said clock source to be stepped thereby to couple said pulse-responsive circuit to said bistable circuits in succession, whereby each bistable circuit adopts a state dependent on the presence of said first or second output signal obtained from said pulse-responsive means in response to the modulation condition of the characteristic frequency signal of the detector unit with which the bistable circuit is associated.
Claim 9
Dependent Claim
54 words
A system as claimed in claim 6 wherein said frequency-selective filter means comprises a digital filter and means for selecting the frequency of operation Of the digital filter according to a predetermined program of said characteristic frequencies, said selecting means being coupled to said clock source to be stepped thereby through said perdetermined program.
Claim 10
Dependent Claim
24 words
A system as claimed in claim 8, wherein said characteristic frequency signal generating means in each of said detector units comprises a crystal-controlled oscillator.
Claim 11
Dependent Claim
36 words
A system as claimed in claim 1 wherein said signal processing unit comprises means coupled to the output of said filter means to indicate the absence of a signal at any one of said characteristic frequencies.
Claim 12
Dependent Claim
37 words
A system as claimed in claim 6 wherein said signal processing unit further includes means coupled to the output of said filter means to indicate the absence of a signal at any one of said characteristic frequencies.
Claim 13
Dependent Claim
60 words
A system as claimed in claim 1 wherein said characteristic frequency signals lie in a predetermined frequency band, and further comprising a further signal source coupled to said communication means linking said detector units and said signal processing unit to provide a signal having components extending over said frequency band and of substantially greater amplitude than said characteristic frequency signals.
Claim 14
Dependent Claim
15 words
A system as claimed in claim 12 wherein said signal source is a noise source.
Claim 15
Dependent Claim
16 words
A system as claimed in claim 12 wherein said signal source is a swept frequency source.
Claim 16
Dependent Claim
60 words
A system as claimed in claim 6 wherein said characteristic frequency signals lie in a predetermined frequency band, and further comprising a further signal source coupled to said communication means linking said detector units and said signal processing unit to provide a signal having components extending over said frequency band and of substantially greater amplitude than said characteristic frequency signals.
Claim 17
Dependent Claim
15 words
A system as claimed in claim 15 wherein said signal source is a noise source.
Claim 18
Dependent Claim
16 words
A system as claimed in claim 15 wherein said signal source is a swept frequency source.
Claim 19
Dependent Claim
183 words
A signal scanning circuit comprising: a digital filter; a frequency source coupled to said filter to control the filter frequency of said digital filter, said source including a programing unit for enabling the filter frequency to be selectable to one of a plurality of prescribed frequencies according to a prescribed program, a clock source connected to said programing unit to cause the latter to advance through its program to cause said digital filter to scan the prescribed frequencies according to the program, and analyser means coupled to said clock source and to the output of said digital filter, said analyser means having a plurality of outputs each associated with a respective one of said prescribed frequencies and being stepped by the clock to provide signals sequentially at said outputs in synchronism with the selection of the prescribed frequencies in the digital filter and said analyser means being operable to analyse the signal at the output of said digital filter at each prescribed frequency thereof and to produce a signal on the associated output indicative of the nature of the digital filter output signal.
Claim 20
Dependent Claim
183 words
A signal scanning circuit comprising: a digital filter; a frequency source coupled to said filter to control the filter frequency of said digital filter, said source including a programing unit for enabling the filter frequency to be selectable to one of a plurality of prescribed frequencies according to a prescribed program, a clock source connected to said programing unit to cause the latter to advance through its program to cause said digital filter to scan the prescribed frequencies according to the program, and analyser means coupled to said clock source and to the output of said digital filter, said analyser means having a plurality of outputs each associated with a respective one of said prescribed frequencies and being stepped by the clock to provide signals sequentially at said outputs in synchronism with the selection of the prescribed frequencies in the digital filter and said analyser means being operable to analyse the signal at the output of said digital filter at each prescribed frequency thereof and to produce a signal on the associated output indicative of the nature of the digital filter output signal.
Claim 21
Dependent Claim
200 words
A monitoring system comprising: a plurality of detector units, a like plurality of condition responsive sensors individually associated with each detector unit, each detector unit including a crystal-controlled oscillator circuit for generating a signal at a frequency individual to and characteristic of that unit, and means for modulating the characteristic frequency signal produced by said signal generating means, said modulating means being responsive to a change from a first to a second condition of the associated sensor to provide a change from a first to a second modulation condition of said characteristic frequency signal; a signal processing unit, and communication means linking said detector units and said signal processing unit; said communication means including at least one source of noise providing noise signals of substantiaLly greater amplitude than said characteristic frequency signals at said signal processing unit; and said signal processing unit including a digital filter and means for controlling the filter frequency such that the digital filter discriminates between the signals at the characteristic frequencies of said detector units and provides corresponding filtered signals, and means responsive to the filtered signals to monitor the modulation condition of each filtered signal and thereby monitor the condition of the associated sensor.
Claim 22
Dependent Claim
200 words
A monitoring system comprising: a plurality of detector units, a like plurality of condition responsive sensors individually associated with each detector unit, each detector unit including a crystal-controlled oscillator circuit for generating a signal at a frequency individual to and characteristic of that unit, and means for modulating the characteristic frequency signal produced by said signal generating means, said modulating means being responsive to a change from a first to a second condition of the associated sensor to provide a change from a first to a second modulation condition of said characteristic frequency signal; a signal processing unit, and communication means linking said detector units and said signal processing unit; said communication means including at least one source of noise providing noise signals of substantiaLly greater amplitude than said characteristic frequency signals at said signal processing unit; and said signal processing unit including a digital filter and means for controlling the filter frequency such that the digital filter discriminates between the signals at the characteristic frequencies of said detector units and provides corresponding filtered signals, and means responsive to the filtered signals to monitor the modulation condition of each filtered signal and thereby monitor the condition of the associated sensor.
Claim 23
Dependent Claim
26 words
A monitoring system as claimed in claim 19 wherein said at least one source of noise comprises a noise signal generator coupled to said communication means.
Claim 24
Dependent Claim
17 words
A monitoring system as claimed in claim 19 wherein said communication means is a power supply line.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-05-27 | 1977-11-26 | 1978-05-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-05-27 | 1981-11-26 | 1982-05-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-05-27 | 1985-11-26 | 1986-05-28 | $7700.00 | Window Closed / Lapsed |