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Title: Supervisory circuit for parallel connected devices
Claims: We claim: 1. In a circuit having a plurality of functional devices at least some of which are connected in parallel between a pair of conductors for enabling energization of said functional devices, a supervisory circuit for supervising continued operability of each of said functional devices comprising a plurality of impedance means each individually connected in series with a different one of said functional devices between said conductors, each of said impedance means including a first circuit means connecting the corresponding functional device in a first circuit path between said conductors to provide an energizing path of a first impedance for enabling operation of the functional device and a second circuit means connecting the functional device in a second circuit path between said conductors to provide a supervisory path of a higher impedance indicative of the operability of the functional device for enabling supervision of the operability of the functional device, and means connected to said circuit and operable in the event of an impedance change in at least one of said supervisory paths to provide an output indicative of the inoperability of at least one of said functional devices. 2. In an alarm circuit having continuously conductive alarm operating devices at least some of which are connected in parallel between a pair of conductors for enabling energization of said alarm operating devices, a supervisory circuit for supervising continued operability of each of said alarm operating devices comprising a plurality of impedance means each individually connected in series with a different one of said devices between said conductors, each of said impedance means including a first circuit means connecting the corresponding operating device in a first circuit path between said conductors to provide an energizing path of a first impedance for enabling energization of the corresponding device and a second circuit means connecting the operating device in a second circuit path between said conductors to provide a supervisory path of a higher impedance for enabling supervision of the operability of the device, the plurality of impedance means and the corresponding devices normally providing a collective impedance of a predetermined value between said conductors, and detecting means for monitoring the impedance between said conductors and for providing an output indicative of the inoperability of at least one of said devices in response to a change in the impedance from said predetermined value. 3. A supervisory circuit for an alarm circuit as set forth in claim 2 wherein said first circuit means comprises a diode means and said second circuit means comprises a resistance means connected in parallel with said diode means, said diode means providing said first circuit path and said resistance means providing said second circuit path. 4. A supervisory circuit for an alarm circuit as set forth in claim 2 which includes control means operable in a first mode to enable a unidirectional current to flow over each of said second circuit paths to permit monitoring of the operability of the functional devices, said control means being operable in a second mode to enable a unidirectional current to flow over said first circuit path to permit energization of said devices. 5. A supervisory circuit for an alarm circuit as set forth in claim 3 wherein said supervisory circuit comprises a bridge circuit having a plurality of branches, said alarm circuit being connected in one of said branches, said detecting means being connected in another one of said branches and balancing means connected in a further branch of said bridge circuit for balancing the bridge circuit, said detecting means being enabled to provide an output whenever an unbalance condition occurs for said bridge circuit. 6. A supervisory circuit for an alarm circuit as set forth in claim 4 wherein said detecting means includes operational amplifier means connected over said control means to said conductors for detecting a potential difference between said conductors established by the unidirectional current flowing over said second circuit path said operational amplifier means normally providing a first output signal and said operational amplifier means providing a further output signal in response to a change in the potential between said conductors, and output means responsive to said further output signal to provide an indication of a trouble condition for said alarm circuit. 7. A supervisory circuit for an alarm circuit as set forth in claim 6 wherein said output means comprises indicator means, first switching means responsive to an increase in a signal provided by said operational amplifier means to enable said indicator means to provide a trouble indication, and second switching means responsive to a decrease in the signal provided by said operational amplifier means to enable said first switching means to thereby enable said indicator means. 8. In an alarm circuit having a plurality of continuously conductive functional devices connected in parallel between a pair of conductors for enabling energization of said functional devices, a supervisory circuit comprising a bridge circuit having a plurality of branches, said alarm circuit being connected in one of said branches, a plurality of impedance means each connected in series with a different one of said functional devices in said one branch between said conductors of said alarm circuit, each of said impedance means including a first circuit means connecting the corresponding functional device in a first circuit path between said conductors to provide an energizing path of a first impedance for enabling operation of the functional device and a second circuit means connecting the functional device in a second circuit path between said conductors to provide a supervisory path of a higher impedance for enabling supervision of the operability of the functional device, energizing means for normally providing current flow over said bridge circuit including the supervisory paths provided by each of said impedance means in said one branch, balancing means connected in a further branch of said bridge circuit for adjusting the balance of said bridge circuit to establish a potential difference of a preselected level indicative of the impedance of said one branch between first and second nodes of said bridge circuit, detecting means connected between said first and second nodes for providing an output signal proportional to the potential difference, said output signal increasing in the event of an open circuit condition in said alarm circuit and said output signal decreasing in the event of a short circuit condition in said alarm circuit, and output means for providing an output indicative of a change in impedance of said one branch in response to a change in the output signal provided by said detecting means. 9. A supervisory circuit as set forth in claim 8 wherein said first circuit means comprises a diode means connected in series with the corresponding functional device between said conductors to provide said energizing path, and said second circuit means comprises a resistance means connected in parallel with said diode means to provide said supervisory path. 10. A supervisory circuit as set forth in claim 9 wherein said energizing means includes control means operable in a first mode to enable unidirectional current flow over said supervisory circuit paths to permit monitoring of the operability of the functional devices, said control means being operable in a second mode to enable unidirectional current flow over said energizing circuit paths to permit energization of said functional devices. 11. A supervisory circuit as set forth in claim 9 wherein said detecting means includes operational amplifier means having first and second inputs connected to said first and second nodes, respectively, said operational amplifier means normally providing an output signal of a predetermined amplitude whenever a potential difference of said preselected level is provided between said first and second nodes, indicating that said first and second conductors are continuous and that all of said functional devices are conductive. 12. A supervisory circuit as set forth in claim 11 wherein said output means comprises first and second switching means and indicator means controlled by said first and second switching means, said first switching means being responsive to an increase in the output signal provided by said operational amplifier means to enable said indicating means and said switching means being responsive to a decrease in the output signal provided by said operational amplifier means to effect enabling of said indicating means. 13. A supervisory circuit as set forth in claim 10 wherein said first switching means includes a first transistor means biased to be normally non-conducting, and means responsive to an increase in the output signal provided by said operational amplifier means for enabling said first transistor means to be rendered conductive to enable said indicating means, said second switching means including second transistor means biased to be normally conducting, and means responsive to a decrease in the output signal provided by said operational amplifier means for enabling said second transisitor means to be rendered non-conducting, said first transistor means being rendered conducting whenever said second transistor means is non-conducting to thereby enable said indicating means. Other info: Inventors: Cooper, Glenn F. (West Springfield, MA, US) Marceau, Daniel J. (Springfield, MA, US) Application Number: 470063 Filing Date: 1974-05-15 Publication_date: 1976-02-03 Assignee: Standard Electric Time Corporation (Springfield, MA) Primary Class(es): 340/510 340/513, 340/691.8 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Pitts, Harold I. Assistant Examiner: Attorney: Johnson, Dienner, Emrich & Wagner |
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