Lamp supervisory circuit

Claim 2

In a supervisory circuit for detecting failure of at least one electrical circuit device, a first circuit branch including said circuit device and resistance means connected in series across a source of potential to provide a voltage at a first level at the junction of said circuit device and said resistance means whenever current is flowing through said circuit device, and a voltage at a second level at said junction whenever current flow over a portion of said first circuit branch, including said circuit device, is interrupted, the value of said resistance means being selected to limit the current flowing through said circuit device to a value insufficient for enabling said circuit device, enabling means connected to said junction and operable to extend a voltage at a third level to said junction to enable said circuit device, and monitoring means connected to said junction, said monitoring means including indicating means enabled whenever the voltage at said junction is at said second level to provide an indication that current flow through said circuit device has been interrupted, and alarm relay means energized whenever the voltage at said junction is at said third level to inhibit the enabling of said indicating means.

Claim 3

In an alarm monitoring circuit including at least one indicator lamp for indicating an alarm condition when illuminated, a lamp supervisory circuit for detecting failure of the indicator lamp comprising, a first circuit branch including said indicator lamp and resistance means connected in series across a source of potential to provide a voltage at a first level at the junction of said indicator lamp and said resistance means whenever current is flowing through said first circuit branch and a voltage at a second level at said junction whenever current flow over a portion of said first circuit branch, including said indicator lamp, is interrupted, the value of said resistance means being selected to limit the current flowing through said indicator lamp to a value insufficient to cause perceptible illumination of said indicator lamp, alarm switch means connected in parallel with said resistance means for shorting out said resistance means in response to an alarm condition to provide a voltage at a third level at said junction to thereby permit current sufficient to cause illumination of said indicator lamp to flow through said portion of said first circuit branch, And monitoring means connected to said junction, said monitoring means including fault indicating means enabled whenever the voltage at said junction is at said second level to provide an indication that current flow over said portion of said branch circuit has been interrupted, and alarm relay means energized whenever the voltage at said junction is at said third level to inhibit the enabling of said fault indicating means.

Claim 4

In an alarm monitoring circuit including at least one indicator lamp for indicating an alarm condition when illuminated, a lamp supervisory circuit for detecting failure of the indicator lamp comprising, a first circuit branch including said indicator lamp and resistance means connected in series across a source of potential to provide a voltage at a first level at the junction of said indicator lamp and said resistance means whenever current is flowing through said first circuit branch and a voltage at a second level at said junction whenever current flow over a portion of said first circuit branch, including said indicator lamp, is interrupted, the value of said resistance means being selected to limit the current flowing through said indicator lamp to a value insufficient to cause perceptible illumination of said indicator lamp, alarm switch means connected in parallel with said resistance means for shorting out said resistance means in response to an alarm condition to provide a voltage at a third level at said junction to thereby permit current sufficient to cause illumination of said indicator lamp to flow through said portion of said first circuit branch, And monitoring means connected to said junction, said monitoring means including fault indicating means enabled whenever the voltage at said junction is at said second level to provide an indication that current flow over said portion of said branch circuit has been interrupted, and alarm relay means energized whenever the voltage at said junction is at said third level to inhibit the enabling of said fault indicating means.

Claim 5

In an alarm condition monitoring circuit including at least one indicator lamp for indicating an alarm condition when illuminated, a lamp supervisory circuit for detecting failure of the indicator lamp comprising, a branch circuit including said indicator lamp and resistance means connected in series across a source of potential to provide a voltage of a first level at the junction of said indicator lamp and said resistance means whenever current is flowing through said branch circuit and a voltage at a second level at said junction whenever current flow over a portion of said branch circuit, including said indicator lamp, is interrupted, the value of said resistance means being selected to limit the current flowing through said indicator lamp to a value insufficient to cause perceptible illumination of said indicator lamp, monitoring means including voltage sensing means, first circuit means connected between said junction and an input of said voltage sensing means, and fault indicating means, said voltage sensing means being operable whenever a voltage at said second level is provided at said junction to enable said fault indicating means to provide an indication that current flow over said portion of said branch circuit has been interrupted, and alarm switch means connected parallel with said resistance means for shorting out said resistance means in response to an alarm condition to thereby establish a voltage at a third level at said junction, permitting the flow of current through said indicator lamp sufficient to illuminate said lamp, said first circuit means including alarm relay means responsive to a voltage at said third level to inhibit said fault indicating means.

Claim 6

In an alarm condition monitoring circuit including at least one indicator lamp for indicating an alarm condition when illuminated, a lamp supervisory circuit for detecting failure of the indicator lamp comprising, a branch circuit including said indicator lamp and resistance means connected in series across a source of potential to provide a voltage of a first level at the junction of said indicator lamp and said resistance means whenever current is flowing through said branch circuit and a voltage at a second level at said junction whenever current flow over a portion of said branch circuit, including said indicator lamp, is interrupted, the value of said resistance means being selected to limit the current flowing through said indicator lamp to a value insufficient to cause perceptible illumination of said indicator lamp, monitoring means including voltage sensing means, first circuit means connected between said junction and an input of said voltage sensing means, and fault indicating means, said voltage sensing means being operable whenever a voltage at said second level is provided at said junction to enable said fault indicating means to provide an indication that current flow over said portion of said branch circuit has been interrupted, and alarm switch means connected parallel with said resistance means for shorting out said resistance means in response to an alarm condition to thereby establish a voltage at a third level at said junction, permitting the flow of current through said indicator lamp sufficient to illuminate said lamp, said first circuit means including alarm relay means responsive to a voltage at said third level to inhibit said fault indicating means.

Claim 7

A lamp supervisory circuit as set forth in claim 3 wherein said voltage sensing means includes a switching transistor having a control electrode connected to said first circuit means, an output electrode connected to said fault indicating means and an input electrode connected to a source of bias potential for normally reverse biasing said switching transistor.

Claim 8

A lamp supervisory circuit as set forth in claim 4 wherein said alarm relay means includes an operating coil connected between said junction and the control electrode of said switching transistor and normally closed contacts serially connected between the output electrode of said switching transistor and said fault indicating means.

Claim 9

A lamp supervisory circuit as set forth in claim 5 wherein said fault indicating means includes a relay having a coil connected in series with said contacts of said alarm relay means between the output electrode of said switching transistor and a source of potential.

Claim 10

In an alarm condition monitoring circuit including a plurality of indicator lamps each individually operable to indicate an alarm condition when illuminated, a lamp supervisory circuit for detecting failure of any of said indicator lamps comprising a plurality of branch circuits, each including a different one of said indicator lamps and resistance means connected in series across a source of potential to provide a voltage at a first level at the junction point of the indicator lamp and the associated resistance means whenever current is flowing through the branch circuit and a voltage at a second level at said junction point whenever current flow over a portion of the branch circuit, including the indicator lamp, is interrupted, the value of the resistance means in each branch circuit being selected to limit the currents flowing through the branch circuits to values insufficient to cause perceptible illuMination of the indicator lamps, voltage sensing means, first circuit means including an alarm relay having a first terminal connected to an input of said voltage sensing means and diode means, including a plurality of diodes each individually connected between a second terminal of said alarm relay and the junction point of a different one of said branch circuits, fault indicating means, said voltage sensing means being operable whenever a voltage at said second level is provided at any one of said junction points to enable said fault indicating means to provide an indication that current flow over the portion of one of said branch circuits including an indicator lamp has been interrupted, and a plurality of switch means, each individually connected in parallel with a different one of said resistance means and each independently operable to short out an associated resistance means in response to an alarm condition to thereby establish a voltage at a third potential at the corresponding junction point, permitting the flow of current through a corresponding indicator lamp sufficient to illuminate the lamp, said alarm relay being energized whenever a voltage at said third level is provided at any one of said junction points to inhibit said fault indicating means.

Claim 11

In an alarm condition monitoring circuit including a plurality of indicator lamps each individually operable to indicate an alarm condition when illuminated, a lamp supervisory circuit for detecting failure of any of said indicator lamps comprising a plurality of branch circuits, each including a different one of said indicator lamps and resistance means connected in series across a source of potential to provide a voltage at a first level at the junction point of the indicator lamp and the associated resistance means whenever current is flowing through the branch circuit and a voltage at a second level at said junction point whenever current flow over a portion of the branch circuit, including the indicator lamp, is interrupted, the value of the resistance means in each branch circuit being selected to limit the currents flowing through the branch circuits to values insufficient to cause perceptible illuMination of the indicator lamps, voltage sensing means, first circuit means including an alarm relay having a first terminal connected to an input of said voltage sensing means and diode means, including a plurality of diodes each individually connected between a second terminal of said alarm relay and the junction point of a different one of said branch circuits, fault indicating means, said voltage sensing means being operable whenever a voltage at said second level is provided at any one of said junction points to enable said fault indicating means to provide an indication that current flow over the portion of one of said branch circuits including an indicator lamp has been interrupted, and a plurality of switch means, each individually connected in parallel with a different one of said resistance means and each independently operable to short out an associated resistance means in response to an alarm condition to thereby establish a voltage at a third potential at the corresponding junction point, permitting the flow of current through a corresponding indicator lamp sufficient to illuminate the lamp, said alarm relay being energized whenever a voltage at said third level is provided at any one of said junction points to inhibit said fault indicating means.

Claim 12

A lamp supervisory circuit as set forth in claim 7 which includes test switch means connected between the second terminal of said alarm relay and a source of potential and operable to extend a voltage at said third level over said diode means to the junction points of all of said branch circuits for effecting illumination of all of said indicator lamps.

Claim 13

A lamp supervisory circuit as set forth in claim 7 wherein said voltage sensing means includes a switching transistor having a control electrode connected to said first terminal of said alarm relay, an output electrode connected to said fault indicating means and an input electrode connected to a source of bias potential for normally reverse biasing said switching transistor.

Claim 14

A lamp supervisory circuit as set forth in claim 9 wherein said alarm relay includes an operating coil connected between said diode means and the control electrode of said switching transistor and normally closed contacts serially connected between the output electrode of said switching transistor and said fault indicating means.