Lamp failure detecting system

Claim 2

A lamp failure detecting circuit for use with at least one lamp and an electric source comprising: first means for detecting an electrical potential of the electric source through said lamp; second means for producing a first signal and including changeover switch means for selectively changing the potential level of said first signal between first and second levels; third means connected to said second means for selectively visibly actuating and visibly deactuating said lamp in response to said first signal when said first signal has the first and second potential levels respectively; logic circuit means having two input terminals connected to said first and second means for producing a second signal when said first means detects no presence of the electrical potential of said electric source and simultaneously said first signal has said second potential level; and fourth means connected to said logic circuit for indicating the failure of said lamp in response to said second signal.

Claim 3

A lamp failure detecting circuit according to claim 1, wherein one terminal of said lamp is connected to said electric source and the other to a grounded point through resistor means, said first means includes a transistor, the base, collector and emitter of said transistor being connected to the other terminal of said lamp, one of the two input terminals of said logic circuit and the grounded point respectively, and said third means includes a relay means adapted to be energized in response to said first signal having said first level and having a normally open contacts connected between the other terminal of said lamp and the grounded point.

Claim 4

A lamp failure detecting circuit according to claim 1, wherein said second means includes an astable multivibrator for generating an output signal of a periodic wave that alternatively changes from one to the other of two fixed values; and a logic circuit, connected to said changeover switch means and said astable multivibrator, for producing said first signal, said first signal being adapted to have said first level when said output signal of said astable multivibrator has said one value and to have said second level when said output signal of the same has said other value.

Claim 5

A lamp failure detecting circuit as in claim 1 wherein said logic circuit means provides an Exclusive Nor function for producing said second signal also when said first signal is at said first potential level at one of said input terminals and the other said terminal is at a level corresponding to said first potential level as opposed to said second potential level.

Claim 6

A lamp failure detecting circuit as in claim 1 wherein said third means is connected to said first means so as to route lamp current, when said lamp is visibly actuated as aforesaid, through said third means instead of said first means.

Claim 7

A lamp failure detecting system comprising: a power supply source, a lamp connected with said power supply source at one side thereof, level-shifting means connected between a reference potential and the other side of said lamp for level-shifting the said other side of said lamp by a predetermined potential with respect to the reference potential, level detecting means having an input terminal connected between the said other side of said lamp and said level-shifting means and an output terminal for generating an output signal indicating the level-shift condition of the other side of said lamp, control circuit meaNs having a control terminal and an output terminal for generating an output signal when unactuated, said control terminal being connected between the said other side of said lamp and the input terminal of said level detecting means for turning on said lamp by decreasing the predetermined potential of the said other side of said lamp toward the reference potential when said control circuit means is actuated, sensing means having at least two input terminals and an output terminal, each of said input terminals being connected with the output terminals of said control circuit means and said level detecting means respectively for generating an output signal at the output terminal thereof when both input signals from said control circuit means and said control means are applied, and indicating means connected with the output terminal of said sensing means for indicating the failure of said lamp in response to the application of the output signal of said sensing means.

Claim 8

A lamp failure detecting system comprising: a power supply source, a lamp connected with said power supply source at one side thereof, level-shifting means connected between a reference potential and the other side of said lamp for level-shifting the said other side of said lamp by a predetermined potential with respect to the reference potential, level detecting means having an input terminal connected between the said other side of said lamp and said level-shifting means and an output terminal for generating an output signal indicating the level-shift condition of the other side of said lamp, control circuit meaNs having a control terminal and an output terminal for generating an output signal when unactuated, said control terminal being connected between the said other side of said lamp and the input terminal of said level detecting means for turning on said lamp by decreasing the predetermined potential of the said other side of said lamp toward the reference potential when said control circuit means is actuated, sensing means having at least two input terminals and an output terminal, each of said input terminals being connected with the output terminals of said control circuit means and said level detecting means respectively for generating an output signal at the output terminal thereof when both input signals from said control circuit means and said control means are applied, and indicating means connected with the output terminal of said sensing means for indicating the failure of said lamp in response to the application of the output signal of said sensing means.

Claim 9

A lamp failure detecting system according to claim 6, wherein said control circuit means comprises: a control circuit for generating a signal to control the potential of the said other side of said lamp so that the lamp can be lit, switching means connected with said control circuit for generating an output signal in response to the signal of said control circuit, and relay means connected with said switching means, having a normally open contact for making contact in response to the output signal of said switching means to allow the control terminal to be at said reference potential.

Claim 10

A lamp failure detecting circuit according to claim 7 wherein said control circuit is an on-off switch.

Claim 11

A lamp failure detecting circuit according to claim 7 wherein said control circuit comprises: an on-off switch, an astable multi-vibrator for generating periodically an output signal of a predetermined duration, and a logical operation means connected to be actuated by said on-off switch and connected to said astable multivibrator to be actuated by the periodical output signal, for generating said signal of the control circuit.

Claim 12

A lamp failure detecting circuit according to claim 6 wherein said level-shifting means is a resistor and said control means is a transistor.