Communications: electrical – Systems – Call station
Patent
1976-02-19
1977-05-10
Caldwell, John W.
Communications: electrical
Systems
Call station
315 83, G08B 2100
Patent
active
040231534
ABSTRACT:
A device for detecting any failure in a plurality of loads connected in parallel with one another comprises an indicator lamp connected in series with first and second magnetically operable switching elements. A control circuit comprising first and second coils associated, respectively, with the first and second switching elements is connected in series between a DC power source and the parallel connected loads. A third coil associated with the first switching element and producing a magnetic field opposing that of the first coil is connected in series with a resistor across the power source. A zener diode in series with a resistance is connected in parallel with the third coil. The sensitivities of the first and second switching elements and the coil constants are adjusted so that the first switching element is opened only when the number of the load failures is between 1 and K-1, where K is an integer between 2 and n, while the second switching element is opened only when at least K loads fail on condition that the intensity of the composite magnetic field produced by the first and third coils is close to zero when the number of the load failures is K-1.
REFERENCES:
patent: 3171096 (1965-02-01), Murray et al.
patent: 3457561 (1969-07-01), Zeisler
patent: 3629799 (1971-12-01), Birtwistle
patent: 3631441 (1971-12-01), Murphy
patent: 3643248 (1972-02-01), Schott
patent: 3644886 (1972-02-01), Sabaroff
patent: 3753224 (1973-08-01), Martin
patent: 3789232 (1974-01-01), Wareing
patent: 3811107 (1974-05-01), Sakurai
patent: 3956733 (1976-05-01), Sakurai
patent: 3975721 (1976-08-01), Franz
Adams Bruce L.
Burns Robert E.
Caldwell John W.
Lobato Emmanuel J.
Myer Daniel
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