Intrinsically safe telephone

Details Intrinsically safe telephone Intrinsically safe telephone

1990-07-13

1992-08-04

Dwyer, James L.

Telephonic communications

Audio message storage, retrieval, or synthesis

379 65, 379387, 379391, H04M 904

Patent

active

051366304

ABSTRACT:
An intrinsically safe telephone as provided for use in hazardous areas. The telephone includes a single line instrument located in the hazardous area which, in turn, is coupled by a two-wire transmission path to a shunt diode barrier and a telephone line interface located in a safe environment. The telephone line interface reduces power of incoming ringing and audio signals. The telephone line interface further includes an off-hook indicating circuit which senses when the single line instrument is off-hook. The intrinsically safe telephone is useful in all hazardous environments as classified by the National Electrical Code and requires no explosion-proof housing.

REFERENCES:
patent: 3997733 (1976-12-01), Sanders
patent: 4064366 (1977-12-01), Wheatley et al.
patent: 4214127 (1980-07-01), Oules
patent: 4741031 (1988-04-01), Grandstaff
patent: 4821319 (1989-04-01), Middleton et al.
patent: 4847888 (1989-07-01), Cox et al.

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