Intrinsically safe telephone

Details Intrinsically safe telephone Intrinsically safe telephone

1986-06-27

1988-04-26

Lev, Robert

Telephonic communications

Supervisory or control line signaling

Signal reception at substation

379391, 379167, 379176, H01M 118

Patent

active

047410310

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 telephone line interface further includes a bootstrap power supply for powering the single line instrument whenever the single line instrument is off hook. The intrinsically safe telephone is line powered and requires no auxiliary power in the hazardous environment. 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: 3558830 (1971-01-01), Bender
patent: 3997733 (1976-12-01), Sanders
patent: 4064366 (1977-12-01), Wheatley et al.
patent: 4113985 (1978-09-01), Day
patent: 4214127 (1980-06-01), Oules
patent: 4400589 (1983-08-01), Synek et al.
patent: 4401847 (1930-08-01), Schneider et al.
patent: 4465903 (1984-08-01), Barber
Texas Instruments Learning Center, Sidetone, 1983, pp. 2-24.

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