Intrinsically safe telephone
First Claim
1. An intrinsically safe telephone for use in a hazardous environment comprising:
- a line powered single line instrument for providing a dialing output and an audio output signal to a telephone network and for receiving a ringing input signal and an audio input signal from that network, said single line instrument being situated in said hazardous environment;
a two wire transmission path coupling said single line instrument to a safe environment;
electrical isolation means situated in said safe environment and coupled between said two wire transmission path and said network for controlling power to said single line instrument, said electrical isolation means includinga telephone line interface for reducing line power from the network to said single line instrument, for reducing the power of incoming ringing signals from the network and for isolating the single line instrument from the network; and
a shunt diode barrier for controlling the maximum power to the single line instrument.
2 Assignments
0 Petitions
Accused Products
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.
85 Citations
8 Claims
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1. An intrinsically safe telephone for use in a hazardous environment comprising:
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a line powered single line instrument for providing a dialing output and an audio output signal to a telephone network and for receiving a ringing input signal and an audio input signal from that network, said single line instrument being situated in said hazardous environment; a two wire transmission path coupling said single line instrument to a safe environment; electrical isolation means situated in said safe environment and coupled between said two wire transmission path and said network for controlling power to said single line instrument, said electrical isolation means including a telephone line interface for reducing line power from the network to said single line instrument, for reducing the power of incoming ringing signals from the network and for isolating the single line instrument from the network; and a shunt diode barrier for controlling the maximum power to the single line instrument. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification