Apparatus and method for determining the state of a telephone line
AssigneeIntertex Data AB
InventorKarl-Erik Stahl
Life of this patent
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Abstract
A line state detector for a telephone line tests a voltage derived from the telephone line by closing a switch in series with a voltage sensing circuit in response to a polling signal. A modem testing the line state go Off-Hook immediately after it finds that the line was in On-Hook state, so it can use a low impedance voltage sensor directly on the telephone line. Monitoring equipment will need a line state detector with high impedance, which can be achieved by a high impedance in series with a capacitor. The capacitor voltage can then be tested by a low impedance sensing circuit.
Claims4
Apparatus for determining the state of a telephone line, comprising:
- (a) a voltage sensing device having a current sensing device in series with a zener diode;
- (b) a normally open switching device connected in series with said voltage sensing device, said series connected devices being connected to a voltage derived from said telephone line;
- (c) means for closing said switching device in response to a polling signal;
- and
- (d) a ring detector circuit connected to said telephone line, wherein said ring detector circuit includes said current sensing device.
Apparatus for determining the state of a telephone line, comprising:
- (a) a resistor,
- (b) a capacitor,
- (c) means for connecting said resistor in series with said capacitor across said telephone line,
- (d) a voltage sensing device including a current sensing device in series with a zener diode,
- (e) means for connecting said voltage sensing device to said capacitor in response to a polling signal, and
- (f) a ring detector circuit connected to said telephone line and including said current sensing device.
Apparatus for determining the state of a telephone line, comprising:
- (a) an inductance,
- (b) a capacitor,
- (c) means for connecting said inductance in series with said capacitor across said telephone line,
- (d) a voltage sensing device including a current sensing device in series with a zener diode,
- (e) means for connecting said voltage sensing device to said capacitor in response to a polling signal, and
- (f) a ring detector circuit connected to said telephone line and including said current sensing device.
Dependencies are inferred from the claim text.