Parallel off hook detector for electronic remote data recorder

Claim 2

Apparatus detecting at least one impedance being connected on a line comprising: a short-term integrator receiving a sample of a voltage on said line and producing a short-term integrated output in response thereto; a long-term integrator receiving said sample of a voltage on said line and producing a long-term integrated output in response thereto; means for producing a difference signal in response to a difference between said long-term integrated output and said short-term integrated output; a threshold circuit; and said threshold circuit including means responsive to said difference signal exceeding a predetermined value for at least a predetermined minimum time to produce a detection signal indicating that said at least one impedance is connected across said line.

Claim 3

Apparatus according to claim 1 wherein said predetermined time is greater than a minimum time required to avoid false detection from transient events on said line.

Claim 4

Apparatus according to claim 1 wherein a first time constant of said short-term integrator and a second time constant of said long-term integrator are related in a manner permitting outputs of both integrators to rise and fall substantially together in the absence of a sudden connection of said at least one impedance across said line.

Claim 5

Apparatus according to claim 1 wherein said at least one impedance includes a telephone and an impedance in said telephone is placed across said line when said telephone is placed off hook.

Claim 6

Apparatus for detecting at least one impedance being connected on a line or removed from said line comprising: a short-term integrator receiving a sample of a voltage on said line and producing a short-term integrated output in response thereto; a long-term integrator receiving said sample of a voltage on said line and producing a long-term integrated output in response thereto; means for producing a difference signal in response to a difference between said long-term integrated output and said short-term integrated output; a threshold circuit; and said threshold circuit including means responsive to said difference signal exceeding a predetermined value for at least a predetermined minimum time to produce a detection signal indicating that said at least one impedance has been one of connected across and removed from said line.

Claim 7

Apparatus for detecting at least one impedance being connected on a line or removed from said line comprising: a short-term integrator receiving a sample of a voltage on said line and producing a short-term integrated output in response thereto; a long-term integrator receiving said sample of a voltage on said line and producing a long-term integrated output in response thereto; means for producing a difference signal in response to a difference between said long-term integrated output and said short-term integrated output; a threshold circuit; and said threshold circuit including means responsive to said difference signal exceeding a predetermined value for at least a predetermined minimum time to produce a detection signal indicating that said at least one impedance has been one of connected across and removed from said line.

Claim 8

Apparatus according to claim 5, further comprising an absolute value circuit in series with said sample of a voltage, said absolute value circuit being effective to produce a constant-polarity output having an amplitude responsive to both positive and negative variations in said sample of a voltage, whereby said short-term integrator and said long-term integrator are equally responsive to both positive and negative variations in said sample of a voltage.