| 摘要 |
A device and method for detecting current-impressed useful signals, added to a DC supply current, for a digital alarm line security system are described. To operate the alarm system using high DC supply currents on the alarm line without significantly affecting the reception of the useful signals, a current bypass branch containing a second current sensor element, a control amplifier, and an actuator for adjusting the resistance of the current bypass branch is provided in parallel to a first current sensor element designed for picking up the signals, the actuator being controlled by the control amplifier in such a way that a constant current adjusted to a setpoint value input at the control amplifier flows through the current bypass branch, the setpoint value being defined by a microprocessor as a function of time in such a way that the current flowing through the first current sensor element contains the useful signals having an essentially unreduced amplitude, and a reduced portion of the DC component of the supply current.
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