| 摘要 |
1. Circuit arrangement for an alarm system, particularly for a burglar or fire alarm system, with at least one alarm sensor (M1, ..., M10) arranged in a closed-circuit current-monitored alarm line and which on responding in the case of an alarm significantly changes its resistance, the alarm sensor in series with a precision resistor element forming a branch of a bridge circuit, whose other branch is formed by a predeterminable number of voltage dividing resistors (R2, ..., R6), a voltage comparator (IC1, ..., IC4) being connected to the bridge circuit and its output is connected to a control stage (10), which evaluates in accordance with predeterminable criteria an alarm signal which detunes the bridge circuit, characterized in that the precision resistor element is formed by a negative feedback operational amplifier (Op) and that the negative feedback is dimensioned in such a way that the potential of the inverting input of the operational amplifier (Op) corresponds to the potential of the non-inverting input, so that the alarm voltage (UM ) remains constant, independently of the flowing alarm current (IM ). |
