Signaling circuit and method to detect zone status

摘要

A bi-directional current limiter may be configured to receive an AC signal and bi-directionally limit the loop current to a predetermined current value. A first and second zone may be configured in series with the AC signal and bi-directional current limiter. The first and second zone may include unidirectional current limiters to limit a unidirectional current that is proportionately less than the bi-directionally limited current. A first opto-coupler circuit (ISO1) may be configured to detect both high and low current states in the current loop circuit. Second and third opto-coupler circuits (ISO2 and ISO3) associated with the first and second zones may be configured to detect only high current states in the current loop circuit. The status of the first and second zones may then be determined by an analysis of the current level in the current loop circuit during two half cycles as determined by the various current limiters.

主权项

1. A current loop circuit comprising:
an AC signal generator to generate an AC signal having a positive half cycle and a negative half cycle; a bi-directional current limiter configured to receive the AC signal and bi-directionally limit the loop current to a predetermined current value (I3); a first zone configured to receive the AC signal, the first zone including a unidirectional current limiter to limit a unidirectional current (I1) that is proportionately less than the bi-directionally limited current I3; a second zone configured to receive the AC signal, the second zone including a unidirectional current limiter to limit a unidirectional current (I2) that is proportionally less than the bi-directionally limited current I3; a first opto-coupler circuit (ISO1) configured to detect both high and low current states in the current loop circuit; a second opto-coupler circuit (ISO2) associated with the first zone and configured to detect only high current states in the current loop circuit; and a third opto-coupler circuit (ISO3) associated with the second zone and configured to detect only high current states in the current loop circuit.