AC Current Loop Zone Status Detection Circuit
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Solution Overview
Problem
Existing security alarm systems face challenges in reliably monitoring zone status due to susceptibility to common mode noise and voltage additive noise, lack of tamper resistance, and high costs associated with complex analog circuitry for zone isolation.
Innovation Solution
A current loop circuit using an AC signal generator with bi-directional and unidirectional current limiters, coupled with opto-coupler circuits to detect current states, ensuring robust immunity to noise and tamper resistance while powering end-of-line sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC voltage drop reading across a resistor is used to read end of line states, then the zone status can be monitored, but the system becomes susceptible to common mode noise and voltage additive noise
Solution Approach 1:
The patent replaces the electrical field-based DC voltage measurement system with a magnetic field-based sensing system. The AC signal generator creates an alternating magnetic field that induces voltages in the zone loop, and the sensing circuit detects these induced voltages to determine zone status. This substitution of measurement principle (from direct electrical voltage measurement to magnetic field induction) provides immunity to common mode noise and voltage additive noise while maintaining reliable zone status monitoring.
2Reliability
If complicated analog circuitry is used to achieve acceptable zone isolation, then zone isolation can be achieved, but the system cost increases
Solution Approach 1:
The patent divides the zone monitoring system into independent, isolated channels. Each zone has its own dedicated sensing circuit that detects magnetic field changes specific to that zone. The AC signal generator and sensing circuits are configured to independently monitor each zone without electrical interconnection, achieving zone isolation through spatial and functional segmentation rather than complex analog isolation circuitry.
Solution Approach 2:
The patent introduces magnetic field induction as an intermediary mechanism between the AC signal generator and the sensing circuits. The alternating magnetic field serves as a non-electrical mediator that transfers energy and information from the generator to the sensing circuits without requiring direct electrical connections between zones. This intermediary approach achieves zone isolation while using simple, low-cost circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides low-cost, reliable, and efficient zone status monitoring with robust immunity to noise and enhanced tamper resistance, ensuring effective zone isolation and power supply to sensors, making it suitable for fire applications.
Implementation Method 1
an AC signal generator to generate an AC signal having a positive cycle (+ve) and a negative cycle (−ve)
Implementation Method 2
A bi-directional current limiter may be configured to receive the AC signal and bi-directionally limit the loop current to a predetermined current value (I3)
Implementation Method 3
A first zone may be configured to receive the AC signal, the first zone may include a unidirectional current limiter to limit a unidirectional current (I1) that is proportionately less than the bi-directionally limited current I3
Implementation Method 4
A first opto-coupler circuit (ISO1) may be configured to detect both high and low current states in the current loop circuit
Data Source
AI summary
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.