Duplex Encoder Decoder for Independent Solenoid Valve Control
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Solution Overview
Problem
Existing systems for operating two independent AC loads from two independent current sources and a single return using two conductors are complex, prone to malfunction, and cannot switch between loads without delays, leading to issues like over-current detection and faulty operation in modern irrigation controllers.
Innovation Solution
A duplex encoder/decoder pair is used, comprising an encoder circuit near the irrigation controller and a decoder circuit near the solenoid valves, with turn-on and turn-off delay timers and LC snubber circuits to manage current flow, allowing independent control of two loads via a single conductor and preventing simultaneous operation to avoid interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electromechanical latching relays are used to operate two independent AC loads from two independent current sources, then the electrical load on the circuit increases, but the system becomes more complex and the relays are subject to malfunction and failure over extended periods
Solution Approach 1:
The system is divided into two separate control circuits, each with its own relay (first relay for first load, second relay for second load). This segmentation allows independent control of each load while simplifying the overall system architecture compared to a single complex latching relay system.
Solution Approach 2:
A common return conductor serves as an intermediary that carries return current from both loads back to the controller. This eliminates the need for separate return conductors for each load, reducing wiring complexity while maintaining independent load control.
2Adaptability or versatility
If electromechanical latching relays are used to switch between two alternating current loads, then a delay is required between switching loads, but this causes the irrigation controller to cut out outputs due to over-current or falsely detect fault conditions
Solution Approach 1:
The switching function is divided between two separate relays with independent control circuits. Each relay handles one load independently, eliminating the need for complex load switching mechanisms and the associated delays that cause false fault detections.
Solution Approach 2:
The controller receives feedback signals from both the first and second loads through their respective control circuits. This allows the controller to monitor the status of each load independently and adjust switching timing to prevent over-current conditions and false fault detections.
3Ease of operation
If one conductor is required to connect each load to each switched current source and one conductor for return, then three conductors are needed per load, but this increases wiring complexity and prevents system expansion
Solution Approach 1:
The return conductors for both loads are merged into a single common return conductor. This reduces the total number of conductors from three per load to two per load (one control conductor plus shared common return), simplifying wiring and enabling easier system expansion.
Solution Approach 2:
The common return conductor serves multiple functions by carrying return current from both the first load and the second load. This multi-functional conductor reduces wiring requirements and provides a scalable architecture for adding additional loads to the system.
Data Source
AI summary
Apparatus 11 and 13 for interfacing two AC sources with two AC loads 17a 17b in the form of solenoid operated valves over a single conductor 25, with a return conductor 19 in an irrigation system is disclosed. The apparatus has an encoder circuit 11 with two inputs 21a 21b for connection to the two AC sources, and an output 23 for connection to the single conductor 25, and a decoder circuit 13 having an input 27 for connection to the conductor 25, and two outputs 29a 29b for connection to loads 17a 17b respectively. When the first input 21 a is powered, the first load 17a will be switched on, and when the second input 21b is powered, the second load 17b will be switched on. The decoder portion 13 incorporates switching circuits 43a 43b, interfaced with turn on delay timers 45a 45b respectively, to delay operating the loads at switch on, and turn-off delay timers 47a 47b to hold the loads on after switch off.