PLC Retrofit Interface Rack Without Legacy Wiring Re-Termination
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Solution Overview
Problem
Retrofitting legacy Programmable Logic Controller (PLC) based systems to non-PLC process controllers is hindered by the need for re-termination of field device wiring and limited space in process plants, leading to difficulties in communication and reliability issues.
Innovation Solution
A method involving the assembly of a custom mounting rack with replacement hardware, including a non-PLC process controller, I/O cards, and a custom interface module that couples to legacy wiring without re-termination, allowing for seamless integration and communication with field devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If legacy PLC systems are retrofitted to non-PLC process controllers, then system modernization and control capabilities are improved, but re-termination of field device wiring is required which increases complexity and downtime
Solution Approach 1:
A custom interface module serves as an intermediary between the legacy wiring mechanisms and the new non-PLC process controller. This module includes a legacy wiring coupling mechanism that interfaces with existing wiring and an I/O coupling mechanism that connects to the new controller, thereby mediating the transition without requiring re-termination of field device wiring
Solution Approach 2:
The retrofit solution segments the control system into distinct functional modules: the legacy wiring coupling mechanism, the custom interface module, the I/O card, and the non-PLC process controller. This segmentation allows each component to be independently addressed and replaced without affecting the entire wiring infrastructure
2Adaptability or versatility
If process plant space is limited, then installation space for new control hardware is constrained, but modernization requires additional control equipment
Solution Approach 1:
The custom interface module and I/O card are nested within the existing control rack structure. The custom interface module mounts in the rack and provides interfaces for both the legacy wiring and the new process controller, effectively nesting multiple functional layers within the same physical space
Solution Approach 2:
The custom interface module performs multiple functions: it couples legacy wiring mechanisms, provides I/O coupling for the new controller, and maintains signal integrity across the transition. This multi-functionality reduces the need for separate dedicated components that would consume additional space
3Ease of manufacture
If legacy wiring is re-terminated during retrofit, then new controller integration is simplified, but system reliability and communication issues increase
Solution Approach 1:
The custom interface module is designed and configured before the retrofit installation, with the legacy wiring coupling mechanism pre-configured to match existing wiring standards. This preliminary preparation ensures that the module can be installed without modifying legacy wiring, thereby maintaining reliability while facilitating smooth integration
Data Source
AI summary
A method for upgrading a portion of a process control system from a legacy programmable logic controller (PLC) to a non-PLC process controller is disclosed. A mounting rack sized to fit into a space occupied by legacy hardware is assembled and populated with replacement hardware that includes an I/O card, an I/O terminal block, and a custom interface module. The custom interface module is coupled to the I/O card via the I/O terminal block and to a plurality of process control field devices via a legacy wiring mechanism coupled to legacy wiring of the process control system, without requiring modification or re-termination of the legacy wiring. The legacy wiring mechanism is disconnected from the legacy hardware, the rack containing the legacy hardware is removed and replaced with the mounting rack, and the legacy wiring mechanism is coupled to the custom interface module.