Gateway Input Output Scanner Offloading PLC Scan Time
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Solution Overview
Problem
In automation networks, the master PLC must spend significant time scanning remote slave units for I/O state changes, which is a time-consuming task, especially when dealing with legacy systems using proprietary protocols.
Innovation Solution
A gateway with an embedded input/output scanner is introduced, capable of polling slave devices and providing event notifications, thereby offloading I/O servicing and processing from the master PLC. This gateway includes a local area network interface, a serial interface, and a processor for protocol conversion, allowing it to communicate between different protocols like Ethernet and Modbus, and can be configured to poll I/O states and notify the main PLC of changes or threshold exceedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the master PLC scans each remote slave unit to determine I/O state changes, then the system maintains reliable communication with slave devices, but the scan time becomes excessively long and processing efficiency deteriorates
Solution Approach 1:
The gateway acts as an intermediary device between the master PLC and slave devices. It receives polling requests from the master PLC, performs the actual scanning of slave devices, and returns results to the master PLC. This mediator approach transfers the time-consuming scanning task from the master PLC to the gateway, reducing scan time while maintaining communication reliability.
Solution Approach 2:
The I/O scanning function is extracted from the master PLC and implemented as a separate embedded module within the gateway. This extraction allows the scanning operation to be performed independently by the gateway's dedicated hardware, removing the time burden from the master PLC's processing cycle.
2Device complexity
If the master PLC performs all I/O servicing and processing, then the control logic remains centralized and simple, but the processing load on the master PLC increases and system productivity decreases
Solution Approach 1:
The control system is segmented into distinct functional components: the master PLC handles high-level control logic, the gateway manages protocol conversion and I/O scanning, and slave devices perform local I/O operations. This segmentation distributes the processing load across multiple components, improving overall system productivity while maintaining manageable complexity through clear functional separation.
Solution Approach 2:
The gateway serves as an intermediary that handles the burdensome I/O servicing tasks, allowing the master PLC to focus on control logic. This mediator role improves productivity by offloading processing while keeping the overall system architecture relatively simple through a well-defined intermediary component.
3Adaptability or versatility
If legacy slave devices using proprietary protocols are connected directly to the Ethernet network, then protocol compatibility is achieved, but the master PLC must handle multiple protocol conversions which increases processing time
Solution Approach 1:
The gateway acts as a protocol conversion intermediary, translating between Ethernet/TCP-IP protocols used by the master PLC and proprietary protocols used by legacy slave devices. By concentrating all protocol conversion operations in the gateway, the master PLC avoids the time burden of handling multiple protocol conversions directly.
Solution Approach 2:
The protocol conversion function is extracted from the master PLC and implemented as a dedicated feature of the gateway. This extraction isolates the time-consuming protocol translation tasks from the master PLC's processing cycle, reducing overall conversion time while maintaining protocol compatibility.
Data Source
AI summary
A gateway having an input/output scanner is disclosed. The gateway includes a local area network interface, a serial interface, and a processor configured to provide protocol conversion between the local area network interface and the serial interface. Further, an input/output scanner module is operatively connected to the serial interface and configured to poll the slave device.