Dual PLC Timing Adjustment for Synchronized Sequence Execution
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Solution Overview
Problem
In PLC systems with functional safety, performance differences between duplicate PLCs can lead to common cause failures and deviations in execution times, making it challenging to ensure synchronized operation without modifying the sequence program, thereby burdening system designers.
Innovation Solution
A PLC apparatus that includes a measurement unit to assess execution times of sequence programs in each PLC, a calculation unit to determine timing adjustment information, and a setting unit to apply this information, allowing for parameter adjustments without modifying the sequence program to synchronize execution speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different parts and designs are used for diversity to avoid common cause failure, then reliability is improved, but performance difference occurs between PLCs
Solution Approach 1:
The patent changes the parameter of execution cycle timing by introducing a timing adjustment mechanism. The system measures the actual execution time of each PLC and adjusts the execution cycle parameters to compensate for performance differences, allowing PLCs with different execution speeds to operate synchronously while maintaining functional safety reliability
2Stability of the object's composition
If sequence program is modified to synchronize execution, then execution synchronization is improved, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary timing adjustment mechanism that mediates between PLCs with different execution speeds. Instead of modifying the sequence program logic, the system uses a timing adjustment unit to synchronize execution cycles, thereby maintaining execution synchronization without increasing program complexity
Solution Approach 2:
The system performs preliminary measurement of execution times before actual operation. By measuring the execution time of each PLC in advance and pre-calculating the timing adjustment parameters, the system prepares synchronization settings beforehand, avoiding the need for complex real-time program modifications
3Speed
If timing adjustment information is set based on measurement, then execution speed difference is absorbed, but measurement and calculation processes are added
Solution Approach 1:
The system performs self-measurement of its own execution times. Each PLC measures its own execution cycle time, and the timing adjustment unit automatically calculates and applies the necessary timing corrections without external intervention, thereby absorbing execution speed differences without requiring complex external measurement and calculation processes
Data Source
AI summary
Provided is a PLC device having a first PLC and a second PLC, the PLC device comprising: a measurement unit that causes PLC execution units of the first PLC and the second PLC to execute test run of a sequence program and measures a period between start and end of the sequence program for each of the first PLC and the second PLC; a timing adjustment information calculation unit that uses the measured periods to calculate timing adjustment information including at least one of an execution time and execution cycle in cyclic execution of the sequence program by the first PLC and the second PLC; and a timing adjustment information setting unit that sets the timing adjustment information calculated by the timing adjustment information calculation unit in at least any one of the first PLC and the second PLC.