PLC Split Logging for Memory-Safe Device Value Recording
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Solution Overview
Problem
The programmable logic controller (PLC) faces memory space issues due to increased log recording, which can lead to insufficient memory space and potential system stoppages.
Innovation Solution
The PLC implements a split logging mechanism, where it collects and stores one-Nth of device values at each program execution, generating new reference data and overwriting old logs when memory space is full, thereby managing memory usage effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If log recording is performed many times to maintain logging function, then logging completeness is improved, but memory space is depleted leading to system stoppages
Solution Approach 1:
The patent divides the logging process into multiple segments: (1) collecting device values at N different time points during one program execution, (2) storing only one-Nth of the total device values as split logs in the log storage area, and (3) maintaining differential logs for changed values. This segmentation reduces the memory burden of continuous logging while preserving logging functionality.
Solution Approach 2:
The patent changes the logging parameter from recording all device values at every execution to recording only one-Nth of device values at N different time points. This parameter change reduces the volume of log data stored in memory while maintaining the ability to retrieve logging information, thus preventing memory depletion.
2Measurement precision
If all device values are recorded at every program execution, then logging accuracy is improved, but processing time increases
Solution Approach 1:
The patent extracts only the necessary portion of device values for logging purposes. Instead of recording all device values at every execution, it collects device values at N different time points and stores only one-Nth of them as split logs. This extraction approach maintains logging accuracy for critical values while reducing the processing time required to handle and store log data.
Data Source
AI summary
A differential logger stores, into a log storage from a device memory, a differential log being a log of a device value that has changed at each execution of a control program. A collective logger collectively stores, at a set time, collection target device values into the log storage as reference data to be used to collect the differential log. A split logger acquires as split logs, after the set time, logs of the device values multiple times, and stores the split logs into the reference data storage. The differential logger overwrites data in the log storage with the differential log after new reference data is stored into the log storage.