Скачать или смотреть Fixing Data Order Issues in Siemens LOGO! PLC JSON Logging

Learn how to resolve data order issues when logging Siemens LOGO! PLC data to JSON. Discover programming tips to ensure data consistency and accuracy in timestamps.
---
This video is based on the question https://stackoverflow.com/q/67819625/ asked by the user 'JD_Bachelor' ( https://stackoverflow.com/u/12491701/ ) and on the answer https://stackoverflow.com/a/67872568/ provided by the user 'JD_Bachelor' ( https://stackoverflow.com/u/12491701/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Siemens LOGO! PLC data in the wrong order

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Fixing Data Order Issues in Siemens LOGO! PLC JSON Logging

When working with Siemens LOGO! PLCs, many developers encounter a common problem: the data collected from the PLC is not saved in the same order it is received, leading to confusion and errors in later analysis. This problem can be particularly troublesome if the data includes timestamps for each entry, as the timestamps may not align with the actual order of the readings.

In this post, we'll explore the challenges faced while extracting data from a Siemens LOGO! PLC and how to implement a straightforward solution in Python to ensure the data is recorded correctly.

Understanding the Problem

In the case presented, the developer and their partner successfully connected to their Siemens LOGO! PLC and were pulling input and output data into a dictionary. However, they noticed that the timestamps and the data were saved in a mixed-up order. Here’s a quick rundown of the initial code setup:

Data extraction: Data is continually read from the PLC every second.

Timestamping: Each set of data is timestamped right at the moment of extraction.

Data storage: The collected data is stored in a JSON file format.

Here’s the Python Code They Started With

The initial code snippet seems functional for connecting to the PLC and extracting data, but it has a significant logical flaw:

[[See Video to Reveal this Text or Code Snippet]]

This loop continues to grow the mydata dictionary over time without clearing it, which causes duplication and disorganization in the saved JSON data.

Identifying the Mistake

The main issue arises because the dictionary mydata is defined outside the data logging loop. As the loop executes, it keeps adding new timestamp entries, leading to duplicated and disordered data in the output file. Therefore, the solution involves resetting the dictionary at the beginning of each iteration.

Implementing the Solution

Step 1: Reset the dictionary

To solve the problem of duplicating data packets, you need to define mydata within the while loop. This way, a clean dictionary is created for each new batch of data:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Store data correctly

The save_to_file function should remain unchanged, as it will now reliably log data without those unwanted duplications:

[[See Video to Reveal this Text or Code Snippet]]

Revised Full Example

Here is how your loop may look after the necessary adjustments:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By defining mydata inside the loop, you ensure that each cycle of reading data from the Siemens LOGO! PLC starts with a fresh state, preventing the confusion of mixed-up timestamps and redundant data entries. Following this pattern will lead to a well-organized log file that is easy to analyze and maintain.

If you run into similar issues with your PLC data management, consider the flow of your data and the structures you use to store it. Sometimes, small changes can lead to significant improvements in clarity and function!