Reading PLC trend data into python.

Peter Nachtwey · Apr 14, 2021

It is pretty easy to read data from xml, json or .csv files using python.
Can Rockwell and/or Siemens trends be saved in any of these formats?

Dmroeder probably knows.

dmroeder · Apr 14, 2021

Honestly, while I use the trend to debug fast/complicated things, I have never really saved them to analyze them. Rockwell uses .dbf extension, because they can never do anything conventional. Python does have a module, naturally:

https://dbfread.readthedocs.io/en/latest/

Libreoffice opens the file fine, which I saved as a CSV, then of course, you could use python's csv module.

Edit: can't speak for Siemens, I only have exposure to Rockwell.

Edit2: it appearst that you can automate converting the files with Libreoffice command line:

internet said:
$ soffice --headless --convert-to csv FILETOCONVERT.DBF

mk42 · Apr 15, 2021

Peter Nachtwey said:
It is pretty easy to read data from xml, json or .csv files using python.
Can Rockwell and/or Siemens trends be saved in any of these formats?

Dmroeder probably knows.

The PLC Trace function inside TIA exports as a ttrecx by default, but CSV is an option as well. The ttrecx, at first glance, seems to be a wacky XML file full of binary data, which includes the formatting for the graph and stuff like that.

Or did you mean trends on the Siemens HMI?

kamenges · Apr 15, 2021

Rockwell trends can be saved as a csv.

Keith

drbitboy · Apr 15, 2021

Oh, this is nice. I wanted to get values from a MicroLogix 1100 data file in RSL Micro into Python:

Go offline from Run, saving running state in the process
Print running state as PDF report
Open PDF with LibreOffice (Writer?)
Export as HTML file
Scrape data from HTML file with Python

Yuk.

dmroeder · Apr 15, 2021

kamenges said:
Rockwell trends can be saved as a csv.

Keith

Thanks Keith, I see that now. My bad.

If you stop a trend, right click and select Create Snapshot, it creates a .dbf file

I see now to the right of the stop button, there is a Log drop down, where you have an option to save as CSV.

Peter Nachtwey · Apr 15, 2021

OK, next questions.
Since both Rockwell and Siemens can export .csv files,
can the order of the data be determined by the programmer?
This is for a tuning application which is done and works but it seems it is always a pain to for people to export the data.
I would like to see the data in this format
time control% PV

0.0, 50, 159,
0.1 50 160, ....

The next question is the units. For temperature system the time units are usually minutes. The control units are counts or percent. I prefer percent.

Can the units be determined by the programmer?

What I don't want to do is to write a module for each type of controller.

BTW, .dbf is an old data base format that was common long ago.

drbitboy · Apr 15, 2021

Peter Nachtwey said:
What I don't want to do is to write a module for each type of controller.

hahahahaha

vewy funny mista wabbit.

mk42 · Apr 15, 2021

Peter Nachtwey said:
OK, next questions.
Since both Rockwell and Siemens can export .csv files,
can the order of the data be determined by the programmer?
This is for a tuning application which is done and works but it seems it is always a pain to for people to export the data.
I would like to see the data in this format
time control% PV

0.0, 50, 159,
0.1 50 160, ....

The next question is the units. For temperature system the time units are usually minutes. The control units are counts or percent. I prefer percent.

Can the units be determined by the programmer?

What I don't want to do is to write a module for each type of controller.

BTW, .dbf is an old data base format that was common long ago.

Seems unlikely that they'd match, but anything is possible.

The columns for the test trace I just created in TIA were sample number, timestamp, tag a, tag b, tag c. Sample number increments by 1 each sample. Timestamp appears to be milliseconds since Jan 1 1970 (1618510671223.024347, in the first sample in the trace I just took). The three tags are in the order I defined for the trace, not automagically alphabetized or anything.

You could easily include a minutes timestamp that's a tag of your own. The Control/PV tags would be whatever units you use in the system. I know Siemens PID blocks tend to have %, Counts, and Engineering Units as options, dunno how you're doing it.

drbitboy · Apr 15, 2021

drbitboy said:
hahahahaha

vewy funny mista wabbit.

Hi Peter, you can use classes and polymorphism to write an input parser for any new format; that way the users are not limited to a single format, while at the same time you do not have to change the tuning class.

Once you write and document the first input parser base class, the rest are easy and quick; the same .py file could handle CSV, TSV, XLS, XLSX, DBF, SQLite, ODBC, whatever.

Put it on Github, I can get it started if you are interested.

Reading PLC trend data into python.

Peter Nachtwey

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