Troubleshoot Siemens programs (S7 300 STL)

Noli2

Member
Join Date
Jun 2012
Location
Belgium
Posts
59
Hi

I wonder what methodology you expierenced Siemens users have to troubleshoot complex programs.

* Reproduceable fault, slow process: this is easy, using VAT tables

* Reproduceable fault, fast process: this makes me wonder already. In my previous job, I used a scope monitor in my Beckhoff PLC's to monitor which state variable or which boolean went wrong for some 10 ms, or to monitor that state_variable_1 went to '5' one cycle too early, compared to state_variable_2.

* Non reproduceable fault, once a week: I don't have a clue here.
 
Diagnostic subroutines.
Troubleshoot until you find the (sub)routine where you suspect the error occurs, then create a capture routine. Capturing the status of relevant variables on the moment the fault occurs, or when the expected action does not occur.
Stored in DB with indexing, so I can get at least the last 5 times it happened, preferably the last 10 times though.

This my favored approach to solving issues with fast processes and those pesky once a week/month/trimester faults.
 
In the past I've set traps to capture data and store it in a DB. It helps to have a guess at where a problem might exist.

The last time I employed these tactics ws some years ago now when diagnosing a data consitency error in profibus comms between a PLC and a motion controller. Whilst the motion controller occupied 10 bytes the motion controller manufacturer's technician insisted that only the first 9 bytes should be sent. About once a day the flying shear would cut the same length twice.

By setting a trap in the software I was able to prove that the correct information had been sent to the motion controller but that the motion controller had ignored it. I changed the software to send all 10 bytes and it hasn't missed a beat since.

People often dismiss data consistency of profibus as a non-issue but it is important! That said, I've only found it as a problem twice since the invention of profibus - once in S5 and once in S7.

Nick
 
It is nice to see that the first two answers convince me that the method I used in previous projects was correct and not too time consuming.

However, this project is my first Siemens project. I learned STL on my own last weeks. The project was done by my predecessor, and there is hardly any information. Of course there were software errors at the startup two years ago, and of course there was no time for a decent fix. And the PLC is 3 hrs drive away from my desk.
Because of my lack of experience with Siemens and STL and the programming environment, I'm not that happy with frequent downloads from my desk to a PLC in another country.

On a side note, how do you know I use profibus? :)
 

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