Step7 TIA Portal - Checking String Length

SDixon578 · Feb 24, 2014

Hello,

Let me start out by saying that I'm new to PLC programming & The Siemens Step7 TIA Portal.

We have a setup that includes 5 cameras looking for a 2D code and comparing that result to the expected 2D code. In a nutshell, it makes sure we are using the correct packaging.

I keep having trouble with my program due to the cameras only returning a partial result - even though they shouldn't. I want to add logic to only fire the output when the string is 8 characters long.

Is it possible to do this?

Thanks,

Stacy

BryanG · Feb 24, 2014

Hi Stacy

Welcome to the Forum.

If you go to Extended Instructions you should find 'String + Char', click the arrow to open the folder, go down to 'further instructions' and you will find LEN. LEN returns the length of a String.

A quick note on strings. A string is a bunch of characters in sequential memory locations followed by a NULL character. If the NULL character is missing then it isn't a string and string operations will fail. So you might need to be careful if the camera is only sending part of a string.

SDixon578 · Feb 24, 2014

BryanG said:
Hi Stacy

Welcome to the Forum.

If you go to Extended Instructions you should find 'String + Char', click the arrow to open the folder, go down to 'further instructions' and you will find LEN. LEN returns the length of a String.

A quick note on strings. A string is a bunch of characters in sequential memory locations followed by a NULL character. If the NULL character is missing then it isn't a string and string operations will fail. So you might need to be careful if the camera is only sending part of a string.

Thank you for the reply.

I can't seem to find Extended Instructions.

Also, the cameras send an array, then the characters move to string where then the comparisons are taking place.

Thanks,

Stacy

BryanG · Feb 24, 2014

Which PLC are you using? I only have access to the S7-1200, so maybe there are differences in the instruction set. You can see Extended in the attached picture.

Mike_RH · Feb 24, 2014

The String instructions are there in the Extended Instructions for a 300 as well.

SDixon578 · Feb 25, 2014

Sorry - please excuse my blonde moment.

I was looking through all of instructions on the website looking for these instructions - didn't realise you were talking about the TIA portal.

Thank you!

Step7 TIA Portal - Checking String Length

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