Problem with "Temp Variable” in FC blocks

wordless · Nov 10, 2009

Hi everyone

First of all I’m beginner and it’s my first program with PLC and OP touch panel. This forum helps me a lot. Hope this time you can solve my problem.

I make a FC block (FC5) that control filling a tank. There are 9 tanks in the project. So I create 9 instances from FC5 and assign different input-output to the every function. Just one of the tanks should be filled at a time. So just one of the functions is running at the time.

I have a problem with “Temp Variable” in FC blocks. The problem is when instance#1 runs(instance#1 of FC5), after filling the tank, when system switches to the next tank (actually next instance of FC5), all temporary variable that defined in the FC, remains and they are not reset for new instance of FC. For example when tank #1 reaches to its full limit level, a temporary Boolean variable will set. Then, When system switches to tank #2 its temporary variable is set at beginning of FC!

I don’t know what to do. I tried my best! After all I decide to convert FC to FB and assign different DB to each instance. But I decide to hear from you experts.

JesperMP · Nov 10, 2009

When using TEMPs you absolutely must initialise them in code. Write to the TEMPs before you read from them. And the writes must not be conditional.
You are assuming that the TEMPs are initially zero, but that is incorrect. The TEMPs contain arbitrary values depending on the code that executed previously.

Maybe what you are really after is to use FBs and define STATs in stead of TEMPs. Beware that TEMPs in FBs behave the same as TEMPs in FCs.

STL??? · Nov 10, 2009

You must condition/intialise/write to all your Temp variables before reading them otherwise what you are seeing will happen.

If you need to store Data between scans for each instance then i suggest using a multiple instance FB and static variables.

Edit: too slow

wordless · Nov 10, 2009

Thanks

I think it's very simple for CPU to reset all temp variables in the block when function exit. I don't know but I think it's far from definition of function!

by the way, thanks for your reply. I'll work on FC to initiate temp variable. I'll test it and then if system worked, I'll switch to FB implementation.

L D[AR2P#0.0] · Nov 10, 2009

Post the source code for FC5

Problem with "Temp Variable” in FC blocks

wordless

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JesperMP

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STL???

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wordless

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L D[AR2P#0.0]

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