TIA PID Compact control

Hi,
I am testing compact pid control. i used %MD0 (Real) as a set value. but when i modify the value then it does not change properly. check the picture. i put 50 but its showing 47 point something. then again inserting some value but it does not change. what is the problem? may be i am doing something wrong. kindly help i am new in TIA portal.

Thanks

Is that memory word used elsewhere?

What is that Tank function doing? Is the SetValue an input or InOut variable that is perhaps changed inside the Tank block?

cardosocea said:

Is that memory word used elsewhere?

What is that Tank function doing? Is the SetValue an input or InOut variable that is perhaps changed inside the Tank block?

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not used anywhere. setvalue is an input of the pid.

Have you use M0.0 - M, or MB0, or MW0 anywhere. A value doesn't change itself, if you enter 50 and it changes it to 47.xxx then something else is accessing that memory. Actually looking at your pictures you are referencing the same memory - MD0 and MD1 and MD2 overlap, if you are using MD0 then that covers memory locations 0,1, and 3, the next memory you can use is MD4. I am surprised that TIA Portal hasn't complained about the overlap.

BryanG said:

Have you use M0.0 - M, or MB0, or MW0 anywhere. A value doesn't change itself, if you enter 50 and it changes it to 47.xxx then something else is accessing that memory. Actually looking at your pictures you are referencing the same memory - MD0 and MD1 and MD2 overlap, if you are using MD0 then that covers memory locations 0,1, and 3, the next memory you can use is MD4. I am surprised that TIA Portal hasn't complained about the overlap.

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i think that is the problem. but why the md0 covers 0,1,2 memory locations?how to know that?

chandrapaul said:

i think that is the problem. but why the md0 covers 0,1,2 memory locations?how to know that?

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MD stands for Memory Double Word. A word is 2 bytes, meaning a double word is 4 bytes. I think the M technically stands for "Merker" in german, but I don't think that really means anything.

M0.0 references bit 0 of byte 0. M1.0 references bit 0 of byte 1. M0.1 references bit 1 of byte 0. MB0 references the whole byte 0, overlapping with M0.0 - M0.7. MW0 references the word starting at byte 0, meaning it overlaps with MB0 and MB1. MW2 references the word starting at byte two, so it overlaps with MB2 and MB3. If you declare a tag at MW1, it uses MB1 and MB2, which means it overlaps with MW0 AND MW2.

MD0 uses MB0-MB3.

The different ways of writing it only change how much data you're getting, it's all the same data area either way.

All that said: If you're using a 1500, I'd recommend declaring your global tags inside a data block. Then you don't have to worry about the addresses at all.

mk42 said:

I think the M technically stands for "Merker" in german, but I don't think that really means anything.

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Yes, Merker. From "etwas merken" -> "to memorize something"

Thomas_v2 said:

Yes, Merker. From "etwas merken" -> "to memorize something"

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Huh, good to know. Merker more or less just translates as memory then?