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The difference between internal tag and external tag when assigning with a variable!

Created by: Viet An at: 12/14/2008 7:08 PM (4 Replies)

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12/14/2008 7:08 PM	Rate (0)
Viet An Posts: 10 Rating: (0)	Hi all, I have a project using WinCC V5.1. I used C function to write the program.I have 2 tags; One is an external tag (Floating-point number 32-bit IEEE 754), one is an internal tag (Floating-point number 32-bit IEEE 754). I have a variable in C function. Then I used GetTagFloat command to assign the value from variable to tag. I used GetTagFloat to assign variable to an internal tag and an external tag. But the value of internal tag is difference with external tag when I display them. Please help me! The program detailed follow as: ukk=netout; temp=10000*ukk; // temp is a variable. SetTagFloat("MD18_ValueAO",temp);//Return-Type :BOOL // MD18_ValueAO is external tag. SetTagFloat("temp",temp);//Return-Type :BOOL // temp is internal tag. Please Help me! , I'm waiting for your reply.
Viet An Posts: 10 Rating: (0)	Last edited by: Viet An at: 12/14/2008 7:41 PM
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12/15/2008 11:35 AM	Rate (0)
automali Posts: 6 Rating: (2)	What is the difference between internal tag and external tag - example? You can use: SetTagDouble("MD18_ValueAO",temp);
automali Posts: 6 Rating: (2)
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12/16/2008 3:52 AM	Rate (0)
Viet An Posts: 10 Rating: (0)	Hi automali, Thank you a lot. My program used while loop to computing a variable. I assign the varialbe with internal tagand externaltagbut the value of them displayedare different. The value of internal tag is accurate than the value of external tag. I think this difference have a cause from the speed computing of WinCC is faster than CPU S7-300.When program used internal tag then it used speed of computer. If I used external tag then WinCC read valuefrom CPU S7-300. Once again, thank you. I'm waiting for your reply. BestRegard.
Viet An Posts: 10 Rating: (0)
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12/16/2008 1:13 PM	Rate (0)
automali Posts: 6 Rating: (2)	Hi What type is MD18_ValueAO in CPU? I have problem in that program: float pom=2.34; int zapis; pom=pom100; SetTagWord("int_zmienna",pom); then in CPU int_zmienna = 233 :-) When I use double pom it is OK 2,34100=234;
automali Posts: 6 Rating: (2)
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12/16/2008 5:28 PM	Rate (0)
Viet An Posts: 10 Rating: (0)	Hi automali! Thankyou for your reply. When I used internal tag then the updated value is very fast but I used external tag then updated value is very very slow. The value of internal tag is updated immediatly, but the value of external tag isn't updated immediatly. Very very very very slow, the value of external is updated. I crazy with this problem. Because I used "while loop" to computing a variable. Then I export them to external tags.. Thank alot. I think I must used another hardware and software to do it. Eg: Matlab or Labview using I/O Cards to communicate with actuactors. I try doing it with 2 type PLCs: S7-200 and S7-300, but not ok. Once again, thank you very much.
Viet An Posts: 10 Rating: (0)
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