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Strane behavior of +R

Created by: Goran_ at: 7/10/2011 11:35 AM (15 Replies)

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7/10/2011 11:35 AM	Rate (0)
Goran_ Posts: 141 Rating: (0)	I have simple mathematical operation. All DBDs are declared as REAL in data block. L db1.dbd0 L db1.dbd4 +R T dbd1.dbd4 and for test I will add another one L db1.dbd0 L db1.dbd104 +R T dbd1.dbd104 If both db1.dbd4 and db1.dbd104 have the SAME starting value, then they will continue to have the same value all the time. However, if I put next starting values: db1.dbd4 = 0.0 db1.dbd104=1000.0 one should think that through the program execution the difference between the two would always be 1000.0 .However, this is not true, and the value in db1.dbd104 increases much faster than in db1.dbd4. PLC cycle time is 5ms, but I dont think it should matter. And the higher the starting value of dbd104, the bigger the difference becomes during execution. Does anyone have an idea why is this happening? Best regards, Goran
Goran_ Posts: 141 Rating: (0)	Last edited by: Goran_ at: 7/10/2011 11:43 AM
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7/10/2011 11:50 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 5/26/2023 Posts: 6802 Rating: (1345)	Goran_ I have simple mathematical operation. All DBDs are declared as REAL in data block. L db1.dbd0 L db1.dbd4 +R T dbd1.dbd4 and for test I will add another one L db1.dbd0 L db1.dbd104 +R T dbd1.dbd104 If both db1.dbd4 and db1.dbd104 have the SAME starting value, then they will continue to have the same value all the time. However, if I put next starting values: db1.dbd4 = 0.0 db1.dbd104=1000.0 one should think that through the program execution the difference between the two would always be 1000.0 .However, this is not true, and the value in db1.dbd104 increases much faster than in db1.dbd4. PLC cycle time is 5ms, but I dont think it should matter. And the higher the starting value of dbd104, the bigger the difference becomes during execution. Does anyone have an idea why is this happening? Best regards, Goran Hi Goran Check this, also please provide more information! Would you please check your program in a cyclic manner (each 100ms).update the results. How accurately can I calculate with REAL numbers that are used in extensive formulas? Regards
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7/10/2011 12:26 PM	Rate (0)
Goran_ Posts: 141 Rating: (0)	hdhosseini Goran_ I have simple mathematical operation. All DBDs are declared as REAL in data block. L db1.dbd0 L db1.dbd4 +R T dbd1.dbd4 and for test I will add another one L db1.dbd0 L db1.dbd104 +R T dbd1.dbd104 If both db1.dbd4 and db1.dbd104 have the SAME starting value, then they will continue to have the same value all the time. However, if I put next starting values: db1.dbd4 = 0.0 db1.dbd104=1000.0 one should think that through the program execution the difference between the two would always be 1000.0 .However, this is not true, and the value in db1.dbd104 increases much faster than in db1.dbd4. PLC cycle time is 5ms, but I dont think it should matter. And the higher the starting value of dbd104, the bigger the difference becomes during execution. Does anyone have an idea why is this happening? Best regards, Goran Hi Goran Check this, also please provide more information! Would you please check your program in a cyclic manner (each 100ms).update the results. How accurately can I calculate with REAL numbers that are used in extensive formulas? Regards Hi, hdhosseini yes, I am running it currently with 0.1s cycle, so I am 100% sure it works correctly at that cycle, but I am concerned about other mathematica operations in program. I will need to find way to set minimum cycle time in PLC, but I read in manual that for S7-300 PLC this property is not relevant. But better first read the article you have provided to see what exactly are "extensive formulas". Thanks.
Goran_ Posts: 141 Rating: (0)	Last edited by: Goran_ at: 7/10/2011 12:27 PM
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7/10/2011 1:22 PM	Rate (0)
Goran_ Posts: 141 Rating: (0)	Link you have provided doesnt solve my problem. Is there a way to set minimum cycle time for 315-2 DP OB1? This property is greyed out on my PLC...
Goran_ Posts: 141 Rating: (0)
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7/11/2011 8:21 AM	Rate (0)
Aret Posts: 2348 Rating: (259)	Are these parts of code in the same OB? Feels like not - could you clarify? Also you can check it in debug mode on PLC or turn "run one cycle" option if you use PLC-Sim. Maybe contents of DBD0 are different for these parts.... If doesnt help - please upload your project here.
Aret Posts: 2348 Rating: (259)
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7/11/2011 10:22 AM	Rate (0)
MM1234 Posts: 270 Rating: (52)	I hope nobody noticed the post I made here before, damn too sleepy, sorry if I confused anyone, lol .)
MM1234 Posts: 270 Rating: (52)
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7/11/2011 12:28 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 5/26/2023 Posts: 6802 Rating: (1345)	Hi I suggest to check the logic online and track the variables with (for example ) Autem PLC analyzer and then discuss the values in each cycle; http://www.autem.de/index.php?site=en_home Regards
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7/11/2011 2:53 PM	Rate (0)
Goran_ Posts: 141 Rating: (0)	Aret Are these parts of code in the same OB? Feels like not - could you clarify? Also you can check it in debug mode on PLC or turn "run one cycle" option if you use PLC-Sim. Maybe contents of DBD0 are different for these parts.... If doesnt help - please upload your project here. Hi, Aret, yes they are, they are in the same function, which is called by OB1. Example, code is in FC1, and FC1 is called only from OB1. DB1.dbd0 in my project contains impulse from encoder, which I am using in calculations to calculate new length. So, the structure goes sometrhing like this: NW1: taking the value from encoder, and doing calculations, which are transfered in db1.dbd0 NW2: here I have code I have posted above. Is it possible at all for DB1.dbd0 to be different in this situation?
Goran_ Posts: 141 Rating: (0)
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7/11/2011 2:56 PM	Rate (0)
Goran_ Posts: 141 Rating: (0)	hdhosseini Hi I suggest to check the logic online and track the variables with (for example ) Autem PLC analyzer and then discuss the values in each cycle; http://www.autem.de/index.php?site=en_home Regards I am working on a real PLC, so its online. If I track the variables, I can see that the difference changes. Example: L db1.dbd0 L db1.dbd4 +R T db1.dbd0 L db1.dbd0 L db1.dbd8 +R T db1.dbd8 if, both variables db1.dbd0 and dbd8 have the same starting value (ex 0), they will always have the same value. so this proves that db1.dbd0 is the same in both calculations. If I set db1.dbd8 to be 5000, then its value grows faster than db0 does.
Goran_ Posts: 141 Rating: (0)
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7/11/2011 4:25 PM	Rate (0)
Aret Posts: 2348 Rating: (259)	Sure it does - please look carefully L db1.dbd0 L db1.dbd4 +R T db1.dbd0 // in your initial example here was dbd4 L db1.dbd0 L db1.dbd8 +R T db1.dbd8 So the question is - what piece of code corresponds PLC programm - this one or initial?) Also you can modify your code- L db1.dbd0 T MD100 // temp variable L db1.dbd4 +R T db1.dbd0 L db1.dbd0 T MD104 // temp variable L db1.dbd8 +R T db1.dbd8 L MD100 L MD104 -R T MD108// temp So if your value inside MD108 is not 0 then DBD0 is different for different parts - you should search why.
Aret Posts: 2348 Rating: (259)	Last edited by: Aret at: 7/11/2011 4:28 PM
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