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maximum capacity of cpu

Created by: nimalak at: 10/1/2012 2:50 PM (6 Replies)

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10/1/2012 2:50 PM	Rate (0)
nimalak Posts: 21 Rating: (0)	dear experts is there a way to understand how a plc is good ijn executing a program.i mean execution capacity.How to see if a program reachs 70% maximum capacity of cpu? Thanks a lot
nimalak Posts: 21 Rating: (0)
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10/1/2012 3:00 PM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 11/18/2024 Posts: 5697 Rating: (715)	Hello, In the Module Information (CTRL + D) there are 2 Tabs that can tell you more, one is the memory tab other is the Scan cycle time. Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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10/1/2012 7:50 PM	Rate (0)
nimalak Posts: 21 Rating: (0)	cpu information can not help me.i can change the max execution time.Where can i find this max for each cpu?
nimalak Posts: 21 Rating: (0)
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10/1/2012 8:19 PM	Rate (1)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 11/18/2024 Posts: 12294 Rating: (2691)	Hello nimalak; Do you mean the "scan time" of your CPUs? There is a way to regulate the scan time so as to avoid runtime errors; the watchdog timer will be called if you exceed the maximum scan time configured in the CPu, and will shutdown the PLC with errors. SIMATIC Programming with STEP 7 V5.5 *23.7.1 Checking Scan Cycle Times to Avoid Time Errors* The "Scan Cycle Time" tab in the module information gives information about the scan cycle times of the user program.If the duration of the longest cycle time is close to the configured maximum scan cycle time, there is a danger that fluctuations in the cycle time might cause a time error. This can be avoided if you extend the maximum cycle time (watchdog time) of the user program. If the cycle length is less than the configured minimum scan time, the cycle is automatically extended by the CPU/FM to the configured minimum cycle time. In the case of a CPU, the background OB (OB90) is processed during this extended time (if it has been downloaded). *Setting the Scan Cycle Time* You can set the maximum and minimum cycle times when you configure the hardware. To do this, double-click in the offline view of the configuration table on the CPU/FM to define its properties. You can enter the appropriate values in the "Cycle/Clock Memory" tab. You can also determine the runtime parameters of the cyclic OBs (OB 35 for s7-300, OB 30 up to OB38 for the largest S7-400) to ensure that the programmed functions in the cyclic Obs are treated within a determined time slice. You will use the cyclic OBs to program functions that are prioritary or that need to be called at very precise intervals (such ad the PID controllers).This is also explained in the manual cited above. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 10/1/2012 8:20 PM
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This contribution was helpful to 4 thankful Users ericson Ayman Elotaify Marcjan poya_xp

10/1/2012 8:58 PM	Rate (0)
nimalak Posts: 21 Rating: (0)	Thank you dchartier very completed answer.different cpus has different code execution capacity.i want to know how select this maximum scan time by each cpu type or only accept step7 value?
nimalak Posts: 21 Rating: (0)
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10/2/2012 2:25 PM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 11/18/2024 Posts: 12294 Rating: (2691)	Hello nimalak; The S7 program is made up of different functions, and each one can be called conditionnaly. That is, in one scan, FC25 (for example) could be executed, the conditions for it to run being validated. In the next scan this FC25 might not be called, as conditions for running it are not allenabled. Or you could have a communication function that operates over more than one scan (this is callred an asynchronous function) so scan time would increase a bit during the call of this communication block. So it is very difficult to try to "force" the CPU to execute all the functions inside a very rigid timeframe. I have had good experience with allowing the CPU to vary the scantime as it needs, within the limits you can setup in the CPU properties. And you can use the cyclic OBs to ensure that yourcritical frnctions will be called at very precise intervals. Hope this helps, Daniel Chartier

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10/7/2012 1:45 PM	Rate (1)
EDL AUTOMATION Posts: 51 Rating: (24)	Thanks Mr.Dchartier
EDL AUTOMATION Posts: 51 Rating: (24)
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