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Choosing the right CPU

Created by: iman12 at: 4/21/2014 8:47 AM (10 Replies)

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4/21/2014 8:47 AM	Rate (0)
iman12 Member Joined: 5/26/2012 Last visit: 8/4/2021 Posts: 16 Rating: (0)	Hello everybody, I have a logic and I want to choose a right CPU from S7-300 or S7-400. But in term of cycle time and memory size, I have some problem. In cycle time, I don't know which CPU to choose in term of processor speed. In fact, I don't know how to estimate the execution time of my logic and other peripheral tasks and consequently choose the right CPU with suitable process speed. In term of Memory also I have problem. I don' know how to estimate the size of my logic. or also does the number of I/Os affect my memory size?? By the way, my I/O number is near 300.

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4/21/2014 9:37 AM	Rate (0)
IBN-Service Posts: 8946 Rating: (1000)	Nobody can advice you because we dont know your program. If you know size of program, you can estimate by using the scantime per 1k operation. Using 400 CPU is mostly more expensive and need more place. 319 CPU is very very fast and has big size of memory. Faster and bigger than a 412 CPU. But no so much expandable.
IBN-Service Posts: 8946 Rating: (1000)
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4/21/2014 10:42 AM	Rate (0)
iman12 Member Joined: 5/26/2012 Last visit: 8/4/2021 Posts: 16 Rating: (0)	IBN-Service Nobody can advice you because we dont know your program. Is not possible for me to estimate the size of my program in KB? I mean, is there any references on the required capacity for each instruction and operation?

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4/21/2014 2:06 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (1000)	Have a look at Operation list of CPU. But if you have no program, in what way you will do calculation? Or is the program is already finished? Than you can check program size in Blocks -> Properties
IBN-Service Posts: 8946 Rating: (1000)
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4/21/2014 2:36 PM	Rate (0)
iman12 Member Joined: 5/26/2012 Last visit: 8/4/2021 Posts: 16 Rating: (0)	Thank for your response. In fact, I have the logic but I haven't writen it in ladder logic or FBD so far. So you mean, I have to write it in STEP 7 and then estimate the size of program. Am I right?

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4/21/2014 2:40 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (1000)	Yes, that is my advice to get a chance finding out the consumtion of memory and scantime. In what way you have the logic? Perhaps you can do an upload to forum to give us a chance to find out what CPU Family is a right selection?
IBN-Service Posts: 8946 Rating: (1000)
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This contribution was helpful to 1 thankful Users Ste39

6/1/2014 9:55 PM
K C Das Posts: 114 Rating: (12)
K C Das Posts: 114 Rating: (12)
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6/1/2014 10:10 PM
KIRAN_DABHI Posts: 60 Rating: (8)	for choosing the cpu , first you have to decide which facility you want? because on basis of this cpu is selected.then which type of communication you needed? because each cpu has own features.some works only on MPI,some works on profibusor ethernet etc. this things also considered. then what is your application?what fuctionality you needed in logic?on basis of this size is calculated for memory. REGARDS, KIRAN DABHI
KIRAN_DABHI Posts: 60 Rating: (8)
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6/2/2014 6:55 AM	Rate (0)
S7 AUTOMAN Posts: 515 Rating: (56)	iman12 Hello everybody, I have a logic and I want to choose a right CPU from S7-300 or S7-400. But in term of cycle time and memory size, I have some problem. In cycle time, I don't know which CPU to choose in term of processor speed. In fact, I don't know how to estimate the execution time of my logic and other peripheral tasks and consequently choose the right CPU with suitable process speed. In term of Memory also I have problem. I don' know how to estimate the size of my logic. or also does the number of I/Os affect my memory size?? By the way, my I/O number is near 300. perhaps the post by Dchartier in the following thread might help you Controller Comparison Sheet
S7 AUTOMAN Posts: 515 Rating: (56)
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6/9/2014 12:05 AM	Rate (0)
Justin fronik Posts: 2 Rating: (0)	I agree that the 319 PLC is the most efficient and cheap way to solve your problem I think hope you will find a way to use this CPU.
Justin fronik Posts: 2 Rating: (0)
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