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Updating cycle between CPU314C and IM151-1

Created by: andreadbx at: 10/23/2012 9:01 AM (4 Replies)

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10/23/2012 9:01 AM	Rate (0)
andreadbx Regular Member Joined: 5/10/2011 Last visit: 2/20/2023 Posts: 20 Rating: (0)	Hello, I want to ask only some informations. For this time I'm lucky and there are any problems. In my project there is a CPU314C-2DP (6ES7314-6CH04-0AB0) connected via profibus DP (speed 1.5Mbit/s) with an IM151-1 HF (6ES7151-1BA02-0AB0). Inside this decentral peripherie there are some 2AI U HS (6ES7134-4FB52-0AB0) used because the main feature is 0.1ms of updating cycle. My question is: The IM151-1 HF device update the values red by 2AI U HS every 0.1ms. The main program runs in OB1 inside CPU314C-2DP. How I can be sure I have the same updating cycle (0.1ms) when the traffic pass through profibus network? In which time the values comes updated from IM151-1 HF inside OB1? Thank you in advance for informations
	Best regards Andrea
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10/23/2012 9:35 AM	Rate (0)
daad Silver Member Joined: 10/31/2011 Last visit: 5/29/2023 Posts: 400 Rating: (5)	Dear andreadbx, According to my knowledge the functionality of AI is .1 ms update its value but CPU consider the value every scan cycle during IO read part.To access the value after a specific time you have to use separate process image and read analog value after every time by reading this process image part as you require. Regards

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10/23/2012 10:06 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/1/2023 Posts: 2966 Rating: (1025)	Hello andreadbx Even though the 6ES7134-4FB52-0AB0 does offer 0.1ms update time per analogue (or 0.25ms worst case if both channels are used), you won't be able to get values updated this fast in your PLC program for a number of reasons, including: 1.) Backplane transmission time from AI card to IM151-1 (at least ~0.2 ms if you have only one 2ch AI module by itselfin the ET200S rack, see chapter 5 of the IM151-1HF manualfor more) 2.) Profibus update/scan time (depends on baudrate and number OF DP Slaves and their I/O's, but at least another 0.2ms if you only have one ET200S with only one 2ch AI module in it at 1.5Mbps, do a test HWconfig and see Ttr typical in the bus properties). 3.) Program scan time in 314C-2DP CPU. The good news is though that you will most likely always have a new AI value every program scan. The question is though, what do you intend to do or why doyourequiresuch a fast AI (assuming the above update times are not fast enough). I hope this helps and below isa link with additionalinfo Chosing Decentral Peripherie for time critical application
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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10/23/2012 10:08 AM	Rate (0)
andreadbx Regular Member Joined: 5/10/2011 Last visit: 2/20/2023 Posts: 20 Rating: (0)	Thank you for this answer. So, if I understand good i.e. every 12ms (depend on CPU cycle time) there is a complete refresh about device and component in profibus network. We suppose to add in this project some other component like Sinamics and other device in profibus network. The situation became worst than before because CPU314C-2DP need more time to refresh all IO. Anyway the real time to read my AI HS is the cycle time of CPU, if special image process is not used.
	Best regards Andrea
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10/28/2012 9:22 PM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/1/2023 Posts: 2966 Rating: (1025)	andreadbx So, if I understand good i.e. every 12ms (depend on CPU cycle time) there is a complete refresh about device and component in profibus network. Hello andreadbx the CPU refreshes all Inputsof the Process Image before it starts a newOB1 scan. For this it will though use whatever latest Input values are available at the time of the Process Image update as the CPU scan is independent of the Profibus scan which is independent of the I/O station update itself (unless Isochrone mode is used which is though not available in your 314C CPU). Have a look at the Isochrone mode manual for more on this and attached is also a pic from it that describes the update when you use "Unsynchronized processing cycles". Should your Profibus scan be considerably faster than your PLC scan you canget access to "newer" Input valuesby doing peripheral access and theFAQ Where and when do you need peripheral addressing?has more on this. You'd then for example call the Block that handles the "fast" AI's numerous times throughout OB1. Alternatively,put in a cyclic Interrupt OB that is called let's say every 5 ms to improve reaction times. I hope this helps Attachment Unsynchronized processing cycles.jpg (91 Downloads)
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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