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Chosing Decentral Peripherie for time critical application

Created by: Saruca at: 6/7/2011 9:44 AM (11 Replies)

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6/7/2011 9:44 AM	Rate (0)
Saruca Posts: 122 Rating: (1)	Hi everyone, I'm designing a network for controlling a time critical conveyor application. I would need to obtain a response in about 20 miliseconds. I takes around 10 miliseconds for the actuator to respond so that leaves me another 10 miliseconds for the network. I've been looking at different options and I would like some help chosing the fastest one. I will be using a S7-314C 2DP/PN CPU as an IO Controller but I don't know the best option for controlling the actuators I have. The budget is not too big so I need to save as much as I can. One of my options is using a ET200M with a PROFINET communication module, a digital input module and a digital output module. The other option is connecting a S7-1214C CPU as an IO Device. The problem I have with the S7-1200 series is that is not possible to simulate the programs, am I right? There is no simulator yet. What option do you recommend me? Can you think of any other faster options? Thanks in advance
Saruca Posts: 122 Rating: (1)
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6/7/2011 1:37 PM	Rate (0)
gre_m Posts: 947 Rating: (45)	Profibus with 12Mbod, more speedProfinet with new asic. On support you can find excel-macros for determine time
gre_m Posts: 947 Rating: (45)	Last edited by: gre_m at: 6/7/2011 1:40 PM
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This contribution was helpful to 1 thankful Users Saruca

6/7/2011 3:40 PM	Rate (5)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/8/2023 Posts: 2969 Rating: (1025)	Hello Saruca your overall reaction time with decentralised peripherycomprises of: 1.) Input card delay (up to 4.8ms for a standard DI card !) 2.) Backplane transmission time from DI card to IM (~1ms) 3.) Profibus/Profinet update/scan time (depends, assume 1 ms if you only have one ET200M at 1.5Mbps, do a test HWconfig and seeTtr typical in the bus properties) 4.) Program processing in CPU (depends, lets assume 5-10ms) 5.) Profibus/Profinet update/scan time (depends, lets assume1ms) 6.) Backplane transmission time from IM to DQ (~1ms) 7.) Output card delay (typical < 0.5ms) This can add up fast as well asbeing a non-deterministic so my suggestion in your case is: Use a HardwareInterrupt capable DI card (e.g. 6ES7321-7BH01-0AB0) OR use the onboard hardware interrupt DI's of your 314-2C CPU and have a look at the FAQ below for more on this: What is a hardware interrupt and how do they work in the S7-300 system? If you use a Profibus DP remote I/O Station, consider using Isochrone mode to achieve reproduceable (or deterministic)reaction times and see theFAQbelow for more on this: Isochrone Mode Have also a look at the SIMATIC S7-300 Automation System Module Data manual to find out DI and DQ reaction times (for completeness, ET200M backplane update times are in chapter 10.5 of theSIMATIC Distributed I/O device ET200M manual). Last but not least, chapter 6 of the SIMATIC S7-300 CPU 31xC and CPU 31x: Technical specificationshas all the general details on how to calculate reaction times. I hope this helps
	Last edited by: fritz at: 6/7/2011 3:54 PM typos 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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6/7/2011 4:42 PM	Rate (0)
Saruca Posts: 122 Rating: (1)	Hi fritz! thank you so much for your excellent answer. I will take a good look at all the information you've given me and I'll post an answer as soon as I get to a conclusion. Thanks again
Saruca Posts: 122 Rating: (1)
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6/8/2011 9:16 AM	Rate (0)
Saruca Posts: 122 Rating: (1)	Hi Fritz, sorry to bother again but I'm confused about something... when you say DI card, are you referring to the DI module? I know DI stands for Digital Input but I had never heard about DI cards. Maybe it's a matter of translation and it's what we call "módulo" in Spanish. Thanks again
Saruca Posts: 122 Rating: (1)
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6/8/2011 9:53 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/8/2023 Posts: 2969 Rating: (1025)	Saruca when you say DI card, are you referring to the DI module? I amdear Saruca I suppose I should call them"modules" from now on though, moreso since Siemens uses theacronym "SM" (Signal Module) for them (the word "card" is however commonly used as well).
	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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This contribution was helpful to 1 thankful Users Saruca

6/8/2011 11:36 AM	Rate (0)
Saruca Posts: 122 Rating: (1)	Thanks Fritz! It's good to know that you can refer to DI modules also as cards. Searching through the forum I've seen it many more times. By the way, your answer to my question was fantastic but you didn't say anything about the second option, using a S7-1214C CPU. Do you think it's better to use the ET200M? I think so but I'm no expert Thanks again
Saruca Posts: 122 Rating: (1)	Last edited by: Saruca at: 6/8/2011 11:46 AM
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6/8/2011 3:15 PM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/8/2023 Posts: 2969 Rating: (1025)	Hello Saruca tough call to say which solution is the better one. The previously outlined reaction time principles also apply to a 1200. Having said that, compared to an ET200M solution you save yourself the bus update time. Since the 1200 also has onboard interrupt capable inputs, it may indeed be a good choice, remember though that you need TIA Portal to program it. Questions for you: 1.) What exactly is the application and why do you (or your customer) need this short reaction time? 2.) Is this a safety related application (in which case you can not use the 314 nor the 1200 which does not yet support it.Even if you'd had anF CPU your reaction times with Safety Integrated will beconsiderablylonger than the 10ms thatyou need). P.S: I mentioned Isochrone mode in my previous entry but failed to mentionthat it can NOT be used with your 314 CPU (it doesn't support it, sorry).
	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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This contribution was helpful to 1 thankful Users Saruca

6/9/2011 10:05 AM	Rate (0)
Saruca Posts: 122 Rating: (1)	Hi Fritz, in my application I need to control a sorting mechanism in a conveyor belt. It has to be able to change its position aproximatedly every 20ms. That's very fast, I know. If I can't reach those times at the end I would have to increase the 20ms anyway that I can. It's a big conveyor belt, that's why I had decided to use a S7-300 as an IO Controller and then an ET200M to connect the sorting mechanisms and the sensors and actuators. I will need to implement a safety network for emergency stops but I will have to do it the old-fanshioned way because with our budget we can't afford safety integrated CPU and modules. I see CPU 314C-2 PN/DP doesn't support Isochronous mode for the RS485 interface but for PROFINET, the technical data says that Isochronous mode is supported, OB61. I don't understand it. Does it mean that Isochronous mode works in that CPU as interrupts? Technical data CPU 314c-2 PN/DP Thanks again . You're helping me a lot.
Saruca Posts: 122 Rating: (1)
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6/9/2011 10:12 AM	Rate (0)
Saruca Posts: 122 Rating: (1)	I see that the next CPU available with integrated communications is 315-2 PN/DP and it supports Isochronous mode both in PROFIBUS and PROFINET and also through OB61...so I'm gessing that's how all the CPUs work? I'm going to look into it and try to understand how Isochronous mode works.
Saruca Posts: 122 Rating: (1)
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