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What is a Difference Between F & H CPU's

Created by: S7Mgr at: 5/6/2010 6:33 AM (3 Replies)

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5/6/2010 6:33 AM	Rate (0)
S7Mgr Advanced Member Joined: 1/22/2008 Last visit: 2/10/2022 Posts: 77 Rating: (0)	Dear All, I have one question Q. What is a difference between F (Fault Tolerent) & H (Hot Standby) CPU's ? As by name we can make out some differences, but what is a true philosophy behind it i.e. any logical arguments. Helps appreciated, S7Mgr

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5/6/2010 8:00 AM	Rate (0)
Aristotelis Posts: 147 Rating: (34)	Hi I would suggest that F stands for "Fail-Safe" and H for "High Availability". I think "H" is referring to the redundant nature of the system. So by having a F-system, you have a fail-safe system but you do not have redundancy, i.e. if the CPU fails, then the system stops. If the system is H-system, then one can implement an F-function, but it is not necessary (however, if one does an F-function, then this is an FH-system). In this system you have redundancy, i.e. if one CPU fails you have the other to continue the process. Also, as far as I know, there are no "H" S7-300 CPU, it is only S7-400. Aristotelis
Aristotelis Posts: 147 Rating: (34)	Last edited by: Aristotelis at: 5/6/2010 8:09 AM
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5/6/2010 8:40 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 9/13/2024 Posts: 3020 Rating: (1054)	S7Mgr Q. What is a difference between F (Fault Tolerent) & H (Hot Standby) CPU's ? Hello S7Mgr Let's get some Siemens related acronyms sorted out first: F = Failsafe (the "F" does NOT stand for"fault tolerant"). S7 CPU'sfor "pure" Failsafe applications are315 F, 317 F, 319 F and 416 F and you'll typcially find these in Machine safety related application (sometimes also called Factory Automation Safety). H = High Availability (aka "Fault tolerant", even though this causes some confusion as it also starts with the letterF). High Availability system are based on a redudant architecture and can have a varying degree of redundancy/availabilty. S7 CPU'sfor High Availabilityapplications are412 H, 414 H and 417 H. Note that Siemens also offers a soSoftware Redundancy based system whcih can be used with 300's and 400's. This is however NOT a "H" system and can also NOT be combined with afailsafe application. F/FH = A combination of the two above (A Failsafe system withHigh Availability/Redundancy, aka "Failsafe and Fault tolerant" to continue the confusion)and you'll typcially find these inProcess safety related applications. S7 CPU'sfor High Availabilityin combinationFailsafe applications arethe same as the same as above (412 H, 414 H and 417 H). And here atwo Siemens related starting point links which have more on this subject: Functional Safety (which divides further into Factory Automation safety andProcess Safety) S7-400 H systems I hope this helps
	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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5/6/2010 11:49 AM	Rate (0)
S7Mgr Advanced Member Joined: 1/22/2008 Last visit: 2/10/2022 Posts: 77 Rating: (0)	Hi, Thanks for your replies. Small things, but sometimes much botherable. Regards, S7Mgr

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