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Actual data loss in datablocks after power failure??

Created by: KGI at: 1/28/2011 3:21 PM (6 Replies)

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1/28/2011 3:21 PM	Rate (0)
KGI Posts: 64 Rating: (0)	On 02OCTt2010 somebody from our maintenance department has switched the power of from the PLC. A day later we noticed that all the configurable parameters that can be changed from the operating panel where changed. How is this possible with this CPU (315-2AG10-0AB0)that contains a MMC card? I thought that when there is a power loss on the CPU, the CPU makes a copy from the data blocks from the working memory to the load memory (MMC). When the power is back on, the CPU is copying the DB's back to the working memory (and other blocks) so the CPU is running with the same parameters as before the power loss....Is my thinking correct? In attachment the diagnostic buffer of the CPU. ps X 8, 9 ,10 Hardware version of CPU = 7 Firmware version of CPU = V2.6.6 Bootloader Firmware expansion A0.21.0 Attachment Diagnostic buffer AUT-002 on 23dec2010.pdf (209 Downloads)
KGI Posts: 64 Rating: (0)
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1/28/2011 3:27 PM	Rate (0)
UMENCHO Diamond Member Joined: 3/21/2006 Last visit: 4/12/2023 Posts: 10221 Rating: (1176)	Hello, Look at What is the effect of the STEP 7 function "Copy RAM to ROM"? When you perform the "Copy RAM to ROM..." function, the runtime-relevant data blocks are copied from the main memory to the MMC. Here the actual values of the data blocks are overwritten on the MMC so that after an overall reset new initial values (the new actual values) are effective. These new initial values are displayed in SIMATIC STEP 7 in the "Actual value" column. I think now is clear the situation. Best regards, Hristo Mihalev
	Last edited by: UMENCHO at: 1/28/2011 3:28 PM
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1/28/2011 4:13 PM	Rate (0)
KGI Posts: 64 Rating: (0)	I did the following test: - a new DB with one variable with the value 100. - download to the CPU - change the actual value to 200. - power off - power on - value of the variable in the DB is 200. I didn't do a copy from RAM to ROM...
KGI Posts: 64 Rating: (0)
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1/30/2011 12:45 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/9/2023 Posts: 2969 Rating: (1025)	KGI A day later we noticed that all the configurable parameters that can be changed from the operating panel where changed. How is this possible with this CPU (315-2AG10-0AB0) that contains a MMC card? Hello KGI you are correct, DB's in S7 PLC's with MMC are generally retentive und you should not have "lost" their values. Nonetheless there are still a few things that can lead to a loss of DB values such as: 1.) Not enough memory left on the MMC to store the values of all retentive DB's 2.) DB's are created on PLC startup 3.) DB's are declared as non-retentive 4.) Someone did an overall reset of the CPU (which would shown be in your Diagnostics Buffer though and does not appear to be the case here) 5. ) Someone downlaoded the DB's (or whole program) after the power failure (which would NOT be shown in the Diagnostics Buffer) Below are a couple ofFAQ's which havemore info onthis: Retentivity behavior of S7-300 CPU 31x and complete devices C7-6xx with MMC How can you back up the actual values of DBs and bit memories? Last but not least, it is also conceivable that your HMI has a function or feature that overwrites the DB's after a power failure. I hope this helps and please let us know what you find
	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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1/30/2011 9:18 AM	Rate (1)
IBN-Service Posts: 8946 Rating: (995)	fritz ... you are correct, DB's in S7 PLC's with MMC are generally retentive und you should not have "lost" their values. ... There is another possibility: saving of DB values is only working, if the HP-capacitor inside the cpu is working. If the capacitor is damaged or also at very high or very low temperatures, it is possible that the CPU has not enough power after power failture to safe DB from RAM to MMC. This RAM-MMC moving only happens after power loss or oncopy request!
IBN-Service Posts: 8946 Rating: (995)
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2/7/2011 10:11 AM	Rate (0)
Testermax Posts: 159 Rating: (3)	Hello! After reading this post, I thought that I had a clear understanding for how the memory is retained. Following the links mentioned in the post, made me unsure by the way.... Do I or do I not need to run the "copy ram to rom" or the specified SFC to be sure to have the actual values in my DBs are retained after powerfailure? Or do I with regular intervals run the "copy ram..." function?
Testermax Posts: 159 Rating: (3)
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2/7/2011 10:39 AM	Rate (0)
KGI Posts: 64 Rating: (0)	What I understand of this issue is that the CPU is making automatically a copy from RAM to ROM when the CPU becomespowerless. It should be working like this because the MMC card is a replacement for the "old" backup mythology withbattery. I have done some tests with theCPU 6ES7315-2AH14-0AB0 (this isthe substitution type of the 6ES7315-2AH14-0AB0 CPUand the results of this test is that the data in data blocks is remanent. Remark. The CPU where I have a problem is the 6ES7315-2AG10-0AB0. Support services from Siemens (Belgium and Germany) told me to upgrade the firmware version. This should cover the problem. Still, to make sure I don't have hardware issues with this CPU a replaced the CPU with the 6ES7315-2AH14-0AB0 CPU. So in this case I'm sure that I don't have hardware problems and the firmware version is OK.
KGI Posts: 64 Rating: (0)
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