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Weekend data loss

Created by: acs1954 at: 5/10/2006 5:53 PM (6 Replies)

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5/10/2006 5:53 PM	Rate (0)
acs1954 Member Joined: 5/10/2006 Last visit: 8/8/2021 Posts: 3 Rating: (0)	Please help... I am counting boxes on a conveyor. The count value is in a DB. The power to the PLC is switched off each weekend. When it is switched on again, the count value has been reset to zero, but I want it to remember the current value when the power goes OFF. I have read that I need to somehow save the count value (DB) back to the MMC card, possibly using SFC84. Question... where can I get an explanation of exactly what SFC84 does, how to configure it, get an example ?. also, is it possible to program it so it only writes to the MMC when the power goes OFF. Is there another way to do this ?? Cpu is a 315 2DP regards...

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5/11/2006 9:12 AM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 11/11/2024 Posts: 8768 Rating: (1170)	Hello, If you' re using a CPU with MMC, it's important to know the firmware! If the firmware < 2, then a DB keeps automatically the actual value (retentive) If the firmware > 2, then the following: You can change the properties of the DB in Step7 (beginning with v5.2 + sp1) whether a DB at Power On/Off or RUN/STOP * keeps the actual value (retentive) * accepts the initial value (non retentive) Some information about SFC84, is found in the following manual: http://support.automation.siemens.com/WW/view/en/1214574 Ps: Be careful with writing to the MMC, because it's limited. Hope this will help you, Best regards Wizard

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5/11/2006 4:23 PM	Rate (0)
acs1954 Member Joined: 5/10/2006 Last visit: 8/8/2021 Posts: 3 Rating: (0)	Thanks, I will look at it again. The CPU firmware is V2.0. In the DataBlock properties... General part 2 At bottom of the window, are some tick boxes. One of the boxes is called "Non_Retain" This, and all of the other boxes are currently Un-Ticked. Should this be Ticked ? alan

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5/12/2006 8:57 AM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 11/11/2024 Posts: 8768 Rating: (1170)	Hi, The option 'non-retain' shouldn't be ticked. If the option is ticked, the db shouldn't be retentive. If your firmware is v2.0: ---------- Retentive behavior of a DB for CPUs with firmware < V2.1.0 For these CPUs, the contents of the DBs are always retentive at POWER ON/OFF or STOPRUN. ---------------- Hope it will help you Best regards, Wizard

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5/14/2006 2:47 PM	Rate (0)
acs1954 Member Joined: 5/10/2006 Last visit: 8/8/2021 Posts: 3 Rating: (0)	In order to try and understand the problem, I have tried to relate it to a PC Assume the following... One Monday morning a man goes to his desk PC, opens MS office and creates an Excel spreadsheet. He enters some data AND THEN HE SAVES IT. (The spreadsheet and its data gets saved to the Hard disk) For the rest of the day he enters/edits/modifies the data in the spreadsheet. BUT... HE DOES NOT SAVE IT AGAIN. During the afternoon there is a power cut. The PC goes OFF. His current data was only in the PC Ram, so the data is lost. When the power is restored he opens the spreadsheet again, but it opens with the data values that were originally saved in the morning. All his afternoon work is lost. Now, what he should have done was the make regular "saves", or configured Excel to save at timed intervals. Relating the above to the PLC, the MCC takes the place of the Hard Disk. The PLC has a "Work" memory that takes the place of the Ram. My count values are in a Data Block, which was initialy downloaded to the PLC and is saved on the MCC card. But at RunTime the PLC uses its work memory, and the current count is only in the work memory (or is it ?) The PLC does not automattically save the data from the Work memory back to the MCC card (or should it ???) If the power is turned OFF, the work memory is lost. The MCC still retains the original Data block, but with the original data values. When the PLC re-boots it starts with the original downloaded data. I believe I can use SFC84 to write the current data back to the MCC, but there is a limit to the number of "writes" so I cannot do this all the time. I would like to think that the PLC does not just stop dead, but that it has some sort of shutdown routine when the Power goes OFF, even if is only last for a few seconds. During this time can an OB block be used that detects the power loss, and can then save the data (using SFC84 ?). PLC is a S7 300 / 315 2DP firmware v2.0 Programmed using Siematic manager v5.3 +sp3

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5/15/2006 9:22 AM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 11/11/2024 Posts: 8768 Rating: (1170)	Hi, The PLC functions as follows: When the power is cut off, the actual value's of the DB are saved on the MMC. Find out in the following links: http://support.automation.siemens.com/WW/view/en/17602317 http://support.automation.siemens.com/WW/view/en/22295462 And the following manual, explains the retentive area's of the S7-300: http://support.automation.siemens.com/WW/view/en/12996906 See chapter 4. Hope this will help, Wizard

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7/3/2006 11:26 PM	Rate (0)
Siemen-Stains Posts: 101 Rating: (0)	I had a weekend data loss last week.yeh i cant remember a thing. I attribute that to copious amounts of alcohol.[;)]
Siemen-Stains Posts: 101 Rating: (0)
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