Safety application

Hi, I have to store my actual process data in case a PLC shuts down unexpectly. Now is the question how can I do this the best. I assume I need to store it in a DB, and then after the power is turned on I can read the data from this DB and start the process from the point it stopped. Does anyone has experience in programming such safety applications and could tell me the way he develops his programs? How is called such an application, I know a name in German - Nullspannungsicher, in English - Zero Voltage Safety?

Hi Martin, I normally continously store important registers to memoryintegers when the power up bit is --|/|-- not, and restore with first scan or with power up bit, but that is the easy part.To start a process exactly where it stops is sometimes very tricky because of things dont realy stops in a second when the power turns off and you can loose some input information, but that of course depend on the process. In some cases I would use the power up bit in combination with "process normally shut down bit" to start its own emergency start up subrutine and fine-tune it to the prosess.

Jack

Thanks jwh, now I consider to use SFCs to safe my data. But so far I found sfcs that cannot be used continously, because they write to MMC. I will have a look in internet for auch a safety programs, but I will be grateful for any hints how to write my program.