S7 CPU memory problem

Hi to everyone, I´m new here so if I´m doing something wrong please forgive me
I have a problem with my CPU 412 (Siemens). The problem is following:

Yesterday I was on project site and I saw the PLC. The problem that I saw is the folowing:
The CPU has one battery and the switch for the battery on the PLC is ON. I measured the voltage of the battery and it was 3,6 V, so that means that the battery is OK.

The next thing that I did was following:

I put out the flash memory card from the slot, and I shut down the main power and rise again. In this case the PLC (CPU) has a problem and couldn't start. When I shut down the power, the CPU didn't memorise the SW program, even though the battery is ON and OK. WHY this happened? I thought that when the power shuts down, battery helps the CPU to memorise the SW, and after when the power is ON again, the CPU start the SW without any problems, and without flash memory card.

Next step:

I put the flash memory card in the slot, and the procedure with the power, I did it again (Shut down, and start Up). With the flash memory card into the slot the CPU starts and there is no problems.

Can some one explane to me what is happening, please?

Thanks in advance

When you started the PLC with the memory card installed then the PLC loaded the program from the memory card and used that program.
You are fortunate that the program on the memory card was a valid program.
You should now check carefully that the program running now is up to date with any recent changes that may have been made.

Regarding your first attempt to restart the PLC. That was not a valid thing to do. Somebody had set it up with the memory card for program storage. When you removed it the PLC needs a new program to be loaded from somewhere. Basically you must decide to either use or not use the memory card. It is messy to swap back and forth between using it or not using it.

I have a proceedure I use for updating the memory card with the current program including operator setpoint changes etc.
I have posted it before on this site but could again if somebody is interested.

Attached proceedure "Writing to EPROM"

Hi John and thanks for your quick reply.

I did that because the costumer called me and said that when he losses power and the power comes again, the PLC doesn´t work properly.
So like I understood:when the power is back ON again, the PLC should load the program from the Flash memory card, isn´t that so? Just to mention, the Flash card was in the memory slot, but the program wasn´t Up to dated before this happens.
BUT this kind of situations were very offen (loss of power and back power on again) before too and before I didn´t have any kind of problems, even through the program wasn´t Up to date in to the Flash memory card. How did the PLC start then?
My question is: where does (if it does) the CPU memorize the program when there is a power loss and Up again, if there is no Flash Memory card?

thanks again

My question is: where does (if it does) the CPU memorize the program when there is a power loss and Up again, if there is no Flash Memory card?

To answer your question:
If the PLC is running with no Flash Memory Card then the program is stored in the PLC memory and will remain a valid program if the power goes OFF and ON but only provided the battery power is OK. (Note that the batteries do not recharge)

If you remove the Flash Memory Card from the running PLC it will STOP and will require a memory reset to restart. It will require a new program to be loaded either from a Flash Card or downloaded from Step7.