24VDC UPS with a leading fault output going to a hardware interrupt on the PLC that stops the PLC and then drops the power cleanly before the blackout/brownout hits the PLC.

All that's required then is to make sure the PLC is configured to start back up no matter the operating state before it lost power.

I use 24VDC UPS devices on my projects.  The criteria is they must keep the 24V DC "bus" high long enough for a controlled shutdown of the system, turn off 24V DC outputs, then trigger a PLC interrupt input so the PLC can issue a stop.

The only problem is if the power comes back after the PLC issues a stop and the UPS has not drained its power.

For a remote PLC, this may not be correct.  Instead, have the PLC simply sit idle as if it had no 24V supply until the 24VDC UPS powers up and issues an output stating the 24V UPS is OK.

Siemens offers several 24VDC UPS devices.

They are worth it for applications where blackout/brownout can cause real problems.

I would consider your PLCs going into stupid mode real problems.

Vippi

Now I can definitively exclude humans armed with SD card.
The same event happened once again in another site, but this time my colleague was present.
He reported a pump overload that caused a power failure. When they restored the line PLC was completely blank.

This time I could not simply reload program, diagnostic reported also another error message:
CPU error: Memory card evaluation error: Unknown or incompatible version of CPU configuration description
current card type: No memory card
Function finished/aborted, new startup inhibit set: ..
- Memory card missing, wrong type, wrong content or protected

I had to reset completely memory and execute a factory restore to be able to load program again.

Now I think we can assume that a power surge can occasionally in some way delete or damage CPU internal memory. Please let's find a way to avoid it, any suggestion for a hardware or software trick is welcome.

If 220V into the enclosure is connected to a UPS, is the 24V DC supply powered by the UPS or straight from the 220V?

Our 24VDC Supply is powered by 3 phase VAC, and the UPS simply connects at the output of the 24VDC supply.  The PLC is connected to the UPS.

We get around 30 seconds with a SFF PC, LCD monitor, basic panel HMI, and PLC powered from the UPS.  The PLC has an input that the incoming power is OK / Not OK, and that the UPS is in alarm mode.  When the incoming power signal goes away, the PLC stops all automatic mode processing, and brings things down quickly and safely.  If the UPS faults, the PLC turns everything off and sits idle, ignoring all requests, both from PC & HMI.

The UPS protects the PLC from brown outs.  The digital inputs protect the process from blackouts.

The combination has yet to place an s7-1200 into a bad state.

We did have one S7-1200 that went into a bad state, but after removing the S7-1200 from the DIN rail for ~30 minutes, we were able to factory reset and reload the project. That PLC did not have a UPS.  I did not design that system, just created the PLC / HMI logic / screens.  FYI, it has a UPS now.

Vippi

I'm not sure if 24V UPS can apply to our configurations: we usually use 220V CPU 6ES7 214-1BG40-0XB0 with relay outputs, and we already protect 220 V line with a UPS

I would bet Siemens uses different levels of "bullet-proofing" or error handling when transferring the entire project compared to updating a block or set of blocks.

To update the entire project, the plc is stopped, so consistency is not a problem.

To update live and keep the plc running, the amount of work the plc can do and keep all the new blocks separated and ready to install at the same time between scans, that may require a certain minimum bandwidth.  It is worth a question to Siemens HQ via Support Request to know the minimum bandwidth required to update s7-1200 PLCs.

Perhaps the next time you need to update the entire project, you can increase the amount of reserved memory for each block - provided you have plenty of memory to spare.

I think the default of 100 may not be enough, and I might be completely off in relating the bandwidth and the reserved memory which allows online updates in the first place.  Support Request.  Please post back what they say.

If it is in a document or manual somewhere, I would also like a link / reference (in case they offer one).

Vippi

Hati

Vippi

Could the memory have been damaged?
Or is it due to slow connection? Italian Vodafone turned off all 3G repeaters to increase 5G, and now old 3G routers can use 2G only...

 That has a huge influence on the transfer.

Sure.

But I would expect the connection error, not the system error.

And if I format and download hardware and firmware separately everything goes right. This sounds quite strange.