S7-400 CPU 414-5H Load Memory Sudden Increase

ry_fern

Member
Join Date
Jan 2008
Location
Caloocan City
Posts
44
Dear Experts,

We are currently in a project commissioning stage now of a Biomass Plant. The above mentioned CPU is used.

2 days ago, our load memory is only 42%. There were no major edits, only online monitoring and some bypassing of signals and adding some "always open" contact. When we checked the load memory again, we were surprised to see that it increased 67%. User memory is only 11%

I would like to ask for your opinion regarding the following:

1. Considering the minor changes, what other things could have caused the sudden increase in load memory?

2. Extra question, one bit, remains ON when the actuating switch is only momentary action and we are certain that it is not latching. I experienced this thrice (3X) already with Siemens systems. Because of the urgency, I wasn't able to find the root cause, only a work around. Now I'm experiencing it here again.

May I request for your technical opinion? It will be highly appreciated.

Thank you.

Ryan
 
If you go into STOP mode and Compress the memory, does it go back down?

Whenever you download a block in RUN, there must be enough space to receive the block again... which means the existing block and new block exist in the Load memory at least for some time. Can you send a screen shot of the Memory tab from the CPU's Module Information?
 
2. Extra question, one bit, remains ON when the actuating switch is only momentary action and we are certain that it is not latching. I experienced this thrice (3X) already with Siemens systems. Because of the urgency, I wasn't able to find the root cause, only a work around. Now I'm experiencing it here again.

No experience on the memory question.

For your 2nd question, there is always a cause for something like that, but they can sometimes come from crazy places.

Is the bit that is sticking on the input, or is it in a DB (or M memory)? If the input bit itself is sticking on, I'd recommend checking the LED on the card, as well as the physical wiring with a meter. You might also want to make sure it is in a process image, as opposed to being part of the periphery. If the input bit responds correctly, then I guess you either need to cross reference on your internal bit, or hope you haven't screwed up in some STL pointers somewhere.
 
Sigmadelta,

Attached is my screenshot yesterday, I now have a 14% load memory. We are doing the same things that we did 2 days ago, minor edits, PIDs in Auto Mode, pumps are running.

mk42,

The bit is inside a DB. It is a button linked to the HMI to start the pump. We are certainly sure that it is not being shared. However, we'll still double check our references. Can you clarify the idea you mentioned about the periphery?

Thank you.

Memory area.png
 
The bit is inside a DB. It is a button linked to the HMI to start the pump.

What function are you using on the HMI? Is it "Set Bit in Tag" or "Set Bit"?

Right click the address in your logic, and choose Go To -> Location, and it will show you a cross reference of where the address is used. Click the checkbox "Overlapping locations" to see if this bit is a part of a byte, word or double-word that is being used elsewhere in a write instruction.
 
In SIMATIC Manager, right-click on the Blocks folder, and click Properties, then select the Blocks tab it will show you how much load and work memory should use. However, I believe downloading of blocks in RUN mode will increase this amount. I am not sure how/when the CPU operating system decides to delete the replaced blocks in the load memory RAM... it could be on a restart of the CPU.
 
Maybe I'm misunderstanding the memory issue, but that shows you have 14% USED, not 14% available. What's the problem? You have tons of space to spare.

On the periphery, I was saying that if the bit you were concerned about was inside the process image (updated every scan, accessed by I6.0) or in the periphery (only updated when accessed by PIW300). Complicating things, the 400H often uses many Process Images, updated with different OBs. My concern is that the IO bit might be updating slower than expected, or not at all if you access it wrong.

If the bit you're concerned about is in a DB, then that isn't an issue. Can you take a screenshot of the code (while monitoring), so we can see the error?
 
@Sigmadelta,

The only reason that we can think of with the sudden increase in load memory is the online edits we made. I believe this is the same thing that you were saying in your previous reply.

@mk42,

Yes, we have 14% memory and plenty to spare but what puzzled us is the sudden increase in the load memory that spiked up to 67%.

I'll keep you updated if we find something.

Thank you.
 

Similar Topics

I can't replace cpu S400 416-3XR05-0AB0 BY 416-3ER05-0AB0 in PCS7 Project when using replace object to keep the original configuration in the...
Replies
4
Views
1,482
Hi All, I have a project that lets me control a Movimot drive via Profibus DP. A quick search on google learned me that a lot of information...
Replies
12
Views
2,641
Hi, does anyone knows what is the problem on an S7-400 cpu in case all the leds are constantly on (not blinking, I think in this case it that...
Replies
8
Views
7,145
I want to replace the exisitng CPU card of our S7 plc with spare card of similar type. Is it as simple as just remove old one after switching off...
Replies
1
Views
1,529
I have a defective S7-400 CPU 412 (6ES7 412-2XG00-0AB0) now can i replace it by CPU 414 (6ES7 414-2XG03-0AB0) without changing the program of the...
Replies
4
Views
5,004
Back
Top Bottom