CPU Stop

Hi,

Yesterday I had a PLC going into stop, and the reason why is not clear for me.

In the diagnostic buffer (in atachment) I found event 147 Maintenance demanded: Safety program: Warning limit cycle time exceeded Event ID: 16# 0D:75ED

event 146 Error: PROFIsafe communication failure (timeout)  Event ID: 16# 08:0318

event 145 Temporary CPU error: Maximum program cycle time exceeded   Event ID: 16# 02:3501

What is the real cause of the CPU would it come from the safety or from the standard program?

CPU is 1516F-3 PN/DP firmware V2.6.1

Kind regards,

You had a regular watchdog fault, a profisafe comm fault, and a safety watchdog fault, in that order.

What OB was running in event 145?  Start there to find your infinite loop.

StragierS

Hi,

Yesterday I had a PLC going into stop, and the reason why is not clear for me.

In the diagnostic buffer (in atachment) I found event 147 Maintenance demanded: Safety program: Warning limit cycle time exceeded Event ID: 16# 0D:75ED

event 146 Error: PROFIsafe communication failure (timeout)  Event ID: 16# 08:0318

event 145 Temporary CPU error: Maximum program cycle time exceeded   Event ID: 16# 02:3501

What is the real cause of the CPU would it come from the safety or from the standard program?

CPU is 1516F-3 PN/DP firmware V2.6.1

Kind regards,

If I look at the timing, the first thing that appears is safety watchdog fault and then the safety comm fault and at last the regular watchdog fault

You are correct.  I did not review the uploaded diag..txt file.

So, you had an infinite loop in the safety part of your project.  How is that even possible?  Does it have anything that sits and waits for another channel's input to match before continuing?  I do not know anything about Siemens Safety programming, so do not read anything more into my question.

StragierS

If I look at the timing, the first thing that appears is safety watchdog fault and then the safety comm fault and at last the regular watchdog fault

145 of 581; Event ID: 16# 02:3501

Temporary CPU error: Maximum program cycle time exceeded

parameter value: 150 milliseconds

Time error, OB80 start requested

PLC_SchuurLijn / PLC_SchuurLijn

Incoming event

Event type:  Error

4/16/2020 1:47:22.436 PM

(Coding:  16#  20 01 00 13 16 06 4A 53  CA 9F A2 8A 35 01 0C 05  00 00 00 96 10 0F 00 34  00 02 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00)

146 of 581; Event ID: 16# 08:0318

Error: PROFIsafe communication failure (timeout)

300MOD00 / 300MOD07.

Incoming event

Event type:  Error

4/16/2020 1:47:22.417 PM

(Coding:  16#  20 01 00 1E 16 06 4A 53  C9 7D AB 84 03 18 00 00  00 00 00 00 00 00 01 1C  00 08 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00)

147 of 581; Event ID: 16# 0D:75ED

Maintenance demanded: Safety program: Warning limit cycle time exceeded

F-runtime group   1

Current cycle time of the F-runtime group   1:  115000 µs

PLC_SchuurLijn / PLC_SchuurLijn.

Incoming event

Event type:  Maintenance demanded

4/16/2020 1:47:22.357 PM

(Coding:  16#  20 01 00 21 16 06 4A 53  C5 E8 A5 83 75 ED 00 00  00 00 00 01 00 00 00 37  00 0D 00 00 00 01 C1 38  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00)

I knew that before I clicked Publish.  My understanding is you cannot create a loop in a safety program.

However, to generate a watchdog fault from the safety system, something has to be in a loop, which is the main OB1 or other cyclic OB outside the safety system.  The safety system will fault more quickly for watchdog I think, so when I see a safety watchdog fault, knowing that's not likely the real cause unless there I something in there that is allowed to _wait_ for something to complete before processing further.  I do not think anything in safety programming offers this, but if I'm wrong, please check your safety program.

Instead, look for loops in your main PLC logic.