S7-400H SFC108 block

[tulip]

Our customer has S7-400H system for turbine control.This system communicated other different systems by CP443-1 card.Plc cycle time 6000ms.SFC108 is used for trip alarms.I could not understand how is operate (sfc108) this block? And customer want a little bit speed.Because İf two trip alarms come same time ,How will you know which alarm came first?Thanks in advance for any ideas.....

 

[JesperMP]

I am not an expert in S7-400H, but are you sure that the CPU has a cycle time of 6 seconds ? That is extreme.
Maybe you are looking at the 'scan cycle monitoring time' which is max 6000 ms.
That is not the actual CPU cycle time.
When online, open the CPU properties (CTRL-D) and check the tab 'scan cycle time'. Post a screenshot of that.

As to how SFC108 works, maybe this FAQ helps:
https://support.industry.siemens.com/cs/de/en/view/23872245

 

[parky]

S7 400H is unlikely to have a scan time of that magnitude, as default I think anything above 200ms would set the watchdog, however, it can be changed.
Are you sure that FC is a standard block, if I remember correctly, block numbers can be changed (well they could be in S5, not tried it on S7), I know we used to re-name S5 standard blocks (ones that were not part of the system).

 

[JesperMP]

SFC block numbers cannot be changed. And SFC108 is for alarming which tulip also describes.

The advantage of the alarm message system is that all alarms gets an accurate time stamp. And that sounds as what tulip actually needs.

I suspect that the problem is something else, and not the CPU scan time.

 

[parky]

Ah.. Missed the "S" on the function

 

[Thomas_v2]

SCF108 as AlarmD uses the same messaging system as AlarmS. AlarmD is a bit unusual for S7-400 CPUs where more of the ALARM_8/NOTIFY methods are used. But as Jesper has said, all methods are timestamped inside the plc. Thus it's relevant to add milliseconds in the alarm system in your HMI system. But if you program is called only in a 6000 cycle, it's almost useless, as it depends on in which position of the cycle the SFC call is done first.

 

[Darrgintari]

Something strange behavior for the s7 processor as a whole, it seems to me that there can be and is the place to be a warranty breakdown ?!