Siemens Error OBs

I am looking for some information about using the Error OBs for Step 7 PLCs. I know what they do and how they prevent the PLC from going into STOP mode. Does someone have some examples of reading the local data out of the OBs block header? I have simulated some hardware faults and rack failures and I have been able to read the Local data into Data Blocks. Does anybody have examples of using these Error OBs to display the fault and diagnostic information on a SCADA by packing the message bits and values into Data Blocks?

Martinvz

It seems to me that you are 90% there, if you are moving the local data to a DB for viewing. I very rarely use these OB's, unless specifically requested, but I will try and give you some pointers.

What I usually do is read off the fault code (HEX) and move it to a DB data area, with that area assigned as an INT (which would convert the HEX to INT for you), then I would use the compare function to set certain bit's (for instance M100 - M110), I would then use these bits to trigger an event/alarm message in a HMI. Of course some OB's (OB82 for example) set local bit's depending on what they are called for, these are very easy to use in your ladder program within the called OB.

For example: -

OB82 local bit 10.5 is battery failed, this could be used as follows:



   L10.5                  M100.0

----| |--------------------(  )

Bit M100.0 will then be used to display a message 'Battery Failed Please Replace' in the HMI or SCADA display.

Sorry I can't be more specific than that, but that might give you some idea on how to get started, have a play and see what works best for you.

Paul