Profibus fault and SF fault

Dear All,

I Need ur help, my PLC siemens S7-300 have problem, led BF2 (blink) and SF (always on). 

I want to know, what is root cause of this. please help me.

Hello,

This means one or more devices connected to profibus network with your PLC are not communicating with PLC. You need to check profibus cables, rules for profibus terminating resistance, loose connections, as primary check. If system is new, I mean still in commissioning stage then you need to also check configuration in step7.

Hope this helps.

Kbv.

Dear Mr. Kbv

Thanks for your reply,

i want to ask, how to measure cable termination resistance? i have check all connector, the connection is good.

In the end of connection have profibus terminator, what is the function of profibus terminator?

Thanks for your kindness.

Hello,

1.) open the Diagnostic Buffer of the PLC and show which error exactly is logged!

With this error informations you can locate the device which is affected.

It can be a adress problem if you change a device with a newer one and set the wrong bus Adress.

Have you change anything on the machine before the BF/SF is goring red?

The termination must be ON at the first and the last device on the PROFIBUS line.

http://www.profibus.felser.ch/en/index.html?busabschluss.htm

http://www.profibus.felser.ch/en/index.html?der_busabschluss_fuer_rs485.htm

Regards

Christoph