N2000 sFlow and OMNM 6.0

Hi All

I have a Dell N2000 switch with firmware 6.1.2.4.

I set up the sFlow destination as the OMNM server.

And I enable sFlow on  some interface.

But I can't see any traffic flow on OMNM "traffic vliew".

The sFlow port number is default.

Does anyone have any idea about N2000 sFlow and OMNM configuration?

Thanks.