I am using ferrite bead at input and output of SMPS. how many turns and what is the diameter required for the ferrite ?

I am not talking about ferrites used in radios I am taking about EMI reduction 6 core soft ferrite RS stock number 2606818 available for 40 Rs. It is readymade thing you don't have to do any winding just buy it it has two terminals mount it just like you mount capactors. The connection I have already shown in earlier schematic.

when i am not switching any contactors there are no problems. i think it is because of power line spikes generated by contactor. i dont know exactly

You are right the problem is EMI that your ciruit receives when you switch contactor apart from the things discussed earlier the following measures might also help.

1. Put your control circuit in a galvanised iron enclosure.
2. Appropriately connect the enclosure ground with the star ground of your system
3. Keep maximum posible physical separation in between control unit and relays.
4. Use a line filter for supply to the control unit. Ask for Emco make thats a good one available here in mumbai and do remember to say Line filter with Spike supressor since there are two version available with and without supressor.

Regards,
Prahlad Purohit