Actually i want to switch between multiple 3-wire RTDs.

Aarghh!

It would have been nice to know that up front, and I suggest that you tell us, in detail, what you want to do and provide a system schematic showing how you propose to get there. Please.

 

check the attachment i am trying in this way.

 

Aarghh!

It would have been nice to know that up front, and I suggest that you tell us, in detail, what you want to do and provide a system schematic showing how you propose to get there. Please.

I am extremely sorry for the inconvenience. I will keep that in mind.

 

Thanks for the brief but for me restriction is to use 3-wire RTD. Can you please show me how to do it with doubling the MUX?

You switch the top three leads with the bottom (FORCE-) lead being common to all the RTDs.
So you will need three mux channels and wires per sensor (along with the common wire for FORCE-).
But you still need to keep the mux resistance below 50 ohms.

 

check the attachment i am trying in this way.

Won't work.
The FORCE- wire is not switched but is common to all the RTDs.
And you can't use a 4051 mux since it has over 50 ohms of resistance, which is the maximum for the MAX31865.

Edit: Here's an example of a low on-resistance mux.
Available here.

 

with 4-wire configuration it works fine. While i configured MAX31865 for 4-wire but i connected 3 wire RTD with RTDIN- and FORCE- short n it works fine. But it takes 4 mux for 8 RTDs i am figuring out if i can reduce that.