the best possible position to mount an inductive proximity switch for obtaining speed feedback of 3 phase induction motor?
The motor shaft…if you are wanting to read the RPM of the motor itself. Generally I have installed a metal flag to act a target for an inductive prox to read properly. I don’t know what brand you are using but I recommend the Eaton iProx for these types of applications. It has a TEACH function that allows the sensor to detect only what you want it to.
If the speed is critical to your process you may want to use a rotary encoder instead…if just for reference, the inductive prox is a great choice.
Also, you mention using an induction motor - is this operated by a variable frequency drive? If so, most VFDs extrapolate RPM based on parameters and frequency reference.