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Alright

I think there are ways to guess speed

estimate the stator/rotor flux indirectly to compute the rotational speed.

You can do spectral search of slip-dependent component in the stator current to estimate the speed of your asynchronous motor. Look at some of my papers.

you can with observer Design Calculate the speed of the motor without sensors.

Easy, if you can read the nominal data on the plate of the motor, and fact.

This is the nominal speed without charge on the axis.

Regards, Héctor R.

Hi

I agree with M.r yasser

hi

I offer to see this article  "Induction Machine

Speed Estimation

Observations on Observers"

I prefer u to read the bimbahara book

section synchronous machine

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Thank you for your answers

Hi

http://www.iust.ac.ir

You can, going back through voltage and current (assume that you measured them) characteristics with mathematical manipulations and it may not be accurate. But why you need as such rather than keeping one speed sensor.  

Jagadeesh Gunda Sir

thank you

Hi

hi

Invertor or Motor controller

http://www.abzaran.com/automation/controller/invertor.php

Dear Ghorbani Sir

thank you for useful link

I am agree with mr Ramezanali Ghorbani