Why speed of ac servomotor is not measured with tachometer?

The speed of an AC servomotor is typically not measured with a tachometer because these motors are often equipped with built-in feedback devices, such as encoders or resolvers, that provide precise position and speed information directly. These feedback systems can deliver more accurate and reliable data compared to a tachometer, which may introduce errors or require additional calibration. Additionally, the control systems for AC servomotors are designed to utilize this feedback for real-time adjustments, making external speed measurement less necessary.