Electric Motor Drives Text book (Krishnan) says, we need to filter the signals from D.C tachogenerator, using a low pass filter, whose time constant is less than 10ms,uency signals. So I be to filter the noise and high freqlieve the commutator or something produces the high frequency ripple in the output. I don't have an oscilloscope, so i do not know how a D.C tacho output would look like. Does anybody know about this, the tacho i am using is BALDOR 601A100-2. So in my project, i am using a D.C tachogenerator (volts per 1000RPM is 50V) so the maximum speed of the motor is 2000RPM, so the tacho output is 0V to 100V corresponding to motor speed 0RPM to 2000RPM. How to design a low pass filter, to get rid of the high freq.

 

That is an unusually high tach output, 50v/1krpm.
Typically a tach would go to a summing opamp in the drive, summed with the command signal.
You could check a typical analogue drive such as A-M-C etc to see the R/C filter used.
BTW, DC tach velocity feedback is seldom used now for positioning applications.
Max.