Mehdi,

The N9M4LRT is a Servo Disk type motor. Your posting gave the impression that this was the tachometer unit.

You should clarify better as to the makeup of your system and maybe even give some details as to the type of tachometer in use.

I think we also need to understand more about what you mean when you say the "motor is subjected to a pulse". Are you talking about a mechanical torque type pulse on the output shaft? An electrical dropout pulse to the motor's electrical drive signal? An overvoltage surge pulse present on the motor wiring? A shock type impulse applied to the motor subsystem through its mountings?

Lastly I think we need to understand better what you believe is a mistake here.

Michael Karas