The purpose of this paper is to obtain the transfer-function of two-phase servo-motor, especially its time-constant.
The two-phase servo motor is usually employed as an actuator of instrument servomechanism such as self-balancing recorder or servo-computing machine. The control winding of motor is usually connected to the anode of vacuum-tube. Under this condition, many people have experienced that some of the servomotors rotate even when the control voltage is not applied to the control winding.
According to the author's analysis, this phenomenon occures when the secondary resistance r2 is low compared with magnetizing inductance Xm, of the equivalent circuit of the motor. In such case, the electromechanical time-constant of the motor becomes negative.In consequence, the author came to the conclusion that it is most preferable to chose the value of r2 between 1.5 xm, and 2xm, because between these values, time-constant is minimized while the stall-torque is not so reduced.
