The Electrically Driven Magnetically Supported Vacuum Type Ultracentrifuge

Abstract

The electrical motor drive and the magnetic support for the vacuum type ultracentrifuge have been revised and improved. The drive is a two‐phase motor and the support a solenoid which attracts a solid steel cylinder fastened to the rotating parts. The armature of the motor consists of a solid steel cylinder and a magnetic core support mounted coaxially on a stainless steel tubular shaft. Cooling water passes through the tubular shaft. A two‐phase salient pole stator produces the rotating magnetic field when actuated by the output of a transitron oscillator and power amplifier. Condensers in series with the motor field windings split the phase and match the load to the power amplifier. At an oscillator frequency of 1188 cycles per second and an input to the motor of 1 kw, the rotating magnetic field produces a torque of 600 g‐cm throughout the starting period up to about 10 percent slip (about ½ hp at 1000 r.p.s.). A 7½‐lb rotor (6¼″ diameter, moment of inertia of 81,000 g‐cm²) has been accelerated to 1000 r.p.s. in about 18 min. Upon reaching the desired operating speed, a slip speed control actuated by a magnetic pick‐up on the centrifuge shaft sharply reduces the power input to the motor and automatically holds the rotational speed constant to within 0.05 percent. When the slip is not too large, the mechanism provides a satisfactory ultracentrifuge drive which is ``run‐away proof'' and which automatically maintains its speed within ½ r.p.s. from day to day.