Specifications

Document No. DER01120 DESCRIPTION AND OPERATION
Page 6 of 9 Effective Date 25 May 07
ELECTRICAL CONTROL BOX (CONT’D)
Figure 1120-4 Electrical Control Box
50 HP DRIVE MOTOR
The 50 HP, 460 Vac 60 Hz or 380 Vac 50 Hz, three-phase, explosion-proof electric motor is
connected to the liquid bowl assembly by a sheave and drive belt. Motion is transmitted to the
sheave by a fluid coupling, which is attached directly to the motor shaft. Protective guards cover
the sheaves and drive belt for personnel protection.
The 60 Hz motor operates at 1760 RPM, and the 50 Hz unit operates at 1475 RPM. A
temperature sensing element in the motor’s stator winding causes the motor to shut down if the
motor reaches an excessively high temperature.
VIBRATION SWITCH
The vibration switch (Figure 1120-5) is a safety device designed to protect personnel and
equipment by shutting down the centrifuge in case of excessive vibration. Normally, the switch
contacts are held closed by a mechanical latch. However, strong vibration or a shock of 2 Gs will
overcome the magnetic latch, causing the switch armature to break away from the normally
closed position, interrupting power to centrifuge run relay CR1. A reset button on the side of the
switch must then be manually pressed to close the contacts and re-engage the magnetic latch.
The vibration trip level is adjustable by means of a set point control, which adjusts the air gap
between the magnet and latch arm plate. Turning the screw counterclockwise reduces the
vibration set point in terms of G force needed to trip the armature. When the control is turned fully
clockwise, the switch will trip at the maximum rated vibration level.