Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 39 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
4.2.5 CASS Power Drive Unit
Refer to the following representative photograph (Figure 4.2.2.2.A) and block diagram
(Figure 4.2.2.2.B) of the CASS Power Drive Unit.
The CASS PDU design is very similar in design to the AZ/ALT PDU. Only the major
differences between the two PDUs will be discussed here.
4.2.5.1 CASS PDU Motor Controllers
One of the major differences is the design of the motor controllers. Due to the small capacity
needed to drive the Cassegrain rotator, the motor controllers have a built in power supply
module and are powered from single-phase utility power. The single-phase utility power will
be derived from the VertexRSI 3-phase to 1-phase isolation transformer.
4.2.5.2 CASS Cablewrap
The Cassegrain rotator cable wrap drive will be slaved and Interlocked to the Cassegrain
rotator (AD01 10.5.3c, e) as depicted on Figure 4.2.2.2.C. An LVDT will be used to ensure
that the cable wrap remains synchronised with the Cassegrain rotator axis. If for any reason a
divergence is noted between the Cassegrain rotator axis and the cable wrap, all motor
controller power will be removed via the Interlock Chain. Additionally, if the cablewrap
motor or motor controller faults out, the Cassegrain rotator axis will be disabled.