Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 43 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
The same reliability concern by the frequent power cycling of the CASS motor controllers, as
discussed in the AZ/ALT PDU section, is applicable to this axis.
A second set of the above Interlock contacts is routed over to the CASS LCU for monitoring
purposes only. A third set of Interlock contacts is fed to the CASS PDU Control or Status
board for fault reporting and axis disabling. This serves as an added safety level of
protection, satisfying the operational safety spec of AD01 13.4.11.
4.2.5.4 CASS PMU Control Logic
The Cassegrain PDU also contains the circuitry for the PMU control logic. From the PMU,
control of the AZ/ALT or of the CASS axis can be selected. Latching relays in the CASS
PDU route either the AZ/ALT or the CASS control/status signals to the appropriate PDU for
control of the axis. The PMU can be operated from the AZ/ALT PDU, CASS PDU, or at
either PMU Junction box (2).
4.2.5.5 CASS Encoder Interface
As with Azimuth and Altitude axes, the Cassegrain rotator encoder scheme will consist of
four read-heads mounted on a Heidenhain ERA 780c optical tape encoder (AD01 11.1.6 g
spec). Heidenhain Encoder Splitter boxes are again used to obtain two buffered outputs; one
going to the VertexRSI equipment and one going to VISTA’s LCU IK320 Heidenhain
Encoder boards.
4.2.5.6 CASS EMC Treatments
The following CASS PDU design features will ensure that the discussed EU EMC standards
are met:
Properly Shielded Conductive Gasketed Cabinets
Completely Connectorized PDU Enclosure
EMI/RFI connector backshells
Properly terminated Shielded Cables
Motor Lead Ferrite Filters
1φ (tech and utility) EMI Filters