Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 72 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
Appendix B - Portable Maintenance Unit
The Portable Maintenance Unit (PMU) is a microprocessor independent unit with the controls
and status indicators to execute manual rate control for Azimuth, Altitude and Cassegrain
Rotator axis. Refer to the following representative photograph of the PMU and of the PMU
junction box. The PMU has a 15 meter connectorized pendant cable that may be interfaced at
the AZ/ALT Power Drive Unit, the CASS Power Drive Unit or at junction box #1 or #2. The
PMU can be plugged at any of the above-indicated ports at any time, regardless of which unit
has control of the MCS. The PMU is capable of performing these operations as an
autonomous, hand-held unit and is functionally and physically independent of the Mount
Control Unit, the AZ, ALT and CASS LCUs, and microprocessor position loop closure
electronics of the AZ/ALT and the CASS PDU.
The PMU is offered control when the MCU enters the Maintenance mode. Also, the PMU is
automatically offered control by default when the MCU-AZ/ALT CCU or MCU-CASS CCU
data link is down. Extra flexibility is provided by the monitor display window of the PMU
where key parameters such as AZ, ALT and CASS position and fault messages may be
observed. The unit has ON/OFF control to individually enable each axis and rate knobs to
issue bi-directional, variable speed commands. Two ranges of axis velocities may be selected
from the PMU. Low speed allows linearly variable commands from zero to 25% (AZ/ALT),
15% (CASS) of full slew velocities while high speed allows linearly variable commands from
zero to full slew velocities. Thus, LO speed allows fine-tuning of the position, while HI
speed allows quick mount repositioning. Summary axis faults and status are reported on the
PMU using LED indicators and an LCD display. The LCD display also shows actual
AZ/ALT/CASS position. Depressing the Rate Select/Display control select button, for
approximately 3 seconds, toggles the LCD from the Position Indication to the Faults/Status
Messages. The LCD display scrolls through the Faults/Status continuously and only the
messages generated at either CCU are displayed.