Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 26 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
4.2.4.6 AZ/ALT Central Control Unit
Refer to the following AZ/ALT CCU Block Diagram, Figure 4.2.2.1.D. Only the CCU
components that are required to meet the requirements of AD01 and AD02 are discussed in
this section. The other components are considered test equipment and are discussed in
Appendix C.
Logic Power is supplied to the off-the-shelf Pentium motherboard from a universal input
300W switching power supply. The power supply supplies power to the Digital Signal
Processor and the DSP Accessory 8E (18-bit DAC) board.
The PDU Central Control Unit (CCU) houses the Digital Signal Processor and the DSP
Accessory 8E (18-bit DAC) that are used to interface to the ALT Heidenhain Tape Encoder
read-heads via the Heidenhain Encoder Splitter boxes (IBV606). The main function of the
DSP is to produce the rate feedback information for the Altitude axis (AD01 11.1.7 a spec)
via the 18-bit DAC board. The ALT rate feedback information, used to close the rate
(velocity) loop is sent to the ALT Rate Loop board via the Status board. The rate feedback is
the derivative of the tape encoder feedback. The software that produces the rate feedback
resides in the DSP and is free running, meaning that once it has successfully booted, it
doesn’t depend on any condition for the algorithm to start producing velocity feedback
signals. This ALT rate feedback signal is also provided to the ALT LCU for monitoring
purposes. A DSP on-board relay is used to monitor the health of the DSP. When the PMAC
has successfully booted-up and is operational, the relay is energized. If the DSP becomes
“locked-up”, the relay is de-energized. De-energizing of the relay results in the disabling of
the ALT axis. A DSP Boot Failure would then get reported to the ALT LCU.