June 2002 Excerpt
Cooperation Leads to Successful Installation Aboard USS Roosevelt
By Kenneth Poole
Roosevelt (CVN 71) received a programmable logic controller (PLC) on her
lower stage weapons elevator (LSWE). Recent feedback from the ship highlights
significant savings in maintenance and troubleshooting.
The installation of the PLC was a successful teaming arrangement between NSWCCD-SSES, Norfolk Naval Shipyard (NNSY), and Fleet Technical Support Center, Atlantic (FTSCLANT). Commander, Naval Forces Atlantic Fleet (CNAL) supported the prototype PLC installation. The Chief of Naval Operations (N785) sponsored the CVN Weapons Elevator RDT&E Program, which supported the land-based testing and evaluation of the prototype PLC.
The SSES CVN Weapons Elevator RDT&E Program initiated the evaluation of PLC technology in 1995 with the installation, testing, and evaluation of a Cutler Hammer Programmable Navy Logic Controller on the Standard Cargo/Weapons Elevator (SC/WE) Land Based Test Site (LBTS). The limitations of that PLC were made evident during testing and various other PLCs were evaluated as alternatives. A commercially available high-end PLC with producer/consumer network capability was decided upon as the optimum PLC for the cargo/weapons elevator application.
The high-end PLC was installed on the SC/WE LBTS and recommended as a replacement for the CVN 71 through 75 Cutler Hammer Standard Electronic Module (SEM) controllers. The existing SEM controller is problematic, and some components are no longer parts supportable. This controller reacts to electrical noise that is inherent in the system and provides false signals to initiate movement.
NNSY was designated the lead for the installation, and NSWCCD-SSES Code 9771 was tasked to provide technical oversight for the design, review, testing, and evaluation of the prototype PLC system. The existing PLC program from the test site was provided to NNSY for use in the development effort. NNSY and FTSCLANT developed the CVN-71 LSWE 3 PLC design drawings and the PLC program and assembled the PLC system.
The prototype PLC system was provided to SSES for installation, testing, and evaluation at the SC/WE LBTS. The test site was configured to mimic the CVN 71 LSWE 3 system. The testing validated the control system design and PLC program against possible failure modes. Several dual failure modes were identified during testing that resulted in PLC program changes. A significant effort was undertaken to develop condition based maintenance, diagnostics, troubleshooting, and repair programming. The end result was a real reduction in maintenance as several maintenance requirement cards were modified to utilize data from the PLC as a indicator to perform maintenance. Troubleshooting time, which is difficult to measure, was also significantly reduced as a result of the visual monitoring and diagnostic capabilities programmed into the PLC.
Current and future cargo/weapons elevator systems will benefit from the utilization of a PLC-based control system. This will be ensured for future cargo/weapons elevator systems as the ship specifications for the CVN 77, LDP 17, and T-AKE have been changed to indicate the use of a PLC control system in place of the current Navy Standard Relay Control System.
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