UFC 3-535-01
17 November 2005
requires only one pair cable to communicate between the vault and tower (or other
station). A multiplexer can also be built into a PLC system.
15-3.1
Some airfield control/monitoring systems have been installed using
Programming Logic Controllers (PLCs), which have good industrial standards and
proven reliability. The PLC industrial systems use high I/O modules that reduce the
need for multipair cable installation. Cables with 2 to 6 pairs are typically needed,
although fiber optic cable can also be used.
15-3.2
PC-based systems have come into use, with computers located in the
tower, the vault, and/or other work stations. Reliable standards for PC equipment do not
exist at this time. These systems have the capability of displaying the necessary
information on a monitor. This is the most flexible system in use today, with off-the-shelf
units readily available. Typically, standard operating software is used, and off-the-shelf
graphics software is tailored for a specific site. The communications cable requirements
are 2 to 6 pairs of cable or fiber optics. Fiber optic cable eliminates the need for
separate ducts since there will be no interference between power cable and fiber optic
cable.
15-3.3
Compared to the traditional FAA Type L-821 control/monitoring systems,
the PLC or PC based systems are easily expanded and provide data for the controller
and maintenance personnel. At this time, the FAA has not issued design standards for
PC or PLC based systems, but commercial standards are available for the components
of such systems. Some industrial standards the PLCs meet are NEMA ICS1, Industrial
Control and Systems General Requirements, NEMA ICS2, Industrial Control and
Systems Controllers, Contractors, and Overload Relays Rated Not More than 2000
Volts AC or 750 Volts DC, NEMA ICS 3, Industrial Control and Systems Factory Built
Assemblies, UL 508, UL Standard for Safety Industrial Control Equipment Seventeenth
Edition; Reprint with Revisions through and including 7/16/99, ANSI/IEEE C 37.90.1-
1989, Standard Surge Withstand Capability (SWC) Tests for Protective Relays and
MIL-STD-810, Department of Defense Test Method for Environmental Engineering
Consideration and Laboratory Tests, and ISO 9000, Quality Management and Quality
Assurance Standards.
15-3.4
Often, the computerized system is based on one specific manufacturer's
equipment, locking the facility to one manufacturer for servicing and parts. A good
system design will avoid this trap by establishing competitive parameters in the
procurement document. It should be pointed out that the newer systems may have a
slight delay between the control action by the tower and the response from the field,
compared to the instant response of the relay systems. This may result in a short
moment of possible uncertainty as to whether the action requested has been
accomplished. Maximum delay should not exceed 2.0 seconds.
15-3.5
Considerations for the design of a computerized control/monitoring system
are in paragraph 13-16.
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