Upgraded system shines light on nation’s ‘first’ airport

Boston’s Logan International Airport has always been an airport of “firsts.” In 1987, the airfield at Logan became the first to computerize airfield lighting. A recent upgrade to the lighting system again makes use of the latest computer technology, innovative software solutions, improved Programmable Logic Controllers (PLCs) and better communication bus systems. The system, designed and built by the engineering firm Edwards and Kelcey Inc. (Morristown, N.J.), is responsible for controlling all lighting on the runways and taxiways.

The main components for Logan’s airfield lighting are a series of Constant Current Regulators (CCRs) that step-up the incoming main voltage of 480 V to the level necessary to provide the FAA-defined levels of brightness. There are five levels of brightness for the runways and three levels for the taxiways. There are a total of 50 CCRs; each is paired with an adjacent monitoring kit.

The monitoring kits provide the relays and contactors of each CCR with an energizing signal so that the correct level of brightness via solid-state silicon-controlled rectifiers (SCRs) can be made. Each kit consists of high- and low-voltage panels. The high voltage panel houses the load voltage transformer, load current transformer, and the ground resistance monitoring circuitry. The low voltage panel has a Siemens (Alpharetta, Ga.) Fiber Optic Profibus Module (OLM) and a Simatic ET 200M remote I/O module with dual Profibus channels. It also contains a step-down transformer, digital input module, relay digital output module, and three analog input modules. It has five analog transducers that takes the raw voltages from the field and converts them to 4-20 mA signals that are read by Siemens’ analog modules.

Redundancy is a method used to provide a failsafe path for possible equipment failure. There are four levels of redundancy in this system. Aside from the redundant controllers, there are redundant Profibus communication paths, Profibus I/O modules, and power sources.

All Human Machine Interfaces (HMIs) are connected to the system via fiber optic cable. Instead of installing a dual fiber-optic ring for the system, the redundancy is accomplished through the use of a “self-healing” fiber optic ring. This means there are two fiber optic trunk lines between the tower and the lighting vault. One path is direct; the other goes around the airfield. At the tower and the vault, there are two Ethernet switches (intelligent hubs). These switches are connected via an Ethernet cable that completes the ring.

In the Logan Airport system, the functional programming blocks that are built into the program were used to automate the changeover between the two PLCs. The redundant, distributed I/O units are also connected to both PLCs via a Profibus DP. In addition to the self-healing ring, there is also a self-healing process available among the monitoring panels. These panels each have a Siemens Fiber Optic Profibus Module (OLM). Each is configured to detect fiber optic breaks and automatically bypass the break by communicating in the opposite direction

Redundancy for sub-systems

The control system for airfield lighting at Logan International simplifies the ability of air traffic controllers to make adjustments quickly and deliver an optimal level of flexibility and customization. The redundancy of the sub-systems assures the highest level of system availability. The use of Profibus provides fast response times (throughput speed). The built-in features of the entire system allow easy Profibus configuration. If additional drops are later required, they can be installed quickly and easily.

For more information, Circle 496 or visit www.controleng.com.

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