Airfield Lighting And Constant Current Regulator Control Systems Stephen J. Korski Honeywell Airport Systems 25-760 Pacific Road Oakville, ON L6L 6M5
[email protected]
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Abstract
The Constant Current Regulator (CCR) is well established as a reliable and necessary element of airport lighting circuits. The control of CCR’s CCR’s has evolved from hard-wired relay logic and pushbutton panels to fully distributed digital control systems linked through communication networks to multiple touchscreen computers. computers. This paper briefly reviews the evolutionary process, process, and discusses the various means of control systems available today.
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Introduction
The original remote control systems developed for operation of airfield lighting equipment are with pushbutton panels and electromechanical electromechanic al relays. Relay control systems remain a popular and low cost option for many installations. With the general acceptance of the Programmable Logic Controller (PLC) as a means of controlling airfield lighting, many modern upgrade solutions include this option. Recent developments with Digital Control Units (DCU) featuring the use of Digital Signal Processors (DSP) and serial interface connectivity provide an extremely accurate and reliable control system system with advanced advanced features. features. The DCU can be installed as an an integral part of a new CCR control system, or placed into existing lighting equipment as a control interface.
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Relay Control Systems
Control systems based on electromechanical or solid state relays are used for a wide range of applications. A considerable considerable number of airfield control towers rely on pushbutton or selector switch panels for operation of the lighting circuits from the constant current regulator (CCR) vault. The relay and pushbutton panels form a hard-wired system that, while reasonably reliable, have some disadvantages. Changes can can be made to these relay control systems, but generally in a limited fashion. The hardware originally originally installed, and the wiring connections to the regulator vault do not provide a great deal of flexibility for making modifications or installing additional equipment. The ability to configure the tower control panels for multiple mode selections using a single switch or selector is either very limited or not possible. For example, example, with more advanced processor based control systems, selecting an approach direction from a single button command can automatically select all associated guidance, approach, runway and taxi circuits. A major disadvantage disadvantage of the relay control control systems systems is that information information on the status of the lighting circuits or the power equipment is extremely limited or in many cases nonexistent. Any problems with a lighting circuit circuit or or tolerance variations variations with the power equipment is made obvious only when the equipment fails to function. Advance notice of a degrading circuit condition with status alarms is not available. available. It is virtually virtually impossible impossible to install install advanced advanced features such as lamp outage monitoring, automatic megger circuits, single lamp control or Surface Movement Guidance Control Systems (SMGCS). Older and more elaborate systems, with a number of multi-conductor multi -conductor control cables and termination points, can be difficult to work with due to undocumented changes over the years. 3.1
Relay Control Advantages • • • •
3.2
Good reliabili relia bility ty Lowest hardware installation installatio n cost Low learning curve for maintenance maintenanc e personnel Easy to troubleshoot, can be done with a standard multimeter Relay Control Disadvantages Disadvanta ges
• • • • • • •
Difficult to add control functions Difficult or impossible to group menu control functions functions Can have problems with with voltage drop on long control wire wire runs Service cost dependent on parts availability for legacy installations Multiple remote wiring interconnections interconnections create create many potential failure points Lack of warning, alarm or logging functions for operations and maintenance Inability to include include or add advanced advanced features such as automatic automatic megger, megger, etc. etc.
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PLC Control Systems
The programmable controller, originally known as a PC, was developed by Bedford Associates in 1968 and 1969. This was in direct response to a request from the North American automotive industry. Dedicated processors or embedded controllers for industrial manufacturing systems were available, but numerical control (NC) and computer numerical control (CNC) units were used exclusively for high-speed position control, generally for precision machining and milling. The first programmable controllers made sequence control available for the first time. Prior to the development of the programmable controller, changes to automotive production lines included the wholesale replacement of large and complex rotating cam switch or electromechanical relay control panels with their associated wiring and remote limit switch connections. In many cases, it was found to be more efficient and productive to throw away existing relay panels and replace them with new, rather than attempt to modify or rework them. Once tested and proven to be effective, Bedford Associates began production of the programmable controller as a direct replacement for relay logic under the Modicon name. As the 84th engineering project of the firm, the first programmable controller was given the model number Modicon 084.
Early Modicon Programmable Controller
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PLC Note With a reasonable cost, and the increasing popularity of personal computers in the early 1980’s, there was some confusion as to the distinction between a PC for controlling industrial machinery and one for word processing or drafting. While the term Programmable Logic Controller (PLC) is a registered trademark of the Allen-Bradley company, it has become a generic description for the programmable controller.
Because of their intended use with industrial environments, PLC’s are specifically designed and packaged for reliable operation with high levels of electrical noise, vibration and temperature. In addition to this, the more advanced models from numerous manufacturers are generally with a life expectancy of greater than twenty years. A major advantage of the PLC is that all programming is done with ladder logic. While this may not appear very friendly to some users, it is much easier to learn and to understand when compared to original computer programming languages such as FORTRAN or BASIC. Input and output wiring to PLC modules is with a fixed program address and associated physical connection, greatly improving the ability to trace, test or troubleshoot any system. 4.1
PLC Control Advantages • • • • • • • •
4.2
Stable program and memory, not affected by power loss Medium hardware installation cost, more expensive than relays Troubleshooting, if program is understood, can be with a multimeter Readily connect to other processors or computers with suitable interfaces Flexible, can be readily changed or modified locally or from a remote office Programmed with easily understood ladder logic, many advanced functions Open architecture, developed ladder logic is accessible and not proprietary Extremely reliable, able to function in harsh industrial environments with long life PLC Control Disadvantages
• •
Considerable experience needed to develop fast and effective programs Depending on the project, input and output wiring connections can be congested
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PLC Control Solutions
PLC control systems are more economical and effective if available as an engineered design solution. This is where the number of inputs and outputs, the basic control functionality and the number of devices that can be controlled or monitored are predetermined, at least to a large extent. A packaged PLC control solution for an Airfield Lighting Control and Monitoring System (ALCMS) will generally be with a specific type of PLC processor, input and output modules, and the operator interface. The operator interface is most suitable with a touchscreen computer for improved ergonomics and positive control action. The nature and type of feedback to the touchscreen computer to verify a selected control action must also be considered, as well as selected alarming. The feedback to verify a control action, and to annunciate alarm messages must be developed with a hierarchy that will provide the necessary information, but not become a nuisance or needlessly obtrusive. For example, a never-ending stream of nuisance status alarms while equipment remains operational will soon result in all alarms being fully ignored. With a more advanced system, and multiple control locations, alarms can be separated into those most pertinent for operations and maintenance personnel. Operations personnel must be aware of whether the constant current regulators and associated equipment is ready for service, and if there has been a lack of control action or a failure. Maintenance personnel appreciate more detailed information, such as regulator output current deviations with a particular brightness step. This does not preclude the need for customizing either control actions or screen displays, but does provide a package where most of the development or technical concerns have been addressed. For example, standard drawings and operation/maintenance manuals can be developed that will support virtually any installation. Additional information for a project can then be included in the form of site-specific termination drawings, and any customized display screens for the control computers. This permits comprehensive PLC programs to be developed and tested before the system is installed at a particular site. The designed control solution is then configured to that site primarily with changes to the Human Machine Interface (HMI) graphic screens and text labels. These types of systems are available from a number of vendors, but as with any industry, airfield lighting control is with detailed and specific needs.
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5.1
Design Elements • • •
•
•
•
•
•
•
6
PLC hardware installed and wired as close as possible to vault location Only communication lines with either copper or fiber connect to the tower computer Availability of dual redundant communication lines if necessary, with bumpless transfer on a line failure Networking capability needed for larger systems to permit installation of a maintenance computer or other remote display and control connections Dial-up connection or availability is desirable, to permit remote troubleshooting, configuration changes and updates Data transfer rates must be fast and reliable, control functions and feedback to the operator must be without any appreciable delays System must be designed so that key functions can be modified, changed or configured directly through the remote HMI without PLC programming changes Particular attention is needed with the design and layout of the graphical screen displays to minimize error potential and to maximize ergonomics As much as possible, functions are programmable with a graphical user interface so that a single control action can remap or reconfigure multiple lighting circuits
Personal Computer (PC) Solutions
The use of PC’s in place of PLC’s is outside the scope of this paper, but still deserving of an explanatory note. There are a number of software programs available for use with a PC that are capable of emulating the processing capabilities of a PLC, and of connection with a suitable communication scheme to external input/output modules. The personal opinion of the author is that while the use of PC control is certainly feasible, it does not have any inherent advantages over a PLC system, with the possible exception of a reduced package price. The disadvantage of PC control, as verified by anyone who has lost computer information due to an operating system or hard drive failure, is the decreased reliability as compared to PLC hardware. From recent history, PC’s and various operation systems have an expected lifespan of only a few years, and then must be updated or completely replaced several times in the expected twenty-year lifespan of the ALCMS.
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ALCMS Solutions
Through an evolutionary process, a number of engineered solutions for the control and monitoring of airfield lighting have been developed. While any system can be customized to suit specific requirements, virtually any airfield can be controlled with a tested and existing design with little change or modification. These proven designs are packaged as an Airfield Lighting Control and Monitoring System (ALCMS) with capabilities to suit all requirements. For purposes of discussion, this paper is with consideration for three different control systems. These are for smaller airfields, larger systems with dual and/or redundant communication systems, and full-featured distributed control schemes. 7.1
ALCMS Evolution • • • • • • •
7.2
1970: 1988: 1995: 1998: 1999: 2000: 2003:
Control systems with relays and pushbutton operator interface panels PLC’s replace relays, hardwired pushbutto ns remain as operator interface Touchscreen replaces the pushbutton panels, integrating directly with PLC PC technology with Microsoft Windows systems merge with control markets Ethernet communication technology becomes viable in industrial applications Focus moves from custom to standardized system design and implementation Digital control provides direct communication to CCR’s and other field devices
ALCMS Design Elements • • • • • • •
7.3
PLC’s specified for continuous trouble-free operation Redundant computers increase reliability of PC technology Use Commercial Off-The-Shelf (COTS) hardware and software Use industrial grade components for all critical control functions Offer PLC and PC based technologies to meet site preferences Failure of a control or monitor computer does not affect operation of system Provide redundancy for Human Machine Interface (HMI) and control computers Operator Interface Criteria
• • • • • • • •
Intuitive operation Superior graphics capabilities Configurable by site personnel Requires minimal training for ATC Simple to understand operator interface Automated functions minimize ATC workload Can be reconfigured online by site personnel (no programming) Provides simultaneous or selective control capability from all locations
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7.4
Small Airport ALCMS
For smaller airports, with a maximum of approximately eight to ten regulators, a PLC based control system will include digital inputs and outputs only. In order to keep the package price as low as possible, there will not generally be any provision for analog connections. With a packaged control system, the control interface is best suited with a touchscreen computer using Windows CE as an operating system. The touchscreen computers with Windows CE are selected because the operating system is stored with static memory, increasing the reliability over a conventional computer hard drive. The developed HMI project for the control of the regulators is loaded and/or updated with a digital camera type Flash RAM module. The Flash RAM can be easily inserted or removed to update the project, or for moving the project to a different compatible computer. This type of package does not offer advanced communication schemes, or multiple control locations. The data connection between the PLC and the Tower computer, to reduce the overall cost, is best suited with a standard RS-232 serial data line. The RS-232 wiring connections can be extended from the vault to the control location with short-haul hard-wired modems, and can communicate with good reliability at a speed up to 19.2 Kbps. The point-to-point wiring (with three or four conductors) from the vault to the Tower can quite often be with existing control wiring that is no longer needed once the ALCMS is installed . If desired, the RS-232 communication network can be replaced with Ethernet, but with an increase in hardware costs. For maintenance purposes or troubleshooting, the touchscreen computer from the Tower, or an identical spare, can be directly connected to the PLC at the vault location. This allows maintenance personnel to operate and test all functions locally to resolve any problems. The smaller PLC system is intended to be a pushbutton panel and control relay replacement for smaller to medium airfields or heliports. The basic configuration of the control system for failsafe operation of regulators, grouping control commands etc. can be accomplished directly through the HMI without any PLC programming changes. • • • • • • • •
Low cost control system High reliability, no moving parts PLC based, non-distributed control Limited monitoring, circuit on/off only Designed to replace L821 pushbutton panels RS232 or Ethernet serial data communication 12 or 15” LCD Touchscreen interface with Windows CE Exclusively off-the-shelf hardware and software components
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7.5
Medium to Large Airport ALCMS
The PLC system for a medium to large airport is with a different focus from the smaller systems. There are no practical limitations on the number of analog or digital input/output modules, as additional connections are accommodated with extra hardware. This can be with additional PLC’s and/or remote adapters at suitable locations. The size and type of PLC used will generally be with a more advanced model that can directly support Ethernet communications and the connection of additional input/output modules. The PLC and the HMI interface program can be developed ahead of time, with some customization for a particular project. This would include display screens suited to the site, as well as any requested control actions beyond the developed features. While a greater level of customization is needed, the developed system relies on a PLC and HMI program developed with an exclusionary approach. Rather than having to include additional functionality, the commands and features that are not needed are removed from the developed system. Because of the size, complexity and capabilities of the HMI program, a computer with a hard drive is now necessary. The touchscreen, either separate or integral to the computer is still desirable, but Flash RAM is not currently economically available to store the programs and log files. One of the key features of this system is with the type of communication scheme that is used. In addition to the PLC and HMI functionality, this type of system provides redundant Ethernet communication using redundant fiber optic and wireless radio hardware. The failure of a communication line for any reason is with a “bumpless” transfer to the backup line, and suitable alarming of the line fault. The addition of Ethernet radio communications provides a third means of control to the Tower location. In the event of a complete failure of the redundant Ethernet fiber network, the radio system maintains full control capabilities. The system allows for operation from multiple locations, and will generally include a dedicated maintenance computer at the vault location. The medium to large PLC control package with the dual redundant Ethernet communication scheme, as well as the radio backup, is well suited for applications where the control of the airfield lighting equipment cannot be lost or interrupted. As with the smaller control system, a considerable number of control changes such as regulator assignment to a specific circuit, failsafe brightness steps, regulators on/off line etc. can be done through the HMI and Tower/Vault computer without any PLC programming changes. • • • • •
High reliability PLC based, non-distributed control Redundant Ethernet fiber & radio backup communication 15” to 21” LCD Touchscreen interface using Windows 2000 Exclusively off-the-shelf hardware and software components Page 9
7.6
Distributed ALCMS
The most advanced system for airfield lighting is with a distributed control and monitoring system. Redundant Ethernet communication using fiber optic and wireless radio technologies is standard, allowing operation from the Air Traffic Control Tower, Flight Service Station (FSS), Electrical Vaults, Maintenance Facility and Operations Center. The system is intended for use with medium to large airfields where the benefits of a distributed control structure are needed or desirable. The distributed control architecture is suitable for use with either PLC or PC hardware solutions. With a distributed control system, each device such as a constant current regulator (CCR) is given a node address. The address is then used for all control and monitoring communications to the CCR. Dependent on the monitoring hardware installed inside the CCR cell, a considerable amount of data is available on the status and operational parameters of the regulator. The communication scheme can be with a number of different protocols to suit the site location, or to interface with any existing communication networks. While a PLC or PC is still included as part of the installed hardware, there are limited input/output connections. This is because the distributed control is only possible with a dedicated digital processor installed at every control location, including the CCR’s and any other lighting equipment such as circuit selector switches. With a distributed control system, the PLC or PC becomes the gateway between the control locations and the controlled equipment. With a suitable control program, the PLC or PC can provide additional alarming capability and supplementary calculations for the individual digital processors. Additional CCR’s can be readily installed and added to the communication network simply by adding another node to the system. • • • • • • •
Redundant networks available Network cabling minimizes wiring Distributed control with p rocessors at each CCR Ethernet, Profibus, Interbus, DF1 and other protocols Redundant Ethernet fiber and radio backup communication 15” to 21” LCD Touchscreen interface using Windows 2000 Additional features available , such as lamp outage & power monitoring
As with the smaller and medium to large systems, the distributed control system can be configured directly through the HMI without program changes. At the digital processor level, and with the connection of additional hardware, advanced monitoring features can be provided. The more significant of these are the lamp outage monitoring and insulation resistance monitoring system (IRMS).
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7.6.1 Lamp Outage Monitoring
Lamp outage monitoring is not practical with a PLC as the processing speed and resolution of the lighting circuit output voltage and current signals is beyond a PLC’s capabilities. With the installation of a suitable CCR output current transformer (CT) and potential transformer (PT), the analog signals are connected to the digital processor through analog to digital (A/D) converters. The signals are then used to determine the status of the lamps connected to the airfield lighting circuit. The system is based on the fact that any airfield lighting circuit with good lamps connected to the secondary side of the isolation transformers is essentially resistive in nature. An open secondary, however, will be seen as largely inductive, and the phase shift can be readily measured. 7.6.2 Insulation Resistance Monitoring System (IRMS)
The IRMS system is used for measuring the resistance of the airfield lighting cables with a true earth ground reference. Ideally, the system will provide an analog signal in relation to the measured resistance value, rather than using a separate hardware device with alarm contacts only. In its basic form, the IRMS includes a dedicated power supply, a resistor network and a filter circuit for the analog signal. Most systems will use a power supply of either 500 VDC or 1,000 VDC; but at a low power value of approximately one or two watts. The maximum current level of the monitoring system is limited to less than 5 mA on the field circuit for personnel safety. For purposes of discussion, consider a filter circuit with an input impedance of 10K Ohm, with one side connected to earth ground. Connection is made to one side of the airfield lighting circuit through resistors connected in series for a total of 1,000K Ohm. The power supply is installed between the filter circuit input and the series resistors. With a 500 VDC power supply, the maximum filter input signal is: 10K Ohm X 500 VDC = 5 VDC 1,000K Ohm With a fully grounded airfield lighting cable, there will be a maximum 5 VDC input signal to the filter circuit. Without any ground(s) on the lighting cable, the input signal is pulled down to 0 VDC. The accuracy of the circuit is dependent on a calibration routine using precision highvalue resistors, and the resolution of the A/D converter to the digital processor. The percentage of accuracy is reduced when the input signals drops down to tenths or hundredths of a volt, closer to the noise threshold. Insulation resistance can be measured with the CCR in an off state or while in service, as the IRMS DC signal is transparent to the AC lighting circuit. With a suitable control program, the IRMS tests can be performed on a scheduled basis, and coordinated with any circuit selector switches fed from a CCR so that all circuits are included. Page 11
7.6.3 Lamp Outage & IRMS Benefits
It could certainly be argued that lamp outage and IRMS functions can be performed by maintenance personnel. The benefits of including these features with an airfield lighting control system, if the original capital expenditures can be justified, are numerous. • • • •
All tests are performed in a predictable and repeatable manner Tests can be performed independent of any workforce schedules All test values are recorded, and include alarms on trending or fixed values System integrity and accuracy can be verified with annual calibration routines
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Digital Control
Control of CCR’s, until quite recently, has been with analog amplifier circuits. While these have provided reliable and reasonably accurate control for years, there are a few disadvantages. 8.1
Analog Control • • • • •
Settings can deviate or drift with time All adjustments and settings are done manually High degree of skill and experience needed for proper setup Advanced features are either not available, or difficult to implement Diagnostic aids, setup help, additional information or prompts are not available
The benefits of a true digital process controller have long been realized, but until the development of the microprocessor have not been feasible. The major advantage of a digital controller is the ability to readily communicate with other devices or computers, and the high level of performance that can be provided. The performance of a digital controller is much greater than any analog type because of the extreme accuracy of the processing function, and the increased complexity that the control function can provide. Overall control of a process can be with accuracies of better than 0.1%. The limiting factor on overall system performance is with any analog to digital (A/D) or digital to analog (D/A) converters that are used. Because of their analog design, the same type of errors with analog controls can be experienced with these devices. There is considerable responsibility placed on the developers of digital controllers to ensure that the firmware program used is properly and thoroughly tested, and customized to the process being controlled. Once the firmware program is completed and stored on the digital processor, the only changes that can be made are those allowed by the developer. These are generally limited to calibration or configuration options. The process control for the CCR output current, for example, cannot be modified; nor should it need to be.
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Digital Control Unit
A Digital Control Unit (DCU) is a packaged system that relies on the accuracy and advanced features that are available with a Digital Signal Processor (DSP). A number of suppliers have developed a DCU specifically for the control and monitoring of a CCR, whether a Ferroresonant or SCR type. Regardless of the supplier, an effective DCU package will have the following key elements. • • • • • •
Power supply for all circuit boards Processor circuit board with DSP and static memory Digital input circuit board Digital output circuit board Alphanumeric display, integrated with keypad for operation For ease of maintenance, all circuit boards should be with a plug-in design
A typical DCU with integral display and membrane keypad is shown below. 1. The first line of the display below details the operation of the CCR in Local mode. The “ok” status indicates normal operation, without any faults. The “7h” indicates a total of 7 hours Local operation. 2. The second display line is with the CCR in operation at B5, and with a total of 7 hours at that step. 3. The third line displays the output current level of 6.60A. 4. The fourth display line, with the CCR in operation, is with the first two buttons available for changing the output current down or up. With the CCR already at B5, in this case only the down button will function. The MENU button allows additional display values to be selected. 5. Depending on whether the CCR is in operation or being configured or calibrated, the function assignment of the four buttons will change accordingly.
DCU Integrated Display & Control Panel
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9.1
DCU Features
The DCU provides advanced features and benefits for the local or remote control of a CCR. All analog measured values are converted instantaneously to digital codes and processed using a custom algorithm designed and optimized for use with CCR’s. The operational data, the status of the CCR and measured values can be monitored on a display with 4 rows of text, 20 characters each. All settings, adjustments, configuration and calibration functions are done digitally using the integrated display and function keys. The user is guided through all menus by means of clear instructions on the display. A numeric password is used to access these functions and to prevent unauthorized changes. The configuration and calibration values that are developed or changed are stored with an Electrically Erasable Programmable Read Only Memory (EEPROM). The contents of the EEPROM can also be stored or transferred to a removable cartridge. The cartridge, with 256KB memory, allows any CCR configuration to be stored and easily read into a different regulator. 9.2
Analog vs. Digital Control
There are considerable advantages with a digital control for the operation of CCR’s. A number of these are covered with a few key points. 9.2.1.1
Current Regulation
With analog control, the overall accuracy of the output current regulation is dependent on matched analog components. Regardless of the analog design, thermal drift of compone nts and long-term drift will decrease the accuracy over time. Even with an effective design, it is generally recommended that a full calibration and inspection be performed at least once per year. With a DCU, the accuracy is determined by the firmware parameters, and by the accuracy of the A/D or D/A converters that are used. There is no thermal or long-term drift, and no affect on the output accuracy as the firmware algorithms remain unchanged. 9.2.1.2
Output Current Adjustment
The adjustment of output current with analog control is generally with potentiometers. The proper setting of the output levels is highly dependent on the workmanship and the skill and training level of maintenance personnel. Long-term stability can only be ensured with an effective preventive maintenance program. The DCU allows output currents to be selected with the use of up/down function keys. A CCR can be changed from a 3 step to a 5 step simply by selecting the appropriate configuration from a displayed menu.
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9.3
Additional DCU Features
The DCU includes a number of standard display and control features. CCR off/on Power supply OK CCR local/remote Open circuit alarm Overcurrent alarm Status of CCR (OK, Failure) Output current & brightness step • • • • • • •
The FAA specification for L-827 monitoring with an L-829 CCR is readily available for new or existing DCU systems with a memory cartridge software upgrade, as long as the CCR is fitted with a suitable output CT and PT. The L-827 monitoring system includes the following. Lamp failure warning and alarm (two settings) Number of failed lamps Additional warning & alarm output relays Input voltage, current & power measurement Output voltage and power measurement • • • • •
With additional hardware, the following optional items can be provided. These advanced features can be installed at any time, either with the original installation or at a later date. Insulation measurement warning and alarm (two settings) Insulation resistance value Serial I/O communication board, for distributed control through Ethernet or other popular protocols Single Lamp Control & Monitoring (SLCM) using power line carrier or serial communication • • •
•
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Distributed Control for CCR’s
Distributed control, while available as a PLC and dedicated processor solution (as detailed with Section 7.6 Distributed ALCMS) can also be included as an integral part of any CCR that is controlled with a DCU. This is achieved with the installation of a Serial Input Output (I/O) card into the rack of the DCU. The Serial I/O card is designed with built-in dual Ethernet ports. This allows full control and monitoring communication with the CCR through an Internet Protocol (IP) address. The Ethernet serial communication protocol provides reliable, high-speed access using standard hardware components. With an electrical vault location, a PLC or PC with Ethernet capability may still be needed to act as a central information processor. The PLC can also provide additional connectivity to other Ethernet devices, or to a maintenance and/or tower computer for control/display purposes. While the DCU itself will annunciate or alarm on critical faults, a PLC or PC program can provide additional configuration options such as alarm filtering and alarms based on calculations from the CCR input or output current and voltage values. With a fully distributed control scheme, the processing capability of the entire system is with increased reliability. The failure of a single CCR will not affect the rest of the communication network. With local processing at each CCR, an intelligent failsafe program can be implemented. If there is a communication failure to a specific CCR, a user configurable default control action is triggered. This can be with the CCR being turned off, or on at a specific brightness step.
Redundant Ethernet Configuration ALCMS
Switch
CCR1
CCR2
Switch
CCR3
CCR4
CCR5
CCR6
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10.1
Serial I/O Communication Card
The availability of a Serial I/O card that can be readily installed into a new or existing DCU controlled CCR provides a number of features and benefits. 1. Built in functions provide a reliable and economical distributed control system. 2. Dual communication ports are ideal for redundant configurations, and provide increased reliability. 3. High level serial communication provides sophisticated technical monitoring and control capabilities. 4. Other communication protocols can be used with the addition of plug-in cards. 5. Failsafe functionality installed directly at each CCR or control point.
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Airfield Lighting Distributed Control
With the availability of the Serial I/O card, additional control schemes for fully distributed control of an entire airfield become possible. While the Serial I/O card is intended for use with the DCU card cage, it can be powered with 24 VDC from a separate power supply. This is so the Serial I/O card can annunciate a loss of power at the CCR along the communication network, but also allows for operation independent of the DCU. With this feature, the Serial I/O card can also be used with standalone applications. Along with suitable and separate circuit boards, Analog I/O and Digital I/O functions can be readily provided. With the companion analog and digital cards, a compact and economical package can be installed to control virtua lly any type of power equipment. Constant Current Regulators (of any type or manufacture) L-847 Circuit Selector Switches Rotating Beacons Runway Guard Light Control Panels Stop Bar Control Panels • • • • •
The communication network can include any combination of fiber optic lines, copper wire control cables and wireless radio modems.
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Summary
The combination of CCR’s with digital controls, and the availability of a standalone digital control package for virtually any other device provides a number of comprehensive options for a high speed distributed control structure. 1. With a new installation for an airfield lighting vault, the Serial I/O card can be included with the DCU of each CCR. The CCR’s, connected with standard CAT 5 Ethernet cables, can provide a comprehensive data stream of all operational parameters to multiple control locations . Any other devices such as L-847 circuit selectors can also be controlled and monitored with the standalone digital control package. 2. For existing installations where new CCR’s cannot be economically justified, installation of the standalone digital control package into all CCR’s and other devices can provide all the benefits of the distributed control structure. 3. With compatible CCR’s, an upgrade kit can be provided that will replace the electronic components and controls with a new regulator door. When any door is upgraded, the Serial I/O card from the standalone package can be “recycled” directly into the DCU card cage. 4. The addition of lamp outage monitoring and insulation resistance monitoring systems can be of considerable benefit to maintenance personnel. In place of an aggressive preventive maintenance program, the control system can be relied upon to record and annunciate not only system faults, but a degrading circuit condition as well. While these functions can be added to any system, they are ideally suited for use with the DCU, and can be selectively implemented with hardware and software upgrades.
October 16, 2003
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