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| Control System Methods For Detention Facilities A Basic Overview |
| By Tim Lincoln P.E. |
| Published: 10/14/2002 |
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There are several basic types of control systems that are used in detention facilities today. These range from the simple to the complex, each having a distinct advantage or disadvantage over the next system. One system is not necessarily better than the other; the individual needs of each facility must be identified and then addressed to properly apply the best technology for the specific application. In many cases, combinations of two or more of the methods may be used to accomplish the task. Hardwired/Relay logic This method uses a power supply, switch and electric door operator at the most basic level. Interposing relays may be added to this system to create relay logic such as simple interlocks. This is the most simple and basic control method, and the most limited. Advantages * Most electricians can troubleshoot and repair a basic level system. * Minimum initial cost. * Minimum repair costs. * Systems with basic control functions have a high Mean Time Between Failures. Disadvantages * The addition of interposing relays for logic functions such as interlocks increases the complexity of the system beyond most technicians abilities. * Changing or modifying system operation is difficult. * Troubleshooting a system with relay logic can be difficult. PLC This method uses Programmable Logic Controllers (PLCs) to receive input (e.g., from control panels, doors position switches, alarms, intercoms) and then provides an output signal based on predetermined (programmed) criteria. A PLC is an industrial type computer and I/O device that has been widely proven in the automation industry. A PLC system can handle an unlimited amount of inputs and outputs with simple to complex logic functions. A trained technician can easily add, delete devices or change existing logic functions. This method is the most flexible and adaptable. Advantages * The system is completely programmable. Logic (criteria) changes can be easily made through programming. * Ease of troubleshooting * Trained third party service is available for most brands. Local service or programmers can be found to assist in maintenance and programming. Disadvantages * A trained technician is required to program (some electricians are PLC trained). * Higher parts replacement costs than Hardwire method. Computer This method covers a broad range of computer-based systems (PC type) that require proprietary I/O devices to connect to the system. The type of system most commonly used is a card access system that is adapted for detention use. Some systems are very basic while others can perform many other functions than door control alone. Some companies have designed systems specifically for detention facilities. These systems are usually proprietary (see Custom Control Systems for issues with proprietary systems). Advantages * One manufacturer/vendor is used for most of the system. * Technicians only need to be trained on one system. Disadvantages * Some systems may only have preprogrammed logic functions that could limit the systems ability to meet the needs of a unique facility. * Card access systems are designed for card access door control -- typical detention facilities have little or no need for card-controlled doors. This would then be using a product in a way it was not intended or designed. * Proprietary parts may be expensive and hard to replace. * Third party service may not be available or local. * Specially trained technicians are required. Custom Control Systems This method uses parts that are made specifically for one or several jobs. These systems are called proprietary. Therefore, installation, parts and service are only available from one source. This method, once constructed, is very limited on the ability to repair, upgrade or modify. Advantages * Possible lower initial cost. * System can be tailored to user's special needs and requirements that cannot be provided from commercial, off-the-shelf applications. Disadvantages * Possible higher costs in design, development and startup. * Replacement parts are difficult to get and, after a few years, most likely will not be replaceable. * Trained, third party service is not available. * Troubleshooting can be very difficult. * Very specialized technical skills are required for maintenance. Operator Interfaces As part of every control system, an operator interface (OI) is required. This is where the operator sends and receives signals to and from the control system. An OI may be a push button at a door or an over the door light indicating an unsecured door or call from within the room. OI's in control rooms may include control panels, computer screens, keypads, keyboards, computer mouse, touchscreens, monitors and audio systems. The most common detention facility OI in control rooms are control panels and computer display units also know as CRTs or "touchscreens." The term touchscreen may be used generically for any computer display OI including mouse or keyboard driven inputs. Control Panels There are numerous control panel sizes and materials for detention facilities. Ninety-nine percent of all detention panels are custom made for the particular facility. These range from the very simple, bare metal panel with switches and lights to metal-plastic, laminated panels with multi-colored graphics to identify each switch and light. There are three main physical components to each control panel: the panel and graphics, the components and the wiring. The layout design of each control panel is the most important component of panel design. Good panel design consists of more than just copying and pasting the floor plan onto the panel. Operator duties, line of sight, number of control points and graphical presentation are a few of the factors that are needed for good operator friendly panels. Advantages * Well designed panels are easy to use and maintain. * Can be maintained by most electricians. * Replacement of individual components is low cost. * Failure of one component does not affect other functions. Disadvantages * Require more real estate for each device on the panel. * Are difficult to modify or relocate. Touchscreens Touchscreens have become common in the commercial market place today for one main reason - the ease and low cost to change or modify the display information. Detention facilities have used touchscreens for another reason - consolidation of controls to a smaller area and the ability to monitor unlimited points. Thhis was previously restricted by the available real estate in a control room for panels. Advantages * Well designed panels are easy to use. * More control points can be consolidated into a smaller area. * Unlimited control points. * Total flexibility, changes and modifications can be easily made. * Trained third party service is available for most non-proprietary brands. Local service or programmers can be found to assist in maintenance and programming. * Redundant touchscreen control stations for busy areas are available. * Take over or shared controls of control panels or other touchscreen stations does not require additional equipment, panels or real estate. Disadvantages * Specially trained technicians required to maintain system. * Not as stable as a control panel (same problems a PC encounters). * Requires a PLC or other proprietary I/O point devices. Definitions: Electrician - A person skilled in the basic knowledge of the installation, maintenance and troubleshooting of electrical wiring, lights, outlets, switches on both 120 volt and less that 70 volt systems. Integrated System - Where two or more different types of systems are combined into a single user interface. I/O - Input / Output Logic - Where two or more inputs or other criteria are required before an output signal is generated. PLC - Programmable Logic Controller Proprietary - When installation, parts or service are from only one source. Non-proprietary is when parts and service are available from independent third party vendors. Technician - A person skilled in the basic knowledge of the maintenance, trouble shooting and programming of electronic systems. Skills may range from soldering circuit boards to programming. Mr. Lincoln is a Principal at Justice Security Inc. which is a consulting firm that specializes in providing Design and Construction Management services of integrated electronic security systems for jail, prison and courthouse facilities. For more information Mr. Lincoln may be contacted at 916 987-6762, lincolnt@jsi-usa.com or visit www.jsi-usa.com. |
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