Controller Classification
Controllers can be categorized by their capabilities and their methods of communicating (controller-to-controller). In general, there are two classifications of controller - primary control units and secondary control units
Primary controllers typically have the following features:
Controllers can be categorized by their capabilities and their methods of communicating (controller-to-controller). In general, there are two classifications of controller - primary control units and secondary control units
Primary controllers typically have the following features:
Real-time accurate clock function
Full software compliment
Larger total point capacity
Support for global strategies
Buffer for alarms/messages/trend & runtime data
Freeform programming
Downloadable database
Higher analog/digital converter resolution
Built-in communication interface for PC connection.
Secondary controllers typically have the following features:
Not necessarily 100% standalone
Limited software compliment
Smaller total point count
Freeform or application specific software
Typically lower analog-to-digital converter resolution
Trend data not typically stored at this level
Typical application is terminal equipment or small central station equipment.
Operator Interfaces
The next critical element in the system architecture is an operator interface. Operator interfaces are required to:
See data
Program the system
Exercise manual control
Store long term data
Provide a dynamic graphical interface.
There are five basic types of operator interfaces. They include:
Desktop computers which act as operator workstations
Notebook computers which act as portable operator workstations
Keypad type liquid crystal displays
Handheld consoles/ palmtops/ service tools
Smart thermostats
Desktop computers are centralized operator workstations where the main function is programming, building and visualizing system graphics; long term data collection; and alarm and message filtering.
Notebook computers may connect to the LAN through a communication interface that stands alone or is built into another device. The notebook computer connected to the LAN at a particular level may not have the same capability as a computer connected to the LAN at a higher level.
Keypad liquid crystal displays typically are limited to point monitoring and control. They may have some limited programming capability, such as changing a set point or time schedule.
Handheld consoles, palmtops and service tools are proprietary devices that connect to primary controllers or secondary controllers. Typically they allow point monitoring and control, controller configurations (addressing and communication set-up), and calibration of inputs and outputs.
Smart thermostats are sensors with additional capabilities. They connect to secondary controllers and have a service mode to allow for point monitoring, control and calibration. They also have a user mode that allows point information to be displayed, setpoint adjustment and an override mode.
PC/Network Interface
The communications interface shown in the Figure 11 is a communication interface device. It provides the path between devices that do not use the same communications protocol. This includes computers, modems and printers.
Notebook computers may connect to the LAN through a communication interface that stands alone or is built into another device. The notebook computer connected to the LAN at a particular level may not have the same capability as a computer connected to the LAN at a higher level.
Keypad liquid crystal displays typically are limited to point monitoring and control. They may have some limited programming capability, such as changing a set point or time schedule.
Handheld consoles, palmtops and service tools are proprietary devices that connect to primary controllers or secondary controllers. Typically they allow point monitoring and control, controller configurations (addressing and communication set-up), and calibration of inputs and outputs.
Smart thermostats are sensors with additional capabilities. They connect to secondary controllers and have a service mode to allow for point monitoring, control and calibration. They also have a user mode that allows point information to be displayed, setpoint adjustment and an override mode.
PC/Network Interface
The communications interface shown in the Figure 11 is a communication interface device. It provides the path between devices that do not use the same communications protocol. This includes computers, modems and printers.
It may be a stand-alone component or it may be built into another device as shown in Figure 12.
Translate protocol
Provide a communication buffer
Provide temporary memory storage for information being passed between the network and the external PC, modem or printer (mailbox function)Larger System Architectures
When systems become larger than the capacity of a single sub-network, a higher level of architecture is added to allow the use of multiple sub-networks.
Multiple site computers can be added to the site LAN/WAN. They can connect the site LAN/WAN via a communications interface, which may be a router. Site LAN/WAN computers can send and receive information from the entire system. Information can be received by each of the site computers, but can not be subsequently shared from one computer to another. Sub-network computers may only be able to see their own sub-network.
Site LANs allow multiple computers to communicate with each other. They may use commercially available computer network software and hardware. Messages, alarms and other data can be re-routed to other computers on the primary site LAN. Information stored in other computers can be remotely accessed. This includes graphics, programming and stored trend and operational data.
Combined Components
Some vendors combine multiple functions into a single device. In the following system architecture, Figure 14, the communication interface is built into the primary controller. A peer-to-peer LAN or sub-network is connected directly to the device.
In Figure 15, the key component in the system consists of a communication interface, a primary controller and an interface to the secondary polling network.
Auto-Answer/Auto-Dial System Architecture
In auto-answer/auto dial systems, a specialized communication interface is substituted which introduces a modem and phone lines into the standard architecture. These communication interfaces are made with built-in modems or use external commercial modems. Auto-answer/auto-dial configurations are used to provide monitoring and access to remote buildings. They are used where traditional direct-wiring methods are impractical; and where central site monitoring is desired; or where remote access to controllers is desired.
In an auto-answer/auto-dial system, the central communications interface may call the individual sites or vice versa. Information and data can be passed to and from the layer above the central communications interface (Figure 16).
The auto-answer/auto-dial LAN architecture is typically used by installations with multiple facilities where control and monitoring needs to be centralized. Multiple LANs are used to maintain the groupings of devices, or to separate controllers into defined groups.
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