Communication networks are typically used in control systems to transfer data between field devices, PLCs, and personal computers, providing the backbone of smart grids tasked with data processing and storage, operator interfacing, and information management. In this blog, we will provide a brief overview of how these communication networks work and the diverse set of industries that use them.
While a communication circuit consists of two pieces of equipment with a circuit between them, the term “network” refers to when many devices are connected together to permit the sharing of data between devices over a single circuit. Data is transmitted through the use of serial communication in which strings of data, or bytes, are transmitted sequentially from one device to another. The collection of data in a single transmission is called a packet, and the rate at which the data is transmitted over a network is defined in bits-per-second.
SCADA communication is one such system that operates with an industrial communication network. Short for “Supervisory Control and Data Acquisition,” this system consists of an industrial control system designed to monitor factory operations either on-site or remotely. In SCADA systems, there is a communication network that connects the individual PLCs to the operator interface equipment located in the central control room. For control system capacities, networks are used at lower levels for communication between different PLCs in the same industrial facility or for communication between field devices and individual PLCs.
While not usually implemented in SCADA systems, local area network (LAN) and wide area network (WAN) are two terms important to management information system communication. A LAN consists of PCs and servers within a particular site. A WAN is created by providing a connection between LANs, usually with long distances between them by using telecommunications industrial facilities. In some instances, large SCADA systems are required to interface to LANs or WANs in order to enable data transfer to management information systems or to allow internet access to SCADA system data.
A majority of communication networks utilize either electrical conductors such as copper wire or optical conductors such as fiber optic cables to transmit data signals between devices. The location on a device where the circuit is connected is called the communications port. It is important to note that the physical and electrical characteristics of the port must mirror the media being used in the network.
Copper-based networks are often used between devices and PLCs or between PLCs, but should not be installed over long distances or across a facility boundary. More than that, they should be of shielded construction, consisting of either a shielded twisted pair (STP), unshielded twisted pair (UTP), or coaxial cable (COAX).
A shielded twisted pair (STP) configuration includes pairs of insulated conductors that are twisted together to reduce inductively coupled interference. More than that, they are wrapped in a metallic foil shield to reduce capacitively coupled interference. These pairs are typically assembled into a cable with an overall jacket that provides protection against environmental stressors.
An unshielded twisted pair (UTP) has a similar configuration and protective jacket, but the major difference is their cost-effectiveness and ease-of-use. STPs are less flexible and have a larger diameter, which can take up more space in a circuit. UTPs, on the other hand, are malleable and provide faster transmissions.
Lastly, a coaxial cable (COAX) consists of a single conductor coated in an annular layer of dielectric material that is blanketed with a metallic braided shield and overall jacket. They are available as twin-ax (two cables) or tri-ax (three cables) styles, and are always shielded.
In fiber-based networks, optical fibers are responsible for transmitting data as pulses of light produced by an LED or laser transmitter. These pulses are then detected by a photodiode or phototransistor receiver at the other end of the fiber. In addition, fiber optic transceivers are used to convert electronic data into pulses of light. Each optical fiber is equipped with a glass fiber core layered with cladding. With the core and cladding having different indexes of refraction, light waves are able to travel through the core and be reflected from the interface.
There are two types of fiber cables used in industrial communication systems: single mode fibers and mutli-mode fibers. A single mode fiber has one core strand with a single transmission path, providing high data transmission rates over long distances. More than that, they are often used for long-distance telecommunications and video applications.
In contrast, multi-mode fibers have multiple core strands, enabling multiple signal paths to transmit data. Due to there being multiple paths, the possibility of distortion is high; therefore, these are better suited for short-distance applications.
If you find yourself in need of cables for copper-based or fiber-based networks, or other components necessary for such circuit applications, rely on Infinite Industrials. Infinite Industrials is a premier supplier for industrial parts and components sourced from thousands of trusted global manufacturers. Kickoff the purchasing process today with a competitive quote for your comparisons, and a dedicated representative will reach out to you with a sourcing solution that best meets your needs and requirements. Alternatively, you can call or email us directly; we are available 24/7x365!
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