INSTRUMENTATION & CONTROL

The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/ Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.

UNSHIELDED TWISTED PAIR CONNECTOR
The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector, as shown in figure. A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

RJ-45 connector

COAXIAL CABLE
Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield, as shown in figure. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial.
Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable is popular in school networks, especially linear bus networks.

COAXIAL CABLE CONNECTOR
The most common type of connector with co-axial cables is the bayone-neill-concleman (BNC) connector (see fig ).

Different types of adapters are available for BNC connectors, including a T- connector, barrel connector, and terminator. Connectors on the cable are the weakest points in the network. To help avoid problems with your network , always use the BNC connectors that crimp, rather than screw, onto the table.

FIBER OPTIC CABLE

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical disturbance. It has also made it standard for connecting networks between buildings, due to immunity to the effects of moisture and lighting.

Facts about fiber optic cables:
Ø Outer insulating jacket is made of Teflon or PVC.
Ø Kelvar fiber helps to strengthen the cable and prevent leakage.
Ø A plastic coating is used to cushion the fiber center.
Ø Center (core) is made of glass or plastic fibers.