GPIB Extenders

GPIB extenders are used to remove the restrictions on cable length specified in the IEEE 488 (GPIB) Standard, while maintaining optimal performance (maximum data rate, transmission quality, etc.). The IEEE 488 Standard specifies that the total cable length of a GPIB system cannot exceed 20 meters. With an extender it is possible to increase the cable length to several kilometers without lowering the overall performance of the system.  GPIB extenders work in pairs transmitting signals back and forth between themselves and the GPIB network.  Each of the extenders has a GPIB port, and in most cases, more than one other type of transmission port. Extenders are used to alter GPIB signals into a different protocol and transmit this data to the other extender, which in most cases is at a different location.  The second extender receives the data, translates it back into a GPIB signal, and transmits it through its local network.  This process can be repeated numerous times allow information to be disseminated quickly through many systems over a wide area of networks.

As with an expander, GPIB extenders can be used to increase the total number of peripherals connected to a system.  The IEEE 488 Standard limits the number of peripherals that can be attached to a system to 14 or fewer.  Each extender is able to receive input from up to 14 devices, but when extenders are used in pairs, they can receive input from 28 total devices.  Larger system extender configurations can interface with even greater numbers of peripherals.

When connecting between systems, GPIB extenders can use a number of cables.  The most common among these are multi-conductor, coaxial, and fiber optic. Each of these cables has their own benefits and disadvantages.  Multi-conductors have a fast transmission rate, but are also the most expensive. Conversely, coaxial cables are the least expensive, but are susceptible to interference and timing delays, especially when used over long distances.  

Fiber optic cables can extend a GPIB system over long distance with the little timing loss, and a high degree of impedance resistance. These cables are especially useful in industrial applications where the cables are routed next to machinery or power lines, as they resist electrical current and surges. Finally, fiber optic cables enhance security. Because the cables transmit light instead of electric current, fiber optic transmission provides a non-emitting signal path immune to unauthorized eavesdropping.

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