Advanced Imaging


Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

Choosing the Optimal Cable for GigE Vision


By Bud Brown

Created and introduced by the Automated Imaging Association, the new GigE Vision™ interface standard provides a unique solution for real-time performance driven applications that require high speed transmission of uncompressed image data. Networked GigE Vision™ cameras use an European Machine Vision Association administered command structure known as GenICam. GigE Vision™ Control and Stream protocols optimize system performance through compatibility with standard, cost-effective Gigabit Ethernet hardware (while providing slightly more bandwidth than 1394b.) Installation connectivity is enhanced through the utilization of field-installable cabling and connectors that are available virtually everywhere in the world.

It has been projected that GigE Vision™ will be a dynamic motivating factor in the rapid expansion of vision into previously untapped and under-utilized markets. For this reason it is essential for both end users and application engineers to recognize the consequences of selecting (or not) the proper cable type for the application. The failure of the cable data path to perform as required both electrically and mechanically will mean the eventual failure of the entire system.

GigE Vision™ Cable

There is no GigE Vision™ designated cable. Depending on the system parameters and the required transmission length (up to 100 meters maximum for copper) GigE Vision™ will perform as predicted using Cat5, Cat5e, Cat6, or Cat6a (augmented) cable and the corresponding RJ45 type connectors. Any of these cables will perform quite satisfactorily when transmitting the amount of data required at the necessary speed at any length up to that 100 meter maximum. However the potential drawbacks come in some of the more unique and challenging applications because traditional category cables might be too stiff or too delicate. It is feasible that in some applications the use of traditional category cable could limit the design prospects due to its rigidity and the fact that it can easily break if not handled or terminated properly.

This potential for failure is due to the fact that category cables are typically produced with solid copper wire or a copper wire with a nominal number of strands. Category cables historically incorporate plenum or riser construction materials and techniques. Plenum cable products are stiff because they are coated with a fire-retardant substance (frequently Teflon®) so they can be installed in buildings in the area used for air circulation in heating and air conditioning systems. Riser type cable incorporates the minimum required cable construction that can be used for a riser application (i.e. floor to floor). Although it may be somewhat less stiff than plenum type cable it is still not suitable for applications in which the camera will be in motion.

These traditional category cable products are excellent products and will function as required when incorporated properly into a system design; but it is important to understand that they are intended for stationary applications. Because of this they may not necessarily be appropriate for applications in which the equipment will be in motion. When a vision application requires even a minimal amount of movement it is possible that a solid wire cable would not only inhibit the freedom of that motion, but it would also be highly susceptible to wire fatigue and subsequent failure due to breakage. In applications that require a significant amount of movement it will be desirable to have a cable that is not only designed to have flex-life but to be soft, tolerant and robust.

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