It may seem as if there are far too many camera interfaces, but they're not all alike. Some, like USB and FireWire, are built on general-purpose protocols. The newest machine vision-specific interface, CoaXPress (CXP), is based on a different idea. A camera and frame grabber incorporating this interface debuted at this year's Vision 2011 show. Added to what's already out there, these items make choice in CoaXPress components a reality for engineers designing industrial vision systems.
Adimec demonstrated its first CoaXPress camera with dual interfaces. Each of the two CoaXPress interfaces of the Q-4A180/CXP area scan camera supports the standard's CXP-6 configuration, resulting in a maximum interface speed of 12.5Gbps. The camera uses two standard coaxial cables, each with a maximum transmission rate of 6.25Gbps over 45 meters.
Enough vision hardware components incorporating the coax-based CoaXPress camera interface, such as the Radient eV-CXP frame grabber from Matrox Imaging, are now available to give engineers a choice.
Matrox Imaging announced its Radient eV-CXP, a CoaXPress frame grabber based on the company's Radient family. The Radient eV-CXP has four independent CoaXPress links. This makes it possible to perform simultaneous image capture from up to four cameras, each of which can run at different CoaXPress speeds. Alternatively, the frame grabber can capture images from a single camera that uses link aggregation to transmit image data at up to 25Gbps.
Before the show, BitFlow began shipping its new Karbon-CXP frame grabber, which achieves video acquisition speeds of up to 6Gbps and sends control commands and triggers at 20Mbps over a single 75-Ohm coax cable up to 135 meters. Other cameras and frame grabbers have been released by Adimec, Active Silicon, Silicon Software, and Imperx.
The serial, packet-based, high-speed CoaXPress protocol was designed to overcome some of the bandwidth and cabling restrictions of the venerable parallel Camera Link protocol. CoaXPress achieves a base speed of 3.125Gbps per cable for distances of 100 meters between camera and computer, or a maximum sustained speed of 6.25Gbps per cable for distances of up to 45 meters. That compares very favorably with Camera Link's cabling limitation of 10 meters and a 6Gbps maximum speed that requires two cables.
Aside from speed, the most important feature of CoaXPress is the fact that it runs on good old coax. Coax cable is already installed everywhere. It's cheap, reliable, well-known, understood, and reliable. Engineers can achieve higher speeds by simply using multiple cables in parallel, and the standard doesn't limit how many cables they can deploy in a configuration. Today, coax cable is also available in many different varieties and quality grades.
There's still a huge legacy of analog cameras in industrial vision systems throughout the world, and a huge number of coax cables are connecting them. More than half of machine vision installations in Japan, for instance, are still dominated by analog cameras and coax cabling. Though CoaXPress is, of course, not backward compatible to analog interfaces, some consider it a relatively easy, cost-effective upgrade path from a cabling standpoint for introducing high-resolution digital cameras. The overall cost for replacing analog camera systems with digital CoaXPress cameras and frame grabbers would be much lower than replacing them with Camera Link cameras and frame grabbers. The opportunity is definitely there to repurpose a coax-based infrastructure with very low installation costs while reducing system complexity and improving performance.