Camera Link 2.0 Improves on Cable Specification

When Camera Link was originally released in 2000, it represented a giant step forward in Machine Vision: it enabled a common interface to replace the proprietary pinouts used by LVDS cameras. All of a sudden, camera and frame grabber manufacturers could work hand-in-hand to offer interoperable products. In fact, version 1.0 was the result of the direct participation of 13 machine vision companies, but not one among them was a cable manufacturer. Perhaps it’s not a surprise that the cable aspects were limited to only 3 pages of the famous Appendix D of the specification.

Camera Link 1.0 indicates a maximum cable length of 10 meters. Though this might have proved adequate in the early days when cameras were using a 40 MHz pixel clock, many recent cameras are pushing the envelope by working with 80 MHz (or even 85 MHz) pixel clocks to achieve the largest transmission bandwidth possible: ten 8-bit taps @ 85 MHz representing 850 MB/s. This is where problems start: increasing the clock frequency puts an additional burden on the cable assembly. At 80 MHz, 6 or 7 meters is a more typical maximum cable distance. Needless to say that a major rework of Appendix D was needed to address the misleading information it presented.

Fortunately, the cable companies were well aware of the cable distance limitation. They rolled up their sleeves and started a collaborative effort to bring more rigor to the Camera Link cable specification. A first step was achieved with Camera Link 1.2 where Appendix D was lengthened to 13 pages. For the first time, the specification indicated that 10 meters was not always possible. But the Automated Imaging Associated (AIA) just released Camera Link 2.0 which provides an extensive description of the connectors and cables. And version 2.0 provides a cable certification procedure. This certification declares the maximum cable length for the pixel clock frequency at which the cable is certified.

I can tell you one thing for certain, since we have been using certified Camera Link cables, our frame grabber designers simply do not trust cables that arrive without a certified maximum clock frequency. And if you have a critical MV system to operate, I am sure you feel the same.


About Eric

Eric is in charge of R&D activities at the Montreal office of Teledyne DALSA where he is surrounded by talented people working on the technologies of tomorrow. Chair of the GigE Vision committee, he enjoys reading and writing machine vision standards, especially the thicker ones.
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