LEADING EDGE VIEWS: Is Camera Link High Speed the ultimate interface?
Donal Waide of BitFlow details the timeline of interface standards development, compares their implementation, and ponders whether there is a clear “winner” that may become most commonly used in the future.
Once upon a time, like with all new technology, there was a lot of confusion as to what constituted avideo interface between camera and computer. It was known that a frame grabber was needed but because the frame grabber and camera manufacturers were from places all over, there wasn't much agreement on how the two should be connected. This led to a time of several cameras with several cables; often the same camera manufacturer may have had different cables for each family of cameras on offer. Couple that with the fact that frame grabber interfaces also had no interface standards and you ended up with a lot of cables, sitting around long after the frame grabber or the camera had served its purpose. This led to standardization, and agreement by all parties on what constitutes an acceptable number of interfaces.
One of the early adopted and agreed upon interfaces was theCamera Link interface, first introduced in late 2000 (v.1.0) and adopted in 2004 (v1.1). The current revision (v1.2) was ratified in January 2007. In 2006, another interface, GigE Vision was introduced and the latest version (v1.2) was adopted in 2010.
As time moved on to 2010, it was accepted generally that Camera Link was the industry standard for vision systems requiring almost real-time data in small-volume systems (large image transfer with low latency) whereas theGigE Vision standard could support data transmission up to 100 m, albeit at a time loss. GigE Vision used standard Cat5 network cables, which are cheap as a cable needed for data transmission. Camera Link was standardized so the customer had a vast array of cameras and frame grabbers to choose from.
While other interfaces (analog, FireWire, USB2, etc.) are still out in the machine vision world, the design rule of thumb was Camera Link for high speeds and short distances and GigE for low speeds at long distances.
As one can see, both of these are fairly new interfaces but each has its own limitations. These limitations weren't realized until sensor technology began to develop at a fast pace in the 2000s. This development resulted in improved resolution and higher frame rates; there was an increasing need for larger bandwidth. It was time to develop a new standard, something that would be an improvement over the GigE and Camera Link interfaces.
An introduction of 10GigE Vision resulted in some benefits, but the resulting power requirements and the fact that the transmission speeds are similar to those of Camera Link Full (850 Mbytes/s) meant that universal adoption wasn't immediate and trepidation by some manufacturers slowed its growth.
Another option isCoaXPress, which was adopted in early 2011. CoaXPress is the current interface that will be the fastest growing for the next 3-4 years. Because of the low cost of cables, and the data transmission rates and achievable distances, this interface looks to be a major player in the coming years. Because CoaXPress can be currently expanded to four ports currently, resulting in 25 Gbits/s of data throughput, the technology expansion is resolved for now and the next few generations of sensor. CoaXPress also has the benefit of being able to operate on industry standard 75-Ω coaxial cable.
Camera Link HS ("high speed"; a new interface, not Camera Link 2.0) has taken some of the benefits of Camera Link and enhanced them, while in the meantime also has taken the weaknesses and eliminated them. Features such as a low-cost solution, scalable bandwidths, and reliable data delivery are part of this new interface.
The Camera Link HS interface is working in an unreleased state currently and it's poised to be a big player in the machine-vision market. However, the timing of its release will be a factor in its success. The recent adoption of CoaXPress and its many benefits has led several frame grabber manufacturers and camera manufacturers to build their newest product to this standard.
So is Camera Link HS the ultimate interface? In a perfect world, one could argue that it is, but in reality, there are too many machine-vision standards and solutions now for one to emerge as the one and only. Sure enough, Camera Link HS can adapt to the required bandwidth, but so can the others. HS can offer varying cable lengths, as can some of the others. HS can transmit data reliably; then again, so can many of the others.
When a customer needs a vision system, cost can be as much a factor as performance. Sometimes a customer needs options for more than one type of camera/frame grabber, and this is where the other standards are currently ahead of Camera Link HS. In the future, possibly as soon as the end of 2012, there will be a variety of cameras and frame grabbers offering HS, but for now, it's still the bridesmaid in waiting.
