Machine Vision & Web Inspection Single-Link CoaXPress is game changer
for machine vision applications By Donal Waide, director of sales at BitFlow
F
or the past decade, system integrators have been promised that that the USB3 and GigE Vision
interfaces they relied upon would gracefully evolve, delivering faster and faster throughput speeds to keep up with increasing camera resolution and frame rates. Ten Gigabit Ethernet via USB3 and GigE
Vision would be within reach without added expense, complexity or heat. And of course, this could all be done without a frame grabber. That has not been the case. Ironically, it was CoaXPress or “CXP”, a new
serial communication interface based on a frame grabber, that answered the machine vision industry’s promises, not USB3 or GigE Vision, in 2009. CXP supports up to 6.25 Gbit/S from camera to frame grabber over a single, long-range coaxial cable; this is approximately six times faster than GigE Vision and 40 per cent faster than USB3. For higher CXP bit rates, two or more coaxial cables can be used in parallel, ie., by scaling to four cables, data rates of 25 Gbps can be reached. In addition, CXP offers the benefits of a low speed uplink channel used for camera control or triggering, while a 24 V power supply can deliver up to 13 Watts per channel to a CXP camera. The newest version of the interface, CXP v2.0, will double data rate speed to 12.5 Gb/S (CXP-12) per link. Prototypes with these new interface speeds will be available in 2019. CXP-12 is on the roadmap of many companies, and will find its way into cameras and frame grabbers and other products very soon.
10 GIGE VISION FALLS SHORT Going head-to-head with CXP 2.0 is the new 10 Gigabit Ethernet (10 GigE Vision) interface. Long before its introduction in 2016, 10 GigE Vision was touted as being the ultimate solution for taking full advantage of the latest generation of high-performance sensors with their higher resolution, frame rates, bit depth and dynamic range. 10 GigE provides a tenfold increase in data transmission speeds over its predecessor, GigE, and was specifically targeted for high- speed testing environments. Unfortunately for its proponents, 10 GigE has fallen short of its hype. Exceptionally power hungry, it requires up to 7 Watts, in addition to the cameras power requirement, roughly twice that of other interfaces. Nor has 10 GigE shown itself to be efficient with handling heavy data loads. It leans on the
38 February 2019
PC’s CPU and internal memory bus for operation because processing and buffering cannot be offloaded to a frame grabber FPGA or to memory. PnP discovery and operation is also required under all circumstances, making for a complex system subject to regular bottlenecks. And while power over cable and real-time triggering are said to be planned for its next version, 10 GigE does not offer them now. Ironically, high-data applications using 10 GigE actually need a frame grabber to offload CPU and memory, therefore eliminating what was the principle benefit of the standard over CXP. Cost benefits of GigE Vision are further diminished because expensive, high-end server components are its backbone. All things considered, 10 GigE appears to be a step backward, rather than forward. Similarly, USB 3.1 Vision (SuperSpeed+) has fallen short of expectations. Limited to 1-3 meters with a passive cable, versus 40 meters for CXP, USB 3.1 Vision requires expensive active cables for each camera on a typical system. Again, like 10 GigE, there is a cost trade-off that reduces the CXP vs. USB 3.1 Vision argument to a toss-up when you factor in the newer, smaller CoaXPress cameras and single channel frame grabbers. Other downsides to USB 3.1 have proven to be significant latency and image jitter, lower PoC wattage and the simple fact that it cannot go beyond 1.25GB/s (10 Gbps).
SINGLE-LINK CXP The original version of CXP (v1.1) and its follow-up (v1.1.1) were designed primarily for larger and quicker sensors, but now that this product category is maturing, a new avenue has emerged: small single-link CXP solutions. It is here that CXP truly shines and holds the greatest potential to disrupt the status quo. First generation CXP cameras were bulky,
energy inefficient, and cost considerably more than similarly featured GigE or USB3 cameras. That has changed with the latest incarnation of single-link CXP cameras that combine ultra-compact dimensions with lower costs, reduced power requirements and all the speed of a full sized CXP camera. CoaXPress v2.0 will push single lane speeds to 12.5 Gbps, qualifying the single link CXP camera/frame grabber solution not only for high-speed machine vision but for airborne and naval optronics, homeland security, and other industrial applications. A single-link CXP system is very easy to
set up. It features a CXP camera with a single link connector, usually BNC or DIN, along with a single link frame grabber with a DIN connector. Street price for a 4MP CXP camera, a single link frame grabber, and a cable of 2-5m is about 15-25 per cent higher than a similar USB3 offering, but offers 40 per cent higher bandwidth. Plus, as the cable length increases, so too does the price gap between CXP and USB3 narrow. As the saying goes, for a little more, you get a lot in return. Some customers opt for higher bandwidth quad-link CXP cameras but at single-link speeds. This versatility enables the system designer to achieve greater distances, yet still maintain all the capabilities and advantages of a frame grabber system. The advantages here of a CXP single-link system are utilization where a small camera will fit (29 x 29mm) but USB3 isn't quick enough any longer. Another advantage of the single-link CXP solution is cable length. In the real world of industrial imaging, cable routes are rarely straight lines. This is especially true in the packaging industry where an entire machine can be as long as 10m. Cabling in these systems can be as much as twice that. With an active USB3 cable, the costs are very high. However, a 20m coaxial cable will be pennies on the dollar in comparison. Another place where CXP is becoming
more commonplace is in the replacement of GigE in high-end surveillance. By delivering six times the bandwidth over the same distance as GigE, CXP allows a security team to deploy high-end facial recognition instead of seeing only a blurry image of the subject from afar. Using functions to control the camera with zoom, pan and tilt, the single-link CXP option becomes a powerful tool for companies.
CONCLUSION The performance advantages of 10 Gbps speed in machine vision are clear but because of several issues, what is not as obvious is which interface represents the most practical, reliable and cost-effective solution: USB3, 10 GigE Vision or CoaXPress. On the surface, USB3 and 10 GigE seem to solve many limitations, but when power consumption and cost increases are introduced, CoaXPress rises as the winner, especially in light of its newest version, CXP v2.0, that doubles its speeds to 12.5 Gb/s.
bitflow.com
convertermag.com
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