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Cables and Connectors: Underestimated, Underappreciated, and Essential
by Winn Hardin, Contributing Editor - AIA Posted 12/20/2016
Cabling may receive the least amount of attention when a vision system is being designed, but like a thorn in the lion’s paw, it can be the tiny thing that brings the beast down. A suitable data cable could mean the difference between flawless widget inspection and damaged product in the hands of end-users. Recent updates to the communication standards, along with cables and connectors themselves, demonstrate the advantages and limitations of selecting the appropriate solution.
Go Rugged or Go Home
For GigE cameras, Components Express, Inc. (Woodridge, Illinois) reports that camera makers are advocating for more industrialized connectors. “In the next few years we expect the RJ45 connector will begin to disappear and the M12 X-code will be adapted in its place,” says Steve Mott, vice president at Components Express. “The M12 X-code isn’t subject to any kind of vibration issues. It has screw-down locking and offers IP67 waterproof protection, versus the RJ45, where even with screws it’s not suitable for use in harsh environments.”
Mott also notes that the M12 has much more standardized mating and connector lengths, making it a plug-and-play option. What’s more, unlike the RJ45, the M12 X-code can be adapted to 10 GigE standards.
That’s not to say that RJ45 will vanish altogether. “If you look at lower-cost GigE cameras like Teledyne DALSA's Genie Nano or Basler Ace, they’re using economical small-form-factor I/O connectors and staying with the RJ45,” says Ray Berst, president of Components Express. “You don’t want a €100 I/O cable for a camera that costs €300. Connector selection really depends on the market segment the camera is built for.”
On the USB3 front, cable length represents the biggest challenge. “The standard itself, USB 3.1, was written for a maximum of 1 meter cables,” Berst says. “The cable companies within USB3 Vision are working to agree on an electrical standard that would allow cables 5 to 10 meters in length.”
One solution is to use active copper cables, “but here again, we get into cable assemblies that are approaching the cost of the camera itself,” says Berst.
Going the Distance
Another protocol that suffers from distance limitations is Camera Link, which has a maximum cable length of 10 m. Though cost prohibitive for some applications, one option for overcoming length restrictions is to convert Camera Link electrical cables to the fiber optic transmission.
Engineering Design Team (EDT), Inc. (Hillsboro, Oregon) makes Camera Link extenders that provide long-range capability up to 100 kilometers from the host computer, depending on the cabling and transceivers.
In addition to length, converting Camera Link to fiber optics offers the benefit of electrical isolation. “They are often used in observatories where there’s a camera on a telescope,” says Cliff Hayes, field application engineer for EDT. “If lightning hits the telescope, it’s not going to come down the wire and damage the computer since there’s no electrical path between the telescope and computer.”
Electrical cables also can be heavy and cumbersome. “A fiber-optic cable is much lighter and offers extra flexibility for certain applications such as in aircraft, when they’re trying to cut back on size, weight, and power,” Hayes says.
VisionLink XF, EDT’s newest product, winnows down the cabling package even further. “A lot of Camera Link cameras have two SDR26 or MDR26 connectors at the camera end and framegrabber end, and for years we have been providing this four-converter system with our existing VisionLink RCX module,” says Randall Henderson, senior software engineer with EDT. “VisionLink XF puts all of that into one box and goes over a higher-rate fiber optic with one duplex or even simplex fiber optic cable instead of two pairs.”
The result is a setup that is “much smaller, much lighter, and can go much farther,” Hayes adds.
EDT’s VisionLink extenders have been purchased for a wide swath of research, military, and commercial applications, according to Hayes. Among them are LCD flat panel inspection, military target tracking, deep ocean videography, and optical measuring and laser marking.
The converters also are used in a few niche but notable scientific applications. At the SLAC National Accelerator Laboratory in California, VisionLink RCX fiber extenders ensure that the laser beam is focused and at the correct power at particular points along the accelerator. Meanwhile, the Laser Interferometer Gravitational-Wave Observatory (LIGO), also in California, employs EDT’s extenders as part of its optical thermal compensation system.
Hayes sees new market opportunities with manufacturers who are expanding their operations. “As they get larger and larger, the company might want to move their machine vision and computer systems off the floor to more of a lab environment, and extending Camera Link over fiber is going to be an important part of that equation,” Hayes says.
Camera Link Sticks, CoaXPress Evolves
By many accounts, Camera Link is sticking around for the count. EDT’s Hayes says the lower-bandwidth modes of Camera Link “have been overtaken by GigE cameras, cables, and network interface cards, and it’s similar for USB 3 as well. But the higher-speed, higher-bandwidth applications still seem to be pretty commonly served by Camera Link products.”
Even then Camera Link has competition as Camera Link HS and CoaXPress (CXP) look to go faster and farther. “Quite frankly, we expected CoaXPress to take over a major portion of market share, but Camera Link is still going strong,” says Components Express’s Berst. “People like that Camera Link is a real-time system. Plus, they are comfortable with the software interface. When system integrators build a system, they go with what they know.”
Although CoaXPress adoption rates may not be as high as expected at this point, Berst touts its advantages. “It allows for long cable length (in excess of 100 m), it’s more robust and relatively inexpensive compared to twisted-pair and other lower-bandwidth assemblies,” he says.
CXP continues to be a work in progress as it targets data rates of 12 Gb/s by mid-2017. “The CoaXPress committee is currently looking at its next generation, and the problem of cables and connectors is very much at the center of the story,” says Reynold Dodson, president at BitFlow, Inc. (Woburn, Massachusetts). “CXP supports BNC and DIN 1.0/2.3. But it turns out that the DIN connector is not ideal for higher speed.”
To that end, UK-based COAX Connectors suggests that CXP adopt what’s known as the mini-BNC. “This should handle 12 Gb/s data and beyond and be mechanically more robust in the DIN connector,” Dodson says. “However, this will be quite a disruption as vendors are not happy about adopting yet another connector.”
Like any aspect of machine vision, cable and connector selection is driven by speed and economy. “For our entire lifetime in machine vision, people have wanted to go longer, faster, and cheaper,” says Component Express’s Berst. “That’s never going to change.
Mike Miethig (January 3, 2017 11:11 AM)
The article didn't provide information about the Camera Link HS connectors. The SFF-8470, commonly called CX4, is about the size of the MDR connector and has thumbscrew locking. A single cable running at 3.125 Gbps, supports 2.1 GByte of effective band width (BW) over 7 lanes of data (21.9 Gbps) and has a high speed uplink giving real time response. At 3.125 Gbps a distance of 15 meter is achieved. As DALSA has used this cabling system for 6 years, there are flex life rated cables available. The connector is used by Infiniband at 5 Gbps and DALSA has released product that runs the cable at 5 Gbps for 3.3 GByte of BW achieving 5 meter distance. Cameras needing longer distance can take advantage of the plug on Active Optical Cables from Alysium and Hewtech at much lower costs than Camera Link to Optical adapter boxes. The CLHS roadmap for the connector calls for operation to 16 Gbps per lane as Meritec improved the electrical performance of the SFF-8470 to 20 Gbps. At 16 Gbps, the single cable is expected to achieve 13 GByte/sec of effective BW using the 64/66 encoding developed for the SFP+ optical connector. CLHS also defines the SFP+ connector, running 10.3125 Gbps with 64/66 coding, which provides 1.2 Gbyte/sec of bandwith and uses low cost SFP+ modules and low cost fiber optic patch cables achieving 300 meter distances. A search on the internet for the transceiver modules and fiber patch cable shows the cable cost is $45 inclusive for 30 meters. Truly a very low cost solution that has proven to be robust as well. You can learn more about CLHS at AIA website www.visiononline.org Mike Miethig, Camera Link HS Chair
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