Over the past decade the machine vision industry has witnessed transformative change in interface standards. For instance, CoaXPress 2.1 (CXP) — the industry’s most powerful interface — can now stream image data from camera to host PC at a previously unattainable 12.5 Gbit/sec per link with the potential of 50 Gbit/sec when a single quad-link camera is connected to a quad-link CXP frame grabber. More gains in throughput are on the horizon as camera manufacturers continue to push bandwidth limits with larger sensors, increasingly higher pixel counts, and faster frame rates.
While this progress has been welcomed by system integrators at the high end, the machine vision landscape can often consist of applications that simply don’t require the blazing speeds of CXP or 25 GigE Vision, and furthermore, can’t justify their expense. These low- to medium-performance use cases include automated inspection processes, science research, medical imaging, and others in a data rate range between 100 MB/sec to 800 MB/sec. Integrators designing these less demanding systems are staying the course with a well-established interface with a robust track record of handling large amounts of data easily and securely: Camera Link. Car Door Wire Harness
Published by the Automated Imaging Association (AIA) in 2000, Camera Link was the first high-speed digital camera interface standard. It works by transmitting serialized data streams based on LVDS (Low Voltage Differential Signaling). Basically, a parallel-to-serial transmitter is used at the camera while a serial-to-parallel receiver is on the frame grabber inside the PC. The current AIA Camera Link standard is version 2.1, which defines the cable, connector, and signal functionality between the camera and the frame grabber.
Over the years, Camera Link has taken modest steps forward. Camera Link 1.1, published in 2004, added the GenCam software standard for plug-and-play interoperability. In 2007, Camera Link 1.2 integrated Power-over-Camera Link (PoCL) and mini SDR connectors. Originally there were only three variations of Camera Link: Base (255 MB/sec at the maximum chipset operating frequency of 85 MHz), Medium (510 MB/sec), and Full (680 MB/sec). Deca mode (80-bit, 10-tap) was later added boasting the power to transmit 850 MB/sec. Like Medium and Full, Deca configurations require the use of a second cable.
In 2012, the AIA launched Camera Link High Speed (CLHS), a standard based on data packet delivery rather than serial. Hypothetically CLHS can transmit 3.125 Gb/sec over copper or fiber optics. Adoption rate for CLHS has been slow, however, hampered by its lack of support for DMA (Direct Memory Access) and not being backwards compatible with older CL devices. Only a handful of manufacturers are offering CLHS products, limiting competition (pricing) and options for customers.
In an industry marked by rapid technological advances, the demand for Camera Link has remained constant for more than two decades. In fact, according to one leading research company, Camera Link is expected to experience continued growth globally due to an increasing need for high-quality imaging in machine vision, healthcare, and surveillance. The North American market for Camera Link products is predicted to grow ten percent annually until 2030.
With so many interfaces available, why is Camera Link still viable? There are several reasons:
Although Camera Link cannot compare to many of the newer interface standards in performance aspects, the interface does support relatively high pixel depths, fast frame rates, and large image sizes. For instance, if you deploy a base-configuration CL camera and a quality frame grabber you can expect to acquire 4MP images at 50-60 frames-per-second or faster. Use of a medium- or full-configuration camera may result in image acquisition of 1280 × 1024 images at 500 frames-per-second. A 4MP camera can hit just under 170 frames-per-second in Deca mode.
When smart cameras were first introduced, many in the machine vision industry assumed that the era of the frame grabber had passed. Smart cameras use USB or Ethernet to connect to the PC, therefore eliminating the need for a frame grabber. Yet even the most advanced smart cameras have proven to be only appropriate in low-end applications— the cabling alone limits the data rates for these cameras. For fast, high-quality imaging with maximum design flexibility, a frame grabber is required, especially in industrial inspection.
Unlike a smart camera system, Camera Link frame grabbers do far more than simply capture images from a video stream. Camera Link frame grabbers can:
So, what should you look for in a Camera Link frame grabber? First, make sure that the frame grabber supports the camera’s mode (base, medium, full, Deca), tap configuration and pixel depth. Also, if you are using PoCL, verify that your frame grabber and cable supports it. If not, you will need to use a power supply for the camera. These are the very basics. Depending on the application you’ll also want to consider Camera Link frame grabbers featuring:
On the high end of the machine vision market, innovation is disrupting the industry —and quickly separating winners from losers. However, with most imaging applications today requiring between 100 to 800 MB/sec data rates, the oldest standard for digital cameras, Camera Link, remains a top choice for system integrators. Before you give into the impulse to specify the latest, fastest machine vision interface, do your homework and explore if Camera Link creates greater performance and value.
Donal Waide is the director of sales at BitFlow Inc, a frame grabber manufacturer in Woburn, MA. He has been involved in the machine vision industry since the 1990s. For more information, call (781) 921-2900, email [email protected] or visit www.bitflow.com.
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