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Section 10: Cameras
Section 10.1: Digital Camera Interfaces
144 +44(0) 1904 788600 | Edmund Optics® targets Digital cameras are available with a variety of interface options that
are often dependent on an application’s requirements. Some formats,
such as the USB varieties, can greatly simplify the setup process by
supplying video output and power via a single interface. Other formats
may require an additional power supply but provide advantages
such as higher data transfer rates, which affects the camera’s framerate,
or support for a greater number of simultaneous devices. Table
10.1 compares the different digital camera interfaces.
Table 10.1: Comparison of popular digital camera interfaces.Scale.
For more information on cameras go to
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Digital Interface Comparison
DIGITAL SIGNAL
OPTIONS
NOTE: images not
drawn to scale
USB 3.1 GigE (PoE) 5 GigE (PoE) 10 GigE (PoE) CoaXPress Camera Link®
Data Transfer Rate: 5Gb/s 1000 Mb/s 5Gb/s 10Gb/s up to 12.5Gb/s up to 6.8Gb/s
Max Cable Length: 3m (recommended) 100m 100m 100m >100m at 3.125Gb/s 10m
# Devices: up to 127 Unlimited Unlimited Unlimited Unlimited 1
Connector: USB 3.1 Micro B/USB-C RJ45 / Cat5e or 6 RJ45 / Cat5e or 6 Cat7 or Optical Cabling RG59 / RG6 / RG11 26pin
Capture Board: Optional Not Required Not Required Not Required Optional Required
External Power: Optional Required (Optional with PoE) Required (Optional with PoE) Required (Optional with PoE) Optional Required
USB (Universal Serial Bus)
USB 3.1 Gen 1, formerly known as USB 3.0, is a popular interface due
to its ubiquity among computers. It is high speed and convenient;
maximum attainable speed depends upon the number of USB peripheral
components, as the transfer rate of the bus is fixed at 5 Gb/s.
In USB3 Vision, camera control registers are based on the EMVA
GenICam standard. The USB3 Vision standard does not match that
of the computer standard of backwards compatibility, but some USB
3.1 Gen 1 cameras are backward compatible making them run at the
slower speed of USB 2.0 (480Mb/s). The most common USB 3.1 connector
used in the machine vision camera industry is the USB 3.1
Micro B connector. Gradually being introduced to the market is USBC
(USB Type C), the connection type designed for the future. It features
single and dual band top speeds of 10 and 20 Gb/s respectively.
Additionally, this connector has a smaller footprint and is reversable.
While cables and cameras that currently use USB-C are still limited
to USB 3.1 Gen 1 data transmission speeds, this newer connector will
be required as the industry adopts USB 3.1 Gen 2 as an alternative
high-speed interface.
GigE (Gigabit Ethernet)
GigE is based on the gigabit ethernet internet protocol and uses standard
Cat 5e and Cat 6 cables for a high-speed camera interface. Standard
ethernet hardware such as switches, hubs, and repeaters can
be used for multiple cameras, although overall bandwidth must be
considered whenever non peer-to-peer (direct camera to card) connections
are used. In GigE Vision, camera control registers are based
on the EMVA GenICam standard. Optional on some cameras, Link
Aggregation (LAG) uses multiple ethernet ports in parallel to increase
data transfer rates. Also supported by some cameras, the network
Precision Time Protocol (PTP) can be used to synchronize the clocks
of multiple cameras connected on the same network, allowing for a
fixed delay relationship between their associated exposures. 5 GigE
and 10 GigE are newer versions of the GigE interface that feature data
transfer rates of 5 Gb/s and 10 Gb/s, respectively.
CoaXPress
CoaXPress is a plug-and-play high-speed digital interface for use in
high-resolution machine vision applications that require a fast frame
rate. It uses a coaxial cable and is scalable for multiple cables; each
cable is capable of up to 12.5 Gb/s, and each cable can provide up
to 13W of power at a nominal 24V. Because of this scalability, there
is no set maximum for a cable length with CoaXPress; the higher the
bandwidth, the smaller the maximum cable length.
Camera Link®
Camera Link® is a high-speed serial interface standard developed
explicitly for machine vision applications. A Camera Link® capture
card is required for use, and power must be supplied separately to
the camera. Special cabling is required because, in addition to lowvoltage
differential pair (LVDP) signal lines, separate asynchronous
serial communication channels are provided to retain full bandwidth
for data transmission. The single-cable base configuration allows 2.04
Gb/s transfer dedicated for video. Dual outputs (full configuration) allow
for separate camera parameter send/receive lines to free up more
data transfer space (6.8 Gb/s) in extreme high-speed applications.
Capture Boards
Image processing typically involves the use of computers, which
means a digital interface is necessary when using analog cameras.
Capture boards allow users to output analog camera signals into a
computer for analysis; for analog signals (NTSC, YC, PAL, CCIR), the
capture board contains an analog-to-digital converter (ADC) to digitize
the signal for further image processing. Users can then capture
images and save them for future manipulation and printing. Basic
capturing software is included with capture boards, allowing users to
save, open, and view images.
The term capture board also refers to cards that are necessary to acquire
and interpret the data from digital camera interfaces but are not
based on standard computer connectors.
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