The essence of industrial cameras is to convert optical signals into electrical signals, which involves the conversion and transmission of electrical signals. Conversion and transmission require various physical interfaces and transmission protocols to undertake. The following will introduce the most common industrial camera interfaces and protocols.
1 1394 interface
1394 interface, also known as FireWire interface, is widely used in the industrial field. Its protocol and coding are very good, and the transmission is relatively stable. The transmission distance of 1394 interface is 4.5m, and the maximum length of single cable can reach 17.5m; add relay can reach 70m, and optical fiber transmission can reach 100m; it has standard DCAM protocol, low CPU consumption; it supports hot swap and can supply power through 1394 bus.
1394 interface is mainly divided into 1394a interface of 400MB and 1394b interface of 800MB, as shown in the following figure:
1394a single 4.5m (S400), plus relay up to 70m, if adjusted to S100 or S200, the transmission distance can reach 25m or even longer. The relevant parameters are as follows:
1394b single 10m (S800), to network transmission, CAT5 line can reach 100m (S100); CAT6 cable can reach 60m under S400; optical fiber transmission can reach 500m (S400 / S800). The relevant parameters are as follows:
Because the early 1394 interface was not well popularized, there was no corresponding interface on the existing PC. if you want to connect the corresponding camera, you need to cooperate with the 1394 interface acquisition card. At present, 1394 interface has been gradually eliminated by the market.
2 USB2.0 Interface
USB2.0 interface is one of the earliest Digital interfaces. Basically all computer hosts are equipped with USB interface, which can be plugged in and out without additional acquisition card. The bandwidth of USB2.0 is 480 Mbit / s, which supports hot swap and is easy to use. The camera can be powered by USB cable, but there is no standard protocol in USB2.0, and the master-slave structure leads to high CPU occupancy rate and the bandwidth cannot be guaranteed. The longest transmission distance of a single cable is 5m, and the relay can reach 30m. The transmission distance is short and the signal attenuation is serious.
3 USB3.0 interface
USB3.0 interface adds two groups of data buses on the basis of USB2.0 interface. In addition to supporting traditional BOT protocol, USB Attached SCSI protocol (USAP) protocol is also added, so that the transmission bandwidth of USB3.0 can reach 5Gbps, It adopts full duplex transmission mode to support simultaneous two-way data transmission; host led asynchronous transmission flow control enables the device to notify the host when data transmission is ready; outstanding real-time compatibility and high reliability. But USB3.0 has not been improved in transmission distance.
4 GigE gigabit network interface
Due to the stability of GigE gigabit network protocol, it is currently the main camera interface. Video signal can be transmitted over a long distance through the network, and the price of network cable is low. Even if the hardware and software of different manufacturers meet the GigE vision standard, seamless gigabit network connection can be realized.
The effective bandwidth of GigE gigabit network interface is 100MB / s, and a single network cable can transmit a distance of 100m; standard Gigabit Ethernet Hardware allows single / multiple cameras to be connected to one or more computers. At present, 10gige interface has gradually become the mainstream interface for fast connection.
5 Cameralink interface
Cameralink interface is a kind of serial communication protocol for digital image signal communication introduced by AIA Association. LVDS interface standard is used, which has the advantages of high speed, strong anti-interference ability and low power consumption. The protocol uses mdr-26 pin connector. It is developed on the basis of channel link interface protocol of NSM (National Semiconductor manufacturer).
Cameralink uses 28 bit channel link chip; 4 data streams and 1 clock signal are transmitted through 5 sets of LVDS line pairs; 24 bit image data and 4-bit synchronous video signal are transmitted, including frame valid, line valid, data valid and spare. The Cameralink interface is divided into three configurations, namely base interface, medium interface and full interface.
Base interface: the number of channel link chips is 1, the number of cables is 1, and the data bandwidth is 2.04 Gbit / S (255 MB / s)
Medium interface: the number of channel link chips is 2, the number of cables is 2, and the data bandwidth is 4.08 Gbit / S (510 MB / s)
Full interface: the number of channel link chips is 3, the number of cables is 2, and the data bandwidth is 5.44gbit/s (680 MB / s)
6 coaexpress interface
Coaexpress (CXP) standard was originally jointly launched by several companies in the field of industrial image processing. Its purpose is to develop a fast data interface and realize the transmission of large amounts of data over a longer distance. CXP 1.0 was officially released as a new interface standard in 2011. Since then, this standard has occupied a place in the field of industrial image processing. Later, it further developed into coaexpress 2.0.
The coaexpress 1.0 / 1.1 standard interface supports a data rate of up to 6.25 Gbps, while the coaexpress 2.0 standard has a transmission speed of up to 12.5 Gbps. Coaxpress 2.0 has better resolution and frame rate than other efficient standards.