Surveillance cameras are used for a wide variety of CCTV access control systems. The video portion of the system has been technologically suited for transmission over an Ethernet network for quite some time, and advances in video compression technologies have made these systems even more economical to implement.
However, unless a fixed position, fixed focus camera is all that is needed, the ability to control what the cameras could see--via Pan-Tilt-Zoom controls--was limited to a local computer with a wired RS-422 connection to the cameras (at a maximum of 4000 feet distances).
Serial device servers cut the cord for PTZ control, and enable remote cameras placed anywhere on an Ethernet connection to be remotely monitored and controlled. Further, they enable a a single computer to control any number of cameras from a central location via a network connection, just as if each one was physically connected to a local COM port on the computer.
In the example above, four security cameras, located any distance away from each other and from the security office, are connected to Quatech SSE-400D RS-232/422/485 serial device servers. The camera's PTZ controls are connected to the device server's serial port, which is configured for RS-422 communication. Each SSE-400D device server is connected via Ethernet to a network. An operator in the control room creates a virtual COM port connection with each device server, and then uses security monitoring software in conjunction with a joystick keyboard controller, to switch between the cameras and to change camera angles and zoom as required.
This serial-over-Ethernet approach has many advantages. Most notably, it eliminates the expense of routing long serial cables between cameras and controllers, it enables multiple computers to access the camera PTZ controls--via a local network connection or even over the Internet, and it permits network-enabling security camera control system without any alteration to software applications designed to use RS-422 communication.
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