Video encoders with PTZ cameras and PTZ domes
In a network video system, pan/tilt/zoom commands from a control board are carried over the same IP network as for video transmission and are forwarded to the analog PTZ camera or PTZ dome camera through the video encoder’s serial port (RS-232/422/485). Video encoders, therefore, enable analog PTZ cameras to be controlled over long distances, even through the Internet. (In an analog CCTV system, each PTZ camera would require separate and dedicated serial wiring from the control board — with joystick and other control buttons — all the way to the camera.)
To control a specific PTZ camera, a driver must be uploaded to the video encoder. Many manufacturers of video encoders provide PTZ drivers for most analog PTZ cameras and PTZ dome cameras. A PTZ driver can also be installed on the PC that runs the video management software program if the video encoder’s serial port is set up as a serial server that simply passes on the commands.
The most commonly used serial port for controlling PTZ functions is RS-485. One of the benefits that RS-485 allows is the possibility to control multiple PTZ cameras using twisted pair cables in a daisy chain connection from one dome camera to the next. The maximum distance of an RS-485 cable, without using a repeater, is 1,220 meters (4,000 feet) at baud rates up to 90 kbit/s.