Glossary
Fibre Optics
Is a method of modulating video, audio or data with a light beam and transmitting it along a glass core.
Field
Is one half of a frame and consists of 312.5 (PAL) and 262.5 (NTSC) lines. Odd and even fields are combined to form a single frame.
Field of View
Is the height and width of the view that can be seen through a lens.
Fixed Lens
Is a lens with a fixed focal length. A wide range of fixed lens are available to suit different applications eg 2.6 mm, 4.8 mm, 8 mm, 16 mm, 25 mm and 75 mm etc.
Flexible Conduit
Is a flexible PVC conduit which is used at the camera point to enclose loose cables between the camera and the junction box or wall.
Fluorescent Lamp
Is a type of artificial light source in which the mercury vapour gener- ated by a low wattage arc strikes the phosphor material to emit light. It is popular in indoor applications.
Fly Back Period
Is the time taken to move from the end of a field, frame or line to the start of the next field, frame or line. It is also called the retrace period.
Focal Length
Is the distance between the optical centre of a lens and the point of focus. It is usually measured in mm.
Focus Ring
Is a ring on a lens which is rotated to obtain correct focus.
Frame Interline Chip
Is a type of CCD chip which is expensive to manufacture and is cur- rently used in broaDCasting video cameras. It overcomes many short- comings of the existing CCD chips used in CCTV cameras.
Frame Switching
Is a process used in multiplexers or
Frame Store
Is an electronic device used to capture and digitally store a video image. It can be an independent unit or inbuilt in other equipment like fast scan video transmitters or video motion detectors.
Frame Transfer Chip
Is a type of CCD chip in which the pixels have a dual role of sensing the light and transferring the charge. This causes picture smearing, a major shortcoming of this chip.
Frame
Is the basic unit of a moving picture. A frame contains 625 lines (PAL) or 525 lines (NTSC).
FSK
Frequency shift keying - Technology to transmit digital information over a telephone line. The information is translated into an audible signal.
Galvanometer
Is a type of auto iris lens in which the DC motor drive is contained in the camera rather than in the lens. This lens is cheaper but it cannot be used with cameras which do not have this inbuilt DC motor drive.
Gamma Correction
Is a correction built into the camera to adjust for the brightness char- acteristics of the monitor. The gamma value ranges from 0.45 to 1.0.
Geometric Distortion
Is an error which causes the reproduced picture to be geometrically different from the original picture.
Ground Loop Current
Is an AC current produced in a video cable when the two ends of the cable do not have the same ground potential.
Ground Loop Insulator
Is an isolation transformer which can eliminate ground loop currents by removing any direct connection between the inputs and outputs.
GUI Graphical User Interface
Interfaces the computer with the matrix switcher. Hot areas on the computer screen can be programmed to activate a matrix switcher, VCR etc. It helps in making the CCTV system more user friendly.
Halogen Lamp
Is a type of incandescent lamp with a good spectral response. It is used in flood lighting of sports stadiums.
Hertz
Is a unit of measuring frequency. 1 Hertz = 1 cycle per second.
Horizontal Resolution
Is the number of vertical lines which can be resolved in a picture. It depends upon the number of pixels in a chip.
Horizontal Shift Register
Is a part of the CCD chip to which the charge from the pixels is trans- ferred line by line. This charge is then converted into an analogue video signal.
Illuminance
Is the amount of luminous flux falling on a surface area and is mea- sured in lux.
Image Intensified Camera
Is a type of camera coupled with an image intensified tube which generates additional photons. This tube allows the camera to be used in low light areas.
Image Intensifier
Is a device which intensifies light by using light sensitive phosphor screens. It is used to improve camera performance under low light conditions.
© Siemens Building Technologies Group |
