Siemens TFT - Manual (Page 208)

Glossary
16-6 © Siemens Building Technologies Group
16
Impedance
Is the input and output characteristic of any electrical system and is
measured in ohms. For maximum signal transfer, the input and out-
put impedance should be the same. CCTV systems have a 75 ohm
impedance.
Incandescent Light
Is a type of artificial light source invented by Thomas Edison in 1862.
It has a good spectral response but low life and efficiency.
Index of Refraction
Is a ratio between the angle of incidence to the angle of refraction of
light. It depends upon the density of a medium. A denser medium
will have a higher index of refraction and will also bend the light
more.
Infrared Detector
Can be used in conjunction with a CCTV system to switch the relev-
ent camera on to the monitor in event of an activation.
Infrared Link
Transmission medium in which video, data or audio are modulated
with infrared light and then transmitted via free space to a receiver
in a remote location.
Infrared Radiation
Is electromagnetic radiation with a wavelength of more than 750 na-
nometers. It is not visible to the human eye.
Interference
Is external energy which interferes with an electrical signal causing
picture distortions.
Interlacing
Is the process of combining even and odd fields to form a frame.
Interline Transfer Chip
Is a type of chip used in most of the current CCTV cameras as the
charge read out method is more efficient than a frame transfer CCD
chip. Vertical streaking and small pixel size are some of the short-
comings.
Iris
The part of a lens that can be adjusted to vary the amount of light
passing through the lens and falling on the CCD chip.
Iris Plug
Push in connector which connects the camera to an auto iris lens to
provide power to the iris motor and to send the video signal which
controls the iris opening.
ISDN
Integrated Services Digital Network is a type of telephone network
which is used to connect networks remotely.
Joystick Controller
Is a control device in the form of a stick in a PTZ controller used to con-
trol the pan, tilt and zoom movement of a pan tilt head or dome.
Junction box
Empty box (mostly weatherproof) to be mounted close to the elec-
tronic device. Simplifies cabling and may contain a twisted pair
transmitter, PSU etc.
LAN
Local Area Network connects different computers so that they can
communicate with each other. Different connection protocols are
possible.
LD
Laser diode is a type of light source which generates a single fre-
quency in the high end of the infrared spectrum and has a band-
width of 1000 MHz. It is used in fibre optics and infrared links.
LED
Light Emitting Diode is a type of light source which generates an
infrared frequency when stimulated by electricity. It is used in fibre
optics, infrared links and as an infrared light source for monochrome
cameras.
Lens Calculator
Is a calculator provided by many lens manufacturers to help calculate
the focal length of the lens that will provide the required image.
Lens Hunting
Is a problem where the iris is continually opening and closing. Using
the ALC adjustment in the lens, this should rectify the problem.
Lens Mount
See C-mount or CS-mount.
Light
Is electromagnetic radiation between 400 nm and 750 nm which is
detectable by the human eye.
Light Sensor (photocell)
Is a device which is activated by a present amount of light falling on
it. It can be used to switch infrared illuminators On/Off.
Limit Switch
Is a device placed inside or outside the Pan Tilt head and used to limit
the angles of pan and tilt.
Line
Is the basic unit of a frame or field containing the charge which is pro-
portional to the light falling at various points on the scanning line.
Looping Switcher
Is a type of switcher with looping outputs. These outputs allow the
camera to be connected to another device without affecting the
usage of the switcher.
Lumen
Is a measurement of light which indicates the amount of light radi-
ated by a one candela light source.
Luminance Signal
Is that part of the video signal which contains the information on the
brightness of the picture.