ACTIVITY DETECTION


Simple video motion detection, activity detection merely produces on alarm indication on change of light levels, often used with video multiplexers to increase the update on cameras when activity is occurring.


AGC


Automatic Gain Control - an electronic circuit normally found in cameras which will increase the video signal in low light conditions, in normal operation it will maintain a constant level.


ALARM ACTIVATED VCR


A VCR that is triggered to start from the idle position, this can take as long 20 seconds to spool the tape and start recording for a usable picture. If the VCR is in the time laps mode an alarm can take considerably less of a usable picture.


ALC


Automatic level Control - On all lenses a manual adjustment also known as Peak/Average, a facility to make the lens respond more to the highlights (peak) or more the darker (average) scenes, providing user adjustment information seen in the highlight.


APERTURE


The measure of a light gathering capability, the maximum aperture is the minimum ‘F’ stop of a lens, the lower the ‘F’ stop the better.


BLC


Back Light Compensation - an electronic feature of modern CCD cameras to allow viewing of highlighted scenes that would normally be silhouetted, thus providing more detail.


CCTV


Closed Circuit Television - A television system used for private purposes and not for public or general broadcast.


DARK CURRENT


The thermally induced current that exist in a photo diode in the absence of incident optical power.


DAT


Digital Audio Tape - a technology for sharing massive amounts of digital information in a small package. Used for archiving digital recorded images.


DVR


Digital Video Recorder, a devise used to record video images directly to a hard drive, the images may then be accessed instantly and archived to CD.


ERROR CORRECTION


The method employed by modems to ensure that data is transmitted and received error free.


FOCAL LENGTH


Of a lens and measured in millimetres, has a direct relationship to the angle of view that is obtained, a short focal length provides a wide angle of view and a larger focal length provides a narrower angle of view.


GROUND LOOP


Picture interference caused by different earth potentials at each end of video coaxial cable, clearly seen as humbars or interference.


HZ


Hertz - Cycles per second, method of which frequency is measured.


IMPEDANCE


Measured in ohms, refers to the combined resistance and reactance in an electrical circuit.


LASER


A source of exceptionally pure light which can consist of a single wavelength concentrated into single beam, used to transmit IR lighting through fibre optic cable.


MONITOR


A video display unit used to display images from a camera or computer.


MULTIPLEXER


A unit that can accept a number of camera inputs and simultaneously display them on a single monitor and/or record them to a single VCR machine, multiplexers can also be used to transmit multiple cameras over the same transmission medium.


NOISE


This normally appears as a snowy or grainy picture.


SN RATIO


Signal to Noise Ratio - the ratio of maximum peak to peak signal voltage to the RMS voltage of the noise at a given time, measured in Decibels.


TOUCH SCREEN CONTROL


Ability to control camera and system controls from the VDU screen, by simply touching the relevant object or icon.


ZOOM RATIO


A lens with a variable elements giving adjustable magnification and differing fields of view in one such as 12:1