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An electronic circuit fitted to the iris of a lens to help compensate for large changes in light level.

Alarm Search

Search criteria, e.g. time, date etc. used to detect alarms from CCTV input signals.

Automatic Level Control (ALC)

On auto iris lenses, also known as peak/average control. Adjusting this control allows the auto iris circuitry to either take bright spots more into consideration (peak), bringing out the detail in bright areas, or less into consideration (average) bringing out detail in shadows.

A signal in which any level is represented by a directly proportional Voltage not digital.

This is what alters (not the focal length) when you use a lens designed for one format on another format. It decreases with format size.

The ‘opening’ of a lens, a measure on its light gathering capability. Relative aperture is a ratio between its focal length and effective aperture, measured in F numbers, generally the lower the better.

Automated process to back-up information from the hard disk.

A feature on a colour camera whereby the light is constantly monitored and adjusts the colour to maintain the white areas.

The mechanical aligning of the of the imaging device with the focal point of the lens. Most important on zoom lenses is to ensure the image stays in focus throughout the zoom range.

A feature of modern CCD cameras which electronically compensates for high background lighting to give detail which would normally be silhouetted.

Video connector (the most commonly used in CCTV).

British Summertime/Greenwich Meantime.

The European TV standard 625 lines 50 fields.

Long established industrial standard for connecting cameras and lenses, widely used in the CCTV industry.

The use of an algorithm to digitally compress a digital picture.

New standard for connecting cameras and lenses. It has a shorter penetration into the camera, needed for many modern CCD designs.

Digital Audio Tape

An auto iris requiring a DC reference from camera rather than the traditional reference.

The result of receiving information in a coded form then transferring it into a useable medium.

The area of acceptable focus for an image. The wider you set the aperture of a lens the lower the depth of field becomes.

Digital Video Management System

External alarm triggers recorded by a VCR running in timelapse mode.

Denotes a 3 hour, high quality video cassette – high quality in that there is reduced oxidisation on the heads offering increased picture quality and longevity of tape usage.

Denotes a 4 hour, high quality video cassette (as above).

Automatically varies a CCD camera’s shutter to mimic auto iris control, allowing fixed or manual iris lens to be used in a wider range of areas.

US TV standard 525 lines in 60 fields.

Transferred information in a coded form to a medium.

Ext. Sync (external sync)

The ability of CCTV equipment (normally cameras), to accept one or more of the standard sync formats so as to align itself to the rest of the system.

One half of a frame, consisting of either the odd or the even numbered lines. 50 fields are transmitted every second.

One complete TV picture made up of approximately 625 line.

25 frames are transmitted every second.

One method of converting the small electric currents produced by auto iris circuits into physical movements of the iris diaphragm. Used in both auto iris and direct drive lenses.

One billion bytes or characters of information.

The non-removable disk in a computer. The disk stores data and information to be used on a PC.

A VCR timer feature that allows you to assign the Sunday timer settings to up to 20 week days per year. Normally used for Bank Holidays.

Method used with alarms or activity detection which allows extra frames of video from alarmed cameras to be added to a time multiplexed sequence whilst a state of alarm exists.

Iris (Iris Diaphragm)

Adjustable diaphragm that regulates the amount of light passing through a lens.

A compression technique which has been widely used in the Security Industry.

Metric measures of the light striking a surface. The light available on that surface depends on how reflective it is.

Feature allowing you to pre-programme frequently used system configurations for selection by a single keystroke or optionally by alarm inputs.

One million bytes or characters of information.

A compression technique which has been widely used in entertainment media.

Using one carrier to send more than one signal. In video multiplexers, achieving this by sending a different camera’s output in each successive field or frame of a video signal, in a form that can later be retrieved as single camera pictures.

Colour TV system used in the USA.

UK Colour TV system.

PIR (Passive Infra Red)

A range of frequencies lower than visible red light used for covert surveillance or as a low cost wireless video link.

The pre-positioning of pan/tilt and zoom cameras by the use of potentiometers in the moving parts of the camera head. These allow the control equipment to store and move to a set reference point when the controller dictates or when an alarm exists. Special telemetry equipment is required.

Multiplexer dual framestore that gives near realtime record capability in 3 hour mode and improves multi-screen updates by 50%.

The actual time during which a process or event occurs.

A data communication industry standard for the serial transmission of information. Distance without modems is limited.

A data communication industry standard for the component transmission of information.

An electronic circuit available on many CCD cameras. Allowing the light gathering period (1/50^th of a second) of the camera to be stopped prematurely (as little as 1/100,000^th of a second).

New format, high resolution VHS video recorders, capable of giving greatly improved picture quality when all features are used. It is also compatible with VHS.

Timelapse VCR

Video recorder that can record frames with pauses between them thereby extending the time that a standard length tape will last.

The maximum number of changes between light and dark on a picture across 3/4 of the width dictates the resolution of a CCTV product, measured in TVL.

The rate which equates to the number of field updates that a VCR and multiplexer would make when connected together in a standard application, e.g. a standard VCR will use a 3 hour videotape, recording 50 fields a second. However, when a VCR is configured to a 24 hour timelapse mode, the updates are slowed by a factor of 8, recording 6.25 fields a second (which on playback gives a slight stroboscopic effect).

Voltage alternative current.

Video Cassette Recorder.

Voltage direct current.

A multiplexer feature that uses a pulse generated by the VCR so that the multiplexer automatically adjusts to the VCR timelapse speed.

Name given to 1/2" tape format domestic video recorders.

State of the art compression technology.

A method of sending video pictures in 2 separate parts down

2 separate cables. The component parts are Y (the monochrome portion) and C (the colour portion).

Taken from: "The Vista Guide to CCTV – Version Two – Summer 2001"

Email: Info@Securasound.co.uk T 01948 667600