Glossary Of Terms D - L - CCTV
Below is a MRR and PLR article in category Computers Technology -> subcategory Web Development.
Glossary of CCTV Terms (D-L)
Overview
This glossary provides definitions for common CCTV terms ranging from D to L, offering clear explanations for professionals and enthusiasts involved in security design and consultancy.
Dark Current
A leakage signal from a CCD sensor occurring without light exposure.Dark Noise
Noise resulting from the unpredictable nature of dark current.Decibel (dB)
A logarithmic measurement used to compare two electrical values, typically applied to power, but also applicable to voltage and current.DC (Direct Current)
An electric current flowing in one direction only.De-Multiplexing
The process of separating multiplexed video, audio, or data signals back into individual streams.Depth of Field
The range within a scene that appears clear and sharp. This range varies with the f-stop, focal length, and distance of the lens; a larger f-stop, shorter focal length, or greater distance increases depth of field.Dielectric
An insulating material between the core and shield of a coaxial cable.Digital Signal
An electronic signal represented in binary format, processable by microprocessors and storable in digital memory.Dome
Refers to discreet surveillance camera housing, typically crafted from smoked glass or plastic and often equipped with a pan and tilt mechanism.DOS (Disk Operating System)
Software that enables a computer to interact with its hardware components like screens, keyboards, and drives.DSP (Digital Signal Processing)
Utilizes electronic circuits to process digital signals.Duplex
A system capable of simultaneously handling two information channels, crucial in CCTV for recording while displaying multi-screen footage.Dwell Time
The duration a video image remains on a monitor before transitioning to the next image, often used in video switchers.EAS (Electronic Article Surveillance)
A system for retail theft prevention that triggers alarms when tagged merchandise passes through detectors, often integrated with CCTV.EBU (European Broadcasting Union)
EIA (Electronics Industry Association)
An American institution setting video broadcast standards in the USA and Canada.Electron Beam
A directed flow of electrons.EMI (Electro Magnetic Interference)
Caused by devices emitting electromagnetic frequencies, leading to signal disruptions.ENG Camera
Cameras used in electronic news gathering, commonly utilizing CCD sensors.EPROM (Erasable Programmable Read-Only Memory)
A chip storing software instructions for various security products.Ergonomics
The study of optimizing interactions between man, machines, and environments for efficiency.Fibre Optic
A method of efficiently transmitting video and telemetry signals over long distances using light transmitted through silica glass cable.Field
Comprises half a frame, either odd or even lines, with 312.5 lines in a PAL system.Field of View
The height and width visible through a lens.Fixed Lens
Lenses with preset focal lengths, typically with focusing control and iris options.Fly Back Period
Time taken for a signal to return to the start after completing a field, frame, or line, also known as the retrace period.Focal Length
The distance from a lens's optical center to its focal point.Focusing Ring
An adjustable ring on a lens for achieving correct focus.Foot-Candle
Unit measuring illuminance: 1 foot-candle equals 1 lumen of light per square foot.Frame
Basic motion picture unit, consisting of two fields or 625 lines in a PAL system.Frame Interline Chip
A CCD device used in broadcast-quality cameras, offering superior performance over standard CCD chips.Frame Store
Captures and digitally stores video images, either as a standalone device or integrated into other equipment.Frame Switcher
A multiplexer recording multiple cameras on a single VCR.Frame Transfer
A CCD device type where pixels act as both light sensors and charge transfer agents, sometimes causing image smearing.Galvanometer
In CCTV, refers to auto iris lens operation through coil-induced current changes affecting the iris diaphragm.Gamma Correction
Adjusts a camera's brightness to match monitor display.Gen-Lock (External Sync)
Synchronizes multiple cameras to prevent image bounce and improve recording quality with switchers or multiplexers.Ground Loop Current
Current produced by differing earth potentials at cable ends, causing signal interference.Ground Loop Insulator
A transformer isolating input and output to eliminate ground loop currents.GUI (Graphical User Interface)
Describes user interfaces in CCTV systems, including touch screen controls.Hardwired
Control method using multi-cored cables between the controller and device within short distances.Hertz
Frequency measurement unit: 1 hertz equals 1 cycle per second.Homing Switcher
A sequential switcher featuring a single output.Horizontal Resolution
Number of resolvable vertical lines in a picture.Horizontal Shift Register
Transfers pixel charge line by line in CCD devices, converting it into video signal.Illuminance
Light falling onto a surface area, measured in lux.Imaging Device
Electronic signal-generating devices like vacuum tubes or solid-state arrays creating images.Image Intensifier
Utilizes phosphor screens to boost camera performance in low light.Impedance
Opposition to current flow in an AC circuit, measured in ohms.Index of Refraction
The angle ratio between light incidence and refraction, varying with medium density.Infrared Light
Light at the red spectrum's end, invisible to the human eye.Infrared Illuminator
Light source emitting infrared light for nighttime monochrome camera views.Infrared Transmission
Uses infrared beams for signal transmission where cables can't be laid, though signal quality may degrade over distances or bad weather.Interference
Unwanted electrical signals causing noise or picture disruptions in CCTV.Interlacing
Combines odd and even fields to create a frame.Interline Transfer
Processes charges based on light, transferring them immediately. Common in today's CCTV systems.IP Rating
Indicates equipment housing protection levels against dust and moisture.Iris
Controls light passage through a lens onto an imaging device.ISDN (Integrated Services Digital Network)
Telecommunication network transmitting digital signals up to 128 kb/sec.LAN (Local Area Network)
Connects multiple computers for device communication over a network.LASER (Light Amplification by Stimulated Emission of Radiation)
Transmits high-quality signals through fibre optic cables.LED (Light Emitting Diode)
A semiconductor producing light when electrically stimulated, used in fibre optic transmission and monochrome camera illumination.Lens
Focuses light onto a camera's imaging device.Lens Calculator
Determines the most suitable lens to capture a given scene with a specific camera.Lens Hunting
Occurs when an auto iris lens can't stabilize light levels.Lens Mount
See C-mount or CS-mount.Lens Wheel
See Lens calculator.Light Sensor
Activates when detecting a preset light level, commonly controlling infrared illuminators.Line
Basic frame or field unit containing light-proportional charge.Line-Locked
Synchronizes cameras to a common AC frequency.Looping Switcher
Switches signals without affecting them as they loop through.Lumen
Measures light radiation: 1 lumen equals the light emitted by a candela.Luminance
Brightness aspect of a video signal representing scene brightness.Luminous Flux
Light flow rate.Lux
Illumination measurement: 1 lux equals light falling uniformly on a square meter, measured in lumens per square meter.This glossary should serve as a comprehensive reference for understanding essential CCTV terminology.
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