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Accounting Glossary Of Terms

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MANUAL IRIS

Type of lens that requires manual focusing.

MATRIX SWITCHER

Advanced type of switcher in which a signal from any input can be switched to any number or combination of outputs. Generally used in larger and more complex systems the matrix will usually also incorporate a range of additional advanced features.

MICROWAVE TRANSMISSION

A method of transmitting signals using a microwave frequency link. Not affected by adverse weather but requires direct line of site. A licence may be required to operate a microwave frequency system.

MODEM

Derived from the term Modulate-Demodulate. A modem is used to convert between analogue and digital signal to then transmit and receive the signals over the PSTN network.

MOIRÉ PATTERN

An unwanted effect that appears in the video picture when a high frequency pattern is looked at with a CCD camera that has a pixel pattern close (but lower) to the object pattern.

MULTIPLEX VIDEO RECORDING

The condensed recording of more than one video signal on a single videotape, or hard disk drive.

MULTIPLEX

The concept of transmitting several signals on a single channel.

MULTIPLEXER

A device that combines a number of signals into one. Often used in CCTV to describe a device that is primarily used to multiplex several video signals into one for the purposes of recording or microwave transmission. It can also refer to a fibre optics multiplexer which combines a number of video signals into one in order to transmit all of them via a single fibre cable.

N/C AND N/O ALARMS

Refers to Normally Closed and Normally Opened contacts. It is usually used to describe alarms in CCTV.

NA

Numerical Aperture. A measure of the angular acceptance of light incoming into a fibre optics cable, in the form of a cone. It is expressed as the square root of the difference of the squares of the indices of the core and the cladding.

NBS

National Bureau of Standards (USA).

ND FILTERS

Neutral Density filters are optical filters that attenuate the light a number of times. This attenuation is equal for all the wavelengths therefore it does not change the colour balance of an image, hence the term neutral.

NIT

A photometric unit for measuring luminance. One nit is equal to one candela per square metre of a projected surface area.

NOISE

An unwanted signal produced by all electrical circuits working above the absolute zero. Noise cannot be eliminated but only minimised.

NTSC

National Television System Committee, an American committee that set the standards for colour television as used today in USA, Canada, Japan and a few other countries.

O/P

Output. Objective. The very first optical element at the front of a lens.

OCULAR

The very last optical element at the back of a lens (the one closer to the CCD chip).

OSCILLOSCOPE

(Also CRO, from "Cathode Ray Oscilloscope"). An electronic device that can measure the signal changes versus time. A must for any CCTV technician.

PAL

Stands for Phase Alternating Line, which describes the colour phase change in a PAL colour signal.

PAN AND TILT HEAD

(P/T head). A motorised unit permitting vertical and horizontal positioning of a camera and lens combination. Usually 24 VAC motors are used in such P/T heads, but also 110 VAC, ie. 240 VAC units can be ordered.

PAN UNIT

A motorised unit permitting horizontal positioning of a camera.

PHOT

A photometric light unit for very strong illumination levels. One phot is equal to 10,000 luxes.

PHOTODIODE

A type of semiconductor device in which a PN junction diode acts as a photo sensor.

PHOTO-EFFECT

Also known as photoelectric effect. This refers to a phenomenon of ejection of electrons from a metal whose surface is exposed to light. Photon. A representative of the quantum nature of light. It is considered as the smallest unit of light.

PHOTOPIC VISION

The range of light intensities, from 105 lux down to nearly 10-2 lux, detectable by the human eye.

PINHOLE LENS

A fixed focal length lens, for viewing through a very small aperture, used in discrete surveillance situations. The lens normally has no focusing control but offers a choice of iris functions.

PIXEL

Derived from picture element. Usually refers to the CCD chip unit picture cell. It consists of a photo sensor plus its associated control gates.

PLUMBICON

Thermionic vacuum tube developed by Philips, using a lead oxide photoconductive layer. It represented the ultimate imaging device up to the introduction of CCD chips.

POLARISING FILTER

An optical filter that transmits light in only one direction (perpendicular to the light path), out of 360° possible. The effect is such that it can eliminate some unwanted bright areas or reflections, such as when looking through a glass window. In photography, polarising filters are used very often to darken a blue sky.

POTS

Plain Old Telephone Service, ie. the telephone service in common use throughout the world today. Also known as PSTN.

PRESET POSITIONING

A function of a pan and tilt unit, including the zoom lens, where a number of certain viewing positions can be stored in the systems' memory (usually this is in the PTZ site driver) and recalled when required, either upon an alarm trigger, programmed or manual recall.

PRINCIPLE POINT

An optical term that refers to one of the two points that each lens has along the optical axis. The principle point closer to the imaging device (CCD chip in our case) is used as a reference point when measuring the focal length of a lens.

PSTN

Public Switched Telephone Network usually refers to the "plain old telephone" service. Also known as POTS.

PTZ SITE DRIVER

(PTZ site receiver, or decoder). An electronic device, usually a part of a video matrix switcher, which receives digital, encoded control signals in order to operate pan, tilt, zoom and focus functions.

QUAD COMPRESSOR

(Also split screen unit). Equipment which simultaneously displays parts or more than one image on a single monitor. It usually refers to four quadrants display.

RAID

Redundant Arrays of Independent Disks. This a technology of connecting a number of hard drives into one mass storage device, which can be used, among other things, for digital recording of video images.

RAM

Random Access Memory. An electronic chip, usually known as "memory", holding digital information while there is power applied to it. Its capacity is measured in kilobytes.

RANDOM INTERLACE

A term describing a camera that has a free running horizontal sync as opposed to a 2:1 interlace type which has the sync locked and therefore has both fields in a frame interlocked together accurately.

REMOTE CONTROL

A transmission and receiving of signals for controlling remote devices such as pan and tilt units, lens functions, wash and wipe control and similar.

RETMA

Former name of the EIA association. Some older video test charts carry the name "RETMA Chart".

RF SIGNAL

Radio frequency signal that belongs to the region up to 300GHz.

RG-11

A video coaxial cable with 75 Ohms impedance and much thicker diameter than the popular RG-59 (of approximately 12 mm). With RG-11 much longer distances can be achieved (at least twice the RG-59), but it is more expensive and harder to work with.

RG-58

A coaxial cable designed with 50 Ohms impedance, therefore not suitable for CCTV. Very similar to RG-59, only slightly thinner.

RG-59

A type of coaxial cable that is most common in use in small to medium size CCTV systems. It is designed with an impedance of 75 Ohms. It has an outer diameter of around 6 mm and it is a good compromise between maximum distances achievable (up to 300 m for monochrome signal, and 250 m for colour) and good transmission.

RMS

An abbreviation for Root Mean Square. All AC voltages are measured with multimeters that show the RMS value of the signal (not the peaks). For a sine wave signal such as the mains, the RMS value happens to be 1.41 times (square root of 2) below the peak values.

ROM

Read Only Memory. An electronic chip, containing digital information that does not disappear when power is turned off.

RS-232

A format of digital communication where only two wires are required. It is also known as a serial data communication. The RS-232 standard defines a scheme for asynchronous communications, but it does not define how the data should be represented by the bits, ie. it does not define the overall message format and protocol. It is very often used in CCTV communications between keyboards and matrix switchers, or between matrix switchers and PTZ site drivers. The advantage of RS-232 over others is in its simplicity and use of only two wires.

RS-422

This is an advanced format of digital communication when compared to RS-232. The basic difference is in the need for four wires instead of two as the communications is not single-ended as with RS-232, but differential. In simple terms, the signal transmitted is "read" at the receiving end as the difference between the two wires without common earth. So if there is noise induced along the line, it will be cancelled out. The RS-422 can drive lines of over a kilometre in length and distribute data to up to 10 receivers.

RS-485

This is an advanced format of digital communications compared to RS-422. The major improvement is in the number of receivers that can be driven with this format, and this is up to 32.

Accounting Glossary Of Terms

DARK NOISE

Noise caused by the random (quantum) nature of the dark current.

DECIBEL (DB)

A logarithmic ratio between two electrical signals or values. Usually refers to power, but can also be used for voltage and current.

DC

Direct Current.

DE-MULTIPLEXING

The process of separating different video, audio, or data signals, which were multiplexed at source.

DEPTH OF FIELD

The distance between the nearest and furthermost object in a scene which appear in sharp focus. Depth of field varies depending on the f-stop and focal length of a lens. Depth of field increases when the f-stop is greater, the focal length shorter or the distance to the object is increased.

DIELECTRIC

An insulating (non-conductive) material. Found between the inner core and outer shield of a co-axial cable.

DIGITAL SIGNAL

An electronic signal, which is represented by binary numbers, and that, can be processed by a microprocessor, or stored in an electronic memory.

DOME

Term used to describe a type of camera housing made of smoked glass or plastic usually containing a pan and tilt head and used for discreet surveillance.

DOS

Disk Operating System. A software package that makes a computer work with its hardware devices such as hard drive, floppy drive, screen, keyboard, etc.

DSP

Digital Signal Processing. Refers to an electronic circuit capable of processing digital signals.

DUPLEX

A system that is capable of handling two channels of information simultaneously. In CCTV, duplex is used to describe a multiplexer that can record in multiplex mode whilst simultaneously displaying multi-screen pictures.

DWELL TIME

When relating to video switchers this is the time that a picture remains on a monitor before being replaced by the next picture.

EAS

Electronic Article Surveillance. System used in retail stores to prevent shoplifting by attaching tags to the merchandise, which activate an alarm when passed through detectors. These systems are often interfaced with CCTV systems.

EBU

European Broadcasting Union.

EIA

Electronics Industry Association. American Association that sets the standard for video broadcast in the USA and Canada (525 lines, 30 frames per second).

ELECTRON BEAM

A concentrated flow of electrons in a nominated direction.

EMI

Electro Magnetic Interference. Interference caused by an item of electrical equipment radiating electro magnetic frequencies.

ENG CAMERA

Electronic News Gathering camera usually refers to CCD cameras in the broadcast industry.

EPROM

Erasable and Programmable Read Only Memory. An electronic chip used in many different security products, which stores software instructions for performing various operations.

ERGONOMICS

The study of man, machine and the working environment to achieve maximum efficiency.

FIBRE OPTIC

A very efficient method of transmitting video and telemetry signals over long distances using a light beam transmitted along a fibre optic cable constructed from high density Silica Glass.

FIELD

Half of a single frame, consisting of either the odd or even lines. In a PAL system this is 312.5 lines.

FIELD OF VIEW

The height and width of view that can be seen through a lens.

FIXED LENS

A lens with a pre-determined fixed focal length. Normally has a focusing control and a choice of iris functions. Available in a range of sizes to suit different applications.

FLY BACK PERIOD

The time taken for a signal to move from the end of a field, frame or line to the start of the next field frame or line. Also called the retrace period.

FOCAL LENGTH

The distance between the optical centre of a lens and the focal point.

FOCUSING RING

Ring on the outside of a lens to allow adjustment to obtain correct focus.

FOOT-CANDELA

Unit of Illuminance. 1 Foot-candela =1 Lumen of light incident on 1sq ft of surface area.

FRAME

Basic unit of a motion picture, made up of 2 fields or 625 lines (in a PAL system).

FRAME INTERLINE CHIP

A type of CCD imaging device, which is expensive to manufacture and is currently used in broadcast quality cameras. This type of chip overcomes many of the shortcomings of the existing CCD chips used in CCTV cameras.

FRAME STORE

An electronic device used to capture and digitally store a video image. Can be a stand-alone unit or incorporated in other equipment such as fast scan transmitters or video motion transmitters.

FRAME SWITCHER

A basic form of multiplexer, which can be used to record multiple cameras on a single VCR.

FRAME TRANSFER

A type of CCD Imaging device in which the pixels have a dual role of sensing the light and transferring the charge. This can result in picture smearing, which is a major shortcoming of this device.

GALVANOMETER

In CCTV this term refers to a method of operating an auto iris lens. The changing light level causes a change in the current induced into a minute coil, which in turn causes movement in the Iris diaphragm.

GAMMA CORRECTION

A method of correction used in cameras to balance the brightness seen by a camera to that of the monitor.

GEN-LOCK (EXTERNAL SYNC)

A method of synchronising a number of cameras in a system to ensure that they all produce fields at the same time. This is used to prevent picture “bounce” when switching between cameras and can improve the overall quality and update time of recordings when using switchers or multiplexers.

GROUND LOOP CURRENT

In CCTV this term refers to a current that is produced in a cable as a result of a difference in earth potential existing at each end of the cable. The result of this is noise (interference) introduced in the signal.

GROUND LOOP INSULATOR

A transformer with no direct connection between the inputs and outputs, used to eliminate Ground Loop Currents.

GUI

(Graphical User Interface). A term used to describe the interface between a computer screen and the user. Now used in CCTV Systems to describe features such as touch screen control of systems and equipment.

HARDWIRED

Refers to a method of controlling CCTV equipment by using multi-cored cable run between the controller and device to be controlled. Only used where the distance between controller and controlled device is short.

HERTZ

The unit of measurement for frequency in a signal. 1 Hertz = 1 cycle per second.

HOMING SWITCHER

Term used to describe a sequential switcher with only one output.

HORIZONTAL RESOLUTION

The number of vertical lines that can be resolved in a picture.

HORIZONTAL SHIFT REGISTER

Part of the CCD image device to which the charge from the pixels is transferred line by line. This charge is then converted into an analogue video signal.

ILLUMINANCE

The amount of light, which falls onto a given surface area. Measured in lux.

IMAGING DEVICE

A vacuum tube or solid state device in which the vacuum tube light sensitive face plate, or solid state light sensitive array, provides an electronic signal from which an image can be created.

IMAGE INTENSIFIER

A devise used to intensify light through the use of light sensitive phosphor screens. Used to intensify camera performance under low light conditions.

IMPEDANCE

The total opposition to current flow in an a.c. electrical circuit. Measured in Ohms.

INDEX OF REFRACTION

The ratio between the angle of incidence to the angle of refraction of light. Index varies depending on the density of the medium. The denser the medium, the higher the index.

INFRARED LIGHT

Light produced at the red end of the spectrum. Not visible to the naked human eye.

INFRARED ILLUMINATOR

Light source, which emits light in the infrared part of the spectrum. Used to illuminate scenes to provide views at night from infra sensitive monochrome cameras.

INFRARED TRANSMISSION

Method of transmitting signals using an infrared beam. Allows CCTV signals to be transmitted where cables cannot be run. Signals can be degraded over long distances or in adverse weather conditions.

INTERFERENCE

Effect caused by the introduction of unwanted electrical signals into an electrical circuit. In CCTV this results in “noise” in the signal or picture, which disrupts the picture.

INTERLACING

The process of combining odd and even fields to form a frame.

INTERLINE TRANSFER

A type of CCD imaging device in which the charge is processed according to the amount of light falling on the sensors and then transferred immediately. This is the most common form of imaging device used in current CCTV systems.

IP RATING

Index of protection that refers to the level of protection provided by equipment housings, against the ingress of dust or moisture.

IRIS

The part of a lens that is used to control the amount of light that passes through the lens and onto the imaging device.

ISDN

(Integrated Services Digital Network). Telecommunications network that is capable of transmitting digital signals at speeds of up to 128kb/sec.

LAN

(Local Area Network). Means of connecting a number of computers to enable communication between each device connected to the network.

LASER

(Light Amplification by Stimulated Emission of Radiation). In CCTV this source of exceptionally pure light can be used to transmit signals along fibre optic cables, providing very high quality signal and data transmission.

LED

(Light Emitting Diode). A semiconductor that produces light when stimulated by an electric current. In CCTV these are used as the light source in some fibre optic transmission systems, and as light the light source for illuminating scenes for use with Monochrome cameras.

LENS

An optical device for focusing light onto the imaging device in a camera.

LENS CALCULATOR

A calculator used to calculate the most suitable lens to provide an image of a given scene when used with a specific camera.

LENS HUNTING

A problem encountered when an auto iris lens opens and closes alternatively because it is unable to find the correct level.

LENS MOUNT

See C-mount or CS-mount.

LENS WHEEL

See Lens calculator.

LIGHT SENSOR

A device that is activated when a preset amount of light is present on the sensor. Used to switch on/off infrared illuminators.

LINE

The basic unit of a frame or field containing the charge, which is proportional to the light falling at various points on the scanning line.

LINE-LOCKED

Refers to a method of synchronising cameras to a common AC frequency.

LOOPING SWITCHER

Refers to a type of switcher where signals are looped through the switcher without being affected by the operation of the switcher itself.

LUMEN

Unit of light measurement of light radiation. 1 Lumen = amount of light emitted by a light source of 1 Candela.

LUMINANCE

Brightness. In CCTV refers to the part of the video signal that contains information about the scene brightness.

LUMINOUS FLUX

The rate of flow of light.

LUX

Unit of illumination. 1 Lux = the amount of uniform light falling onto a surface of 1sq metre. Measured in Lumens per square metre.

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