Glossary - N

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N/C & N/O alarms: N/C refers to normally closed, and N/O is Normally opened. It is used to describe alarm connections in security and CCTV.
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 luminace. 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 can not be eliminated but only minimised.
NTSC: National Television System Committee, an American committee which set the standards for colour television as used today in USA, Canada, Japan and a few other countries.

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