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Glossary - P
PAL stands for Phase Alternating Line. This is the color phase change in a color PAL signal.
- Pan and tilt head
Aka P/T Head. A motorised unit permitting vertical and horizontal positioning of a camera and lens combination. Usually 24VAC motors are used in such P/T heads, but also 100VAC, ie. 240VAC units can be ordered.
- Pan Unit
A motorised unit permitting horizontal positioning of a camera.
A photometric light unit for very strong illumination levels. One phot is equal to 10,000 luxes.
A type of semiconductor device in which a PN junction diode acts as a photosensor.
Also known as Photoelectric-effect. This refers to a phenomenon of ejection of electrons from a metal whose surface is exposed to light.
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 10^5 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.
Derived from picture element. Usually refers to the CCD chip unit picture cell. It consists of a photosensor plus its associated control gates.
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 degrees 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.
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.
- Principal point
An optical term which 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.
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 the operate pan, tilt, zoom and focus functions.