B C D
E F G
H I J
K L M
N O P
Q R S
T U V
PAL. Phase Alternate
(sometimes alternating) Line. Describes the colour phase change in
a PAL colour signal. PAL
is the European colour encoding TV system featuring 625 lines per
fields per second and
a 4.43361875 MHz sub-carrier (4.43 MHz). Used mainly in Europe,
Malaysia, Australia, New Zealand,
the Middle East and parts of Africa.
Pan and tilt head (P/T head).
A motorized unit permitting vertical and horizontal
a camera and lens combination. Usually AC motors (24 VAC, 110 VAC,
& 240 VAC) of fixed speed,
are used in such P/T
heads, but increasingly DC variable speed
motors are being installed.
Pan unit. A motorized
unit permitting horizontal positioning of a camera.
Pulse Coded Modulation. A technique used in analogue to digital
The amplitude (voltage) difference between the most positive and the
most negative excursions (peaks)
of an electrical signal.
Peak White Inverter. An
electronic circuit that turns white parts (highlights) of a picture,
a set threshold, to black or a
shade of grey.
Pedestal (or set-up).
Where in a video waveform, at the start of the active line period, the
steps up by up to
100mV, to differentiate between blanking level and black level.
is not often
found in CCTV waveforms nowadays.
Phase Locked Loop (PLL).
A circuit containing an oscillator whose output phase or frequency
locks onto and tracks the phase
or frequency of a reference input signal.
To produce the
locked condition, the circuit then
detects any phase difference between the two
generates an error voltage which
can be used independently or to correct its own oscillator
phase or frequency.
A photometric light unit for very strong illumination levels. One
phot is equal to
A type of semiconductor device in which a PN junction diode acts as a
Also known as photoelectric-effect. This refers to a phenomenon
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
The range of light intensities, from 105
lux down to nearly 10-2 lux,
detectable by the human eye.
Pigtail. A length of optical fibre with
one "bare end" and the other end terminated in a
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
may offer a
choice of iris functions.
PIP. Picture in Picture
Pixel. Derived from
PIcture ELement. Usually refers to the CCD chip unit picture
comprises a photosensor plus its
associated control gates.
Pixel or picture element.
The smallest visual unit that is handled in a raster file, generally a
single cell in a grid of numbers
describing an image.
A highly light-sensitive device. Advantages are its fast
signal-to-noise ratio and wide
dynamic range. Disadvantages are fragility (vacuum
high voltage and sensitivity to
An optical filter that transmits light in only one direction
the light path), out of 360°
possible. The effect is such that it can eliminate
bright areas or reflections, such
as when looking through a glass window or the surface of
water. In photography,
polarizing filters are used very often to darken a blue sky.
POTS. Plain Old Telephone
Service: the only name recognized around the world for basic
analogue telephone service. Telephone
System takes the lowest 4kHz of bandwidth on twisted
pair wiring. Any service sharing
a line with Telephone System must either use frequencies above
Telephone System or convert Telephone
System to digital and interleave with other data signals.
P-picture (or P frame).
Prediction-coded picture. An MPEG term to describe a picture
that is coded using
motion-compensated prediction from
the past reference picture.
A function of a pan and tilt unit, including the zoom lens, where a
certain viewing positions can be stored in the system's memory
(usually this is
in the telemetry receiver) and
can be recalled when required, either upon an alarm trigger,
programmed or manual recall.
Primary colours. A
small group of colours light that, when combined, can produce a broad
other colours. In television, red, green and blue are the primary
which all other colours in the
picture are derived. White light is a summation of 11% blue,
30% red and 59% green.
Principal point. One
of the two points that each lens has along the optical axis. The
closer to the imaging device (CCD chip in our case) is used as a
point when measuring the focal
length of a lens.
read only memory. A ROM that can be programmed by the
equipment manufacturer (rather
than the PROM manufacturer).
Protocol. A specific
set of rules, procedures or conventions relating to format and timing of
data transmission between two devices.
A standard procedure that two data
accept and use to be able to understand
each other. The protocols for data communications
cover such things as framing, error
and line control.
PSTN. Public Switched
PTZ camera. Pan, Tilt and
PTZ site driver (or telemetry
receiver or decoder). An electronic device, usually located
with the camera equipment, which
receives telemetry control signals in order to operate
tilt, zoom and focus functions.
Pulse. A current or
voltage that changes abruptly from one value to another and back to the
original value in a finite length
of time. Used to describe one particular variation in a series
of wave motions.