|
MAC. Multiplexed analog components. A system
in which the components are time multiplexed into one channel
using time domain techniques, i.e., the components are kept separate
by being sent at different times through the same channel. There
are many different MAC formats and standards
Manual iris. A manual method of varying the size of a
lens’s aperture.
Matrix. A logical network configured in a rectangular
array of intersections of input/output channels.
Matrix switcher. A device for switching more than one
camera, VCR, video printer and similar, to more than one monitor,
VCR, video printer and similar. Much more complex and more powerful
than video switchers.
MATV. Master antenna television.
MB. Megabyte. Unit of measurement for computer memory
consisting of approximately one million bytes. Actual value is
1,048,576 bytes. Kilobyte × Kilobyte = Megabyte.
MB/s. Megabytes per second. Million bytes per second or
8 million hits per second. Also written as MBps.
Mb/s. Megabits per second. Million bits per second. Also
written as Mbps.
MHz. Megahertz. One million hertz.
Microwave. One definition refers to the portion of the
electromagnetic spectrum that ranges between 300 MHz and 3000
GHz. The other definition is when referring to the transmission
media where microwave links are used. Frequencies in microwave
transmission are usually between 1 GHz and 12 GHz.
MOD. Minimum object distance. Feature of a fixed or a
zoom lens that indicates the closest distance an object can be
from the lens’s image plane, expressed in meters. Zoom lenses
have MOD of around 1 m, while fixed lenses usually much less,
depending on the focal length.
Modem. This popular term is made up of two words: modulate
and demodulate. The function of a modem is to connect a device
(usually computer) via a telephone line to another device with
a modem.
Modulation. The process by which some characteristic (i.e.,
amplitude, phase) of one RF wave is varied in accordance with
another wave (message signal).
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.
Monochrome. Black-and-white video. A video signal that
represents the brightness values (luminance) in the picture,
but not the color values (chrominance).
MPEG. Motion Picture Experts Group. An ISO group of experts
that has recommended manipulation of digital motion images. Today
there are a couple of MPEG recommendations, of which the most
well known are MPEG-1 and MPEG-2. The latter one is widely accepted
for high definition digital television, as well as multimedia
presentation.
MPEG-1. Standard for compressing progressive scanned images
with audio. Bit rate is from 1.5 Mbps up to 3.5 Mbps.
MPEG-2. The standard for compression of progressive scanned
and interlaced video signals with high quality audio over a large
range of compression rates with a range of bit rates from 1.5
to 100 Mbps. Accepted as a HDTV and DVD standard of video/audio
encoding.
Noise. An unwanted signal produced by all electrical circuits
working above the absolute zero. Noise cannot be eliminated but
only minimized.
Non-drop frame time code. SMPTE time code format that
continuously counts a full 30 frames per second. Because NTSC
video does not operate at exactly 30 frames per second, non-drop-frame
time code will count 108 more frames in one hour than actually
occur in the NTSC video in one hour. The result is incorrect
synchronization of time code with clock time. Drop-frame time
code solves this problem by skipping or dropping 2 frame numbers
per minute, except at the tens of the minute count.
Noninterlaced. The process of scanning whereby every line
in the picture is scanned during the vertical sweep.
NTSC. National Television System Committee. American committee
that set the standards for color television as used today in
the US, Canada, Japan and parts of South America. NTSC television
uses a 3.57945 MHz sub-carrier whose phase varies with the instantaneous
hue of the televised color and whose amplitude varies with the
instantaneous saturation of the color. NTSC employs 525 lines
per frame and 59.94 fields per second.
Numerical aperture. A number that defines the light gathering
ability of a specific fiber. The numerical aperture is equal
to the sine of the maximum acceptance angle.
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).
Ohm. The unit of resistance. The electrical resistance
between two points of a conductor where a constant difference
of potential of 1 V applied between these points produces in
the conductor a current of 1 A, the conductor not being the source
of any electromotive force.
Oscilloscope (also CRO, from cathode ray oscilloscope).
An electronic device that can measure the signal changes versus
time. A must for any CCTV technician.
Overscan. A video monitor condition in which the raster
extends slightly beyond the physical edges of the CRT screen,
cutting off the outer edges of the picture.
Output impedance. The impedance a device presents to its
load. The impedance measured at the output terminals of a transducer
with the load disconnected and all impressed driving forces taken
as zero.
PAL. Phase alternating line. Describes the color phase
change in a PAL color signal. PAL is a European color TV system
featuring 625 lines per frame, 50 fields per second and a 4.43361875-MHz
sub-carrier. Used mainly in Europe, China, Malaysia, Australia,
New Zealand, the Middle East and parts of Africa. PAL-M is a
Brazilian color TV system with phase alternation by line, but
using 525 lines per frame, 60 fields per second and a 3.57561149
MHz sub-carrier.
Pan and tilt head (P/T head). A motorized unit permitting
vertical and horizontal positioning of a camera and lens combination.
Usually 24 V AC motors are used in such P/T heads, but also 110
VAC, i.e., 240 VAC units can be ordered.
Pan unit. A motorized unit permitting horizontal positioning
of a camera.
Peak-to-peak (pp). The amplitude (voltage) difference
between the most positive and the most negative excursions (peaks)
of an electrical signal.
Pedestal. In the video waveform, the signal level corresponding
to black. Also called setup.
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 photosensor.
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 photosensor
plus its associated control gates.
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 detects any phase difference between the
two signals and generates a correction voltage that is applied
to the oscillator to adjust its phase or frequency.
Photo multiplier. A highly light-sensitive device. Advantages
are its fast response, good signal-to-noise ratio and wide dynamic
range. Disadvantages are fragility (vacuum tube), high voltage
and sensitivity to interference.
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.
Plumbicon. Thermionic vacuum tube developed by Philips,
using a lead oxide photoconductive layer. It represented the
ultimate imaging device until the introduction of CCD chips.
Polarizing 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, polarizing filters are
used very often to darken a blue sky.
POTS. Plain old telephone service. The telephone service
in common use throughout the world today. Also known as PSTN.
P-picture. Prediction-coded picture. An MPEG term to describe
a picture that is coded using motion-compensated prediction from
the past reference picture.
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 system’s memory (usually this is in
the PTZ site driver) and recalled when required, either upon
an alarm trigger, programmed or manual recall.
Primary colors. A small group of colors that, when combined,
can produce a broad spectrum of other colors. In television,
red, green and blue are the primary colors from which all other
colors in the picture are derived.
Principal point. One of the two points that each lens
has along the optical axis. The principal 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.
PROM. Programmable 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 devices must accept
and use to be able to understand each other. The protocols for
data communications cover such things as framing, error handling,
transparency and line control.
PSTN. Public switched telephone network. Usually refers
to the plain old telephone service, also known as POTS.
PTZ camera. Pan, tilt and zoom camera.
PTZ site driver (or 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.
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. |
