Salvo switching:
is a feature in matrix switchers. On command from the matrix switcher or an alarm event. a group of cameras can be switched simultaneously onto a group of monitors.

SECAM Sequential Coluleur A'Memorie:
a color television system used in France and a few other countries.

Sensitivity of a camera:
is the minimum light level required at the CCD chip which will generate a usable video picture. It is measured in lux.

Sequential switcher:
is a type of switcher that allows multiple cameras to be displayed or recorded one at a time.

Shield:
is a copper braid which covers the dielectric and centre core of a coaxial cable. It protects the video signal from EMI.

Signal loss:
is a reduction in signal strength expressed in decibels.

Signal to noise ratio:
It is the ratio between the signal voltage and the noise voltage generated by an electronic circuit. It is measured in decibels (dB).

Simplex:
is a system which can handle only one channel of video, audio or data signal.

Single mode cable:
is an expensive type of fibre optic cable with a narrow glass core which allows only a single path for signal transmission.

Silicon wafer:
is a semiconductor material on which the CCD chips are etched.

Snow:
is a fault in the picture, appearing as small dots on the monitor and is caused by heavy noise in the video signal.

Sodium vapour lamp:
is a type of artificial light source which is very efficient and uses sodium vapour to produce a yellow-orange light.

Spectral response:
is the sensitivity of a device to different light frequencies.

Standard angle lens:
is a type of lens which provides a view having the same proportions as seen by the human eye. It has a magnification ratio of 1.

Step down transformer:
is a transformer used in power supplies to step down or lower the main line voltage. The ratio between the number of turns of the primary coil to the secondary coil determines the step down voltage.

Stranded cable:
is a type of cable in which a number of wires enclosed in an outer jacket are used to transmit the electrical signal.

Sunshield:
is a movable accessory placed on top of outdoor housings to prevent direct light falling on the camera.

Sync generator:
is a device which generates sync pulses which are then used to synchronise cameras.

Synchronisation:
is a process which ensures that the formation of frames in a multi camera system start at the same time. There are different ways to achieve camera synchronisation.