Introduction To The Operating Principle Of Multiplexers - Ganz ZS-SX Series Installation And Operating Instructions Manual

Appendix

Introduction to the operating principle of multiplexers

Multiplexer were originally developed in order to allow the signals from various video sources (e.g. cameras) to be
recorded on a single tape. This requires that all video sources be connected to the multiplexer. The multiplexer
can then very quickly switch from one video source to, an ability which gave rise to its original name of name
frame switcher. As the system switches from one video source to another, an output video signal is produced
containing the images from each source stored on top of one another. In order to be able to display the different
images together without interference, the video sources have to be synchronized. This process is carried out by
the digital image storage system, and can also by optimized means of external synchronization via the network
phase.
Each video image is assigned a digital code, which is stored – in the non-visible part of the image – in video lines
10 – 20. The multiplexer can then use this code to identify taped images as they are being reproduced and can
display the information on-screen if desired. In this way, it is possible – for example – to select only the images
produced by a certain camera from a series of recordings and play them back via the monitor, while ignoring the
other cameras.
Video recorder
Cameras ZS-SX Multiplexer
The multiplexer must be adjusted to match the time setting of the video recorder. When set to long-term opera-
tion, the recorder does not operate in real time, i.e. instead of displaying 50 frames a second, it displays – for
example – just eight frames in the same period. In this case, the multiplexer should not move too quickly from
one source to another, as some images may be missed and certain video inputs may not be recorded. The
purpose of the VCR clock-pulse control signal is to provide synchronization between the video recorder and the
multiplexer.
In using the VCR clocked-pulse output signals, the recorder controls the sequencing function of the multiplexer.
This procedure permits the optimized synchronization of both devices. Example: If the internal programming of
the VCR causes the recording speed to change (e.g. in the event of an alarm), the multiplexer reacts immediately
to the altered clock-pulse signal. Important: the speed of the ZS-SX multiplexer will only be synchronized auto-
matically if T.L.1 is activated in the REC/ALARM menu.
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ZS-SX Series