VIDEO CONTINUITY ALARM SYSTEM (VLM473)
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VIDEO CONTINUITY ALARM SYSTEM
The purpose of the Video Continuity Alarm System is to provide an unambiguous indication of a video facility failure. Current alarm systems cannot distinguish between a transmission facility failure and the video signal being turned off or disconnected at the source.
The Video Continuity Alarm System is comprised of the VLM473 Video Loss Monitor located at the video source interface and the VLI771 Video Loss Indicator located at various critical locations in the system. The function of the VLM473 is to replace sync pulses when the video source is turned off. This insures that sync pulses will always be present at the source interface. Now, when the VLI771 alarm contacts close, it is an unambiguous indication that the transmission facility has failed.
The VLM473 monitors the video sync pulses coming from the origin video interface. Upon failure of source video, the VLM473 initiates a series of sync pulses of its own. If source video returns, the VLM473 ceases to produce sync pulses, but does pass source video through. There are no active electronic devices in-line between VIDEO INPUT and VIDEO OUTPUT of the VLM473, therefore no distortion of the video signal is possible due to the presence of the unit.
The VLI771 is a video loop-through device that senses the presence of video sync pulses and closes an alarm contact if the sync pulses cease for any reason.
When the VLM473 Video Loss Monitor and the VLI771 Video LOss Indicator are connected at opposite ends of a video transmission facility, any alarm signal generated by the VLI771 will unambiguously report a failure of the video facility. An alarm contact closure at the VLM473 will report that the incoming video signal has dropped out and that the replacement sync and Video Loss Monitor location is being transmitted into the video facility.
In transmission systems consisting of multiple tandem video facility links, the VLM473 and VLI771 may be connected at each baseband video location in order to separately identify each facility that may have failed so as to sectionalize the location of the failure.
Please contact Frank McClatchie at 1-800-235-6960 or 1-714-979-3355 for further information on this Video Facility Continuity Alarm System.