[SBE] black detector

[Chris Hoopes]

Does anyone know of a device that can detect black in the video chain?  I have seen the devices that would detect signal loss, usually loss of sync.  What I am looking for is a device that would provide a contact closure after say 90 sec. of black. What do you guys who have unattended periods of operation do to alert extended periods of black?  SDI or analog will work for me.
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