Videograph B Fog Signal Detector

As the Coast Guard automated their lighthouses and removed Keepers who visually sighted fog and turned on the fog signal, a means to detect fog electronically was invented. This device became the standard sensor used by the US Coast Guard to detect fog and turn on the fog signal.

The detector consists of two parts, a projector, and a receiver. The projector sends out strobe-type flashes of light which hits air particles of fog, which are refracted back to the receiver as "backscatter light". The receivers threshold is adjusted to turn on the fog signal at a specified density level.

This device was located in the electrical/battery room adjoining the light tower here at Beavertail.

The sensor is a VM 100, which is an infrared detector measuring atmospheric particles