Foghorn Malfunction

[toucana]

People living near Lands End Cornwall UK have been advised to buy earplugs due to a lighthouse’s broken fog alarm

https://www.bbc.co.uk/news/articles/cdelld75wgro

The Longships Lighthouse has been sounding a loud beep every 13 seconds for the last week after a visibility sensor malfunctioned. Trinity House who manage all of England's lighthouses say they are aware of the fault, but are waiting for a spare part to arrive.

The lighthouse which dates from the later 19th century has been unmanned ever since automation was installed in 1988.

https://en.wikipedia.org/wiki/Longships_Lighthouse

The previous pneumatic supertyfon foghorn was removed at the same time, and replaced with an electric audio emitter linked to a visibility sensor. An article in Ocean Navigator explains how these work:

Quote

 

“Employing the principle of backscatter, a properly calibrated fog detector can sense when visibility lowers to a pre-set threshold value and will turn on its associated horn.

Inside the fog detector is a strobe that flashes at the rate of three Hz (three flashes a second). If the air is clear (low humidity, low dust, low pollutants), the vast majority of the light from this strobe will depart from the detector, never to return. If, however, fog particles are present (10 to 30 microns in size), some percentage of strobe light will be bounced back to the collecting lens. (The spherical drops act like small corner reflectors…

Behind the collecting lens is a photodiode that converts reflected light pulses to electrical pulses. These pulses are displayed on the unit’s “visibility meter.” (The best way to determine visibility is to have a separate light source and detector about 100 feet apart, with each component pointed at the other. This is the method used at airports. It is not used at lighthouses because there usually isn’t enough real estate to mount the separate components.)

Once the flash lamp and the photodiode are properly calibrated, the voltage of the electrical pulses can be directly related to visibility. In other words, a voltage of x indicates two-mile visibility, while y is 1/2-mile visibility. The local aids to navigation team sets the visibility level that turns on the fog signal."

https://oceannavigator.com/electronic-fog-signals/

 

 

Edited Friday at 04:23 PM by toucana
Corrected 'Britain's' to 'England's' p.2