What does a flashing yellow railroad signal mean?
When the top yellow light is flashing it upgrades the signal from an Approach indication to an Approach Medium indication. In the continuing pursuit for the elimination of unneeded signal heads some railroads eliminated the center head if there was no Limited or Medium speed route at a location.
What is a semaphore indicator?
Semaphore indicators are designed to perform on Instrumentation. Control & Relay Panel’s mimic diagram. It indicates the ‘open’ or ‘close’ position of the circuit Breaker. PT ON / OFF switch, Earth Switch, Isolator etc.
How is semaphore used?
semaphore, method of visual signaling, usually by means of flags or lights. Before the invention of the telegraph, semaphore signaling from high towers was used to transmit messages between distant points.
Where is semaphore used?
Semaphores are typically used in one of two ways: To control access to a shared device between tasks. A printer is a good example. You don’t want 2 tasks sending to the printer at once, so you create a binary semaphore to control printer access.
Why do railroads use semaphores instead of signals?
Compared to earlier signals, they provided the railroads with a superior method of transmitting track conditions to the engineer So what is a semaphore, and what makes it different than other signals?
What is a semaphore signal?
This semaphore system involves signals that display their different indications to train drivers by changing the angle of inclination of a pivoted ‘arm’. Semaphore signals were patented in the early 1840s by Joseph James Stevens, and soon became the most widely used form of mechanical signal.
Where was the first railway semaphore signal placed?
The first railway semaphore signal was erected by Charles Hutton Gregory on the London and Croydon Railway (later the London Brighton and South Coast Railway) at New Cross, southeast London, about 1842 on the newly enlarged layout also accommodating the South Eastern Railway.
What does the colour of the light on a semaphore mean?
For most types of semaphore arm, the colour of light shown when the arm is in the “on” (most restrictive) position generally corresponds to the colour of the arm itself (i.e. red for a stop signal, yellow for a distant signal). When the arm is in the “off” position, a green light is displayed.