An additional safeguard is included in the distant-signal control wiring to ensure the AWS " clear " indication is only given when the distant is proved " off " mechanical semaphore distants have a contact in the electromagnet coil circuit closed only when the arm is raised by at least 40 degrees, whilst colour-light distants have a sensing relay in the DR ( green ) filament circuit, and the newest type of single-aperture LED main signal unit has a " Green-Proved " output from its driver electronics that is used to enable the electromagnet via the SSI.
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