The following items were discussed at the Signal Class on June 28, 2003:
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| Signal Aspects: |
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- Green Signal = Clear to Proceed
- Yellow Signal = "Approach" next signal at less than 10 mph prepared to stop short of the signal
- Red Signal = Stop (and do not procedd - stay stopped)
- Red with Number Plate = Stop and proceed at restricted speed
- Restricted speed = 10 mph but no more than able to stop in half distance you can see
- Flashing Red = Pass at restricted speed (do not need to stop first); it can also indicate diverging
track to an unsignaled section
- Lunar (bluish white) = Same as "Flashing Red"
- Signals with Multiple Heads: Upper Head = Straight ahead Main Line; Lower Head = Diverging route
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| Relays: |
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- Energized = Front Contact Normally Open (won't weld - Carbon)
- De-eneregized = Back Contact Normally Closed (usually Silver)
- Heel = Common Contact
- Gravity insures return to Back Contack in case of failure
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| Impedance Bonds: |
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- Impedance bond connection to track looks like open circuit to AC track circuits
- Electrified Road usually DC Propulsion with AC signals --
since DC Propulsion and DC Signals can cause false "NO-TRAIN"
if one side of train draws less current than the other
- Both AC Propulsion and AC Signals is OK as long as each uses a different frequency
- Metro LA Trains uses non-standard 750 VDC Propulsion
- Oil Junction has no insulated joints (except at switches) so new signals will use
all audio circuits and overlays
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| Typical Train Circuits: |
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- Basic Train circuits were discussed to get everyone a basic understanding
- Basic circuit consists of a relay coil (HR) with contacts from multiple devices controlling
if that relay should display a clear or restricted approach
- The multiple device contacts could be Track Relays (train present),
Switch Relays (switch thrown to undesired position) and other related circuits
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