FRA Signal Employee flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Fail-Safe Principle

Any component failure, loss of energy, or broken wire must drive a signal system to its most restrictive aspect. Vital relays are energized for the permissive condition so that dropping out produces stop.

Ohm's Law in Signal Circuits

E = I × R, with P = I²R. Track lead, relay coil, and lamp resistance all add to the circuit; the current must still exceed pickup and fall below drop-away at the worst-case supply voltage.

Relay Pickup and Drop-Away

Pickup is the current at which a relay energizes; drop-away is the lower current at which it releases. Vital relays are tested to the release value because a partially stuck relay can hold a false clear.

Vital Versus Non-Vital Circuit

Vital circuits affect train movement and must be fail-safe and immune to single-component failure. Non-vital circuits, such as indications and alarms, may use standard industrial logic without fail-safe design.

Coded Track Circuit

A track circuit that alternates its energization in a code pattern to convey aspect information. Loss of code for the set interval is interpreted as occupancy or a broken rail, so the decoder drops to the restrictive state.

Standard Shunt Test

A specified resistance, commonly 0.06 ohm, applied across the rails to simulate a train. The track relay must drop at both the near and far ends of the circuit for the test to pass.

Broken Rail Protection

A properly designed track circuit loses current when a rail breaks, dropping the track relay to the restrictive state. The far-end shunt test verifies that this protection actually functions.

Impedance Bond Function

In electrified territory, an impedance bond carries propulsion return current around insulated joints while maintaining track circuit balance. A failed bond unbalances the circuit and can cause false operation.

Insulated Joint Failure

Insulated joints separate adjacent track circuits. A shorted or failed joint can bridge two circuits, producing a false clear or false occupancy that must be tested and reported as a defect.

Constant Warning Time

A grade crossing predictor measures train speed and distance to compute a consistent warning interval, commonly about 20 seconds, before the train reaches the crossing, regardless of train speed.

Island Circuit

The short track circuit at a grade crossing that detects a train occupying the crossing. Loss of island detection can cause gates to rise on a train, which is a critical defect.

Grade Crossing Gate Timing

Gates descend only after flashing lights and the bell start, and rise after the train clears the island plus a set delay. Timing is verified during inspection and recorded.

Crossing Battery Backup

Grade crossing warning systems require a primary supply and a battery backup sized for a specified operating period. Low battery or charger failure is a reportable defect under Part 234.

Highway Signal Interconnection

Preemption links a nearby highway traffic signal to the crossing so traffic clears before gates descend. A failed interconnection is a defect because vehicles may be trapped on the crossing.

Route Locking

An interlocking function that holds a cleared route so conflicting routes cannot be established while a train occupies or approaches it. Locking releases only when the route is proven clear.

Switch Point Detection

A circuit controller proves the switch points are fully seated in normal or reverse before a signal can clear. A broken detector rod or unseated point is a false-clear hazard.

Part 236 Scope

49 CFR Part 236 sets the rules, standards, and instructions for signal systems, including required periodic inspections and tests and the records that must document them.

Part 235 Malfunction Report

Part 235 requires reporting signal malfunctions that affect train movement, including the cause and corrective action, within the regulatory time limit.

Interim Protection for Defects

When a safety device is defective and cannot be restored immediately, the affected movement is protected by restricting speed, flagging, or taking the signal out of service until repair is verified.

Foul Time

A dispatcher-granted period during which a worker may occupy a track with protection from train movements. The worker must not foul the track before receiving it and must release it when done.

Watchman/Lookout Duty

A lookout is positioned to see approaching trains and warn workers in time to clear, using a whistle or horn. Restricted sight distance requires additional lookouts or foul time.

Job Briefing Content

Before work, the briefing covers location, tracks affected, train movements, working limits, and the protection method. Workers must understand and acknowledge it before fouling any track.

Lone Worker On-Track Safety

An individual worker must establish on-track safety, such as train approach warning or foul time, before fouling a track. Walking near tracks without protection is prohibited.

Lead-Acid Battery Hazard

Lead-acid batteries contain corrosive electrolyte and lead, and charging produces explosive hydrogen gas. Use PPE, ventilate the area, avoid sparks, and neutralize spills with the approved agent.

Safety Data Sheet Access

An SDS must be available for every hazardous material on site, including batteries, solvents, and cleaners. Workers must know the hazards, handling, and first aid before use.

Capacitor Stored Energy

Signal capacitors can retain a charge after power is removed. Discharge them and verify zero voltage before handling, or the worker may receive a shock from stored energy.

Hazardous Waste Shipping

Batteries and other regulated waste shipped off site must be packaged, labeled, and manifested per DOT rules, with shipping papers prepared by a trained employee.

Lockout/Tagout Steps

Isolate every energy source, apply a personal lock and tag, and verify zero energy by testing for voltage. Only the person who applied the lock may remove it.

Test Before Touch

Verify the voltage tester on a known live source, test the circuit, then re-verify the tester. A failed tester can give a false dead reading and cause a shock.

Voltage-Rated Gloves

Rubber insulating gloves must be rated for the voltage class of the work, inspected before each use, and removed from service if damaged. Leather protectors are worn over them.

Signal Test Record Content

Each record must identify the device, location, date, test performed, results, and tester, and must be legible and retained for the required period. Missing or altered records are defects.

Defect Closure Verification

A defect is not closed until the repair is verified by a test that proves the failure mode is corrected. The log shows discovery, interim protection, repair, and verification.

PTC Enforcement

PTC enforces movement authority and speed profiles; exceeding the profile or passing a stop point triggers a penalty brake application. It is a safety overlay, not a replacement for signals.

PTC Wayside Interface

Signal aspects and switch positions feed the PTC onboard system. A failed interface must be detected so authority is not granted beyond what the signal system permits.