Control Systems and Automation – Railway Applications

Vocabulary flashcards covering analog/digital signals, sensors, PLCs, compressors, and locomotive brake system components and functions.

Analog Signal

A continuously variable electrical signal (voltage or current) that represents a physical quantity such as temperature, pressure, or speed.

Digital Signal

An electrical signal with only two discrete states—high/low, 1/0—used to indicate on-off conditions or logical states.

4–20 mA Standard

Industrial current loop in which 4 mA represents the minimum measurable value, 20 mA the maximum, and <4 mA is interpreted as a sensor fault.

Electrical Noise Immunity (Digital)

Resistance of digital signals to electromagnetic interference, making them ideal for logical control tasks.

Encoder (Speed Sensor)

A rotating disc with optical or magnetic marks that generates electrical pulses; pulse rate is proportional to shaft speed.

Control System (Railway)

Coordinated set of sensors, logic, and actuators that supervises and manages train operation for safety and efficiency.

Closed-Loop Control Cycle

Continuous sequence of sensing, decision-making, and actuation executed by a control system.

Sensor

Device that receives a physical stimulus and responds with an electrical signal.

Active Sensor

Sensor requiring external excitation (e.g., RTD, load cell).

Passive Sensor

Sensor that generates a signal without external power (e.g., thermocouple, photodiode).

Transducer

Device that converts one form of energy into another, typically a physical variable into an electrical signal.

PLC (Programmable Logic Controller)

Industrial computer that executes control programs to automate machinery and processes.

PLC Input Module

Section of a PLC that receives digital or analog signals from sensors.

PLC CPU

Central processing unit that executes the logic program and makes control decisions.

PLC Memory

Stores user program, variable data, and I/O status inside a PLC.

PLC Output Module

Interface that sends control signals from the PLC to actuators such as motors or valves.

PLC Programming Port/Module

Hardware interface used to load programs into a PLC and perform diagnostics.

PLC Scan Cycle

Repetitive sequence: read inputs → execute program → update outputs → diagnostics/communication, usually in milliseconds.

Locomotive Air Compressor

Machine that compresses ambient air to feed pneumatic systems such as brakes and doors.

Piston Compressor

Reciprocating compressor that compresses air in stages using pistons.

Rotary Screw Compressor

Modern, quiet compressor that provides continuous air flow via intermeshing rotors.

Aftercooler

Heat exchanger that lowers the temperature of compressed air to protect downstream components.

Air Dryer

Device that removes moisture from compressed air to prevent condensation in the pneumatic circuit.

Main Air Reservoir

Tank that stores compressed air (≈8–10 bar) for use by locomotive pneumatic systems.

Pressure Regulator

Valve that maintains air pressure within a safe, preset range.

Automatic Brake Valve 30-CDW

Locomotive brake control with six handle positions: Release, Minimum Service, Full Service, Suppression, Handle Off, Emergency.

Release Position (Automatic Brake)

Fills brake pipe and equalizing reservoir to ~500 kPa to fully release train brakes.

Minimum Service Position

Reduces equalizing pressure ~50 kPa, producing a light service brake application.

Full Service Position

Creates ~170 kPa brake-pipe reduction for maximum service braking.

Suppression Position

Cancels penalty brake applications; similar pressure reduction to Full Service.

Handle Off Position

Drops equalizing pressure to 0 kPa, leaving brake pipe at ~55–69 kPa; used when cab is unattended or unit is a remote slave.

Emergency Position

Vents brake pipe to 0 kPa rapidly for quickest possible stop and dumps equalizing reservoir to atmosphere.

Equalizing Reservoir

Small reservoir whose pressure mirrors brake-pipe commands; controls gradual brake reductions.

Brake Pipe

Main pneumatic line (~500 kPa charged) that transmits brake commands along the train.

Independent Brake Valve

Controls only locomotive brake cylinders with two main positions: Release and Full Application, plus a proportional application zone.

Light Locomotive Operation

Running one or more locomotives without train cars; relies chiefly on the independent brake for stopping.

Penalty Emergency

Automatic emergency brake triggered by vigilance device, overspeed, emergency stop button, train separation, or door opening while moving.