Coded Track Circuits | D.C. Coded Track Circuits

Indian Railway Signalling Metro Rail General Rules Network Rail

Coded Track Circuits

• D.C. Relay Coded Track Circuits
• Solid-State Coded Track Circuits

– Electrocode
– Microtrax

D.C. Coded Track Circuits
• Transmitter – Sends a coded D.C. voltage (Square Wave)

• Receiver – Decodes signal
• Dependent on the code rate, receiver will :

– Pick the appropriate track relay repeater

– Display appropriate signal aspect
– Perform function according to relay wiring



• Improved Shunting Sensitivity (Relay must fully “pick” each “on” code)

• Improved Broken Rail Protection (Relay must fully “pick” each “on” code)

• Increased Average Track Circuit Length – Less ballast leakage

• Increased Protection Against Foreign Current – Must receive correct “code rate”

• Improved Protection Against Failure of Insulated Joints – Must receive correct “code rate” and usually correct polarity


Coded Track Circuits


The TR Relay is a biased code following track relay (picks and drops on each pulse)

• As long as the TR is coding, the TPR and the CDR relay will remain energized

• Any interruption of the coding OR constant D.C. Voltage causes the TPR and/or the CDR to drop.
• Either relay, de-energized causes the signals to display a restrictive aspect

•Different rated code following relays allow signal aspect information to be sent and received
• Typical code rates include 75, 120 or 180pulses per minute

Information is sent in one direction only

• A duplicate set of coding relays is required for dual direction signaling
• traffic relays can be used to switch transmit and receive ends

Non Coded Track Circuit

Non Coded Track Circuit

Style “c“ Circuit


Style ``c`` Circuit

Coded Track Circuits | D.C. Coded Track Circuits | ADVANTAGES |Style “c“ Circuit | Non Coded Track Circuit

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