For detection of differential current between 2 primary conductors carrying opposite currents, with galvanic isolation between the primary circuit and the secondary circuit

CD - Railway current monitoring and leakage current sensor

The CD current sensing family is designed for monitoring and detecting leakage current on railway applications (fixed installations and onboard).

CD sensors’ high sensitivity allow for the measurement of a differential current that is only 0.1 % of the main current flowing in each primary conductor. For example, a differential current of 1 A can be measured with a main current of 1000 A, or 0.1 A with a main current of 100A. The measurement accuracy is about 5 to 10 % within the specified operating temperature range.

CD current sensors are based on the closed loop Fluxgate technology (C type).

CD – Features and benefits

CD current sensors traction

Main characteristics

  • Closed Loop current sensor using Fluxgate C Type
  • Insulating plastic case recognized according to UL 94-V0


  • Very good differential resolution (able to measure low differential currents with high main currents)
  • Possibility to have an external adjustment by the user of the level of the differential current to be measured (a special design provides external terminals in the housing, where an adjustment resistor is connected)
  • Special designs allow the adjustment of the time constant of the measured differential current, which is convenient when the output signal of the transducer is used as a trigger in a safety system
  • Options to define several levels of differential currents to be measured (the transducer is then designed with a separate individual output for each current level)
  • Protection against primary current overloads

Typical applications

CD current sensors are commonly used in traction applications:

  • Railway security systems
  • Railway fixed installations
  • Onboard trains, trams, locomotives, metro…

LEM CD – Download & Technical Characteristic

Product Document Primary nominal RMS voltage Supply Voltage range Op. Temperature
CD 100-S/SP8


1 A 15 to 15 -40 to 85 °C
CD 1000-S/SP6


1200 A 15 to 24 -25 to 70 °C
CD 1000-S/SP8 Datasheet 1200 A 48 to 48 -25 to 70 °C


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