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Open Loop vs Close Loop Current Transducer

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Update time : 2022-04-24 16:36:57
According to the principle of Hall effect, the open-loop sensor is the principle of Hall direct release, and the output of the open-loop Hall current sensor is proportional to the vertical magnetic induction intensity of the Hall chip.
 
The magnetic induction is not only related to the measured current, but also related to the magnetic permeability of the iron core. Under different currents, the magnetic permeability of the iron core is different, so the open-loop Hall current sensor has poor linearity and low precision.
 
The closed-loop Hall current sensor is different, the closed-loop is the principle of magnetic balance. The closed-loop Hall current sensor is divided into two windings, the primary side and the secondary side. The secondary side current is generated by the electronic circuit, and the magnetic field generated by the current is exactly offset by the magnetic field generated by the primary side current. The ratio is equal to the inverse of the turns ratio. Since the magnetic fields cancel each other out, the actual magnetic flux in the iron core (induced by the Hall plate) is zero, not affected by the nonlinearity of the iron core, and the precision is high.
 
Therefore, the response time and accuracy of the closed loop is much better than that of the open loop. Both open-loop and closed-loop can monitor alternating current. Generally, open-loop is suitable for high-current monitoring, and closed-loop is suitable for small-current monitoring. Often the open-loop sensor outputs a voltage signal, and the closed-loop output is a current signal.

Features of Open Loop current transducer:
  • Small package size
  • Reduced weight
  • Extended measuring range
  • Low power consumption
  • Quick response
  • No insertion losses

Output characteristic:

  • While positive primary current applied on/through CT, it will output +4V (standard type, dual power supply); on the contrary, when negative current applied, it will show -4V.
Features of Close Loop current transducer:
  • Wide frequency range (about 2 times of nominal current load)
  • Fast response time
  • Excellent linearity
  • No insertion losses
  • Low temperature drift
  • Good overall accuracy
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