Current Sensor Info
Hall-Effect Current Sensor Features:- Measure: DC, AC, and Pulsed waveforms
- Galvanic Isolation
- Fast Response
- Zero Insertion Loss
- Cost Effective
Current Transformer Features:
- Measures AC only
- Electrical Isolation
- No Power Supply
- Lower Cost
The Basic Principle
In a hall effect-based current sensor, the magnetic flux, proportional tothe primary current, is concentrated in gapped magnetic corecontaining the hall effect device (Fig. 1). The primary current ismeasured without electrical contact with the primary circuit providinggalvanic isolation.
From Figure 1, the magnetic flux, concentrated in the gap of themagnetic core, induces a potential difference, Vh, the Hall voltage,given by the Vh=k*Ic*B. The output signal of the Hall device, Vh, isthen further amplified by additional internal signal conditioning circuitryto provide an output voltage proportional to the primary current.
Closed Loop Operating Principle
In a closed loop current sensor the same principles apply with theaddition of a secondary coil and feedback circuitry. The closed loop or‘zero-flux’ hall effect sensor feeds back an opposing current into asecondary coil wound on the magnetic core to zero the flux producedin the magnetic core by the primary current. The output current of aclosed loop current sensor is an exact representation of the primarycurrent scaled by the number of turns in the secondary coil. As with theopen loop design the closed loop design provides galvanic isolation.
The output of a closed loop current sensor can be scaled with theaddition of a burden resistor, Rm1 , to produce a voltage level outputproportional to the primary current.
1 Within limits - Consult Tamura Engineering
Application notes & tips:
- Insure power supply polarity is respected to prevent damage to internal circuity.
- Non-linearity due to magnetic core saturation can occur at primary currents in excess of 2X the nominal rated current.
- Hall effect based current sensors are affected by static and dynamic electric and magnetic field; usetwisted and/or shielded cables to mitigate these affects.
- Frequency bandwidth in open loop current sensors is limited at high frequency due to magnetic core losses and eddy current induced temperature rise.
- The Primary conductor should pass straight throughthe aperture or, in the case of multiple primary turns, wound around the body of the current sensor.
- Care in placement and orientation of the current sensors in presence of high electromagnetic fields can lessen EMF effect on the current sensor.
