Flux Concentrator

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Description

Flux concentrators are made up of thin strips of soft magnetic materials (High permeability, low remanence and low eddy current losses). When surrounded to current carrying conductors it increases the flux density. As the effective permeability of the material is high, it amplifies the flux density. At the same time the gap or air gap of flux concentrator aids in positioning the hall effect sensor in appropriate distance from the conductor. The distance between sensor and conductor determines the accuracy of measurement.

Factors like type of current measurement (either low or high), Frequency, Atmospheric conditions and end application determines the specific material grade to be used.

FAQ for Flux Concentrator

Q.1. What is flux concentrator and what is the working mechanism?
  • Ans: Flux concentrators intensify the magnetic field in certain areas and can assist in increasing efficiency in power or heat transfer. Without a concentrator, the magnetic field is more likely to spread around and intersect with any electrically conductive surroundings.
Q.2. What is the Hall effect?
  • Ans: When a current-carrying conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field. This principle is known as the Hall effect
Q.3. How to decide the minimum air gap for a magnetic shield/flux concentrator?
  • Ans: The minimum air gap for magnetic shield depends upon the dimensions of bus bar,sensitivity of the current sensor.
Q.4. Which are the parameters needed to consider for designing a magnetic shield/Flux concentrator?
  • Ans: In designing, fabricating, and testing shields, the following parameters are essential to developing the best “strategy” for shield design and for predicting how the magnetic shield will perform in attenuating magnetic fields.
    • Geometry
    • Shape
    • Size
    • Magnetic field continuity
    • Closer
    • Length to Diameter Ratios and the Impact of Openings
Q.5. How to choose material for the Flux concentrator?
  • Ans: Soft magnetic alloy like 48% NiFe, 80% NiFe, SiFe can be used for flux concentrator, Selection of material for flux concentrator is depends upon the following factor
    1. Permeability of material
    2. Saturation
    3. Coercivity
    4. Material Cost
Q.6. What is the Clamp on Current sensor and how does the hall effect current sensor work?
  • Ans: A clamp on a device/ module is a circuit used to measure current flowing through a wire without any physical connection made to it. The clamp consists of 2 part flux concentrator which encapsulates the current carrying wire and the magnetic flux produced by the current is focussed on to the Hall sensing ic. A Hall effect sensor is a device that is used to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. The flux concentrator in the module focuses the magnetic field on the ic, which senses the field strength and produces voltage as output.
Q.7. What is a current sensor and how does it operate?
  • Ans: A current sensor is a device that detects and converts current to an easily measured output voltage, which is proportional to the current through the measured path. When a current flows through a wire or in a circuit, voltage drop occurs. Also, a magnetic field is generated surrounding the current carrying conductor. Current sensing or measurement is required for revenue generation or feedback control mechanism or monitoring. Current can be measured by a Hall Sensor with Flux concentrator logic, Shunt logic, Current Transformer or Rogowski Coil. Modules are integrated assemblies incorporating flux concentrators, Shunts, Hall Sensors, Temperature sensors, CAN and IOT. Current sensing is widely used in industries likeEV/HEV,Renewable Energy, Aerospace, Defence, Medical, Safety, Energy meters
Q.8. Different methods of current sensing. Table for comparison….
  • Ans:
    MEASUREMENT METHOD ACCURACY ISOLATION EMI (TAMPER RESISTANCE) ROBUST SIZE COST
    Hall effect High Yes High Moderate Moderate High
    Rogowski coil High Yes Moderate High Large Moderate
    Current Transformer High Yes Moderate High Large Moderate
    Shunt Resistor High No High High Small Low
Q.9. How to select Geometry of flux concentrator ?
  • Ans: Geometry of the flux concentrator depends on the shape of the busbar & conductor. Commonly, flux concentrators are circular to concentrate the flux lines in one direction and to avoid angle effects, But rectangular concentrators can be used as well. With rectangular cores, it is recommended to round the inner & outer corners of the core to avoid breaking magnetic concentration effects.
Q.10. What is significance of air gap in soft magnetic components ?
  • Ans: Air gaps directly define the gain of the system. The smaller the air gap (at a constant cross-sectional area) the higher the gain. However, if the air gap is too narrow the residual magnetic hysteresis of the core becomes significant, thereby lowering the accuracy performance at smaller currents. The recommended air gap is between 3 and 8 mm. The air gap obviously has to be adjusted to the sensor package thickness.
Q.11. Why laminated core better than solid core
  • Ans: Laminated magnetic cores are made of stacks of thin sheets, Due to stack of lamination, eddy currents can only flow in narrow loops within the thickness of each single lamination. Since the current in an eddy current loop is proportional to the area of the loop, small lamination thickness prevents most of the current from flowing, Hence laminated cores have less eddy current loss than solid core.
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