**Measurement of High Value DC Current by Hall-Generator**

Q. With a neat sketch explain Hall generators for measurement of high currents.

**What is Hall effect ?**

If an electric current flows through a metal plate perpendicularly located to the on magnetic field Lorenz - forces will deflect the electrons in the metal structure in a direction normal to the direction of both the current and the magnetic field. This is known as "Hall effect".

**What is "Hall Voltage" ?**

The charge displacement generates an e.m.f in the normal direction. This e.m.f. is known as Hall EMF or "Hall voltage".

**Magnitude of Hall voltage (V**

_{H}) :V

_{H }is directly proportional to current i. Therefore V

_{H }∝ I=i.

V

_{H }is directly proportional to flux density B. Therefore V_{H }∝ B.V

_{H }is inversely proportional to plate thickness. Therefore V_{H }∝ 1/d.Hence Hall Voltage V

_{H }∝ Bi / d∴ V

_{H }= R . Bi / dWhere R is the constant of proportionality and is called as Hall coefficient

∴ V

_{H }= R . Bi / dHall co-efficient R has a low value for metals but greater value for Semiconducting material.

Actual set up of Hall generator : It consist of

**Circuit arrangement explaining Hall effect :**Figure A |

- Hall element strip
- Battery source with protective resistance
- Iron core rectangular magnetic circuit
- Path of current (I)

Figure B |

- The current carrying conductor is surrounded by a rectangular core magnetic circuit shown above.
- The Hall-element strip is located in the air gap of the magnetic core across the thickness of which a Hall voltage V
_{H }produced. - Hall voltage V
_{H}measured by a low range voltmeter. - The magnetic field intensity H = 1 / δ is produced in a small-air gap in the core
- A small constant current (I) is allowed to pass through the clement by the battery source E.
- The voltage V
_{H}developed across the Hall element in the normal direction is proportional to the current I. - The Hall element material is to be so selected that Hall co-efficient R is suitable for the set.
- Hall generator is used for measuring high valve D.C. currents as well as measuring
**"Unidirectional ac."**and also impulse currents. For such measurements the Hall generator in modified form with compensating circuit is used.