Measurement of High Value DC Current by Hall Generator

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 / d

Where R is the constant of proportionality and is called as Hall coefficient

∴ V_H = R . Bi / d

Hall co-efficient R has a low value for metals but greater value for Semiconducting material. 
Circuit arrangement explaining Hall effect :

Figure A

Actual set up of Hall generator : It consist of

1. Hall element strip
2. Battery source with protective resistance
3. Iron core rectangular magnetic circuit
4. 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.