BH Curve - A brief description

The BH Curve is a plot of the Magnetic Flux Density (B) versus the Magnetic Field Strength (H).  This is an important curve in selecting materials for electric machines.  The curve tells us about the change in the Flux density of a material as the magnetic field strength is increased.

When the magnetic field strength is increased gradually, the domains inside the material exposed to the field get aligned gradually.  This results in the increasing flux density of the material. As the magnetic field strength is increased further, there comes a point where the curve flattens.  This implies that the magnetization is complete and further increase in the flux density is not possible.  This is the point of maximum positive saturation, b in the curve.

If the magnetic field strength is decreased at this time, shown by section b–c , it is observed that the magnetic flux density does not come to zero even after the magnetic field strength has been reduced to zero. 

This indicates that the material is able to retain the magnetism.  This is known as residual magnetism.
In order to bring the residual magnetism to zero, the magnetic field strength is applied in the opposite direction such that H is now negative.  

This is shown in the region of the curve c–d.  The magnetic field strength required to bring the flux density to zero is known as the coercive strength of the magnetic field.  

If the magnetic field strength is increased in the opposite direction, the magnetic flux density also increases until it reaches negative saturation, point e.  If the magnetic field strength is brought to zero, the material still retains magnetism in the opposite direction.  This is known as the negative residual magnetic strength, indicated by point f.  

If the magnetic strength is increased in the positive direction, the magnetic flux density becomes zero once again.  This is point g of the curve.  

The BH curve is also known as the hysteresis curve as the reversed curve does not follow the original curve.  
BH curves help compare the magnetic properties on one material over another while selecting a material for a specific application.  

Posted by: Electrotechnik

Manganin Alloy - An Overview

Manganin is an alloy of copper (86%), Manganese (12%) and nickel (2%).  Manganin is widely used in the construction of resistors as it has near zero temperature coefficient of resistance which means that its resistance does not change for an increase in temperature. 

The temperature coefficient of Resistance of Manganin is 

This is an vital aspect when designing resistors used in measurement and control circuits. 

Until recently, Manganin was used in designing laboratory standards for the ohm. 

Manganin was developed by Edward Weston in 1892.

Posted by: Electrotechnik
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