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Magnetic Hysteresis Loop Tracer

Order Code: 55540

Category: Physics Trainers

  Measures magnetic parameters accurately Demagnetisation, eddy currents and sample cross-sectional area have been accounted for Capable of detecting the number of magnetic phase present in a sample   Introduction A pr...



SPECIFICATION

 
Measures magnetic parameters accurately Demagnetisation, eddy currents and sample cross-sectional area have been accounted for Capable of detecting the number of magnetic phase present in a sample
 
Introduction
A precise knowledge of various magnetic parameters of ferromagnetic substances, viz. coercivity, retentivity, saturation magnetisation and hysteresis loss, and ability to determine them accurately are important aspects of magnetic studies.
 
The information about the aforementioned properties can be obtained from a magnetic hysteresis loop which can be traced by a number of methods in addition to the slow and laborious ballistic galvanometer method. Among the typical representatives of AC hysteresis loop tracers, some require the ring form of samples while others can be used with thin lms, wires or even rock samples. Ring form samples are not always practically convenient to make while in others demagnetisation effects sometime become quite important. The present set-up can accept the samples of thin wires of different diameters. The demagnetisation effects, different diameters of samples and eddy currents (due to the conducting property of the material) has been taken into account within the design or graphically.
 
Design Principle
When a cylindrical sample is placed coaxially in a periodically varying magnetic eld the magnetisation in the sample also undergoes periodic variation. This variation is picked up by a coil, placed coaxially with the sample. For the uniform eld Ha produced, the effective eld H acting in the cylindrical sample will be
 
H = Ha  NM                                                             (1)
 
where M is magnetisation, N is normalised demagnetisation factor including 4p and J is the magnetic polarisation de ned by
 
            B = m0H J
 
with B=mH or m0(H M) as magnetic induction. The signal corresponding to the applied field, Ha can be written as
 
e1 = C1Ha                                                              (2)
 
where C1 is a constant
Further the ux linking with the pick-up coil of area Ac due to sample of area As will be
f = m0(Ac  As)H’ AsB
 
where H’ is the eld in the excess area of the pick-up coil. Under certain conditions this equation reduces to
f = m0AcH AsJ
 
The signal induced in the pick-up coil (e2) will be proportional to df/dt which after integration yields
           e3 = C3f = C3m0AcH C3AsJ                      (3)
 
Solving (1), (2) and (3) gives
 
Based on these equations the electronic circuit has been designed to give values of J and H and hence the hysteresis loop. Further different magnetic phases present in the sample may also be identi ed by electronically manipulating the pick-up signal.
 
Description of the set-up
The block diagram of the set-up is given next and a brief description now follows:

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