Lake Shore 420, Руководство пользователя

Страница: 47 / 54

Lake Shore Model 420 Gaussmeter User’s Manual
Appendix A
A-3
APPENDIX B
HALL GENERATORS
B1.0 GENERAL
This chapter covers useful information about Hall Generators including: Theory of Operation (Paragraph
B2.0), Generic Hall Generator Hookup (Paragraph B3.0), Hookup to a Model 420 Gaussmeter (Paragraph
B4.0), Specifications (Paragraph B5.0), and the HALLCAL.EXE Program (Paragraph B6.0). Obtain additional
installation and calibration information in Lake Shore Document Number C2S001.
B2.0 THEORY OF OPERATION
E. H. Hall discovered the Hall effect in 1879. For nearly 70 years it remained a laboratory curiosity. Finally,
development of semiconductor and ceramic material brought Hall generators into the realm of the practical.
A Hall generator is a solid state sensor which provides an output voltage proportional to magnetic flux density.
The device relies on the Hall effect which is the development of a voltage across a sheet of conductor placed
in a magnetic field with current flowing. See Figure B-1.
Electrons (the majority carrier most often used in practice) “drift” in the conductor when under the influence of
an external driving electric field. When exposed to a magnetic field, these moving charged particles
experience a force perpendicular to both the velocity and magnetic field vectors. This force charges the
conductor edges, one side positive with respect to the other. This edge charging sets up an electric field
which exerts a force on the moving electrons equal and opposite to that caused by the magnetic-field-related
Lorentz force. The voltage potential across the width of the conductor is called the Hall voltage. This Hall
voltage can be utilized by attaching two electrical contacts to the sides of the conductor.
The Hall voltage can be given by the expression: V
H
=
γ
B
B sin
θ
where: V
H
= Hall voltage (mV)
γ
B
= Magnetic sensitivity (mV/kG) (at a fixed current)
B = Magnetic field flux density (kilogauss)
θ
= Angle between magnetic flux vector and the plane of Hall generator.
The Hall voltage varies with the angle of the sensed magnetic field, reaching a maximum with the field
perpendicular to the plane of the Hall generator.
B2.1 ACTIVE AREA
The Hall generator assembly contains the
sheet of semiconductor material, normally
called a “Hall plate”, to which the four
contacts are made. In its simplest form, the
Hall plate is a rectangle of fixed length,
width, and thickness. Due to the shorting
effect of the current supply contacts, most
magnetic field sensitivity is contained in an
area approximated by a circle, centered in
the Hall plate, with a diameter equal to the
plate width. Thus, when the active area is
given, the circle as described above is the
common estimation.
Figure B-1 Hall Generator Theory
B
High Mobility III-V
Semiconductor
a) Indium arsenide
b) Gallium arsenide
–
–
–
– +
+
+
+
e
v
Conventional
Current
Ic (–)
(Green or Black)
B
VH (–)
(Clear or Yellow)
VH (+)
(Blue)
Ic (+)
(Red)
v
F
F = –e (v • B)
(force on electron)