Lake Shore 475, Руководство пользователя

Страница: 22 / 148

Lake Shore Model 475 Gaussmeter User’s Manual
2-6 Background
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.
As can be seen from the formula, above, the Hall voltage varies with the angle of the sensed magnetic field, reaching a
maximum when the field is perpendicular to the plane of the Hall generator.
2.3.1 Active Area
The Hall generator assembly contains the sheet of semiconductor material to which the four contacts are made. This
entity is normally called a “Hall plate.” The Hall plate is, in its simplest form, a rectangular shape of fixed length, width
and thickness. Due to the shorting effect of the current supply contacts, most of the sensitivity to magnetic fields is
contained in an area approximated by a circle, centered in the Hall plate, whose diameter is equal to the plate width.
Thus, when the active area is given, the circle as described above is the common estimation.
Figure 2-6. Hall Generator Theory
2.3.2 Polarity
If the control current enters the red lead (with +I
C
connected to the positive terminal of the current supply), and the
magnetic field direction B is as shown in Figure 2-6, a positive Hall voltage will be generated at the +V
H
lead. Reversing
either the current or the magnetic field will reverse the output voltage.