40
c
HAPTER
3:
Operation
F71/F41 Teslameter
3.6 Probes
Full details on FP Series probes are provided on our website. Please see:
.
3.6.1 General Probe
Information
FP Series probes make use of Hall sensors to characterize magnetic fields. A Hall sen-
sor is a solid state device that provides an output voltage proportional to magnetic
flux density. As implied by its name, this device relies on the Hall effect.
The Hall effect is the development of a voltage across a sheet of conductor when cur-
rent is flowing and the conductor is placed in a magnetic field. 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 causes the charging of the edges of the conductor, 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 mag-
netic-field-related Lorentz force. The voltage potential across the width of the con-
ductor is called the Hall voltage.
The generated Hall voltage for a given field will vary with temperature. Each standard
Hall probe contains a temperature sensor at the tip, allowing the detection of sensor
temperature, and applying temperature compensation around room temperature.
Cryogenic probes do not measure temperature and should be compensated manu-
ally.
FIGURE 3-35
Hall voltage
V
H
B
Z
L
W
t
ȟ
DŽ
ȟ
X
I
V
X
–
–
+
+
–
Electric
field
