HALL
EFFECT TRANSDUCER
Principle
of operation:-
When a
current-carrying conductor is placed into a magnetic field, a voltage will be
generated perpendicular to both the current and the field. This principle is
known as the Hall Effect.
Figure
1 illustrates the basic principle of the Hall Effect. It shows a thin sheet of
semiconducting material (Hall element) through which a current is passed. The
output connections are perpendicular to the direction of current. When no magnetic
field is present, current distribution is uniform and no potential difference
is seen across the output.
When a
perpendicular magnetic field is present, as shown in Figure 2, a Lorentz force
is exerted on the current. This force disturbs the current distribution,
resulting in a potential difference (voltage) across the output. This voltage
is the Hall voltage (VH). The interaction of the magnetic field and the current
is shown in equation form as equation 1.
VH µ I ´B (1)
Fig 1:- Hall Effect principle, no magnetic field
Fig 2:- Hall Effect principle, magnetic field present
Basic
Circuit of A Hall Effect Transducer:-
The Hall Effect
sensor is a magnetic field sensor, it can be used as the principle component in
many other types of sensing devices (current, temperature, pressure, position,
etc.). The block diagram of a basic circuit of a Hall Effect transducer is
shown in the fig 3. In this generalized sensing device, the Hall sensor senses
the field produced by the magnetic system. The magnetic system responds to the
physical quantity to be sensed (temperature, pressure, position, etc.) through
the input interface. The output interface converts the electrical signal from
the Hall sensor to a signal that meets the requirements of the application.
Fig
3:- Basic circuit of a Hall Effect Transducer
Basic
Circuit for Hall Effect Measurement:-
The
Hall element is the basic magnetic field sensor. It requires signal
conditioning to make the output usable for most applications. The signal
conditioning electronics needed are amplifier stage and temperature
compensation. Voltage regulation is needed when operating from an unregulated
supply. Figure 4 illustrates a basic Hall Effect transducer.
Figure
4:- A Basic Hall Effect Transducer
If the Hall voltage is measured when no
magnetic field is present, the output is zero (see Figure 1). However, if
voltage at each output terminal is measured with respect to ground, a non-zero
voltage will appear. This is the common mode voltage (CMV), and is the same at
each output terminal. It is the potential difference that is zero. The
amplifier shown in Figure 2-4 must be a differential amplifier so as to amplify
only the potential difference – the Hall voltage.
Fig 5: Transfer function of a Hall
Effect Transducer
The Hall voltage is a low-level signal
on the order of 30 microvolts in the presence of a one gauss magnetic field.
This low-level output requires an amplifier with low noise, high input
impedance and moderate gain. A differential amplifier with these
characteristics can be readily integrated with the Hall element using standard
bipolar transistor technology. Temperature compensation is also easily
integrated. As was shown by equation 1, the Hall voltage is a function of the
input current. The purpose of the regulator in Figure 4 is to hold this current
constant so that the output of the sensor only reflects the intensity of the
magnetic field.
