HALL EFFECT CURRENT MEASUREMENTS

The Hall sensor based current measurement can be realized
as open loop or closed loop. While in open loop, there is only
primary winding and it can be coiled as 1 turn for practical
applications such as clamp meter but to increase measurement
accuracy it should be coiled as multi turns. The Hall sensor
produces an output voltage proportional to primary current.
Generally intensity of output voltage is not adequate for
measurement and it is necessary to be amplified by an opamp.

Fig. 1. Basic connection scheme of an open loop current transformer

In closed loop, operating principle is very similar to open
loop. Output voltage of the Hall sensor is transformed to
current by means of a transistor circuit and passed from a
secondary winding. The purpose is compensating of the
magnetic flux created by primary winding. The basic
connection schemes of open loop and closed loop Hall Effect
current transformer are given in Fig. 1. and Fig2. [1].

Fig. 2. Basic connection scheme of a closed loop current transformer

The primary current to be measured creates magnetic
flux in the core. The Hall sensor produces voltage in
proportion to the magnetic flux in the core. In other words, the
primary current and output voltage of sensor is proportional.
The output voltage is amplified by means of the amplifier
circuit. Generally, an operational amplifier is preferred. The
amplified voltage is applied to a push-pull transistor circuit
and transformed to secondary current passed from the
secondary winding. In this way, a second magnetic flux is
created in the core. The secondary current is symmetric of the
primary current and its secondary winding is generally coiled
as 1000 turns. In this manner, secondary current create
secondary magnetic flux to balance primary magnetic flux.

The basic equation is;

Source pdf

Hall Effect Sensor and Artificial Neural
Networks Application in Current Transformer
http://www.naun.org/journals/circuitssystemssignal/cssp-64.pdf