Two probes of a voltmeter can be connected to the plate in opposite directions to the other sides of the plates . When there is no magnetic field perpendicular to the plate, as shown in situation (a) in
In case where there is a magnetic field present, the voltmeter will show a reading as shown in the (b) part of the diagram. This phenomenon is known as the Hall-effect. A Hall probe can be used to measure the Hall-effect that was demonstrated above . When an electric current runs in a conductor in a magnetic field, a traversal force is exerted  on the charge carriers by the magnetic field. Therefore the charge carriers are pushed on one side of the conductor  as shown in the (b) part of the diagram. This phenomenon was discovered by E. H. Hall in 1879 . This is the basic principle used in the operations of Hall-effect devices.
A sensor used for measuring thickness or the compactness based on Hall-effect has been developed; this sensor is called in situ sensor . Whenever there is a change in the magnetic force being applied, the Hall sensor, which is works as a transducer , generates an output voltage. This output is variable and is dependent upon the thickness of the material being measured and the force of magnetic field being applied. The distance between the sensor and the magnetic source is the main determinant of the output voltage .
Vacuum failure and vacuum bag leaks can be detected with the use of the sensor . This sensor is primarily used in the quality control departments and cure cycle  of the factories producing different material which need a reliable sensor. Most of the times, the sensor is paired with a monitoring device to demonstrate the readings. For the purpose of online monitoring and compaction of a curing composite, the sensor is quite successful.
This device is being used in the quality control departments and the manufacturing departments of many businesses. They