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Integral Hall sensors

2014-11-09 08:34  
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Hall sensors are common sensors of many types measuring devices including linear or angular motion, magnetic field, current, etc. main convenience of hall sensors is that they don’t have to be mechanically connected to object. Also they are simple, cheap that makes them attractive in many industries like automotive, manufacturing, aviation. There are manu manufacturers who produce hall sensors: Honaywell, Melexis, Allegro Microsystems, Micronas Intermetall, Siemens, Analog Devices, etc.

One of simplest are linear Hall sensors, that are used for measuring magnetic field strength. Integral hall sensors include sensor signal amplifier, also temperature compensation and supply stabilisation circuits. Sensor output signal voltage and polarity depends on magnetic field strength and direction. If there is no magnetic field near sensor, then output is equal to zero.

integral_hall_sensor.PNG

 

To achieve this differential amplifier has to be used, then characteristics will be corrected to be output voltage zero when there is no magnetic field.

Other group of hall sensors have comparator built in. This allows to have digital level signals on output. There can be two types of such hall devices: switches and triggers.

Unipolar Hall switchacts as unipolar device which is a€?OFFa€? if there is no magnetic field or it’s direction is opposite, and a€?ONa€? when magnetic field is present and direction is positive.

histeresis_hall.PNG

 

Bipolar Hall triggerreacts on both directions of magnetic field. It switches a€?ona€? when reaches positive or negative magnetic field level and switches off when this field lowers to some value. And of course there can be many variations on where threshold is positioned.

For instance two Hall sensors HAL556 and HAL566 have only two active pins:

hal556.PNG

 

These sensors change power consumption depending on external magnetic field.

Ok lets see where can be hall sensors used.

Linear Hall sensors

Current sensors;

Frequency measuring;

Control and protection of electrical motors;

Displacement sensors;

Consumption measurement;

Brush-less electrical motor control;

Non contact potentiometers;

Angle sensors;

Vibration sensors;

Tahometers.

Digital Hall sensors

Rotation speed measurement;

Synchronisation devices;

Car Ignition;

Displacement sensors;

Pulse counters;

Door blocking;

Brush-less electrical motor control;

Consumption measurement;

Non contact relay;

Close object detectors;

Magnetic card readers;

Paper sensors (printers).

Hall current sensors

As an example – linear hall sensors are used for current measuring from 250mA to thousands of amps.

??hall_current.PNG

 

Such measuring devices don’t have to be connected physically to the circuit. This way you can measure DC and AC currents. According to picture above- if Hall sensors is very close to wire with current, then sensor output voltage will be proportional to magnetic field strength which is proportional to current which generates this field. Current can be calculated by formula:

B=1.57I?·N/d

where B a€“ magnetic field strength(??T), I a€“ current strength(A), d a€“ gap in concentrator(m), N a€“ number of wire turns.

 


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