Hall Effect Sensor

           A Hall effect sensor is a transducer that varies its output voltage proportional to a magnetic field surround it. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications.

Hall Effect Applications

              Hall effect sensors are activated by a magnetic field and in many applications the device can be operated by a single permanent magnet attached to a moving shaft or device. There are many different types of magnet movements, such as “Head-on”, “Sideways”, “Push-pull” or “Push-push” etc sensing movements. Which every type of configuration is used, to ensure maximum sensitivity the magnetic lines of flux must always be perpendicular to the sensing area of the device and must be of the correct polarity.

Also to ensure linearity, high field strength magnets are required that produce a large change in field strength for the required movement. There are several possible paths of motion for detecting a magnetic field, and below are two of the more common sensing configurations using a single magnet: Head-on Detection and Sideways Detection.

Head-on Detection

       As its name implies, “head-on detection” requires that the magnetic field is perpendicular to the hall effect sensing device and that for detection, it approaches the sensor straight on towards the active face. A sort of “head-on” approach.

           This head-on approach generates an output signal,V_H which in the linear devices represents the strength of the magnetic field, the magnetic flux density, as a function of distance away from the hall effect sensor. The nearer and therefore the stronger the magnetic field, the greater the output voltage and vice versa.

           Linear devices can also differentiate between positive and negative magnetic fields. Non-linear devices can be made to trigger the output “ON” at a pre-set air gap distance away from the magnet for indicating positional detection.

Sideways Detection

           The second sensing configuration is “sideways detection”. This requires moving the magnet across the face of the Hall effect element in a sideways motion.

           Sideways or slide-by detection is useful for detecting the presence of a magnetic field as it moves across the face of the Hall element within a fixed air gap distance for example, counting rotational magnets or the speed of rotation of motors.

           Depending upon the position of the magnetic field as it passes by the zero field centre line of the sensor, a linear output voltage representing both a positive and a negative output can be produced. This allows for directional movement detection which can be vertical as well as horizontal.

Positional Detector

         This head-on positional detector will be “OFF” when there is no magnetic field present, (0 gauss). When the permanent magnets south pole (positive gauss) is moved perpendicular towards the active area of the Hall effect sensor the device turns “ON” and lights the LED. Once switched “ON” the Hall effect sensor stays “ON”.

          To turn the device and therefore the LED “OFF” the magnetic field must be reduced to below the release point for unipolar sensors or exposed to a magnetic north pole (negative gauss) for bipolar sensors. The LED can be replaced with a larger power transistor if the output of the Hall Effect Sensor is required to switch larger current loads.

        In the experiment, we will observe what the change of Hall effect sensor.When it used in the different situation such as the different angle, different magnetic pole etc. 

Equipment

1. Sensor allegro 1302                       

2. Magnet                                            

3. Set of Hall Effect Sensor                 

4. Generator                                       

5. DC Voltmeter                                   

Procedure

- First experiment

1. Connect circuit in fig.1 and set magnet same as fig.2

2. Change magnet in angular 30 degree step by step to 360 degree. Then record the results.

3. Plot the voltage vs degree graph.

- Second experiment

1. Connect circuit in fig.3

2.  Set Magnet at north nearly sensor and change distance 2mm step by step to 20 mm.Then record the results. 

3. Do in step 2 but change magnet at south nearly sensor.

4. Plot the voltage vs distant graph.

Experiment result

The graph of voltage vs degree in first experiment.

 The graph of voltage vs distant in second experiment.

Analysis and conclusion

-         Hall Effect Sensor is devices which are activated by an external magnetic field. We know that a magnetic field has two important characteristics flux density and polarity (North and South Poles). The output signal from a Hall Effect sensor is the function of magnetic field density around the device. When the magnetic flux density around the sensor, sensor will detect it and generate an output voltage. In this experiment, we have 2 mains parts. First we can observed from the results that a high performance at 90 degree around 2.7 voltage and a low performance at 270-300 degree around 2.61 voltage. Second part when the north polar nearly sensor we get the high voltage around 3.6 and when the south polar nearly sensor we get the low voltage around 1.6 voltage, But when we get too far the voltage will linearly that same in theory. From the experiment, the output voltage in this IC around 2.5-3 voltage that same in theory.



Notice : The data in the experiments maybe inaccurate or incorrect. Therefore, the results may be different on other trials or a distortion of the theory.