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 Hall Effect Mag Sensor 


Hall Effect Magnetic Field Sensor Science Experiment: This is an ongoing development project using Hall Effect magnetic field sensors (instead of Fluxgate sensors) to measure the two primary Magnetic Axes (or Axis's). This project was intended to prove that an economical, portable yet sensitive sensor could be constructed using cheap, readily available materials (as can be acquired from a local Radio Shack!). Additionally, this project intended to prove that accurate sensors could be made without using a fluxgate process model/hardware.

The design uses two Hall Effect Sensors carefully placed a few millimeters away from a cylinder shaped Magnet while the entire assembly is oriented North so the magnetic cylinder is pointed north while remaining a consistent distance away from the Hall Effect Sensors.

The Sensor is housed inside a small acrylic box purchased from Radio Shack and wire Exfiltration holes are penetrated on the side of the container. The Magnetic Cylinder is suspended by a aluminum wire using a simple fishing swivel to reduce overall resistance to the Earths magnetic field. I tried many differing suspension models and the final, most effective position is to orient the swivel as close to the Magnetic Cylinder as possible (not pictured!). This improved the "Up/Down" or "Z" angle movement freedom of the sensor. 

The Hall Effect sensor is designed to be very effective at determining movement/distance to metallic objects nearby and we use this capability to our advantage. Our goal is to measure the Earth's magnetic field flux (or field effect) as it gently moves the freely suspended magnetic cylinder over several hours/days. Once our sensor assembly is oriented north, the magnetic cylinder will eventually come to rest in a north-south orientation as depicted above and will only be moved by a magnetic field.

Here you can see the Sensor suite's basic principle of operation by positioning one hall effect sensor to measure the distance (or movement) of the suspended magnetic cylinder in an east/west direction and another hall effect circuit to measure the movement up/down.

The two sensors work together to illustrate a very accurate measurement of the sensed cylinder's movement ({"Z" or up/down} or {"H" or East/West} movement) caused by magnetic fields acting upon the magnetic cylinder (hopefully due to the Earth's Magnetic field effects!). We achieve this by independently measuring the voltage of each Hall Effect Sensor's Circuit voltage. 

By using the Hall Effect sensor to measure a very heavy, magnetic object, the slightest movement should be detected.

It's CRITICAL to note that the Black, Acrylic sensor container must be enclosed within another assembly of some type to help reduce the undesired movement of the magnetic cylinder because of Air pressure changes (wind) or Shock.  After noting the shock disturbances of large trucks driving down our street and air pressure changes due to doors in the house opening/closing, I resorted to a dual shock/air resistant enclosure by placing the container above inside a 10 Gallon Aquarium, with a floor of foam and shock resistant rubber... Which was again sealed inside a 25 Gallon Aquarium with a similar base to reduce Shock and Wind affects.  This worked well once finally positioned north and wind/shock no longer affected the experiment.

Hall Effect Sensor Output Data measurement was accomplished by connecting the output of each of the two circuits to a Dataq 194 Acquisition instrument which yielded very good output (pictured below).   Using Some Custom Software I was able to plot the following output (below).

Bottom Line: The Output Comparision Below (and coordination with experts in the field of Magnetic Interferometry/GeoMagField Sensor Measurement) led me to assess that the Hall Effect sensors I used were only able to measure large changes in the Earth's magnetic field and were not sensitive enough to measure the small changes I was looking for. I will replace them with a more sensitive Hall Effect sensors to garner more accurate readings and determine if this process model will be effective in sensing miniscule changes in the Earth's magnetic field

The data below clearly illustrates how the sensors were sensitive enough to measure the large, dirunal variation but much beyond that would be impossible given the sensitivity of the current Hall Effect sensors.

We've ordered the most sensitive Hall Effect Sensors we can find and will be re-creating this experiment by the end of this summer. Below is the Dataq Field Comparison output (with statistical data depicted below)

We executed this experiment for 30 days while modifying cylinder suspension methods and various voltage/sensor combinations. We also simultaneously compared our readings with magnetic sensor data originating from established sources in our area (USGS Sensors). The sensor readings where quite similar for this area of the world and we are eager to receive our new, more sensitive Hall Effect sensors to decisively confirm or deny our economic sensor implementation theory! Below is the Earth's Z Component measurement from one of the evaluated test periods. 

Below is the H Component from the same time period.

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