Why Anisotropic Magneto Resistive

Why use Anisotropic Magneto Resistive Sensors 

Anisotropic Magnetoresistive (AMR) Sensors Technology used by CIES Inc  for our fuel level solutions   These sensors use the basic premise that the electrical resistance of certain ferromagnetic alloys, such as permalloy, are influenced by external magnetic fields.

Like a compass that always points North no matter how you move - our sensor always points to the float.

For larger fuel tanks like those in aviation or marine applications  - we need more information or position information to correctly depict the amount of fuel in the tank.  Our sensor technology does this we can measure tiny fractions of a degree. So not only pointing North but also with a high degree of precision.  In fact we have thousands of discrete data points to measure fuel level.

Automotive resistance sensors re-configured for these critical applications - are just not adequate.   60 discrete points might be good enough for 18 gallons - but it falls short  handing 5 times that volume - plain and simple.  The 60 or so discrete points found on thick film resistance cards just don't cut it.  Fuel movement found in aviation and marine applications adds additional problems to resistive senders - float motion out of of the pivot plane tends to make the resistance wiper act as a make and break switch.

These compromised systems attempting to scale current automotive ceramic resistive elements by adding a longer float arm or other measures - simply provides poor performance.  

CIES Inc Patented Method

Utilize a solid state magnetoresistive effect or anisotropic magnetoresistance can be fabricated in thin film technology, allowing the production of a very precise yet cost-effective angular measurement sensors.  Replace the coarse variable resistor with a solid state device.

From Wikipedia: 

Anisotropic Magneto Resistive - (AMR) is the property of a material in which a dependence of electrical resistance on the angle between the direction of electric current and orientation of magnetic field is observed. 

Why is this a better way to measure fuel 

It works under all conditions, temperatures and with moving fluid volumes - PROVEN IN AVIATION 

And there is a combination of influences but for an AMR sensor the built in 

strong magnetic external field attached to the float arm locally saturates the sensor, the actual magnitude of the local field strength has no impact on the measurements. - Remember temperature effects on both the magnetic strength and the efficiency of the sensor.

Only the direction of the field is evaluated.

Only the local magnetic field on the rotor has influence - the presence of other nearby magnetic fields such as motors will have no effect on the sensor as long as the rotor magnetic field strength is dominant. 

While other magneto resistive sensors are available - AMR has the capability to work under all conditions and give proven repeatable results. 

Non-contact fuel level sensing is a good idea.  It was a good idea to remove the electronics from the fluid measured.

Other fuel level reporting systems don't measure up


SUMMARY OF AMR ADVANTAGES

• Voltage in the case of our AMR sensor is converted to a bit stream digital output.
• More information for every degree of float travel
• Independence of magnetic drift during lifetime
  
• Independence of magnetic drift with temperature
  
• Independence of mechanical assembly tolerances
  
• Independence of mechanical shifts caused by thermal stress