user18476: I'm using a hall effect sensor A1356 (linear application) to measure the amount of fluid in a container. The fluid is in constant use. My doubt is I'm placing the sensor and the magnet assembly in place, such that when it is exactly half filled, the magnet's center will align with the center of the sensor. In this condition I get 100% duty cycle output from the sensor. 
Condition 1: If the fluid is filled then the magnet moves above the sensor and the duty cycle reduces say to 90%.
Condition 2: If the fluid is consumed then the magnet will move below the sensor and the duty cycle reduces to say 90%.
How do I differentiate between the rise and fall of the fluid? Or is there a better way of orienting the magnet and the sensor such that this problem could be avoided?
I'm interfacing it with an Arduino UNO

user5168: According to the data sheet (see below) the no-field PWM output is mid-range; north poles reduce it & south increase.    
So if you had an arrangement whereby the float had north down & south up, ie a vertical bar-magnet, this would presumably give a rise-before-0 or fall-before-0 at the float vanishes, or a fall-to-minimum an rise-to-maximum as the float centres? The bit in the middle could be interesting!    
From the datasheet:
"The presence of a south polarity magnetic field,
perpendicular to the branded surface of the package face,
increases the output duty cycle from its quiescent value toward
the maximum duty cycle limit. The amount of the output duty
cycle increase is proportional to the magnitude of the magnetic
field applied. Conversely, the application of a north polarity
field decreases the output duty cycle from its quiescent value."

18476: <p>I'm using a hall effect sensor A1356 (linear application) to measure the amount of fluid in a container. The fluid is in constant use. My doubt is I'm placing the sensor and the magnet assembly in place, such that when it is exactly half filled, the magnet's center will align with the center of the sensor. In this condition I get 100% duty cycle output from the sensor. </p>

<p>Condition 1: If the fluid is filled then the magnet moves above the sensor and the duty cycle reduces say to 90%.</p>

<p>Condition 2: If the fluid is consumed then the magnet will move below the sensor and the duty cycle reduces to say 90%.</p>

<p>How do I differentiate between the rise and fall of the fluid? Or is there a better way of orienting the magnet and the sensor such that this problem could be avoided?</p>

<p>I'm interfacing it with an Arduino UNO</p>
 5168: <p>According to the data sheet (see below) the no-field PWM output is mid-range; north poles reduce it &amp; south increase.    </p>

<p>So if you had an arrangement whereby the float had north down &amp; south up, ie a vertical bar-magnet, this would presumably give a rise-before-0 or fall-before-0 at the float vanishes, or a fall-to-minimum an rise-to-maximum as the float centres? The bit in the middle could be interesting!    </p>

<p>From the datasheet:
"The presence of a south polarity magnetic field,
perpendicular to the branded surface of the package face,
increases the output duty cycle from its quiescent value toward
the maximum duty cycle limit. The amount of the output duty
cycle increase is proportional to the magnitude of the magnetic
field applied. Conversely, the application of a north polarity
field decreases the output duty cycle from its quiescent value."</p>
