Digital Output - Fuel Level Sensors

Digital Fuel Level 

When you enter the term above in Google you get a variety of responses most of them showing a display indicating fuel as a digit value on a screen.

What this is a numerical  manipulation of the the analog signal that most fuel level senders provide as an output:

Simple electronic analog values are the tradition for fuel level measurment.

• Resistance
• Capacitance
• In the case of Reed Switches  - Current or No Current.

But what we have is just another way of showing what analog sensors are providing digital is display only.

Digital output at the Sender is Unique - there are several aftermarket Capacitive Sensors in the Marine industry or Telematics that use a conditioned digital output.  There are conversion processes for these senders - temperature compensation signal conditioning maybe a de- bounce (smoothing) function.

Capacitive senders take an analog signal give it a binary component and communicate the signal.

What if the native language of the sensor were digital in that each fuel level was represented by a binary stream - natively   No conversion - no compensation - and if non contact

 No issues with Fuel quality or Fuel type  - NONE .

 In fact no compatibility issues with the measured liquid in question whatsoever

When Fuel is Important or Critical to Operation
Fuel level is important but what if knowing how much remained meant the difference between an inconvenience or something more significant.

The manner in which we handle the digital output signal is proven in aviation applications -

Signal integrity is paramount - in an environment where static charge and exposure to radiated fields would bring most fuel level systems to their knees.  If you couple the requirements for vibration shock and the extremes in temperature - it is surprising that any fuel level sender works at all in aviation.

So why Digital 

• The level output is provided continually -
• The Fuel Level is reported over and over again to the gauge or display
• The signal does not suffer from signal loss or interference
• Either the complete signal is transmitted or nothing at all 
• Not effected by voltage variation
• Many more data points to map the fuel tank
• 3,800 distinct points for 80 degrees of travel possible 
• No Temperature Effects 
• No compensation
• The device will output fluid temperature if required
• Failure is hard and the results predictable
• False signaling of tank volume due to wear is virtually eliminated.

Imagine a level sender that thrives in the critical  aviation environment and think what it could do for your application.

Fuel Level Sensors for Collector Vehicles

Aviation Float Fuel Sender - Historical Perspective

Dawn of Aircraft Instrumentation

The initial non-electrical float system was used on various aircraft, the most famous being the Piper J-3 "Cub." which used a cork with a wire imbedded in it that extended into the view of the pilot. Lots of wire showing, lots of gas; no wire showing, no gas.  Equally glass sight gauges are used in high wing aircraft and high wing fuel can to flow to the engine by means of gravity.

Electrical Aircraft Instrumentation Comes of Age

With the addition of electrical systems in aircraft the float was connected to the arm of a variable resistor whose electrical leads are brought through the wall of the tank and connected to the fuel quantity gauge and to the ship's electrical bus. 

Thus, the change in resistance as the float follows the level of the fuel.  This electrical value causes the needle on the fuel quantity gauge to deflect indicating the quantity of fuel in the tank.  Simple and direct.

For odd shaped tanks, particularly a flat tank in a wing with dihedral, multiple resistance floats are connected in series to correctly categorize this onger sloped tank.

This is the fuel gauging system on most, if not all, automobiles, the majority of piston engine aircraft, and some turbine aircraft. This system has been given very poor reviews over the years, some of which is deserved, but a large portion of the criticism is not.

If the resistance float is poorly designed and constructed, if the gauge is poorly designed and constructed, if the gauge is poorly marked, if the damping of the complete system is not suitable for aircraft or it's particular use,  or if the system is poorly installed and calibrated,  criticism for poor operation is rightly deserved. 

Digital Display and Interface  

In the instance of fuel level - Nothing really 

Well in the case of Commercial Aircraft the capacitance value was converted to ARINC 429 protocol and transmitted to the cockpit.

Until Now 

The First Digital Output General Aviation Fuel Level Sender