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Monday, February 25, 2013

Resistance is Futile

When you are talking about Fuel Level.  

When we designed our new digital fuel level sender we gave a lot  of thought on how to interface with older aircraft systems.

The question was:

Could we produce an resistance output to mimic an existing resistance fuel level reporting system.  

There would be a few clear benefits:
  • We could interface with many more legacy aircraft 
  • Incorporation of our system in aircraft already using resistance based sending would be easier.
However some of the issues of legacy aircraft were directly related to relaying resistance through the aircraft wiring as issues with resistance can provide false or error prone signals.   Resistance measurement on an aircraft was identified by us early on in the design process as not the most favorable method for accurate fuel measurement:
  • Aircraft have long wiring runs
  • There are multiple sensors and connections
  • The connections needed to be ordered to produce a series for multiple sensors
  • There were other connections in the aircraft - bad connections produced resistance 
  • There were multitudes of different resistance values even for the same aircraft
  • There were amplifiers in some aircraft to address the issues above
  • The wire run was subject to aircraft vibration 
  • The gauge quality and accuracy in legacy aircraft was - not ideal
The favorable aspect of resistive gauging was that it was easy for the average mechanic to diagnose.
  • All they needed was an Ohmmeter.
    • We had heard stories of Cessna 210 Centurion and Cessna Twin Aircraft with the dreaded Cessna breakout box to tune and diagnose the capacitive system.
So what we needed was a simple digital signal that could be read with the modern equivalent of a ohmmeter  - the Digital MultiMeter (DMM).  We can now get a digital frequency output of any connected sender.

We found that Digital Frequency gave us clarity for fuel level information over all the known wiring challenges - corroded contacts, poor splices and induced signals.  More importantly it gave us a good signal or nothing - induced errors did not conspire to give bad fuel level.

What seemed more natural is that the signal was similar to that used by the fuel flow transducer.  It seemed a natural  - and we could read the read and diagnose the signal on a DMM.

When we sat down after months of delivering a fuel level sending product that had zero issues and was easy to diagnose.  ---

We had come to  realized that we had found the best method for reporting fuel level on the aircraft and a communication standard for any application we applied our product to

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