Altitude compensation (Re: 286 Vindication)

[Bruce Bowling]

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~ ~ >Isn't it true that for a speed density efi system with an _absolute_ MAP 
~ ~ >sensor, then altitude compensation is not needed?  For example, if you 
~ ~ >changed altitude, the barometric pressure changes, which changes the 
~ ~ >pressure in the manifold, which the MAP sensor directly measures. 
~ ~ > Temperature (air density) compensation is still needed.
~ ~ >
~ Yes, this is true iff one cares only about pressure differential across
~ the throttle plates.  This is the method employed in air flow benches.
~ 
~ - Bruce
~ 
~ 
Forget my statement directly above - the original statement (at the top) is in error.
If you are using an absolute pressure sensor, and you wish to perform differential
pressure measurements, you need a reading reflecting the barometric pressure
(taken when the engine is off or a hardwired value) in order to determine
the differential.

My statement above applies if you are using a differential sensor, with one side
looking above the throttle plates, and the other below.

- Bruce


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               Bruce A. Bowling
  Staff Scientist - Instrumentation and Controls
 The Continuous Electron Beam Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23602
                 (804) 249-7240
                bowling at cebaf.gov  
        http://devserve.cebaf.gov/~bowling
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