We originally copied some of Tony K's idea using the pressure transducer and op
amp he designed to get a 0-5 volt signal for our GRT EIS. It worked OK for
several years but there was always a problem of RF from the com transmitter
causing
interference when transmitting.
We have now switched to Freescale (Motorola) integrated sensors, MPXV4006DP
which
provide a 0-5 volt output for 0 - .87 psi. They are a differential sensor
so the liquid side is connected to the water drain pipe from the tank bottom
and the other side is connected to the tank vent. They only require a 5 volt
supply that we take directly from our EIS. We calculated that a full fuel tank
will have a head of pressure equal to about .4 psi. So we programmed the EIS
so that 0 - .4 psi gives an output of 0 - 100.
We have two of these sensors, one on the port (main) and one on the stbd
(reserve).
In our GRT Sport EFIS we made the fuel calibration scales so that each side
goes from 0 - 3 gal and when there is 6 gallons in the tank so fuel is over
the saddle, then both read the same. The calibrations are in level flight
attitude.
We have a sight gauge behind the seat back that is calibrated in the taildown
attitude
(we have a mono). We use that to confirm at the end of the flight that
fuel used determined by the fuel totalizer in the EIS/EFIS is correct. We also
use the sight gauge to determine how much fuel to add.
We calibrated the sensors in level flight attitude so we have a in flight check
that the fuel totalizer and actual fuel used is correct. The other purpose
of these sensors is to give more confidence of how much fuel is aboard when the
tank is getting empty.
We've had no problems with using sensors with flouorosilicone seals and autofuel
(very seldom do we use 100LL). For our sight gauge we use Tygon SE200 which
has a flouoropolymer tube inside conventional clear tygon tubing. This tubing
does not discolor or degrade when exposed to gasoline. Use with single barbed
fittings.
Jim & Heather
N241BW XS, Mono, 914 500 hours
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