[Flying again!]

My RV-10 has been flying since 2005. Standard Vans flaot sender.

I removed the tanks to have them sealed by Weep No More. I installed them and put 10 gallons in the both tanks. The left tank was showing 7 gallons with 10 in them. I checked to make sure the "AuxSF" and AuxOff" had not changed in the setting. I then changed the Aux SF by 5 to see what change that would make to the displayed fuel level. The fuel level changed to 131 gallons! I changed back to the previous setting and the fuel level was 112.

I drained the fuel and went through the calibration steps. I also measured the resistance of the sender empty (248 ohms) and full (52 ohms at 23 gallons when the sender tops out). The sender seems to be operating correctly. I did the math and came up with AuxSF and AuxOff that were the same as the last time I calibrated 5 years ago.

I plugged in the new values and now it shows 91 gallons!

I am stumped - anyone have any ideas?

I am finally cleared to fly again and now I can't get the fuel leve to display correctly - very frustrating.

Thanks in advance for any ideas -- TJ

 

[Mike S]

GRT instrument correct??

Tis truly a PITA---------I finally got ours close, never did get it on the money. I trust/use the fuel flow totalizer as my in flight indicator of fuel more than the tank gauges.

While you are doing the "add 5 gal" thing, I suggest you make up a dip stick.

 

[Carl Froehlich]

Go back to high school algebra for the equation for a straight line:
Y=mx+b

Y is the readout (AuxDisplay). You want it to equal the amount of fuel you put in (two gallon increments) when you are done.

m is the slope - in this case the (aux voltage *the scale factor) / 2.5.

To simplify the process you start with the scale factor at 1.0 and . Also set the auxOffset at 0.0.

Now as you put in fuel in two gallon increments, create a table:
Gallons AuxDisplay
2 x2
4 x4
up to a full tank
20 x20

As you want a straight line, throw out the values where you obvious are out of range for the float sender. This is typically anything above 16 gallons or so - but could be at the bottom of the range depending on how you set up the float sender.

Now you have the data to solve the equation for AuxVoltage (remember that you have AuxScaleFactor set at 1.0 and Auxoffset set at 0.0):
AuxDisplay = (AuxVoltage * AuxScaleFactor / 2.5) + AuxOffset so
AuxDisplay = AuxVoltage/2.5

Now that you know the AuxVoltage for each increment of fuel, you can now solve for AuxScaleFactor and AuxOffset such that your AuxDisplay reads out in actual gallons for each AuxVoltage you have on your table. If memory serves one or both the AuxScaleFactor and AuxOffset were negative numbers - but I could be wrong.

I flew with the EIS for many years and the fuel readout was always within a gallon of actual.

Carl

 

[Carl Froehlich]

Also remember to do this calibration with the plane in flight attitude.

Carl

 

[KatieB]

Could be that you inadvertently changed a decimal setting during your reprogramming.