GRT EIS AUX Settings?

RV7A - 523RM. Purchased from builder in April 2015. I am having trouble getting my EIS system to provide reasonably accurate fuel tank readings. The tank floats were changed out with bends on the floats according to VANS instructions. I followed the procedures outlined by GRT for calibrating the readout but when I enter the AUXSF and AUXOFF numbers I have computed, the resultant fuel level readouts were NOT VERY USEFUL. I went back to the original EIS settings and they got closer but still significantly off.

Right now the AUXSF setting I use is 250 and the AUXOFF setting is 571. Example: When actual fuel levels were measured by draining the tanks, actual fuel on board was approx. 11 gallons and while the EIS system indicated 16 to 17 gallons with these EIS settings. Thankfully, the total fuel on board, as measured by fuel flow, is very accurate (within tenths of gallons). I would like the EIS settings to at least closer reflect actual fuel in each tank.

I assume I am not the only person who has experienced this issue. Does anyone have recommended AUXSF and AUXOFF settings they use that work well for them?

I recall the instructions from GRT are quite clear, I recommend you follow those closely, however, to start, my numbers 'might' get you closer:
left tank: SF 29; Offset 47
right tank: SF 33; Offset 91

GRT EIS AUX SETTINGS

Thanks for sharing your numbers. My problem has been when I follow their instructions (which I agree are clear) my numbers were AUXSF 157 and AUXOFF 203. Unfortunately, these numbers gave very poor results when looking at L and R tank readings and trying to compare to fuel total reading base on fuel flow (which is quite accurate).

If you don't mind sharing some more information - what were your full and empty readings when you set the AUXSF to 100 and the AUXOFF to 0?

GRT EIS Tankage scaling

My EIS tankage dosen't see a change at all until about 10 gal left in the tank, then it scales down to empty (+/- 1 Gal) nicely. Those AUX numbers are dependent on the geometry of your senders and what voltage they are putting out. I think anyone else's numbers would be essentially meaningless.
I scaled mine by pumping fuel back and forth between tanks using a Tygon tube on the outlet of the mechanical fuel pump. Keep in mind, there is a fair amount of hysteresis of the float going down Vs going up. So you can only take the readings while emptying the tank. I took EIS readings every gal (using the fuel flow transmitter) and used those numbers in the GRT fuel table.

ALSO, keep in mind, that when using the fuel flow transmitter to measure gallons when pumping to atmospheric pressure, you won't get the same "gallons" as when it's pumping under pressure. The transducer output is pressure sensitive so you'll have to recalibrate the fuel flow scaling factor after you start flying. Mine was off about 15%.

Good luck, it was a tedious process......

Appreciate your insight.

rv9av8tr said:

My EIS tankage dosen't see a change at all until about 10 gal left in the tank, then it scales down to empty (+/- 1 Gal) nicely. Those AUX numbers are dependent on the geometry of your senders and what voltage they are putting out. I think anyone else's numbers would be essentially meaningless.
I scaled mine by pumping fuel back and forth between tanks using a Tygon tube on the outlet of the mechanical fuel pump. Keep in mind, there is a fair amount of hysteresis of the float going down Vs going up. So you can only take the readings while emptying the tank. I took EIS readings every gal (using the fuel flow transmitter) and used those numbers in the GRT fuel table.

ALSO, keep in mind, that when using the fuel flow transmitter to measure gallons when pumping to atmospheric pressure, you won't get the same "gallons" as when it's pumping under pressure. The transducer output is pressure sensitive so you'll have to recalibrate the fuel flow scaling factor after you start flying. Mine was off about 15%.

Good luck, it was a tedious process......

Click to expand...

Thanks for the information. I will keep working on this and hopefully see some improvement.

If you have not done so, I suggest you plot the eis output on a graph.
Actual gallons across the bottom and eis reading as vertical axis.

You may find that the plot is not a single straight line which is hard to get EIS math (y=mx+b) to represent. The non linear shape in not caused by the eis. It is the tank shape.

I have capacitive sensors so my situation is different in detail but you should have some non linearity effects with the floats too, including a reading ceiling at roughly 16 gallons I have read. I chose to match closest the data on the linear section that described the 0 - 10 gallon readings

My setup process was very similar to Bill with somewhat different numbers. With the float type, my L&R tanks will read 18 G when tanks are totally full or at least 18G of fuel added and only will start moving when it gets below 18G. It also reads zero when I actually still have a gallon or so left in the tank. I have set it up this way partially as a way of being conservative with how much fuel I have. But the primary setting that I use to determine the amount of fuel on board comes from the fuel flow meter. It is accurate within 0.2 or 0.3 G and I use the float type
1- As a way of confirming the total fuel based on fuel flow meter
2- Balance between the two tanks

Think I have if figured out!

Part of my problem with the EIS float settings was "I'm dumber than dirt sometimes." One of the responders sent me a spreadsheet he used to compute his AUXSF and AUXOFF numbers. In studying that spreadsheet I realized I was using the "tank full" EIS number incorrectly on my computation. Once I figured that out, I re-did my calculations and got number settings that all of a sudden allowed the EIS/EFIS fuel tank readings to correspond to actual fuel in the tank (at least much more closely than ever before).

To confirm the new settings I again drained my tanks to see how closely the new EIS settings followed actual fuel tank decline. Guess what - the fuel readings did not decrease until the "full tank" measurement corresponded to my float high limit number (17.7 gallons) but once fuel dropped below that number during the drain test, fuel tank readings appeared to track pretty close to actual fuel in the tank.

I really want to thank Mr. Roger Evenson for his spreadsheet that allowed me to discover my error.