GRT Fuel Level Indication

[DanH]

Hey gang, this one is whipping my butt......help. Probably something simple and I'm being a knothead.

Subject is an EIS 4000 and Sport SX EFIS with standard Stewart Warner fuel tank senders.

Initial (and current) EIS configuration settings are AuxSF "100" and AuxOff "0", per the instruction sheet for float senders.

Initial fill saw the fuel level indication get lower with increasing fuel quantity, from 6 gallons empty to 2 gallons when full. Obviously not right. However, an ohmmeter check at the senders read 30 ohms for a full tank and 248 ohms for an empty tank, which I think is correct. So, I changed the Auxiliary Forward/Reverse Sensing Selection to reverse (negative), increasing voltage = decreased value. That immediately gave me a 20 gallon reading for the full tank, which is about right. However, the empty tank indication is still way off.......and I don't seem to be able to find the correct settings.

Yeah, I can ring up GRT on Monday, but hey, this is VAF

[nucleus]

to follow, I think Sandy can fax it to you. You have to have the plane in flight attitude and you test different known fuel levels and set the EIS accordingly.

Hans

[pgroell]

Have a look here :

http://www.vansairforce.com/communit...2&postcount=49

Regards

[DanH]

Thanks guys....posted last night when I came in tired from the airport, and after two cold ones.....shame on me. Reading through the archives now.

Postscript:.....very interesting.....SF and Off values vary widely between builders. Still some good clues, so I'm off to the airport.

[DanH]

.....and the winner of an IOU for a fly-in beer goes to (drum roll please)....

John Dalman
http://www.vansairforce.com/communit...1&postcount=51

John's published numbers worked as perfectly as anyone could expect. Tweaking the AuxSF from 286 to 295 gave me an oscillating -0 to 0 at the unusable fuel point and 16 at an actual 16 gallons or more. At levels in between accuracy is reasonable; 5 is 5, about a gallon error at 10, and by 15 it is back on track.

Happy to cheat on this one (thanks John). South Alabama this time of year is too darn hot to sit in the cockpit and fiddle; the OAT readout was 105F in the hangar yesterday.

[TomVal]

Dan,

I am presently dealing with the same calibration issue. Using John's numbers as a guide, was your Aux forward / aft sensing still set to negative?

Regards,

[Bubblehead]

Dan - I feel honored that my numbers worked for you. Any time my work gets anywhere close to your standard I feel I have done my very best!
Glad to have helped. I have learned a lot from your posts especially on oil coolers and urethane and composites and your work has inspired me to work to a higher standard.
John

[DanH]

Originally Posted by DAGO

Dan,I am presently dealing with the same calibration issue. Using John's numbers as a guide, was your Aux forward / aft sensing still set to negative? Regards,

Sorry Tom, missed your post yesterday....yes, negative.

[rzbill]

0 at the unusable fuel point and 16 at an actual 16 gallons or more. At levels in between accuracy is reasonable; 5 is 5, about a gallon error at 10, and by 15 it is back on track.

Dan,
If you are running a GRT display in addition to the EIS, and are showing fuel indication on the graphic display, there is an additional curve fitting tool within the graphic display. I have not done it yet since my flying will be 2011, but this was discussed with GRT at length during SnF.

You have done the first part by optimising the y=mx+b linear curve fitting in the EIS. The display (H1 or sport) has a two column signal mapping table facility that will interpolate between multiple points you specify. Left column is EIS input number and right column is desired display number. So, you can create a curve with some bends in it to correct for the mid filled region error.
Please call GRT for details. I don't remember the specific command tree to get to it.

[RV6airplanePilot]

the submenu that has the correction table for the tank readings, last item in the group. I leveled the plane to do the initial adjustments, then on a long cross country in smooth air I compared tank readings to the info from fuel remaining calculated on the Sport to cross check the results. If the slip/skid ball is the slightest off center the readings will be off. My 6a taxies with pitch up of about 1.5 degrees which throws off the readings, understandably. For initial calibration of the EIS numbers it was handy to have one tank full and the other empty. I input the same factors for both tanks to see how they would effect both ends of the spectrum. This way I could experiment without moving fuel so often. I found SF (scale factor) and Offset values that worked well, then I fine tuned them for each tank separately. In my case zero, 6 gallons and 15 gallons were within one tenth. 8 gallons was only off 3 tenths. Then I did the EFIS table. I am not assuming this accuracy in the air, of course.