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fuel Quantity calibration

Postby glk0346 » Sun Mar 31, 2019 4:46 pm

Calibrating fuel qty indication on HXr EFIS in my RV9A. Scale factor is set to 100 and offset is 0, decimal, fwd sensing, pull up resistor is ON.

With fuel tanks empty my Rt tank fuel qty reading on the EFIS is - .2 Gal. Left tank reads +18.3 Gal. If both float resistors are reading approx the same, e.g. Rt reads 250 ohms while the left one reads 248 ohms, should not the EFIS fuel qty indications both read nearly zero before I start adding fuel for calibration? I'm able to calibrate my Rt tank but the left one is way off. Since both are wired through the EFIS, Aux 1 and Aux 2 respectively, voltage should be the same.

Any help would be greatly appreciated.

George
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Re: fuel Quantity calibration

Postby Bobturner » Mon Apr 01, 2019 5:24 am

I think you want reverse sensing.
Certainly, left and right should behave the same. Is one on reverse, the other forward? Both pull up resistors on?
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Re: fuel Quantity calibration

Postby glk0346 » Tue Apr 02, 2019 3:25 am

Let me start over again on this subject as I spent some time reading previous posts wrt to this subject after I tried fueling/calibrating today with unsatisfactory results. I've reread the documentation as mentioned regarding calibration with the EFIS, Revision A1, dated 1 July 2013 to ensure I didn't miss something.

I'm going to give this another try tomorrow so I went and zeroed out my previous inputs to the fuel data scale tables so as to start fresh.

With configuration set as per page 7 of referenced doc should the gauge readings be 0 or close to it? How close does it need to be? Should I adjust the scale factor up or down to achieve this reading?

As I mentioned previously, my resistors are working correctly, 250/248 Ohms empty and 30 Ohms full as I tested them previously to eliminate them as a source of bad data.

George


George
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Re: fuel Quantity calibration

Postby GRT_Jeff » Wed Apr 03, 2019 5:59 am

The uncalibrated reading may never be zero because the probes always have some resistance. It doesn't matter what the limits are as long as they are consistent because the table will replace the scaling and offset. If the probe works in reverse, you can adjust the sensing mode or let the table correct it. It will show a higher uncalibrated reading (higher voltage) at higher ohms in Forward Sensing mode. It sounds like yours is reversed so you may want to use reversed sensing. If you aren't seeing enough range of values from empty to full, a larger scale factor (250) may give you more resolution to work with when using the table calibration. Before calibration (blank table or "Uncorrected" value), both levels should read about the same when they are about the same resistance.
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Re: fuel Quantity calibration

Postby glk0346 » Thu Apr 04, 2019 11:26 pm

Thanks, Jeff, for the info.

I think I've got it worked out after I tried a few configurations and lots of de-fueling refueling my tanks.

I used reverse sensing but quickly changed it. I thought it a bit odd after I configured each tank to integer that the tables were still in digital format. Is this by design? Nonetheless, I switched to digital because I could never get a satisfactory result with the integer configuration. The results were way off.

In digital format, the results are satisfactory as far as I'm concerned, although the left tank reading never settles down, it continually fluctuates. For example, at 15 or 15+ gallons added, it fluctuates between 14.3 and 15 gallons.

I may toy with the scale factor, like 150 or 250 to see what I get. I look at it this way ...... I'm okay with full tank, half tank, and something around 3-5 gallons before empty where it counts. Besides, I always use my watch and switch tanks every half hour anyway.

George
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Location: Huntsville Executive Airport, Meridianville, AL

Re: fuel Quantity calibration

Postby glk0346 » Fri Apr 05, 2019 1:53 pm

Oops, made and error. I meant to say I first used Forward sensing, but changed it after the numbers decreased as fuel was added.
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Location: Huntsville Executive Airport, Meridianville, AL

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