fuel Quantity calibration

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glk0346
Posts: 32
Joined: Wed Jun 06, 2018 3:51 am
Location: Huntsville Executive Airport, Meridianville, AL

fuel Quantity calibration

Post by glk0346 »

Gentlemen and or Ladies,

New member here. I share Walkman's sentiments. Allow me to explain and seek your help.

I own a RV9A and am in he process of upgrading my panel to full IFR capability. Have the following equipment installed and integrated with GRT products:

GRT HXr 8.4 EFIS
GRT Mini GA EFIS
GRT 4000 EIS
PSE PMA 6000b Audio Panel
Val Com 2000
Val Com 2KR remoted
Val Nav 2KR remoted
Garmin GPS 400WAAS
Garmin GTX 330es
TruTrak Autopilot

Was hoping to have this aircraft flying months ago but am continually frustrated by a number of nitpicking issues, fuel qty indication being the principal one for I cannot fly the aircraft without a fuel qty indicating system. Just so you'll know, I originally had my fuel qty, fuel pressure, and electrical load (Auxes 1-4) wired through the 4000 EIS and one wire from the EIS control module integrated with my HXr EFIS via a serial port.

After finding out about this Forum, registering, and seeing Walkman's comments I couldn't help but say "Yeah, somebody else shares my feelings on this issue as well." Since then I've taken my L and R fuel qty float resistor sensors out of the 4.8V excitation and 470 Ohm pull up resistor circuit, and wired the float resistors directly to the HXr EFIS via Analog inputs without the 470 ohm pull up resistor.

I have gone through the calibration procedures per instructions in the supplement identified on this forum with negative results. Checked my L tank and the float resistor reads 30 Ohms with a full tank (18 gal); Emptied my L tank. Checked the float resistor and it reads 248 Ohms tank empty. Went through the HXr EFIS Analog setup procedures and configured both tanks per instructions - very easy and simple. When I started adding fuel to the L tank, the bar graph read 182 gal or maybe it was 82, regardless, I continued to add fuel until I eventually had 5 gal and all the graph did was fluctuate between 182 and 183. I stopped fueling and checked the resistance on my float resistor and it read 143 ohms, clearly indicating that the float resistor is working properly.

Prior to going through this procedure, I went back to my EIS control module and the Set Configuration procedure for Aux 1 and 2, and zeroed out the SF and Offset just to make sure those numbers, via 232 serial interface didn't conflict with the analog signals directly from the sensors.

So, here I am still pulling out my rapidly thinning hair trying to get this system to work to no avail. I figured if I can't get the L tank indicating system to work properly so why bother with the R tank.

Any suggestions would be greatly appreciated.

George
Bobturner
Posts: 444
Joined: Mon Mar 11, 2013 6:34 pm

Re: fuel Quantity calibration

Post by Bobturner »

Start simple. For those analog channels you connected to the fuel gauges,did you electronically turn the pull down resistors on?
GRT_Jeff
Posts: 802
Joined: Tue Dec 11, 2012 12:11 am

Re: fuel Quantity calibration

Post by GRT_Jeff »

The EIS is better suited to accurately sensing the low resistance range of resistive float senders so it is still recommended but the behavior should be similar on both. On the HXr you have to turn on the Pull-Up for that analog input if you aren't using the 4.8V or other excitation. The wire between the HXr and sender will have a very low voltage range, about 0.06 V to 0.60 V proportional to the fuel level (0.06V when your tank is full and 0.60V when your tank is empty). The 4.8V excitation and 470 ohm resistor would have a 0.28 V to 1.67 V range on the wire going to the Aux input.

When using the Fuel Data Scale table, you must start with an empty table and record your values on paper or something other than the EFIS. Don't enter any data in the table until you're done, otherwise the table entries will alter the probe readings as you go. If your table page displays an "Uncorrected" value below the table, you can use that as your probe reading instead of the bar graph because it is unaffected by the table.
glk0346
Posts: 32
Joined: Wed Jun 06, 2018 3:51 am
Location: Huntsville Executive Airport, Meridianville, AL

Re: fuel Quantity calibration

Post by glk0346 »

Re Calibrating Restive Float - Type Fuel Senders with Horizon EFIS


Need some help with this issue. Started with the Rt tank. Drained it as per instructions in the document noted above.

Initially started with the EFIS configured as such:

Sensing: Foward

Integer/Decimal: Integer

This didn't work as it took 5 gallons for the gauge to indicate a movement in the float resister. Additionally, the value decreased instead of increasing. So I changed the configuration to Reverse Sensing and Integer/Decimal to Decimal.

Started adding fuel and everything seemed to be working as required.

Empty tank Probe Reading: 18.3

At .8 gallons added the Probe read 18.4

Continued adding fuel in 1.5 gallon increments with corresponding increases in the Probe reading til I got to 15.1 gallons added at which point the Probe stopped moving with a reading of 20.0 gallons.

Went to the Set Menu page, Engine Limits, Fuel Data and noticed the reading on the screen: "Disabled/Invalid". Hmmmm, nevertheless, I went to the input table and entered my data. Hit Save to save my data and exited the Menu. Went to the Engine screen and the Rt vertical bar graph read 20 gallons.

I repeated my entries again to make sure I did everything correctly only to get the same reading. Clearly this is not what I was expecting as the gauge should be reading 15.1 gallons. I haven't a clue as to what may be wrong except the "Disabled/invalid" reading as noted above.

Appreciate any comments and or recommendations you may have.

George
GRT_Jeff
Posts: 802
Joined: Tue Dec 11, 2012 12:11 am

Re: fuel Quantity calibration

Post by GRT_Jeff »

If the table was empty, then it will be "Disabled/Invalid" because there's no data in it. It will be enabled as soon as there's valid data in the table. After you filled in the right tank table it should have changed to "Enabled: Right". If it didn't then something was wrong with the way the table was filled out.

When using the scale table, the direction (increasing/decreasing) doesn't matter as long as the probe value doesn't end up negative.

One common mistake is entering two entries at the same Probe value when the probe stops moving. At the limits of the probe you have to decide on one value to use and stop there. For example, if you reached 15.1 gallons and your probe said 20.0, and you added another 1.5 gallons to get 16.6 gallons total while the probe has stopped at 20.0, you can't put 20.0 15.1 and 20.0 16.6 into the table. Your probe can't read beyond 15.1 gallons so you have to stop there and accept that your display will never show above 15.1 and won't change until the probe drops below that. The same goes for the low end.

You could have a similar problem in the middle of the table. If the probe value doesn't change you can't enter two actual values at the same probe value. If that happens in the middle that means you don't have enough resolution to detect the change. That could be because you don't have enough of a voltage range, or your scale factor is too small. A scale factor of 250 will give you more resolution than the recommended 100, but that will make the data more noisy/jumpy.

You don't need to fill in every row in the table. If you don't have enough usable data, leave some rows empty. If you enter a probe value into the table, you must enter an actual value for it. If you don't have an actual value for a probe reading you should clear the probe value. The probe value clears when you try to set it negative.
glk0346
Posts: 32
Joined: Wed Jun 06, 2018 3:51 am
Location: Huntsville Executive Airport, Meridianville, AL

Re: fuel Quantity calibration

Post by glk0346 »

Aha!!
Makes perfect sense.

Thanks
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