Fuel Calibration

speedbird1

I love flying!
Joined
Feb 2, 2018
Messages
15
Can someone throw some light on an issue I'm trying to understand.

I have 40 gallon tanks (80 total). 3 gallons in both sides is considered unusable. When I calibrate the system I put 3 gallons in the tank and then tell sky view that the tanks have 37 gallon capacity and that I'm ready to calibrate. It then has me add 7 lots of 5 gallons (total of 38 at this point) and then tells me to full the tank. As far as the skyview knows I have 37 gallons in the tank. Why then does it show as 35+ on the fuel levels and not 37?

TIA!
 

airguy

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Nov 10, 2008
Messages
780
Location
Gods Country - west Texas
Can someone throw some light on an issue I'm trying to understand.

I have 40 gallon tanks (80 total). 3 gallons in both sides is considered unusable. When I calibrate the system I put 3 gallons in the tank and then tell sky view that the tanks have 37 gallon capacity and that I'm ready to calibrate. It then has me add 7 lots of 5 gallons (total of 38 at this point) and then tells me to full the tank. As far as the skyview knows I have 37 gallons in the tank. Why then does it show as 35+ on the fuel levels and not 37?

TIA!
As the fuel indicator float rises, it finally reaches a point of maximum travel and any further fuel added after that does not change the indication on the output. Skyview knows how much fuel you have added and in what increments, and calculated that the float arm stopped travelling at 35 gallons, but you still had some more fuel to add - therefor it does not know how much fuel is in the tank, but it knows that there is more than 35 since the fuel sensor is at the maximum up travel. It reports 35+ based on that. As you burn fuel and the level drops, and the float arm gets back into its calibrated territory, the 35+ will be replaced with 34 ... 33..... 32... etc
 

speedbird1

I love flying!
Joined
Feb 2, 2018
Messages
15
Makes sense. Why though does my gauges show two different level RIGHT after completion? (I rebooted too!)
SVC.jpg
 

airguy

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Nov 10, 2008
Messages
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Gods Country - west Texas
Same reason I posted above. Different float senders may have different final output voltages at the top end of their travel. One of them reaches the limit of travel before the other one, thus a slight difference in output.
 

Rafsqnldr

New Member
Joined
Dec 29, 2020
Messages
3
My HDX fuel quantity has never, since aircraft and HDX were new, agreed. I keep seeing mention, within the forum, of adding fuel in batches and calibrating the HDX, but have not found the procedure to be used. Where is this process written?
 

cbennet12

Member
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Mar 21, 2011
Messages
127
My HDX fuel quantity has never, since aircraft and HDX were new, agreed. I keep seeing mention, within the forum, of adding fuel in batches and calibrating the HDX, but have not found the procedure to be used. Where is this process written?
Page 7-63 of the HDX installation manual instructs the user where to start the calibration. Once started, the Skyview walks you through the process on screen.
 

Rafsqnldr

New Member
Joined
Dec 29, 2020
Messages
3
Page 7-63 of the HDX installation manual instructs the user where to start the calibration. Once started, the Skyview walks you through the process on screen.
Thank you! I have now downloaded the install manual which did not come with the aircraft!
 

Jaque

Member
Joined
Jul 9, 2019
Messages
37
Just did my calibration and have a question on the process. The tank has a 57 litre capacity. After adding the first few 5 litre batches, there is no change on the resistive sender voltage. This is somewhat expected with the design of these tanks (CH750 Cruzer). After each pour and pushing add, I am asked if I want to save or discard the pour because there was no voltage change. I assume that you do want to keep the pour, correct?
 

CanardMulti

Member
Joined
Apr 1, 2021
Messages
43
On the subject of calibrating the fuel senders: There's a situation that's not addressed well in the installation manual.

When I calibrated my Princeton capacitive senders in my left tank the first time, I simply poured in a 5 gallon increment and promptly hit save, and went on to the next 5 gallon pour. When then doing the right tank, I had a few distractions that caused me to pause before hitting enter a couple of times and I noticed that the voltages, and therefor the associated quantities, continued to take a while to stabilize. The times were longer the closer the tank was to empty, on the order of 10 minutes for zero and the first 5 gallons. Near the tank's 50 gallon full capacity they took only a few seconds. I recalibrated the first tank and fuel quantities on the EMS have been accurate ever since.

I cannot say if my experience w/ capacitive senders is applicable to float type sensors, but it couldn't hurt to be especially observant that the voltages are truly stable during any point in a calibration sequence before saving the value.

Ken
 

airguy

Active Member
Joined
Nov 10, 2008
Messages
780
Location
Gods Country - west Texas
Just did my calibration and have a question on the process. The tank has a 57 litre capacity. After adding the first few 5 litre batches, there is no change on the resistive sender voltage. This is somewhat expected with the design of these tanks (CH750 Cruzer). After each pour and pushing add, I am asked if I want to save or discard the pour because there was no voltage change. I assume that you do want to keep the pour, correct?
If the change is not "large enough", Skyview will throw that warning up. There may still be SOME change - and it's usable - it's just smaller than Skyview expects. Restart the calibration process and note the voltage before and after each pour - if there is actually a change, even small, then Skyview can use it. Tell it to accept the datapoint and go to the next pour.
 

djones

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Staff member
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Jul 19, 2010
Messages
227
To expand further, SkyView is looking at 5 decimal places during the calibration. Often the displayed voltage doesn't change(2 decimal places) even though it did change by an amount too small to be seen on the calibration page. This is most common with capacitive level sensors. Resistive don't usually have this happen, the voltage changes are quite a bit larger between pours.
Don't get in a hurry to push the button, don't jump up on the wing and push the button, let the fuel stop sloshing before accepting the point and continuing. If you get the warning about voltage not changing, continue as if it had.

Here is my tip of the day, particularly with resistive sensors. Write down the voltage and the amount of fuel at each point. Should something happen the cal table can be created manually and you won't have to drain fuel and start over.
I can help if you have issues..... support@dynonavionics.com
 

airguy

Active Member
Joined
Nov 10, 2008
Messages
780
Location
Gods Country - west Texas
To expand further, SkyView is looking at 5 decimal places during the calibration. Often the displayed voltage doesn't change(2 decimal places) even though it did change by an amount too small to be seen on the calibration page. This is most common with capacitive level sensors. Resistive don't usually have this happen, the voltage changes are quite a bit larger between pours.
Don't get in a hurry to push the button, don't jump up on the wing and push the button, let the fuel stop sloshing before accepting the point and continuing. If you get the warning about voltage not changing, continue as if it had.

Here is my tip of the day, particularly with resistive sensors. Write down the voltage and the amount of fuel at each point. Should something happen the cal table can be created manually and you won't have to drain fuel and start over.
I can help if you have issues..... support@dynonavionics.com
Listen to Don - he knows stuff :cool:
 
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