bobmarkert
Well Known Member
I am having trouble calibrating the capacitance fuel quantity system in my RV-8. I have the Princeton 2 point capacitance computers and VANs capacitance plates feeding a Gramin G3X. The left tank calibrated perfectly. The right tank failed calibration and does not register the first 8 gallons of fuel. From 8 to 21 gallons, the system can be calibrated. Below is my troubleshooting procedure and thoughts about this problem. Input from those smarter than me appreciated.
When the tank did not register the first 8 gallons (no voltage change) during the first calibration attempt:
1. I recalibrated the Princeton computers. I drained the tank and set the empty point (reading was 0.118 volts), and refilled the tank and set the full point (reading was 4.963 volts). I then drained the tank to start the calibration process.
2. I added fuel two gallons at a time. There was no voltage change for the first 7-8 gallons.
Conclusion:
1. The inboard (lower in the dihedral) capacitance plate is not sensing the fuel.
2. The entire voltage change (0.118 v – 4.963 v) is occurring on the outboard capacitance plate once the fuel reaches it (~8 gallons).
Troubleshooting:
1. I re-drained the tank
2. I used a meter to check the connections. The outer lead goes to ground on the airframe as I believe it should and the inner connection has no continuity…. which I also believe is correct as the fuel bridges the gap between the plates and the fuel tank skin to register the capacitance.
Is it possible that an aluminum oxide has formed on the plate and is acting as an insulator? The tank was built 2 years ago and is just now being put in service. I am considering removing the tank and cutting into it to scuff up the plate in the hope that it will register the fuel…….sigh
Any thoughts or suggestions?
I’ve also sent this to Princeton support and haven’t heard back yet
the first picture below show the failed calibration curve in the right tank. The second picture shows the left tank which calibrated properly
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Thank You
Bob
When the tank did not register the first 8 gallons (no voltage change) during the first calibration attempt:
1. I recalibrated the Princeton computers. I drained the tank and set the empty point (reading was 0.118 volts), and refilled the tank and set the full point (reading was 4.963 volts). I then drained the tank to start the calibration process.
2. I added fuel two gallons at a time. There was no voltage change for the first 7-8 gallons.
Conclusion:
1. The inboard (lower in the dihedral) capacitance plate is not sensing the fuel.
2. The entire voltage change (0.118 v – 4.963 v) is occurring on the outboard capacitance plate once the fuel reaches it (~8 gallons).
Troubleshooting:
1. I re-drained the tank
2. I used a meter to check the connections. The outer lead goes to ground on the airframe as I believe it should and the inner connection has no continuity…. which I also believe is correct as the fuel bridges the gap between the plates and the fuel tank skin to register the capacitance.
Is it possible that an aluminum oxide has formed on the plate and is acting as an insulator? The tank was built 2 years ago and is just now being put in service. I am considering removing the tank and cutting into it to scuff up the plate in the hope that it will register the fuel…….sigh
Any thoughts or suggestions?
I’ve also sent this to Princeton support and haven’t heard back yet
the first picture below show the failed calibration curve in the right tank. The second picture shows the left tank which calibrated properly
\
Thank You
Bob