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  #1  
Old 09-09-2022, 12:35 PM
BrianMatice BrianMatice is offline
 
Join Date: Feb 2016
Location: Riverview Florida
Posts: 11
Default Capacitive Fuel Sender Calibration - RV-7A

Afternoon everyone.

Does anyone remember the capacitive plates? You know, the ones that Van's doesn't sell anymore So here is my issue. Bought a set of second hand wings, the tanks were completed some time ago with the capacitive senders. I am attempting to calibrate the fuel gages (Dynon HDX) however I am now realizing that with the wing dihedral the fuel doesn't even touch the outboard plate until there is about 5 gallons and doesn't seem to read anything meaningful until about 8. The HDX reads about 0.1v difference between each of the 4, 6 and 8 gallon marks. Each time the HDX says "there was no change, are you sure fuel was added."

Anyway, is this normal/acceptable to anyone that the fuel gage stops at 5 gallons remaining? Is anyone happy with these senders? Should I order the float type today and be done with it?
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  #2  
Old 09-09-2022, 01:44 PM
sinjin sinjin is offline
 
Join Date: Aug 2021
Location: Norwalk, ca
Posts: 51
Default Fuel

I have a G3x and my fuel left and right gauges dont work great ( i havent done any add 2 gallons testing though). I use a fuel stick before each flight and my fuel totalizer works within a gallon or 2. How often are you going to be running sub 5 gallons ? I hope not much. Switch tanks on 30mins reminders and leave yourself an hour of fuel.
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  #3  
Old 09-09-2022, 01:52 PM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,956
Default

Something wrong there. I have calibrated this set up many times and have been able to get accurate readings the full range down to empty.
Is it at all possible the sense wire was only connected to the outboard plate or bad connection to the inner plate?
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Last edited by Ralph Inkster : 09-09-2022 at 01:55 PM.
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  #4  
Old 09-09-2022, 01:56 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,965
Default

Quote:
Originally Posted by BrianMatice View Post
Afternoon everyone.

Does anyone remember the capacitive plates? You know, the ones that Van's doesn't sell anymore So here is my issue. Bought a set of second hand wings, the tanks were completed some time ago with the capacitive senders. I am attempting to calibrate the fuel gages (Dynon HDX) however I am now realizing that with the wing dihedral the fuel doesn't even touch the outboard plate until there is about 5 gallons and doesn't seem to read anything meaningful until about 8. The HDX reads about 0.1v difference between each of the 4, 6 and 8 gallon marks. Each time the HDX says "there was no change, are you sure fuel was added."

Anyway, is this normal/acceptable to anyone that the fuel gage stops at 5 gallons remaining? Is anyone happy with these senders? Should I order the float type today and be done with it?
Are you using the interface adapter, that is required to convert the variable capacitance to a variable voltage?

The whole point of the capacitance sensor is that there is a plate at the inboard end and the outboard end so it is able to read a change through the entire fuel level range, but is does require an adapter.
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Scott McDaniels
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Formerly of Van's Aircraft Engineering Prototype Shop
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  #5  
Old 09-09-2022, 03:16 PM
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airguy airguy is offline
 
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Location: Garden City, Tx
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That is true if using the old capacitance-to-voltage converters originally supplied by Vans, but the Princeton version is much better.

If you go ahead and tell it you added fuel despite the warning, you'll get a reasonable calibration, but the resolution is just not as good with the original converters as it will be with the Princetons.
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  #6  
Old 09-09-2022, 03:19 PM
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pilotkms pilotkms is offline
 
Join Date: Mar 2007
Location: WARNER ROBINS, GA
Posts: 636
Default

Mine work fairly well. Dynon Skyview, Touch.
Lowest Ive ever allowed either to go to was 3 gallons. Had over 10 in the other tank and headed for an airport for gas. Never want to be below 10 total, in case I have to takeoff for another airport for gas.
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  #7  
Old 09-09-2022, 03:36 PM
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RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Quote:
Originally Posted by airguy View Post
That is true if using the old capacitance-to-voltage converters originally supplied by Vans, but the Princeton version is much better.

If you go ahead and tell it you added fuel despite the warning, you'll get a reasonable calibration, but the resolution is just not as good with the original converters as it will be with the Princetons.
Same experience here. I never did get a good calibration curve using the original Dynon C2V converters, so after the first year I switched to the Princeton 2-point converters, and after one calibration, they've been dead-nuts on for 9 years now.

The Dynon converters used only a tiny fraction of the available 5V range, whereas the Princetons use the entire 5V.

ETA: And the whole point of capacitive sensors is they measure the capacitance from one end to the other *regardless* of orientation, fill level, etc.
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  #8  
Old 09-09-2022, 08:00 PM
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BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,838
Default Sources for something that works full range.

Quote:
Originally Posted by rvbuilder2002 View Post
Are you using the interface adapter, that is required to convert the variable capacitance to a variable voltage?

The whole point of the capacitance sensor is that there is a plate at the inboard end and the outboard end so it is able to read a change through the entire fuel level range, but is does require an adapter.
Every thing on my plane works pretty well. If it is there it works, except the fuel gauges. I rationalize that they are absolutely accurate below 7 gallons. The left works from 9 down and the right maybe 14 and down. Above that they can not be trusted. I know it and live with the exception as a totalizer is pretty accurate and I have a dip gauge that is accurate within 1/2 gal, and consistent with the totalizer. So I know what I start with and the gauge(s) is/are good for the end of flight. Usable but not acceptable.

Is there a Kit Planes article? Vans RVAtor report? Vendor report?
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  #9  
Old 09-10-2022, 06:17 AM
BrianMatice BrianMatice is offline
 
Join Date: Feb 2016
Location: Riverview Florida
Posts: 11
Default Thanks for the replies!!!

Thanks everyone for the good conversation. My only thought here is that there will be no reading while the fuel has not reached the second plate (because of wing dihedral) which will be under 5 gal or so.

I am using the Dynon adapters which are brand new, but I do see that they only increment at very tiny amounts. I will definitely look into the Princeton adapters. Does anyone have a source for these?

I also know that I will need to switch these out at some point anyway to be ready for the new unleaded fuel that is coming out. No way to calibrate for an unknown mixture of two different fuels.
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  #10  
Old 09-10-2022, 06:37 AM
Desert Rat Desert Rat is offline
 
Join Date: Aug 2018
Location: Wichita KS
Posts: 1,048
Default

I think I see a basic misunderstanding here.

You're not measuring the delta between the two plates. Each plate measures the delta between the plate and the rib it's mounted on. The reason there's one in each end of the tank is specifically because of the dihedral.

FYI I have the same situation with used wings from 2007. I'm not at that point yet so I'm very interested in how this works out for you.
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