Fuel calibrations failing, both sides

[swatson999]

Trying to get fuel levels calibrated, but having some issues.

I have Van's capacitive sensors, and they were verified correct (isolated, etc.) during and after the build. Using the Dynon capacitive-to-voltage sensors on both sides. They're both getting power, and they're never jumping around (which would be indicative of an open line, IIRC), but they won't calibrate...

They both start out around 0.88 and never get much change, on the order of 0.01 or perhaps a tad more, but not much, no matter how many times I add 2 gallons. I got to 16 gallons on one side and it was reading 1.06, so I quit, went to the other and saw the same behavior.

Bad sensors? The only thing I can think of that I would have done which would make both of them bad, and tell me if you think this is it, was (on the advice of another builder LOL) covered the bare wires on the back of the sensors with some silicon waterproof cauling gook from the aviation department at OSH. Could that cause the sensors to be messing up?

If that's not it, what else could it be?

 

[mmarien]

I didn't have much change when I calibrated my fuel level (0.004 volts/litre) but my fuel gauge seems to work just fine. See the discussion on this thread.

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1330258885/10#10

 

[swatson999]

Hmmmm....so it seems I may have given up a little too early? I found some posts on VAF that indicate that the full range (empty-to-full) on an RV-7 is about .4 volts (927 mV to 1325 mV). This leads me to believe that perhaps it will work just fine, although it is disappointing that it doesn't use the full range of 0-5V for more accuracy.

Guess I'll try the calibration again tomorrow and then just fly and see how it does...

does that range seem correct for others who have calibrated Van's tanks?

 

[dynonsupport]

We can't use 0-5V since we don't know the capacitance of your tanks beforehand. You might have an RV-4, and RV-10, an RV-12, or even a Comp-10. We sell a generic capacitance to voltage converter, not one for a specific RV. Thus, we have to support a large range of capacitances.

In order to output 0-5V, you'd need to calibrate the converter first, and in fact some converters on the market that cost a lot more dot that. They also mean you have to empty and fill the tank before you can do the calibration inside SkyView. But there isn't a real advantage. We digitize the voltage we get into 16,000 levels. Thus a 0.4V change is still almost 1,300 digital changes for us. Given that your tanks are probably about 20 gallons each, that's still a resolution of 1/64th gallon (2oz). We only display in full gallon increments on the screen, so this is more than sufficient.

So yes, 0.4V sounds normal, and it sounds like all is working fine. You should have good accuracy when you're done.

 

[swatson999]

Calibrated the tanks today...looks like ti should be fine! Thanks for the response, and we'll see how it works out under operational conditions.

Thanks again...

Steve

 

[swatson999]

BTW...quick question...

I have an RV-7A, so 21 gallons per tank. The "last pour" during calibration was, as it should have been, 1 gallon almost exactly, and I hit "Full". Calibration done! Now, is there a way to get the fuel gauges to show "21" instead of "20+"?

It's not that big a deal, and I set all the widgets and ranges and such correctly so "Full" when the system comes up does, in fact, set 42 total...just wondering if I could get a "nicer" display on the individual tank widgets...

TIA!

Steve

 

[Dynon]

You'll see 20+ (or XX+) whenever the sensor rails out before you're done pouring. In your case, after 20 gallons, the sensor didn't move again, and so the most SkyView can ever know is that you have 20 gallons, or maybe more. Hence the 20+. It's the digital equivalent of the gas needle sitting on the peg in your car for a while.

 

[rick789pb]

I have a Glasair III and tried calibrating the fuel yesterday and as I pumped 5 gallons at a time and pressed add I noticed the voltage increase each time. When the fuel tank was finally full, I pressed the full and accept buttons and the Skyview said unable to calculate. Any ideas why?

Thanks,
Rick

 

[Dynon]

If the voltage actually went the down at some point, that would cause the computation to fail. Did you happen to record the voltage readings?