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-   -   Fuel levels not registering (https://vansairforce.net/community/showthread.php?t=161191)

Flying Canuck 06-07-2018 07:45 AM

Fuel levels not registering
 
This is probably just going to be a forehead slap opportunity but maybe someone knows this one. I started doing my fuel level calibration last night - Dynon Skyview HDX, standard resistive type fuel senders connected to default EMS pins (20 and 21). I started with the left tank and was prompted to do repeating 5L pours. I did 3 pours and the sensor reading wasn't changing, Skyview was complaining about that. I decided to abandon my calibration and check the sensor levels on the debug screen, think that maybe I'd reversed left and right. What I found was the left value was ~3.7V and the right value was ~2.9V. The left one was the same value showing on the calibration screen. I decided to try a pour in the right tank to see if the sensor value changed. It didn't. I don't get any movement on either sensor.

I expect that this is an installation error. I recall checking the senders with a multimeter before installing them and they worked fine. Unless I completely missed the point, there is only one wire connecting the screw on the sender to the EMS wire. I'll climb under my panel tonight to confirm the connections but hoped that maybe someone has an idea of what I did wrong?

Thanks for your help.

Mich48041 06-07-2018 07:51 AM

Make sure the sender plate is well grounded by connecting a ground wire to the plate. I am assuming the sender is the float type with potentiometer and round mounting plate.

airguy 06-07-2018 12:30 PM

Didn't get ANY change on the measurement, or just didn't get a LARGE change on the measurement? Skyview with the standard float sensors is known for having very small voltage changes between the fuel pours during calibration - typically complaining between each pour that it didn't change, when in fact it changed SOME but not enough to keep Skyview happy. Rather than using the full 5 volt range on the float potentiometer, it's common that empty-to-full range with the Vans tanks and the standard float pickups you'll see a difference in 1-volt range. Skyview will still do an adequate job of interpreting the fuel levels if you complete the calibration, but you're looking for changes between pours of tenths and hundredths of a volt from the sensor.

larrynew 06-07-2018 12:47 PM

I had one tank's float stick when I first tried the Skyview calibration pours. I ended up giving the round plate a few raps with a rubber hammer and it unstuck and has read accurately for 600+ hours. Guess it hadn't moved for a year or two while building and just needed a little coaxing.

Flying Canuck 06-07-2018 01:28 PM

Quote:

Originally Posted by airguy (Post 1265428)
Didn't get ANY change on the measurement, or just didn't get a LARGE change on the measurement? Skyview with the standard float sensors is known for having very small voltage changes between the fuel pours during calibration - typically complaining between each pour that it didn't change, when in fact it changed SOME but not enough to keep Skyview happy. Rather than using the full 5 volt range on the float potentiometer, it's common that empty-to-full range with the Vans tanks and the standard float pickups you'll see a difference in 1-volt range. Skyview will still do an adequate job of interpreting the fuel levels if you complete the calibration, but you're looking for changes between pours of tenths and hundredths of a volt from the sensor.

I had a 0.02 V move after the 2nd pour, none before or after though. The right side didn't move at all but I only put in maybe 8L.

airguy 06-07-2018 01:55 PM

I just went back and looked at mine, I have about .35 volts delta between full and empty.

Flying Canuck 06-07-2018 02:47 PM

Tonight I'll connect a temporary ground to one of the plates to see if that helps. I'll see too if I can get my inspection camera up inside the emptier tank to check the position of the float. Maybe a mirror, a flashlight and an eyeball is safer.

I'll bring a new battery for my multimeter and check the resistance too. I'm not going to let this little problem beat me! Need to get this done so I can do my first start on Saturday and final inspection in 10 days or so.

Mark Dickens 06-07-2018 05:13 PM

Connecting a ground wire *may* help but probably not. These senders are grounded through their mounting plates and the tanks through the plate nuts. I went through this with my hangar mate when we attempted to calibrate his senders and the best we could achieve was not satisfactory at all. Bottom line is that with the SW senders in these tanks, it is very difficult to get anything approximating a full range, and then adding to that the inability of the Dynon EMS to sense the very small differences in voltage, and you have a situation where you just do the best you can, and then really work on fine tuning your fuel flow sensor K factor. To say I don't trust my fuel level readings is a huge understatement. Sometimes I think they are on target and other times, they are wildly off. The only value they might provide is an indication of a fuel tank leak....enough said, do the best you can and move on.

Flying Canuck 06-07-2018 10:01 PM

Well that wasn't a very productive night. I checked resistance between my firewall and the sender plate and got tiny numbers, so I can't see this being a ground issue. I pushed through the calibration for both tanks. The right tank stayed at the peak level until my 45L pour (out of 67L) when it jumped a lot. It stayed at the second level right through to full. The left tank never budged from 2.67V.

The one thing I managed to get was a calibrated dip stick, so at least I can tell how much fuel I have on the ground. I think my next step will have to be emptying the tanks and seeing if I can tell if the floats are free to move either with my inspection camera or by poking some hinge pin or something up through the drain. That's probably going to have to wait until after I do my first engine start on Saturday.

Carl Froehlich 06-08-2018 07:32 AM

Quote:

Originally Posted by Mark Dickens (Post 1265500)
Connecting a ground wire *may* help but probably not. These senders are grounded through their mounting plates and the tanks through the plate nuts. I went through this with my hangar mate when we attempted to calibrate his senders and the best we could achieve was not satisfactory at all. Bottom line is that with the SW senders in these tanks, it is very difficult to get anything approximating a full range, and then adding to that the inability of the Dynon EMS to sense the very small differences in voltage, and you have a situation where you just do the best you can, and then really work on fine tuning your fuel flow sensor K factor. To say I don't trust my fuel level readings is a huge understatement. Sometimes I think they are on target and other times, they are wildly off. The only value they might provide is an indication of a fuel tank leak....enough said, do the best you can and move on.

I have to disagree.

The tanks cannot read beyond a certain level as they angled up. On the RV-8, there is no reading beyond 16 gallons or so. On the RV-10 this is 24 gallons. However, from 16 (or 24) gallons down to 2 gallons the fuel reading is within a gallon of actual on the SkyView (level flight). I crosscheck these readings with the fuel flow totalizer on all flights to make sure I?m not leaking fuel.

When you build the tanks it helps to adjust the fuel sender arm range such that it goes all the way to the bottom of the tank. This means you will have most accuracy at low fuel levels (desired).

Do the calibration per the instructions and they work well.

Carl


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