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Vans Capacitive senders

I am looking for the capacitive values for a full tank and a empty tank for vans capacitive senders if anyone has that information.
Looking for those values to do some trouble shooting.
Thanks in advance
Gerry
 
I am looking for the capacitive values for a full tank and a empty tank for vans capacitive senders if anyone has that information.
Looking for those values to do some trouble shooting.
Thanks in advance
Gerry

Jim Weir wrote 2 articles about DIY capacitance fuel gauge systems. If memory serves, he gives the info you want in those articles [Kitplanes]. I "think" I have both those articles stashed somewhere on one of my 12+ hard drives [spread over 4 computers]. Found them! The first article is in the September 1989 issue. The second is a 3 part article found in June, July and August 2000 issues. Send me a PM with your email address. I can send those articles to you.

Charlie
PS Use of E10 will alter the calibration needed. A subscription to Kitplanes is an extremely worthwhile investment
 
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I breadboarded and bench tested the Jim Weir designs. They worked fine. I was at the point of deciding on a hobby box and drawing a PC board when I found the tiny Dynon convertors.

I measured the dry Vans Cap sensors at the BNC (so both plate sets) at 180 picofarad.
Avgas is supposed to double that to 360 pf. Those were the values I used for test caps on the breadboarded Weir design.
 
I breadboarded and bench tested the Jim Weir designs. They worked fine. I was at the point of deciding on a hobby box and drawing a PC board when I found the tiny Dynon convertors.

I measured the dry Vans Cap sensors at the BNC (so both plate sets) at 180 picofarad.
Avgas is supposed to double that to 360 pf. Those were the values I used for test caps on the breadboarded Weir design.

So this has been mentioned before, but just to throw it out there again...I (and others) have had pretty bad luck with the Dynon converters, as they use only a tiny portion of the available 0-5V range of output. I couldn't get mine calibrated worth a s**t.

Opted for 2-point Princeton converters which, while they necessitated another wire for power, have been working like champs for years now.
 
I happened to get a message through to Todd at Princeton. Unfortunately I neglected to ask if I could republish his response.
I will say that there is a plan to continue building products.
 
Princeton

I happened to get a message through to Todd at Princeton. Unfortunately I neglected to ask if I could republish his response.
I will say that there is a plan to continue building products.

So they still manufacture?
 
Dynon Capacitance fuel gages

The capacitance value is determined by the plate size and geometry so if you have already built the tanks you are stuck with the dry capacitance values. I did a dummy calibration (using a number of fixed capacitors in parallel) when checking out the wiring and Skyview system while still in the shop before moving to the airfield. You are correct that the full range of 0-5 volts is not used at the output from the Dynon capacitance to voltage converter. I did a fuel calibration on each tank at 2 gallon intervals and have now been flying for about 12 hours. I have found the Dynon C to F converters to be reliable and accurate and consistent with the fuel flow and refueling amounts. So far - so good. I too was concerned that the small values of capacitance and the low dielectric constant of 100LL would create a problem that would result in the need to do something else for fuel gaging but so far- not a problem.

KT
 
HELP Please...
I have taken over an RV8 project and it has the capacitance senders half installed. But I have no paperwork to check they are correct. Could some one please send me a copy of the instructions.
I am concerned about the number of spacers between plates and the rib.
Thanks, Tim
 
HELP Please...
I have taken over an RV8 project and it has the capacitance senders half installed. But I have no paperwork to check they are correct. Could some one please send me a copy of the instructions.
I am concerned about the number of spacers between plates and the rib.
Thanks, Tim

Here is the drawing for the cap senders
View attachment OP07 RV-8 Cap Fuel Sndr.pdf

close up of stand-off
Screen Shot 2021-11-15 at 13.20.20.png
 
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Is Capacitive Senders ready for prime time?

I have an RV-9 QB kit on order with delivery estimated Jan 2023. I specified traditional float sensors because capacitance seems to still have growing pains. Have things improved enough to make it viable and is the added complexity worth the money? In 20 years I have replaced my float senders once. I noticed the old ones used resistance wire and the new ones replaced wire with the resistor built into the slider bar. One of the old sensors had a broken wire which precipitated replacing both.
 
Going on 18yrs with my original Van's capacitive senders with no issues. Pretty darn accurate from full to empty. Just my experience. If installed correctly there's not much to go wrong.
 
I have an RV-9 QB kit on order with delivery estimated Jan 2023. I specified traditional float sensors because capacitance seems to still have growing pains. Have things improved enough to make it viable and is the added complexity worth the money? .

9 years now with not a single issue with mine. Frankly, what *could* go wrong, at least with the parts inside the tank? There are no moving parts. I used the Princeton 2-point C2V converters and they've been working great.
 
Thread hijack: Wondering if anyone on VAF has any tips on "debugging" problems with the Princeton converters for Vans plates. So far, even after doing the 2 point calibration on the converters, I am seeing no difference in output voltage (to a G3X) when tanks are full vs. empty. I'd like to somehow test the tanks directly to rule out my building the plates incorrectly. And then maybe test the converters directly minus the tanks. Not sure where to start.
 
I am using the Dynon/AFS converters for my Van's capacitance senders, and find them to be quite accurate. The AFS software allows you to calibrate the gauges in multiple increments in both ground and flight attitudes. I have also calibrated several float installations and found the gauges to remain at FULL until approx. 15 gallons, when they begin to indicate somewhat accurately. When Van first offered the capacitance system it was all the rage, then seemed to fall out of favor which I think was due to problems interfacing them with different mechanical and EFIS systems. The Dynon converters simply plug into the BNC connector on the tank, careful calibration results in excellent results.
 
Only issue I've ever had with a Capacitance sender installation was a seeping leak through the center pin of the B&C connector. Easily fixed by generously painting the whole inside connector & wire lead with Proseal.
Otherwise, sensors in these planes have performed flawlessly:
RV7A 1700hrs, RV7 400hrs, RV7A 400hrs, RV6A 350hrs & counting.
 
Thread hijack: Wondering if anyone on VAF has any tips on "debugging" problems with the Princeton converters for Vans plates. So far, even after doing the 2 point calibration on the converters, I am seeing no difference in output voltage (to a G3X) when tanks are full vs. empty. I'd like to somehow test the tanks directly to rule out my building the plates incorrectly. And then maybe test the converters directly minus the tanks. Not sure where to start.

I would start with a simple ohm test of the empty tank to make sure there is no short between the plates and the skin/ribs.

Then of course, then make sure there actually is a connection between the plates and the wiring. Find a way to make connection with the plates from the fill opening.
 
To test the converters, put a capacitor across the inputs. 120pF should be near empty, 250pF should be near full. These are rough numbers, heavily dependent on the details of your installation.

If you're using a common digital multimeter to measure capacitance of your tank installation, note that most of them won't resolve down to the picoFarad level, so "empty" and "full" will both appear about the same.
 
Hmmm... So I had a chance to do some experimenting with the tanks and Princeton converters tonight. The good news is no shorts between the tank and the plates! Measuring the capacitance between the center pin on the BNC connector and the tank skins, I see the following:

Left tank empty: 145pF
Left tank ~5.3gal: 160pF
Left tank ~10.6gal: 172pF
Left tank ~15.9gal: 188pF
Left tank full: 227pF

Right tank empty: 155pF
Right tank ~5.3gal: 170pF
Right tank ~10.6gal: 182pF
Right tank ~15.9gal: 196pF
Right tank full: 233pF

So not too bad. Capacitance varies with fuel level, as I'd expect. Conclusion: Tanks are probably fine.

Then, I calibrated the (right) 2 point Princeton converter: Empty tank, push button, Fill tank, push button. That should be it (?).

Now I fill up the tank, observing the voltage output by the converter into the G3X. All fuel levels lower than ~13 gallons result in 0.1V to the G3X. Greater than 13 gallons, the voltage level grows exponentially to around 4.8V when full. (Blue line is tank capacitance, Red line is voltage output from converter, as read by the G3X):



This does not look right. The converters cannot seem to distinguish fuel levels below around 13 gallons, and therefore the G3X will not be able to, either. It's looking like I might need to contact Princeton for help at this point.
 
More experiments with the Princeton capacitive converters. Spoiler: My converters seem to be bad, but they happen to be bad in a way that is measurable and predictable, and I think I have worked around the problem!

I grabbed an assortment of little electronics capacitors, with the goal of "simulating" a fuel tank. Did a fake calibration using a 120pF capacitor as "empty" and a 270pF capacitor as "full". Then afterwards, tried a bunch of other capacitance values between 120 and 270 and found that the converter correctly output voltages between 0.1V and 4.9V as I changed capacitors from "fake empty" through "fake full". So it's possible for them to work.

I then did a calibration as close as possible to the real tanks' empty and full capacitance: set the empty point to 150pF and full to 230pF, again using electronics store capacitors. Plugged in the tank and filled, and saw the same behavior as yesterday. Output stuck at 0.1V until tanks are about 2/3 full. It looked like the "empty" set point was not low enough, even though it matched what I measured from the empty tanks.

On a hunch, I set the "empty" point to 60pF, way below what I measured from my empty tank. Now, when connected to the tank, the converter output was not 0.1V--It was around 1.4V, and adding additional avgas caused that number to rise! So there must exist some capacitance value for "empty" and "full" that will work with the tanks. Just have to find it.

Through LOTS AND LOTS of trial and error, I found that calibrating my left tank with 102pF as empty and 220pF as full results in an output range of 0V-4V from the converter when used with a real tank, and calibrating the right tank with 83pF empty and 193pF full also resulted in that usable voltage range from the right converter when used on a real tank. Once that was set up, performing the gallon-by-gallon calibration on the G3X was straightforward.

Very strange that using the actual tanks to calibrate the converters did not work, but it seems that I have managed to fool them into working, despite this defect. I plan to never touch these things again.
 
Multiple calibration points?

Doesn't the Princeton converters have multiple calibration points.
Or is that some other converters?

Because of the tank shape, the capacitance is not linear with fuel quantity.

Come to think of it, would it be possible to shape the plates to produce a linear capacitance output?

Re-reading your post, looks like whatever instrument you used to measure capacitance may have a low limit above what you need. Or cable length introduced a bottom capacitance above actual tank empty capacitance. What did your instrument show with the cable disconnected at the tank BNC?

Finn
 
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As far as I can tell, there are three different types of Princeton converters: 1 set point (empty only), 2 set points (empty and full) and 5 set points. Mine are 2 set point models. You are correct, the relationship between gallons, tank capacitance, output voltage is not linear. In a G3X setup, the mission for the Princeton converters is to at least get a rough output between 0 and 5 volts, and then use the upstream system (with up to 50 set points) to do fine tuning.

I measured my tanks by probing the female connector itself, no cable. It is possible my cheap capacitance meter has trouble reading the tank capacitance accurately, but it seems to be accurate measuring capacitors with known values. And the Princeton converters work exactly as expected (calibration and measurement) when inputs are faked with electronics capacitors. That's the real puzzling part.
 
9 years now with not a single issue with mine. Frankly, what *could* go wrong, at least with the parts inside the tank? There are no moving parts. I used the Princeton 2-point C2V converters and they've been working great.

Sorry, I thought I answered this years ago. Providing that all 12 #8 screws remain tight, you won't have problems with Vans spacer design. However, if the screws in one plate loosen a bit, it allows the plates to slide downward [gravity] between the spacers. Now, the only thing keeping the plate from shorting out is that 0.040" thick vinyl tubing. Won't take long for the edge of the plate to cut through the tubing and short the sender out via the screw. The spacer style that Dick Martin designed in conjunction with the engineers at Electronics International doesn't have that weakness. This is the design that both Bjorn & I use. Vans kit is simply a "cheapo" version of Dick's design.

http://www.mykitlog.com/users/display_log.php?user=N741BN&project=2288&category=9329&log=206547&row=129
 
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