Guys..
Just a FYI..if you've got a Dynon its worth noting.

I'd had an intermittent problem for some time where very occasionally all the CHT's and EGT's wouldn't work. The CHT's would show -99. It was only a very transient thing. Dynon said I had a wiring error but I couldn't find one. They recommended I slowly remove senders until the problem went away but I couldn't reproduce it to find it.
Then it dawned on me.. it only happened when my front tank was full. So obviously the sender was incompatible somehow. On measuring the output it was going over 5V despite the marking clearly saying 0-5V output. It was going to about 5.5V. After tweaking it down to 5V the problem was solved.
Like all intermittent problems the key was figuring out when it was failing but anyhow..
Just thought I'd add it so you guys can double check your own senders before finally fitting the tanks since getting to the buggers can be no fun once the tank is in for the last time.

George,
This comes at a very opportune moment for me as I am about to calibrate my fuel senders.
I had initially fitted capacitance sensors, but found out from Dynon that the only ones the unit would accept were 0 - 5 volts, so here goes another £220!
Anyway to the nub of my query. What is the input voltage to the sensors, 12v. or 5 v.? As you say, once they're in it becomes impossible to alter the sender.
Regards, GeorgeII
p.s. I'm calibrating them in tank as I need the capacities, useable, fuel remaining after empty signal etc.
pps. anyone want two unused capacitance rod sensors 11 inches long for half price!!!

GII..
Sorry.. should have said.. the senders I have are capacitance senders.. the rail voltage is 12V and their output is a variable voltage which was presumably 0-5 volts (as per what is printed on them) but evidently went slightly over that until adjusted..
The variable resistance senders would possibly not have the same issue since there is a selection in the settings that would possibly change the input requirements although that is only from memory so could be entire rubbish.
Either way.. worth checking nonetheless.

What brand of capacitance senders did you have?

Regards

Hey GR,

I've got Princeton capacitance probes but I didn't know you could (had to!) adjust the output voltage.

Is it done on the probe head itself or via the Dynon setup?

Evening Gentlemen.
My original fuel sensors were supplied by Airworld here in the land of UK, and state in the maual that they supply a max. of 80ma. to a gauge. They do not produce a voltage. I queried this with Dynon by phone(good old Skype!) and was told that the D180 would not recognise this output even with their Capacitanc to Voltage add-on Unit, and that the sensors must send between 0 and 5 volts hence my lack of beer money. I gather I have to poke 12 volts in and limit output to 5 volts max. for the full reading. The empty reading is presumably 0 volts
Regards,
GeorgeII

Hi Rob.. my probes are Westach capacitance probes.. They adjust on the probe head themselves.. obviously you need the tank full to do this.. the Westach probes have two adjustments actually.. one for zero and one for full and each one effects the other.. its a bit of a buggers muddle but eventually it ends up where you need it. With the Dynon its usually not such an issue since it calibrates off anything really.. provided the max value is below 5V though.

GII.. Ohms law might be a good help for those probes.. a simple resistance ladder should do the trick although I guess you aren't interested now since you have replaced them..
Just for the hell of it.. 12V in and max current of 80mA to give 5V - so the bottom resistance is 5/0.08 = 62.5 Ohms and the top variable resistor (probably not needed but for adjustment)... (12-5)/0.08 = 87.5 Ohms.. this is assuming that the Dynon has a high input impedance of course(Which I'm sure it would).. and since that value can't be purchased.. two close variable multiturn Potentiometers should do it. About $5-$8 worth.

Cheers

EH?
GeorgeII
(Wiggly amps are amystery to me!)

GR,

The Princeton has a couple of buttons and a light on the head.
I have the type with 5 set points so you start with minimum fuel then press a button, add 25% of your tanks capacity, press it again, etc.

(Yes, it is 25% not 20% There are 5 points which gives you an "Empty", a "Full" and 3 levels in between)

This will no doubt define a voltage output for each point, but if the "Full" level is greater that 5 volts I'll have your problem. Will be interesting to see how it all works when I get to that stage.

Rob,

So, it looks like you have 2 choices, you can: 1) do the 25%, 50%... and hope that full is not >5V or, 2) fill the tank, adjust the 5V, then empty and do the 25%, 50%... thing. Either way can be a rectal pain, what with all the transfer of gasoline. But this is a minor inconvenience compared to some parts of the Falco project, I.E. making a canopy.

Roger

Roger,

How right you are!

With the filling of the tanks however, I have an idea that will enable me to only use a small quantity of fuel, as follows:

I intend to fill the tank with water in 25% stages, dip it with a stick and mark the level at each stage. Because of the weird shape of the tanks the distance between the marks on the stick will obviously not be linear, but this is of no consequence.

The plan then is to get a clear plastic tube about 25 - 30mm dia, the same height as the tank and transfer the marks on the stick onto it.
The capacitance probe is then inserted and the tube filled with fuel in stages corresponding to the marks, calibrating the probe at each set point.

This way I'll have less than a litre or so of fuel to deal with, but the probe doesn't know that - it's just looking for a fuel level, which it then reports as a quantity.

It may even be possible to calibrate the probes directly in the tank using the water, but the water will have a different electrical resistivity to that of the fuel, so I doubt this will work, or if it does it may not be accurate.

Hi,

I recently designed a Capacitive circuit for measuring the Ethanol content of Mogas.
I doubt that water will be of any use as the Dielectric constant is about 40 compared to fuel
which is around 2 so you will over read by a large margin.
The other thing to watch out for is the stray electric field around the probes.
From experience I would allow around 2cm outside of the probe dimensions to minimise
the effects. That's experience of my circuit only!


John

Rob,

You may be "all wet" using the water system I have never tried it using water, but I am a skeptic You may also find that the plastic insert will also give you inaccuracies. My vote for the best, most accurate, and reliable system is, use gasoline

You could use auto gas for the calibration. I have not heard of large inaccuracies when switching from avgas to mogas. You can then dump in your auto when finished, solving the storage problem. Just a few more things to ponder

John,

OK, thanks for the tip - I'll use a larger tube.


Roger,

I have to agree - I didn't think water would be suitable - I just thought I'd mention it because I KNEW someone out there (that would be YOU, JohnS - thankyou!!) would have the smarts to know why, and to confirm, that it wouldn't work!
I'll use Avgas.

Gotta luv this forum!