Resistive fuel sender

[d3mac123]

I am considering to install fuel senders in my main tanks (builder decided not to do that). I was suggested to use capacitive senders but, unfortunately, I do not have any Enhanced General Purpose inputs available, which will force me to use resistive senders with General Purpose inputs.

I have no idea/knowledge of which senders to buy. Thoughts?

Any help is appreciated.
Thanks!

 

[Rhino]

There is no specific recommended, one size fits all, type. Resistive senders are pretty basic. A float moves the arm on a variable resistor to change the voltage. It really doesn't matter which one you use on the Skyview end. What matters most is what works best on the tank end in your aircraft. For that, most folks just ask previous builders of their kit model what worked best for them. Absent that, they usually just wing it.

 

[tniel7331]

CIE Makes some that are voltage cap or resistive. I have added a power wire up to tank to use them. Because people say it digital. Not just voltage variation. But found their no better than generic resistive from Aircraft Spruce

 

[Rhino]

Skyview does not use a digital signal for fuel level from a resistive sensor. It doesn't even constantly display fuel level, so a digital signal would provide no benefit anyway, as far as I can see. Instead, it uses sample levels over a time interval to account for variations as fuel moves around in the tank. That interval is adjustable for your aircraft and situation. Pins 20 and 21 come preconfigured for that. You have to manually configure any other pins you may want to use in that regard.

 

[d3mac123]

Taking advantage of this conversation (I am learning a lot), is there any benefit to use the capacitive over resistive? Can I install a resistive laterally to the tank (I can do that with the capacitive) or does it work only top of the tank?

 

[Albee]

You can definitely mount resistive on the side (or bottom) of a tank, you just have to arrange it so the float is at the 'full' end of travel at the top of the tank and "empty" on the bottom. Usually by bending the support arm. I'm not sure there isn't a capacitive option for side mounting but it sounds like an interesting experiment. When I replaced my old resistive (top-mounted) sensor with capacitive, my fuel quantities finally started to match (within a few percent of capacity) what the fuel flow and refill numbers say. Just my anecdote; YMMV.

 

[Rhino]

Capacitive needs to be vertical, or at least the sensor element does. Fuel has to fill the sensor between the plates in a tube assembly from top to bottom so it can sense the change in fuel level by detecting the difference in capacitance between the plates. The two plates resemble a rod suspended inside a tube. That doesn't mean no one has ever developed a capacitive sensor that enters the tank from the side, and then extends vertically within the tank. I've never seen or heard of one, but I'm not exactly the world's most experienced person in that regard.

 

[maartenversteeg]

The are capacitive sensors available at aircraft spruce that allow you to bend the tube and make it fit withing your tank

 

[Rhino]

There ya go! Told you I wasn't the most experienced there.

 

[Rhino]

And since you asked about relative benefits, I'll tack on to what Albee said earlier. Capacitive sensors are generally far more accurate than resistive. I don't have any data at hand to support it, but I imagine they're probably more reliable too, since the don't have the mechanical component.

 

[maartenversteeg]

but the capacitive sensors need separate calibration for different types of fuel (like avgas and mogas)

 

[Rhino]

Another interesting point. The difference in dielectric constant measured by a capacitive sensor is not as great as the manual seems to suggest. The constant of Avgas also varies with temperature, which is also likely with auto fuels (don't have the stats for those). So you can still get variations using the same fuel all the time. The variation might be somewhat equatable to the inaccuracy that's common with floats. The effect of the variation is also smaller as the tank gets smaller. However, even though both sensor types have inaccuracies, the inaccuracy of a float sensor is constant. Changes in dielectric constant are not. Anyone planning to vary the type of fuel they use should probably stick with a resistive sensor that uses a float. Those with capacitive sensors might also want to consider recalibrating when going from one temperature extreme to another, such as Arizona in the heat of summer to Alaska in the dead of winter.