Capacitance Sending Units

[Brockster]

I am ready to install the baffle on my second tank and while double checking everything I noticed a couple things. My first tank was done about 5 months ago and I cannot remember what I did and my pictures don' t show enough detail. I coated the nuts with pro seal where the wires attach to the plates. I didn't coat the head of the screw. I can unscrew the plates from the ribs and coat the head of the terminal screw, but I would rather not disturb everything. Is the pro seal just used as a locking device here or does it offer some type of insulating benefit. Also, does it matter which side the washer for the terminals go on. The pictorial on the print shows them under the screw head, but the instructions on the print calls for it to be on the same side as the nut. I don't quite understand how these capacitance plates work so I might be making a mountain out of a mole hill.

[RV8RIVETER]

The very basic version. The capacitive fuel sendors work by being, in essence a very large capacitor inside your fuel tank. A capacitor a merely 2 conductive plates seperated by a dielectric (insulator). The value of the capacitor is governed by the size of the plates, their distance apart, and the resistance/type of dielectric. The only value that changes in your tank is the fuel level, so that is how fuel level is measured, by measuring the change in capacitance.

I put the washer on the nut side. The only thing that is important is that you have a good electrical connection from the terminal to the plate. Make sure you ohm check all connections before closing the tank.

Proseal is an insulator, but I believe that Van's is using it as a fastening aid, because there is no point insulating a screw that is attached to a large non-insulated plate. I coated the entire screw as both a double fastening method (the mechanical lock washers really don't need back-up though) and to insulate the entire capacitor. To accomplish this I had my plates anodized as well, which insulates the outside. I did this to cover the very very remote possibility ( 1 in a million chance) that if the plates came loose they could not make an electrical contact with the inside of the tank. This is a very low voltage application and the chance of a spark is again extremely remote, but it is possible if the plates came loose and contacted the walls of the tank.

I hope that answers your question. Happy building.