Capacitance Plates -- How to test functionality

[aparchment]

Guys:

How do you test the functionality of the capacitance plates in the fuel tank? I want to do this before closing the tanks. I assume I use a voltmeter and set it to measure resistance, but that's where my knowledge ends.

CJ, or others, if you have time could you explain how this works.

Antony

[4kilo]

Antony,

There should be no measurable resistance between the plates or between the plates and the center conductor of the connector. There should also be no resistance between the outside conductor of the connector and the ribs in the tank. When you have checked those, make sure that there is no connection between the plates and the rest of the tank (should have infinite resistance).

A simple capacitor is formed by having two metal plates seperated by a dielectric. In a store bought capacitor, this is usually something like two metal foil sheets seperated by some type of plastic and then rolled up into a small package (oversimplified, but you get the idea).

In our fuel tanks, the capacitor is formed by the plate and the wing rib. These two plates are seperated by either fuel or air. Since air and fuel have different dielectric constants (ie, the capacitor can hold more charge if there is fuel in the gap than if air is in the gap), as fuel fills the gap between the plate and the rib, the capacitance of the sender changes.

One last thing - not all fuel gages can measure capacitance. There are several small computer chip type converters available which will convert capacitance to resistance. Most fuel gages and all of the EFIS and engine monitor systems I am familiar with can measure the resistive output from one of the converters.

Pat

[aparchment]

Thanks Pat:

I think I get it.

I will give it a shot this week and see how I make out.

Antony

[Wicked Stick]

I seem to remember the instructions explaining how to check them pretty much the same way. But Pat's explanation does give better details.