Sounds about right for a fuel gage


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Posted by D Sherman on Saturday, November 01, 2008 at 20:24:15 :

In Reply to: ground short to gauges posted by Robert N. on Saturday, November 01, 2008 at 18:15:32 :

I don't think the other gages should have any continuity to ground, but the fuel gage does. It operates on a balanced principle with two coils. B+ voltage goes into the gage via one terminal. One coil, pulling the needle one way, is grounded to the gage housing, which theoretically should be grounded to the chassis via various screws along the way. The other coil is grounded to some varying degree by the sender in the fuel tank.

The reason for this is to compensate for varying battery voltage. If the battery voltage drops, for example, the current through both coils will drop, canceling out the pull on the needle. The cancellation is imperfect because the resistances on both sides aren't the same, but it's a big step in the right direction and definitely helps out compared to having just one coil. If I get a chance, I'll take a look at some of my other military gages and see if any of them have 2 coils, but I don't think they do.



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