Hello,

I am a hardware developer working on a project related to fuel monitoring and I am a little confused about a couple of things, it would be really great if someone could help me out with it.

The fuel gauge in vehicles is attached to a sender unit. Between the fuel gauge that consists of a float and the needle you can see on the indicator unit, there is a damping circuit placed somewhere. What this damping unit does is damp the constant vibrations from the float which may come as a result of fuel sloshing. I want information regarding this damping circuit. I need to know the following:

1) Where exactly is this circuit placed?
2) The input voltage of the sender unit is 12V however, the fuel gauge would be damaged if 12V flows through the gauge directly. I have observed that int input on the gauge itself is from around 7V to 12V, there is a resistor placed in between. I want to know the value of this resistor in ohms.
3) There's roughly a 5V potential difference in the gauge, I need to know the current consumption of the fuel gauge.

If anyone can answer these questions, it would be super helpful.
TIA!

 

Starting around ~1995-ish, some manufacturers started using complex and proprietary
methods of measuring Fuel-Tank-Levels.

Before this, the common operating principles were quite crude,
but at least "most" of them operated on "quasi-standard" Voltage-Levels,
and none of them employed any type of Semi-Conductor-Circuits.

In Modern Cars the Fuel-Level is calculated by the Engine-Computer.

You need to be very specific in describing the problem You are
trying to solve before any assistance can be given.
.
.
.

 

In answer to your questions:
1) There is no damping circuit in old-school gauges. Inertia of the sender components and the gauge movement provides a little damping, but gauge readings can jitter. Modern gauges feed signals to the engine management computer, which can process the sender data digitally.
2) 12V doesn't flow. Current flows. The resistor value in old gauges depends on the ammeter's sensitivity and can vary according to make/model of the vehicle.
3) Current depends on the old gauge's internal resistances and on the sender's resistance.

 

Historically the fuel gauge used a bimetallic strip with resistive wire adjacent or around it. With a regulated voltage passing through that resistance in series with the variable resistance in the tank there was natural damping of the gauge needle. Simple and effective although not very accurate

 

Later ones used two coils at right angles to each other, and a highly frictionally damped needle. The direction that the needle points is determined by the relative currents in the two coils (works like a stepper motor. One has a fixed current and the other is in series with the sender.
They can be identified as the needle does not return to zero when the engine is off.
They went out of fashion because it made if obvious to a thief which vehicles had plenty of fuel in the tank.