We understand the features of the operation of capacitive fuel level sensors.

The fuel level sensor further DUT is  a capacitive meter, the principle of which is based on measuring the level between two electrodes - two tubes of different diameters. The principle of measurement is based on measuring the level, not the volume of fuel!
 

Factors affecting the error

Tilt of the vehicle when refueling.

Refueling on uneven terrain can cause fuel measurement errors of up to 4%. The lower the level in the tank, the greater the inaccuracy due to the baffles inside the tank, as the fuel flows towards the slope more.

Under ideal conditions, the FLS is mounted in the center of the fuel tank, and

this fuel error can be minimized, but it is not always possible to put the sensor in the right place, since there may be a standard sensor, an intake, a partition inside the tank or a clamp holding the tank, so the sensor can be installed with an offset  .


Fuel composition.

FLS determines the level by measuring the dielectric component, that is, it measures the electrical resistance of the fuel. Because of this, the size of the inaccuracy may depend on the winter / summer fuel and additives in it. The error of the fuel level sensor for different types is up to 1%. With the same volume of summer / winter diesel fuel or fuel filled at different gas stations, the FLS at the output will give different readings. To exclude this, it is necessary to calibrate the tanks with a certain fuel and operate the vehicle only on the brand of the fuel on which the tank was calibrated.

Temperature.

Everyone knows that a material contracts when cooled and expands when heated. The specific change in fuel when the temperature changes by 1 degree per 1000 liters is 1 liter, therefore, if there are 500 liters in the tank and the temperature outside has dropped from 0 degrees to -10 degrees, then the fuel level in the tank will change from 500

liters up to 495 liters, and when heated by 10 degrees, the level will change to 505 liters.

For example: A car drives up to a gas station with a tank of 200 liters and the driver fills up 200 liters, the temperature at the gas station in the underground tank is about 0 degrees, and on the street it is -20, by the end of refueling, underfilling according to the FLS will be determined in the amount of 2 liters, that is, the measurement error will be 1% of the filled volume.

Tank shape .

The error of the LLS may be related to the shape of the tank. On some types of vehicles, the tank may have an "irregular" geometric shape, which is why the FLS is placed below the actual upper point of the fuel level limit; in such cases, the FLS cannot take into account fuel filled above its upper limit. A similar situation can also be observed on equipment with a large neck and, when refueling "under the cap", some amount of fuel may not be taken into account.