Fuel Gauges :: essays research papers

the is cut and pasted off howstuffworks.com to get an account If you're like me, you like to squeeze every last mile you can out of your tank of fuel. If you could get 20 miles extra from each tank, that could save you two or three trips to the gas station over the course of a year. The main impediment to stretching your mileage is the fuel gauge on your car, which makes you think you have less fuel than you actually do. These devices are notoriously inaccurate, showing empty when there are gallons left in the tank and showing full for the first 50 miles. In this edition of HowStuffWorks, we'll learn why our fuel gauges behave the way they do. There are two main parts to a fuel gauge: the sender, which measures the level of fuel in the tank, and the gauge, which displays that level to the driver. First, let's see how a typical sender works. The sending unit is located in the fuel tank of the car. It consists of a float, usually made of foam, connected to a thin, metal rod. The end of the rod is mounted to a variable resistor. A resistor is an electrical device that resists the flow of electricity. The more resistance there is, the less current will flow. In a fuel tank, the variable resistor consists of a strip of resistive material connected on one side to the ground. A wiper connected to the gauge slides along this strip of material, conducting the current from the gauge to the resistor. If the wiper is close to the grounded side of the strip, there is less resistive material in the path of the current, so the resistance is small. If the wiper is at the other end of the strip, there is more resistive material in the current's path, so the resistance is large. In the sending unit, the fuel has to drop below a certain level before the float starts to drop. When the float is near the top of the tank, the wiper on the variable resistor rests close to the grounded (negative) side, which means that the resistance is small and a relatively large amount of current passes through the sending unit back to the fuel gauge. As the level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current sent back to the gauge decreases.