General Aircraft Technical Knowledge Practice Test

A float-operated device that varies resistance is used to translate liquid level into an electrical signal. In this type, the float rides with the liquid level and moves a contact along a resistor (a potentiometer or variable resistor). As the float rises or falls, the resistance changes in proportion to the level, and the indicator circuit converts that changing resistance into a fuel quantity reading. This is different from other gauge methods: capacitance gauges rely on changes in capacitance rather than resistance, and mechanical gauges use direct mechanical linkage to move a pointer without changing electrical resistance. Ratiometer-type instruments compare resistance values but don’t rely on a float changing a single resistance to produce the reading.