Fuel level sensor

A fuel level sensor is a device used to measure the amount of fuel within a container, most commonly a vehicle's fuel tank. The measurement is then typically displayed to an operator via a fuel gauge. These sensors are used in automotive, aviation, and industrial applications to provide operators with fuel level information.

Aftermarket fuel level sensor, fuel gauge to control fuel

Fuel level sensors are produced and utilized in two distinct market segments. Original Equipment Manufacturer (OEM) sensors are installed in vehicles during production by automotive manufacturers and are a standard component of modern passenger and commercial vehicles.^[1] In contrast, aftermarket fuel level sensors are designed to be installed after a vehicle's purchase, typically as part of a fleet digitalization process. These sensors are often installed with a telematic control unit as part of a fuel management system for commercial fleets to help prevent fuel theft and track consumption.^[2]

How it works: core technologies

While the goal is the same, fuel level sensors operate using several different technologies. The choice of technology often depends on the required accuracy, the type of fuel, and the cost.

Float-type (potentiometer)

This is the most traditional and common type of sensor found in passenger vehicles. It consists of a buoyant float connected to a metal rod, which is in turn attached to a variable potentiometer. As the fuel level in the tank changes, the float moves up or down, causing a sliding contact on the potentiometer to change its resistance. This change in electrical resistance is then translated into a fuel level reading on the dashboard gauge.^[3]

Capacitive

Capacitive sensors are a more advanced, no-moving-parts alternative, common in high-precision aftermarket applications. They consist of two concentric tubes that act as the plates of a capacitor. The fuel itself serves as the dielectric medium. Because the dielectric constant of fuel is different from that of air, the sensor can accurately measure the fuel level by detecting the change in capacitance as the tank empties and more of the sensor is exposed to air.^[4]

Ultrasonic

Ultrasonic sensors are another non-contact method. A transducer, typically mounted on the outside of the tank, sends an ultrasonic pulse toward the fuel. The sensor then measures the time it takes for the pulse to reflect off the surface of the fuel and return. By knowing the speed of sound, the sensor can calculate the distance to the fuel's surface and thus determine the fuel level.

Installation of Aftermarket Sensors

The installation of high-precision aftermarket sensors, such as capacitive or ultrasonic models, is a common procedure in fleet management. Unlike OEM sensors, which are integrated during manufacturing, aftermarket sensors must be retrofitted.

This process typically involves drilling a new hole in the fuel tank, often in or near its geometric center, to ensure the most stable and accurate readings. The sensor is then inserted and securely sealed to prevent leaks.^[5]

Once installed, the sensor must be connected to a GPS tracking unit or telematic control unit to transmit its data. This is achieved in two common ways:

• Wired Connection: The sensor is connected to the tracking device using a cable, typically using a serial interface like RS-485 or RS-232, or an analog voltage output.
• Wireless Connection: Many modern sensors use Bluetooth to transmit data wirelessly to a nearby telematics device, which simplifies the installation process by eliminating the need to run cables along the vehicle's chassis.^[6]

Applications

Automotive and transportation

Industrial and bulk storage

See also

• Fuel gauge
• Fuel-management systems
• Telematic control unit
• Telemetry