Fuel level sensing Using multiple Reed Sensors

Automobile fuel level gauges serve a crucial role in providing drivers with real-time information about the volume of fuel remaining in the tank. These gauges rely on potentiometric feedback mechanisms to accurately measure fuel levels, a process facilitated by the integration of reed sensors, resistors and magnets within the fuel tank.

Inside the fuel tank, a magnet attached to a foamed float interacts with reed sensors to generate potentiometric feedback signals.

These signals are then processed by a printed circuit board (PCB), which combines the reed sensors with resistors to produce the desired output. The design of these PCB circuits must be carefully tailored to accommodate the limited space within the fuel tank, particularly in smaller vehicles where the tank dimensions are characterized by a long and wide shape with minimal height.

To ensure reliable operation within the confined space of the fuel tank, specially designed reed sensors with close differential capabilities are utilized. These sensors are strategically mounted in close proximity to one another, guaranteeing continuous actuation of at least one reed switch at any given time. Additionally, integrated resistors are incorporated into the PCB design to further optimize performance and accuracy.

In larger vehicles with spacious fuel tanks, standard reed switches with a regular 45% differential can be employed. Despite variations in tank size, the PCBs generate potentiometric feedback across two outputs, with resistance levels corresponding to the fuel volume. This allows the fuel level gauge to provide drivers with accurate readings ranging from a full tank to an empty tank or vice versa.

One of the key advantages of using reed sensors in fuel level sensing applications is their hermetically sealed design, which ensures safe and reliable operation even in explosive environments such as fuel tanks. This feature enhances the overall safety and durability of the fuel gauge system, making reed sensors the preferred choice for automotive applications where precision and reliability are paramount.

Application Classification

Applications are classified as Position Sensing, Pulse Counting, Electromagnetic or Relay, Temperature Sensing or Magnet Biasing types. This application is classified as follows and the link gives more information on best practices to help select the most suitable AT band and matching magnet.

Position sensing Type

When an application requires the end position of a movement sensed, or the sensing of a part when it comes into a zone, or when the Continue reading -> Jul 14, 2025

Recommended Products

The Reed Switches and Sensors used in such fuel level sensing applications need to be robust, durable and efficient in meeting a high life expectancy. Our engineers work hard in life testing our products under various conditions, and our intention is to ensure end product durability and life. Although we wouldn’t want to restrict any of our products for use in only certain applications, the recommended products for use in this application are listed below.

Micro Miniature Reed Sensor, R3

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Micro Miniature Reed Switch, MM-1018

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Micro Miniature PCB Mountable Reed Sensor, MS-105

Drawing of MS-105 Reed SensorDrawing of MS-105 PCB Pad Layout starFeatures10W Contact Rating. 12.7 mm PCB Pitch. Normally Open Continue reading -> Jun 18, 2025

Reed Sensor with Integrated Resistor, IR-xxxx

IR-xxxx Reed Sensor DrawingIR-xxxx Reed Sensor PCB Layout Drawing starFeatures10W Contact Rating. Includes integrated Resistor. Continue reading -> Sep 3, 2024