Fuel level sensor (fuel sender and tank level sensor)

01

Choose sensing principle and output signal

US patent 4,931,764 (Low wear resistor card for use in a liquid fuel sender circuit) describes conventional automotive fuel level systems in which a float on a pivoting rod sweeps a wiper contact over a resistor card, selecting a resistance that indicates fuel level. The card carries metallised conductor pads joined by thick-film resistive ink, with resistance values set empirically for the shape and volume of the tank; the example card gives 15 Ω at empty to 160 Ω at full. [1]

Aether describes the float connected to a variable resistor or potentiometer as one fuel level sensor working principle and lists capacitive, mechanical, Hall-effect, ultrasonic and other level sensor types. [3] Dianyingpu lists its DYP-U02 ultrasonic fuel level sensor, which measures liquid height without contact through a 0.6–5 mm metal or plastic tank wall, over 5–100 cm with 1 mm resolution and 5 mm accuracy, using a 2.0 MHz transducer, temperature compensation, IP67 potted metal housing, a built-in magnet for steel tanks, −20 to +60 °C operation and RS485, RS232 or 0–5 V output. [2]

Editorial note: a replacement sender must match the gauge's resistance range at empty and full; give the supplier the gauge or controller input and the tank drawing.

Give the supplier the tank type, material, shape and depth, fuel (petrol, diesel, biofuel), vehicle or equipment, gauge or telematics input (resistance range, voltage, digital bus), required range, resolution and accuracy, mounting (top flange, side, external), vibration and temperature, ingress protection, and calibration to tank volume.

02

Check range, accuracy and wear over service life

The same patent explains that while the card is immersed, fuel lubricates the wiper on the metallised contacts, but when the fuel level is below the card the wiper wears the contacts; vehicles shipped long distances with a constant fuel level suffered repeated wiper movement from vibration and occasional wear-through to the substrate, leaving dead spots that upset the fuel gauge. Its remedy is a thick-film resistive layer about 0.012 mm thick over the pads, adding contact resistance of about 0.01 Ω. [1]

Editorial calculation: 0.01 Ω of extra contact resistance is under 0.1% of the 15 Ω empty value; the 145 Ω span from 15 to 160 Ω is spread over the tank depth according to its shape. For the ultrasonic sensor, 5 mm accuracy is 1% of a 500 mm deep tank and 0.5% of its 1 m maximum range. [1] [2]

Editorial note: ask the supplier for durability test cycles, vibration test data and fuel compatibility (including biofuel blends) for the sensing element and seals.

03

Correct capacitive readings for fuel blends

US patent 5,051,921, filed in 1989 by the David Sarnoff Research Center, explains why a capacitive fuel level probe calibrated for gasoline reads wrongly when the tank holds a gasoline–methanol or gasoline–ethanol blend: the blends have dielectric values different from pure gasoline, and those differences cause errors in capacitive or inductive level readouts. The patent gives the dielectric constant ε as about 2 for gasoline, about 24 for ethanol and about 30 for methanol. [4]

Its remedy uses two interdigitated capacitors: one mounted vertically to sense level, and a second mounted horizontally near the tank bottom, always immersed, to sense composition. The immersed capacitance equals approximately ε times the capacitance in air, so the processor solves for ε and scales the level signal so the output slope stays constant whatever the blend. In the worked example the level capacitor measured 159.0 pF in air and the composition capacitor 80.0 pF; the composition meter was calibrated linearly from 0 V for 100% gasoline to 5.0 V for 100% methanol. [4]

Editorial calculation from the patent's relation C(fuel) ≈ ε × C(air): the 80.0 pF composition capacitor would read about 160 pF in gasoline (ε ≈ 2) and about 1,920 pF in ethanol (ε ≈ 24), a twelvefold change. [4]

Editorial note: when ordering a capacitive sender, state the fuel and blend range and ask whether the probe carries a reference or composition cell, or how the supplier calibrates for each fuel.

04

Compare what suppliers offer

Suppliers linked to this page list fuel level sensors; each card links to the page reviewed.

The suppliers reviewed list float, capacitive or ultrasonic fuel level sensors; ask each for principle, output and resistance range, accuracy and how tested, fuel compatibility, ingress protection and calibration method.

05

Trace the sensor parts

This is a functional reference built from the sources cited; it is not one maker's design.

06

Fill the specification fields with values for your tank

A fuel level sensor quotation needs values for your tank. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the tank, fuel and signal data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Tank: [type; material; shape; depth]
Fuel: [petrol; diesel; biofuel]
Principle: [float; capacitive; ultrasonic]
Signal: [ohms empty/full; voltage; RS485]
Performance: [range; resolution; accuracy]
Environment: [vibration; temperature; IP]
Calibration: [tank volume table]

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