Katerina Swanson
Fuel tank levels can be read using voltages in a variety of ways. One common method is to use a fuel level sensor or a float connected to a potentiometer, which sends an analogue voltage signal to a fuel sender unit. Another approach is to use a capacitor with two plates, where the capacitance changes based on the presence of gasoline or air between the plates. Circuits using LMC555 chips can also convert resistance values into a square wave with a varying pulse width, which can be used to determine fuel levels. Additionally, fuel tank level sensors like the ESP8266 and the Jaeger sensor can be connected to a microcontroller or a board to read voltage levels.
| Characteristics | Values |
|---|---|
| Fuel level measurement in most cars | Floater connected to a potentiometer |
| Panel reading | Analogue voltage signal from the fuel sender unit |
| Cheapest way to read voltage | Electric imp |
| Power supply | 12V:3.3V switching power supply |
| Fuel level sender | Low resistance rheostat |
| Capacitance | Changes as the permittivity of the space between the plates changes |
| Fuel sensor | A floating cork inside a metal box |
| Formula for voltage | Voltage = Reference Voltage x (sensor resistance / total resistance) |
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What You'll Learn
Using a fuel level sender
In most cars, the fuel level is measured by a floater connected to a potentiometer. The panel reads an analogue voltage signal coming from the fuel sender unit. The fuel sender unit, also known as a level sensor, is a low-resistance rheostat.
To read the fuel tank level with voltages, you can use an ESP8266 Serial WiFi Wireless Transceiver + Voltage Divider sensor for Arduino. This device takes care of the WiFi and has a suitable ADC (10-bits) for the gas tank level. The ESP8266 runs on 3.3V, so it would be ideal to use a 12V:3.3V switching power supply.
Another option is to use an electric imp, which will require some electronic tinkering because the voltages won't match and it needs a breakout board. However, the WiFi functionality is already taken care of.
If you want to calculate the voltage output from the sender, you can use the formula: Voltage = Reference Voltage x (sensor resistance / total resistance). The total resistance is the pullup value (in ohms) plus your sensor resistance. For example, if you have a 5V source and a sensor resistance of 89.8 ohms, the formula would be: Voltage = 5 x (89.8 / (1000+89.8)) = 5 x 0.0825 = 0.412v.
Additionally, there are common circuits using LMC555 chips that can convert a resistance value into a varying frequency square wave or a square wave with a pulse width that varies with resistance. These circuits use a single chip and a few resistors and capacitors.
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Calculating fuel sender voltages
One common type of fuel level sensor is a floater connected to a potentiometer, which provides an analogue voltage signal that corresponds to the fuel level in the tank. The voltage signal is typically in the range of 0 to 5 volts, and it needs to be interpreted to determine the actual fuel level.
To calculate the voltage output from the sender, you need to consider the resistance values in the circuit. In a voltage divider configuration, the fuel level sensor forms one part of the circuit, with a known resistor in series. By measuring the voltage drop across the fuel level sensor, you can determine the fuel level. The formula for calculating the voltage output is:
> Voltage = Reference Voltage x (sensor resistance / total resistance)
For example, if you have a 0-90 ohm fuel sender in an 80-litre tank, you can measure the resistance at different fuel levels. Let's say at 80 litres, the resistance is 89.8 ohms, and you want to calculate the voltage output. The total resistance is the sum of the pullup resistor value (1000 ohms) and the sensor resistance (89.8 ohms). Using the formula, the voltage output at 80 litres would be:
> Voltage @80 litres = 5 x (89.8 / (1000 + 89.8)) = 5 x 0.0825 = 0.412 volts
It's important to ensure that the circuit can handle voltage variations. As mentioned in one source, the voltage divider approach ensures that when the tank is empty, the voltage is 5V, and when the tank is full, the voltage is 0V. Additionally, protective measures should be implemented to prevent damage to the ADC in case the sensor becomes disconnected. This can be achieved by using a 10 kΩ resistor in series with a 5.1 V Zener diode to ground.
Overall, calculating fuel sender voltages requires an understanding of voltage dividers, resistance values, and the characteristics of the fuel level sensor. By applying the appropriate formula and considering the specific resistance values at different fuel levels, you can accurately determine the voltage output and, consequently, the fuel level in the tank.
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Using a capacitor to sense fuel levels
Capacitive fuel level sensors are devices that measure the level of fuel within a tank by detecting changes in capacitance. These sensors have become a vital technology in multiple industries, including automotive, marine, aviation, and industrial sectors. They are highly precise, resistant to mechanical wear, and able to operate in harsh environments.
The operation of these sensors is based on the principle of capacitance, where two conductive plates are separated by a dielectric medium, which, in this case, is the fuel, forming a capacitor. As the fuel level changes, the dielectric constant also changes, affecting the capacitance. This change is measured and interpreted by the sensor's electronics, providing an accurate fuel level reading.
The sensor includes a probe inserted into the fuel tank, which forms an electric field between itself and a reference electrode, creating an electric circuit. As the fuel level fluctuates, so does the dielectric constant surrounding the probe, resulting in variations in capacitance. The sensor then converts these changes into readable signals, offering precise measurements of fuel levels.
The AS8579 capacitive sensor is a notable example, capable of measuring the level of multiple liquids in a container. It employs a type of capacitive sensing technology called I/Q demodulation, which measures both the resistive and capacitive elements of a system's impedance. This method is highly sensitive to slight changes in capacitance, making it effective in detecting small fluctuations in fluid levels, such as gasoline in a tank.
To send fuel level readings via WiFi, additional components like the ESP8266 Serial WiFi Wireless Transceiver or a microcontroller can be used. These components can be integrated with the sensor to transmit fuel level data wirelessly to a remote monitoring system.
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Using a float to minimise sloshing
Fuel tank levels can be read using a voltage signal from a fuel sender unit. This is typically measured by a floater connected to a potentiometer.
Sloshing is the movement of liquid contained within an enclosed area, such as a fuel tank. It is an undesirable effect that can cause instability and even crashes and explosions. Sloshing occurs when there is an abrupt change in motion in a vehicle with a partially filled fluid tank. This causes the free surface of the liquid in the tank to distort, and the liquid moves in large amplitudes, exerting impact pressure on the tank walls. This can lead to structural and stability problems, with hydrodynamic forces acting on tank walls potentially causing fatigue damage or structural failure.
To minimise sloshing, manufacturers often design specialised baffles within fuel tanks. Baffles are sections within the tank that limit the amount of area available for the liquid to move, preventing large changes during manoeuvres. The number of holes in a baffle is also important, as the lateral force decreases as the number of holes increases. Some aircraft also use mesh or plastic bladders within the fuel tanks to prevent sloshing and maintain stability during extreme manoeuvres. The mesh is lined across the walls of the tank, taking up approximately 2% of the tank volume. It is important to note that the mesh only prevents the shift in CG during routine manoeuvres.
Another way to minimise sloshing is to distribute the fuel over several sections of the tank to prevent significant CG shifts. This can be done through the use of plastic bladders, which collapse as the fuel is depleted, or by using wing tanks that are subdivided into sections with a baffled design.
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Sending fuel level data via WiFi
In most cars, the fuel level is measured by a floater connected to a potentiometer. The panel then reads an analogue voltage signal from the fuel sender unit.
To send this data via WiFi, you can use an ESP8266, which has a suitable ADC (10-bits) and takes care of the WiFi connection. You will need to connect a small bit of circuitry between the ESP8266 and the level sensor (a low-resistance rheostat).
Another option is to use an electric imp, which will require some electronic tinkering as the voltages won't match, and it needs a breakout board. However, the WiFi functionality is effectively taken care of.
To power the ESP8266, you could use LiPo batteries, although these only last about a day, or you could recharge it from the car battery.
The ESP8266 can communicate with the car and server, and you can write a script to check the fuel level and send the data via WiFi to your smartphone or post it on Twitter.
Additionally, you can use a TTL ODB2 connector, which can be connected to an Arduino or Raspberry Pi to read the fuel level data and send it via WiFi.
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Frequently asked questions
In most cars, the fuel level is measured by a floater connected to a potentiometer. The panel reads an analogue voltage signal from the fuel sender unit. The fuel sensor is like a cork that floats up and down inside a metal box.
The cheapest way to read the voltage is to use an ESP8266 Serial WIFI Wireless Transceiver + Voltage Divider sensor for Arduino. It takes care of the WiFi and has a suitable ADC (10-bits).
The formula for calculating the voltage output is: Voltage = Reference Voltage x (sensor resistance / total resistance). The total resistance is the pullup value (in ohms) plus the sensor resistance.
Modern fuel tanks have a partition that envelopes the float to minimize sloshing. The float also has a delay so that it is not constantly changing readings when moving back and forth. Additionally, the baffle effect helps to reduce fuel sloshing.
