What is the best way to measure the level of diesel fuel in a very shallow tank, for example, one that is only 20 centimetres (about 8 inches) deep?
Measuring liquid level in very shallow tanks presents a challenge, as standard submersible sensors may have a minimum range that is too high, leading to poor measurement resolution. For a tank just 20 cm deep, it is crucial to select a sensor with a very low measurement range.
A suitable solution is a pressure transmitter with a variable capacitance flush ceramic diaphragm. These sensors are available with a low pressure range of 0 to 40 millibar (mbar), which corresponds to 0 to 40 centimetres of water column (cmH2O).
Featured shallow depth liquid level sensor products
LMK351 High Overpressure Flush Level Transmitter - Flush capacitive ceramic pressure sensor for measuring corrosive and viscous liquid level from levels 0.4 metres of water up to 200 mH2O. 
LMK458 Marine Approved Hydrostatic Level Transmitter - Marine approved level transmitter with 4-20mA output for measuring level of contents inside ship ballast, fuel, liquid cargo or wastewater tanks
To determine the pressure range needed, we can calculate the pressure exerted by the diesel fuel. The specific gravity (SG) of diesel is approximately 0.832. Therefore, a 20 cm depth of diesel exerts a pressure equivalent to: 20 cm x 0.832 (SG) = 16.64 cmH2O.
This pressure (approx. 16.6 mbar) fits comfortably within the 0-40 mbar range, utilizing over 40% of its measurement span. This ensures a much better signal resolution compared to a sensor with a higher standard range, such as 100 mbar (1 mH2O).
Furthermore, the flush diaphragm design is particularly advantageous for diesel fuel, which can be viscous. A flush surface prevents the accumulation of residue that could otherwise clog a sensor with a recessed diaphragm, ensuring accurate and reliable readings over the long term.
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