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).
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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
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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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