Maretron FPM100 Theory of Operation, Accuracy of Tank Level Measurement, Revision, Page

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oConfigure for Tank Depth and Shape

ƒConfigure or Program the Tank Depth (Section 3.3.5.1)

ƒCustom Calibration (Section 3.3.5.2)

1.6Theory of Operation

The FPM100 operates by measuring the current transmitted by pressure transducers. When you are using the FPM100 in conjunction with a pressure transducer to perform tank level measurement, it is important to understand the relationship of tank depth, the range of the pressure transducer, and the accuracy of the resulting tank level reading.

1.6.1Choosing a Pressure Transducer Mounting Location for Tank Level Measurement

Choosing a proper mounting location for pressure transducers is critical to obtaining accurate tank level measurements. The pressure transducer should be mounted as close to the bottom of the tank as possible, as the pressure transducer will not be able to measure fluid levels below the pressure port on the transducer.

1.6.2 Accuracy of Tank Level Measurement

Maretron offers two pressure transducers that are suitable for indicating tank levels: a 0-3 PSI transducer and a 0-5 PSI transducer. For maximum accuracy, you should always use the transducer with the smallest range that is sufficient for your application.

The accuracy of these transducers is specified to be ±2% full scale. However, if you are using a transducer to measure the level of a tank where you are using only a portion of that transducer’s range, the accuracy will be less than this. For example, if you are using a 0-3 PSI (0-0.21 bar) pressure transducer to measure a tank level of water in a 41.5” (1.05m) deep tank, the pressure measurements will vary over a range of 0 to 1.5PSI (0 to 0.10 bar) – only half the designed range of the pressure transducer. Therefore, the ±2% full scale accuracy specification of the transducer means that the accuracy of the transducer in this example will actually be ±4%. You can use the table in Figure 1 below to look up the depth of your tank and see the actual accuracy for either a 0-3 PSI (0-0.21 bar) transducer or a 0-5 PSI (0-0.34 bar) transducer.

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