Endress+Hauser Liquiphant FTL51/FTL31 and similar tuning-fork level switches output a frequency that depends on whether the fork is in air or immersed in liquid. The reference frequencies follow the NAMUR NE 43 convention so that diagnostic faults (broken wire, sensor failure) are distinguishable from normal operating states.

This calculator gives a quick verdict for a measured frequency — useful for commissioning, troubleshooting and proof tests.