The level measurement of a medium in a tank, as shown to the right, is accomplished by taking advantage of the capacitance theory. The tank wall, the probe and the medium are all capacitors. A high frequency sine wave is then applied between the probe and the tank wall. The level change of the medium will consequently change the current of the applied sine wave. From the formula Z=1/(2pfc), we know that if the capacitance increases, the impedance gets smaller and the current gets bigger. If the capacitance decreases, the impedance gets bigger and the current gets smaller. When the small current change is amplified and sent to a MG series meter, the output signal is 0/4-20mA or 0-10VDC.

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