CS01 and CS02 RF capacitance electronic level measurement utilizes the same fundamentals as any electronic capacitor (diagram A). A capacitor is formed when an AC signal is applied across two conductive plates separated by an insulating medium, or dielectric. The value of a capacitor is determined by the:
1. Area of the conductive plates (A)
2. Distance between the plates (D)
3. Dielectric of the insulating medium between the plates (E)
Capacitance = E*A/D
The resultant capacitance value increases as the dielectric increases. Capacitance is measured in an extremely small unit called a pico Farad (pF).
In industrial applications, (diagram B), the probe is one plate of the capacitor, the outer shield is the other plate (ground reference). The insulating material that separates them is the dielectric. A tank that is empty is actually filled with air that has a dielectric of 1, the baseline of the dielectric scale. All materials have a dielectric higher than air, (e.g., oil = 2.5, alcohol = 18, tap water = 80, etc). As a tank is filled with media, the air (dielectric 1) is being displaced by the media having a higher dielectric; consequently, the amount of capacitance being generated between the center probe and shield increases. This capacitance change, corresponding to the rising or falling of media in a tank, can be detected by the transmitter yielding a continuous output.