Here's how it works...
In its simplest form, a capacitor consists of two flat plates separated by a dielectric. The amount of capacitance is determined by:
1.) the size of the plates, 2.) the distance between the plates, and 3.) the dielectric constant of the material between the plates.
For level measurement, one plate is the metallic tank wall, the other plate is the probe, and the process media (or probe sheath) is
the dielectric. Since all measured materials will have a dielectric greater than air, as the process media rises, covering more of
the probe, the capacitance rises. However, the method of measuring the capacitance is what makes NEW WAVE CAPACITANCE™ unique (see
Figure #2).
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The basis of operation uses the principle of a timed period of charge transfer to an unknown value (C x ). A constant current source
is used to charge the unknown probe capacitance (C x ) to a fixed positive amplitude (V + ). When the voltage is reached, the polarity
shifts to charge C x to a fixed negative amplitude (V - ). The polarity is shifted again to bring the net overall integrated charge
to zero. This bipolar charging sequence is used to prevent the possibility of plating. A fixed time window is set (T 0 to T 4 ). This
time period is equivalent to the selected calibration range of the unit. The ratio of the actual charging time (T 0 to T 3 ) to the
fixed time window (T 0 to T 4 ) is directly proportional to the ratio of the probe capacitance (C x ) to the selected range (C RANGE
). This technique is similar to the method used in Digital Volt Meters (DVM), and results in an extremely high degree of accuracy,
linearity, and repeatability.
This device is protected by multiple patents both domestic and international.
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Gagecocks