| 摘要 |
A capacitive sensor for water level measurement in an oil tank is sensitive to all kinds of parasitic capacitances up to an input capacitance of a measuring instrument. In a "one port measurement" with "active guard" said parasitic capacitance of the input of a measuring instrument can be prevented by using "charge/discharge" as the measuring method and to have the measurement of the amount of charge that flows thereby take place by means of a charge-controlled oscillator. The output frequency of the charge-controlled oscillator is a measure for the amount of charge that has flown through, and that in turn is a measure for the capacitance of the sensor, which in turn is a measure for the height of the water at the bottom of the oil tank. |
