| 摘要 |
<p>The invention relates to a measuring circuit for measuring the capacitance of a measuring capacitor (C x ) which has a first and a second measuring electrode and which is coupled to a charging resistor (R 1 ), wherein the frequency of the output signal (u, f) of the measuring circuit is a measure of the capacitance of the measuring capacitor, and the measuring circuit comprises a buffer amplifier (6, 14) with which the point between the charging resistor and the measuring capacitor is connected to the other components of the measuring circuit. The buffer amplifier changes the high impedance level of the combination of the measuring capacitor and the charging resistor to a level at which low-pass filters can usefully be applied. Buffer amplifiers are also available with an input capacitance and input resistance such that the buffer amplifier already functions in itself as a low-pass filter. An external filter is then not necessary because the filter is already present in the buffer amplifier.</p> |
