Abstract: The invention relates to an apparatus for measuring the capacitance between at least a conductive part of a wall of a vessel and a measuring electrode situated in the vessel and carrying a measuring voltage, comprising a measuring circuit and a compensating circuit for applying a compensating voltage as nearly as possible the same as the measuring voltage to conductors present in the vicinity of conductors carrying the measuring voltage, wherein the capacitance between the measuring electrode and the vessel wall is connected as frequency determining element in an oscillator, so that the frequency of the measuring signal is related to the value of the capacitance. Frequency is a quantity which can be measured much better, can be determined much more precisely, requires less complicated circuits and can be largely implemented in integrated form.

Abstract: The invention relates to an apparatus for determining the condition of a fluid in a space, comprising: a measuring electrode extending inside the space; a second electrode placed in the space; and a measuring circuit for measuring the impedance between the measuring electrode and the second electrode and calculating the condition from the impedance, wherein the measuring electrode extends at least partially uncovered in the space.According to a preferred embodiment the apparatus is therefore provided with a measuring circuit which is adapted to measure the ohmic impedance between the measuring electrode and the auxiliary electrode. As stated, this provides the option of measuring the impedance of the substance present in the vessel so that with determined material properties it is possible to arrive at a better and more accurate measurement result.It is pointed out herein that the present electrode also enables determining of the capacity between electrode and second electrode.