| 摘要 |
<p>A method for the measurement of capacitances, in particular of low capacitances, utilizes measurement electronics which includes a measurement oscillator whose output frequency is a function of the capacitance to be connected to the input terminals of a circuit determining the frequency of such oscillator. In the method, two reference capacitances are used, whose electrical values are placed within the range of measurement and which are connected, being alternately exchanged with the capacitance or capacitances to be measured, to the measurement oscillator while making use of a switching arrangement. Two external auxiliary references are used in the method. The auxiliary reference signals obtained from the auxiliary references are compared with the corresponding output signals of the measurement electronics, derived from the reference capacitances. Signals representing the differences between the output signals and the signals coming from the external auxiliary references are formed. Feedback signals controlling the measurement electronics circuit are formed from the signals. The measurement electronics is controlled by the feedback signals in such a direction that the differential signals approach zero or a preset corresponding value. The output signal corresponding to the capacitance to be measured is determined by the measurement electronics adjusted correctly. The object is to provide a more precise method as well as such a two-reference measurement method and measurement circuit in which complicated computation operations are avoided. The output variables corresponding to the reference detectors remain unchanged, even if the measurement electronics should creep. Such a circuit may be used in the telemetry of radiosondes in the measurement of atmospheric pressure, temperature and/or humidity.</p> |
