| 摘要 |
The invention concerns a method for the measurement of capacitances, in particular of low capacitances, in which method a measurement oscillator (10) is used, whose output frequency (f) is a function (f = F(Cin)) of the capacitance (Cin) to be connected to the input terminals (a, b) of the circuit determining the frequency of the said oscillator. In the method, a known reference capacitance (CR) is used, which is connected, being alternatingly exchanged with the capacitance (CM) to be measured, to the input terminals (a, b) of the measurement oscillator (10) while making use of a switching arrangement. The capacitance to be measured (CM) and the reference capacitance (CR) are connected, alternatingly one after the other, to the input terminals (a, b) of the same said measurement oscillator (10) for the time (T1 and T2) of an equal number (N) of cycles (T = 1/f) of the measurement oscillator (10). The frequency (f) dependent on the capacitances (CO, 6R, CM) connected to the input terminals (a, b) of the measurement oscillator (10) is passed to a distributor (11), whose distribution ratio (N) directly determines the number (N) of the said switching cycles. The square wave (Vin) obtained from the output (d) of the said distributor (11) is used for controlling the switches (k1, k2) which, while alternatingly exchanging them, connect the known reference capacitance (6R) and the capacitance (6M) to be measured, each in its turn, to the input terminals (a, b) of the measurement oscillator (10), so that an exchange of the level of the said square wave (Vin produces an operation of the said switches (k1, k2) in such a way that the capacitance (CM) to be measured that is the next one in the sequence is connected in place of the reference capacitance (CR) and vice versa. The invention also concerns the use of the method in radiosondes, in telemeter measurement of pressure, temperature and/or humidity. By means of the invention, and accurate measurement circuit is obtained by means of which the effects of switching phenomena can be eliminated. |
