| 摘要 |
A circuit for measuring the capacitance of a variable capacitor by charging the variable capacitor to a fixed voltage at the same time that a fixed reference capacitor is charged to an output voltage which upon balance of the circuit will represent the value of the variable capacitor. The charged capacitors are connected in a series circuit which may include a fixed sampling voltage during the next phase of the two phase measuring cycle and the charges are allowed to redistribute. The voltage drop across the reference capacitor at the end of the redistribution of charge is compared to a predetermined value established as the balance value and the output voltage is varied in sense and direction to tend to bring the voltage drop to equality with the balance value so that the balance value after a number of measuring cycles will be representative of the capacitance of the variable capacitor. A second reference capacitor which is switched between the sampling voltage potential and circuit common can be added to the network by connecting it to the node. This added reference capacitor will provide for offset in the range to be measured. If the variable capacitor is a capacitive humidity sensor the reference capacitors and the variable capacitor should be constructed at the same time by the same process and of the same materials so that they all have the same characteristics thus making unnecessary any trimming of the circuits used for measuring the variable capacitor. |
