Capacitive sensor and method of measuring changes in capacitance

Apparatus for measuring the capacitance of a capacitor comprising:

• means for providing a continuous source of constant electrical current to an electrode of the capacitor;
• separate means for generating a first series of timing pulses;
• comparator means for comparing the voltage on the capacitor to a reference voltage;
• means for generating an electrical signal when the comparator means indicates that the voltage on the capacitor reaches a first voltage which just exceeds the reference voltage;
• means for counting the first series of timing pulses emitted by its generating means from the time that the charging of the capacitor beings until the electrical signal is generated;
• means for generating an output signal corresponding to the number of timing pulses counted during the time required to charge the capacitor to the first voltage;
• means for converting the total count of the first timing pulses to an output signal representative of the magnitude of the capacitor;
• and
• the comparator being connected to the counting means so that the output pulse from the comparator resets the counting means.