ELECTROSTATIC CAPACITANCE TYPE DISPLACEMENT METER

摘要

PROBLEM TO BE SOLVED: To improve the measurement accuracy and measurement range of an electrostatic capacitance type displacement meter which measures the change in the spacing between counter electrodes by utilizing the electrostatic capacitance formed between these electrodes. ;SOLUTION: The sensor electrode 5 with a guard ring set to face a measuring object is connected to the inversion input of an operational amplifier 9 via the central conductor 7a of a shielded wire 7 and a reference capacitor is connected between the output of this operational amplifier 9 and this input. The external conductor 7b of the shielded wire is connected to the non-inversion input of the operational amplifier 9 and the operational amplifier 9 and the reference capacitor are connected to a shielding case 8 for shielding static electricity, by which a detecting circuit 100 is constituted. This detecting circuit 100 is made into a floating structure with respect to the circuit ground together with the shielding case 8. The detecting circuit 100 is driven together with the shielding case 8 by an AC signal and further the amplitude of the AC signal is so controlled that the specified output of the detecting circuit 100 is obtd., by which the measuring capacitor is subjected to constant current driving and, therefore, the detection sensitivity is high. Since the amplitude value of the AC signal and the measured displacement are in a proportional relation, the excellent linearity is obtd. and the accuracy and measurement range are improved.;COPYRIGHT: (C)1997,JPO