A capacitive sensing technique for measuring displacement with one floating target electrode

We present a capacitive measurement technique used to measure small displacement in industrial environments without electrical contact with the target. The range of the measured capacitance is up to 10 pF in less than 100μs. This type of technique also enables remote sensing of small displacement since the feedforward active shielding technique is used to obtain a tolerance of up to 10 meters cables. More importantly, this type of technique not only reduces the leakage effect caused by the floating target, but it also prevents the interference picked up by the floating target from significantly influencing the performance. The technique has been prototyped using a printed circuit board, and measurement results show a dynamic range of 15 bits.