Research And Design Of Capacitive Micro-Displacement Sensor Based On Film Electrode

The rapid development of automobile industry makes the higher and higher precision requirements for auto parts,The precision of auto parts depend on the high precision machining and measuring technology.Capacitive micro-displacement sensor is a kind of non-contact measuring instrument,which has the advantages of high sensitivity,small nonlinear error and simple construction,and is very suitable for small displacement detection.In this paper,we research the key principle and then design the capacitive displacement sensor,which was expected to achieve high-precision micro-displacement detection.Firstly,in order to reduce the edge effect and ensure the homogenous electric field between the two parallel plates,a capacitive sensor with Kelvin guard ring was designed.Besides,to reduce the capacitance introduced by the thick paltes,the sensing electrode was made of Al₂O₃ with metal coating forming sensor eletrodes.The results showed that the sensor made of thin conductive film electrode with Kelvin guard ring can effectively reduce the edge effect of the electric field.Further,an insulating substrate with a through hole was used,and the hole was filled with conductive material,one end of the conductive material was connected to the conductive film.Thereby,the conductive film was imparted with a standard Kelvin guard ring.The results showed that the sensitivity and linearity of the capacitive sensor with standard Kelvin guard ring were greatly improved.Then,the operational amplification detection circuit was designed to convert the capacitance to voltage.The active driving shielding cable was used to keep the guard ring and sensing electrode at the same potential.The results showed that the detection circuit has good anti-interference ability and high linearity.Finally,the capacitive sensor was tested by measuring the liquid level.The experimental results showed that the capacitive displacement sensor with standard gurad ring conductive film electrode has a sensitivity of 9.78mV/um,and a non-linearity error of 0.757%with the full range of 1mm.