Study On Inductive Proximity Switch With Wide Temperature And Long Distance Measurement

Since the 21st century,there is a growing demand for proximity switches in various fields.Due to various demands,proximity switches are developing towards diversification.According to different applications,the proximity switch meeting the requirements shall be selected.Because the capacitive proximity switch is easy to be affected by some non-metallic pollutants,and the inductive proximity switch has the advantages of simple structure and strong anti-interference ability,which makes the application of inductive proximity switch more and more widely.With the development of aerospace and industry,the requirements of inductive proximity switch are higher and higher.It is not only required to have smaller volume,higher measurement accuracy,farther detection range,but also to be able to work normally in harsh environment.Therefore,the research on inductive proximity switch with wide temperature range and long distance measurement is of great practical significance.This paper studies the remote measurement technology of inductive proximity switch.The bridge differential inductance detection circuit is adopted,and the working principle of the bridge differential inductance detection circuit is analyzed in detail.Based on the measurement method of bridge differential inductance detection circuit,most of the external interference signals(common mode noise signals)can be eliminated,and the detected information(differential mode signals)can be ensured as effective as possible,so that the system has a strong anti-interference ability.In order to obtain the further distance detection,the paper samples the complementary structure of the transmitting coil,and uses the full bridge inverter circuit in the power electronics technology to realize the oscillating excitation circuit,so as to enhance the magnetic field strength and realize the remote measurement.This paper studies the wide temperature range application technology of inductive proximity switch.In this paper,the method of separate design of probe and bridge differential inductance detection circuit is put forward.The probe is placed in a relatively bad environment,while the measurement circuit is placed in a better environment with a wider working temperature range.Through the simulation of the temperature field of ANSYS,the layout method of PCB is studied,so as to realize the application technology of inductive proximity switch in a wide temperature range.Based on the study of the bridge differential inductance detection circuit,an inductive proximity switch with attenuation coefficient of 1 is proposed.In this paper,the electronic measurement circuit of inductive proximity switch is composed of conditioning circuit and FPGA.When the target metal object is close to the sensing surface,the inductance of the detection coil changes to produce inductance increment,which changes with the change of proximity distance.The changed inductance increment signal is detected and amplified by conditioning circuit and sent to FPGA.In FPGA,the target is obtained by querying proximity distance table The approach distance of metal objects,for different target metal objects,the corresponding approach distance table can be queried,so as to realize the inductive proximity switch with attenuation coefficient of 1,that is,multiple target metal objects can be detected at the same induction distance.In the design process of the bridge differential inductance detection circuit,the paper studies the working principle of the reference inductor realized by the on resistance of the general impedance converter and JFET Junction FET,and proposes a measurement self-tuning method based on the integral proportional integral differential(I-PID)controller.In the bridge differential inductance detection circuit,FPGA is used to output the gate control signal of JFET to realize the variable on resistance of JFET,so as to realize the adjustable reference inductance.When the inductive proximity switch is far away from the measured object,the incremental inductance signal detected in FPGA is adjusted by the integral proportional integral differential controller,The regulating signal is used to control the gate of JFET to obtain the corresponding on resistance,which makes the equivalent reference inductance in the bridge differential inductance detection circuit equal to the inductance of the detection coil,so that the output of the bridge differential inductance detection circuit is 0,that is to say,the automatic zero adjustment of the inductive proximity switch is realized.This technology is helpful to the consistency and high reliability of the inductive proximity switch mass production,and avoids the disadvantage that the reference inductor is difficult to make accurately.In this paper,ANSYS and PSPICE software are used to simulate the key technologies of the inductive proximity switch.On the basis of the simulation,the bridge differential inductance detection circuit and FPGA algorithm of the inductive proximity switch are designed preliminarily,and the verification prototype is made.Experiments are carried out on three different metals of iron,aluminum and copper on the prototype platform.The test data show that the inductive switch studied in this paper Proximity switch technology can realize the measurement of long distance and attenuation coefficient of 1.The feasibility and correctness of the theory and design method are verified.