Contact Resistance Of Connector Based On Kelvin Four-wire Method Design And Implementation Of Automatic Testing

J27,J29 and J30 series connectors belong to micro-rectangular series connectors.Contact resistance is a key parameter of micro-rectangular series connectors,which is an important factor to determine product failure rate.At present,the contact resistance is basically measured manually.The efficiency of manual testing is low.Long-term testing will also cause fatigue of operators and affect the quality of measurement.Therefore,it is necessary to develop a test equipment which can automatically test the contact resistance of micro-rectangular connectors and record the contact resistance instead of manual testing.In this paper,an automatic test method of contact resistance of connectors based on ARM9 platform is proposed.According to this technology,the physical test system is developed,and the contact resistance of micro rectangular connectors is automatically tested and recorded.In a thesis,an automatic test system for contact resistance of micro-rectangular connectors is designed based on Kelvin four-wire method,which can automatically test and record the contact resistance of micro-rectangular connectors.The test method adopts Kelvin four-wire method and field calibration.Contact resistance data of 200 connectors in 10 acquisition boards of the lower computer are collected by RS485 bus.After processing,contact resistance data are transmitted to the upper computer display software through TCP/IP network for calculation,display,printing and storage.In order to make the test system meet the requirement of contact resistance acquisition accuracy(+0.1m?),a filter is used in hardware to filter the signal and remove the interference signal.The instrument amplifier with low deviation input voltage and low temperature drift is used to amplify the small signal of contact resistance voltage.A 16-bit synchronous AD converter with 8 channels with low signal-to-noise ratio,wide dynamic range and high resolution is used for analog conversion.The software filters the small voltage signal of contact resistance,and filters the collected AD conversion data,which can prevent the abnormal fluctuation of AD value from affecting the acquisition accuracy.The acquisition of small voltage signal of multi-channel contact resistance is realized by switching the electromagnetic relay matrix in turn.The electromagnetic relay is controlled by mechanical contacts.The signal is turned off by physical isolation and there is no leakage current.It can ensure that the input signal passes through without loss and that the testing accuracy and stability of the signal are guaranteed.The test range of contact resistance of micro-rectangular connectors is 0.5?~2?.Because the contact resistance of micro-rectangular connectors ranges from 5 m?~20m?,and the contact resistance value is much smaller than that of cable,the Kelvin four-wire method and on-site calibration method are used to test the contact resistance of micro-rectangular connectors,which can basically eliminate the contact between the test cable resistance and micro-rectangular connectors.The influence of resistance acquisition ensures the test accuracy and consistency of contact resistance of connectors.The automatic test system for contact resistance of connectors based on Kelvin's four-wire method is tested with the specified line length test line in the practical test application.The precision meets the requirement of <0.06 m_,and the test period reaches 9S~11S,which meets the requirement of the test system.