The Development Of Measuring System For Contact Resistance Of Wire Harness

With the increasing complexity of control components,the demand for wiring harness is increasing,and the failure has become one of the main faults of component products.The contact resistance is an important parameter to judge the electrical contact performance of the interconnected devices in the component products.When the control components are mass produced,in order to confirm whether the multiple output of the electrical control box is connected normally and meet the technical requirements,The output of the contact resistance measured in turn,the efficiency is very low.Based on this,this paper developed the harness contact resistance test system,the purpose is to achieve multi-channel low resistance measurement automation,to improve the electrical control box type of product testing efficiency and ensure the production schedule.Firstly,a low resistance measurement design scheme based on "four-terminal measurement" and "on-site calibration" is proposed for the functional requirements of the test system.A variety of feasible schemes are proposed for the development of bus protocol,low resistance measurement,measurement switching circuit,user interface and system power supply.Through comparison and analysis,a low cost and high reliability design scheme is proposed.The system has a wide temperature measurement range,measurement error is small,easy to operate and so on.Secondly,the hardware circuit of harness contact resistance test system is designed,which includes power supply circuit,constant current source circuit,analog switch measurement switching circuit,signal amplifying circuit,USB transfer SCI circuit and signal isolation circuit,and MCU function module.Thirdly,the lower computer software and the host computer software of the harness contact resistance test system are designed.For the next crew,draw the software work flow chart,and developed a communication protocol.Lower computer software includes online testing,calibration of low resistance 10? file,calibration low resistance20? file,with low resistance 10? file to measure and use low resistance 20? file to measure five functional modules.The main functions of the system include: main interface,save and load of measurement configuration,save of measurement result and other functions.At last,the system test platform is set up,and the ZX54 DC resistance box and BL1206 milliohmmeter are selected to test the measurement accuracy of the contact resistance test system at room temperature.The low resistance test at room temperature Accuracy in the following 10m?.At the same time,CMR-128 micro-ohm meter(micro-ohmmeter)was used in low temperature and high temperature to verify the accuracy of the test system under the whole temperature environment.The test precisionwas below 10m? and all the functions of the system were verified.In addition,through the reliability analysis of the test system,the feasibility of satisfying the reliability index is fully verified,and finally the MTBF forecasting value of the mean time between failures is obtained.