Abstract:The friction state is the essential reason to influence brake performance of mechanical brakes.In order to monitor the friction state in real time of the mechanical brakes,three friction state monitoring systems based on PCI,PPI and free port were established respectively,by selecting two common signal acquisition hardware,namely the PLC and data acquisition card as hardwares,and based on the measurements of analyzing the state variables,arranging the signal channel reasonably and scientific programming.The applicability and characteristics of three friction state monitoring systems were discussed.The monitoring experiments of friction state were carried out under continuous braking condition,the friction state parameters of friction temperature rise,friction torque and brake pressure were monitored and analyzed by the friction state monitoring systems.It is indicated that the monitoring system based on PLC’s free port can accurately caught the information of friction state,including friction temperature rise,friction torque and brake pressure,which can realize the accurate monitoring of friction state.