a device for detecting and adjusting the tension of a scraper chain . the device identifies broken chain as it leaves the return sprocket and enters the top race of the conveyor . when detected , the chain can be stopped automatically by the armored face conveyor control system , to avoid the potential for further damage , and warn the operators that repair of the chain is required . the device also has a conveyor with sliding frames at both ends to allow the conveyor ends to be independently adjusted to each end of the coal block , while maintaining good chain tension and control .