Qualitrol T/Guard 408 and 408XT Fiber optic temperature monitoring system
https://www.allbro.com/itemdetails/qualitrol-t-guard-408-and-408xt-fiber-optic-temperature-monitoring-sys?category=transformer-equipment&type=2&access=2&id=b4985e7b-1791-4a30-bb30-bd58acff365b