The HYDROCAL 1001+ is a permanently-installed composite gas-in-oil sensor for the analysis of six dissolved key fault gases such as Hydrogen (H2), Carbon Monoxide (CO), Methane (CH4), Acethylene (C2H2), Ethylene (C2H4), and Ethane (C2H6). To detect an even wider range of potential transformer faults, the HYDROCAL 1001+ analyses additionally the content of Moisture (H2O) in the transformer oil.