Back in Nov 2016, I bought an APC AP9619 Network Management Card w/ Temp Probe AP9512TBLK. It is installed in an APC UPS SUA2200RM2U (see photos https://imgur.com/a/0XG72 ). @LibreNMS nicely graphs both the internal and external and internal temperatures (https://i.imgur.com/dZpg3nX.png )