One common failure mode for the NOVAC scanners is a loose or incorrectly positioned scanner end switch. When working properly, the end switch defines the reference position of the scanner and tells the instrument which way is up. Problems with the end switch can cause the scanner to rotate indefinitely without the measurement ever starting, or make the instrument scan the ground rather than the sky. A new video in the Tutorials library shows how to troubleshoot this issue.
Network for Observation of Volcanic and Atmospheric Change