This block processes a relay switch output and calculates the length of
the on period, tOn, and the length of the off period, tOff, as shown below.
Note that tOn is sampled when the relay switch output becomes false.
Likewise, tOff is sampled when the relay switch output becomes true.
J. Berner (2017). "Automatic Controller Tuning using Relay-based Model Identification." Department of Automatic Control, Lund University.