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.