.Buildings.Controls.OBC.CDL.Reals.Less

Information

Block that outputs true if the Real input u1 is less than the Real input u2, optionally within a hysteresis h.

The parameter h ≥ 0 is used to specify a hysteresis. For any h ≥ 0, the output switches to true if u₁ < u₂, and it switches to false if u₁ ≥ u₂ + h. Note that in the special case of h = 0, this produces the output y=u₁ < u₂.

To disable hysteresis, set h=0.

Usage

Enabling hysteresis can avoid frequent switching.
In simulation, adding hysteresis is recommended to guard against numerical noise. Otherwise, numerical noise from a nonlinear solver or from an implicit time integration algorithm may cause the simulation to stall. Numerical noise can be present if an input depends on a state variable or a quantity that requires an iterative solution, such as a temperature or a mass flow rate of an HVAC system.
In real controllers, adding hysteresis is recommended to guard against measurement noise. Otherwise, measurement noise may cause the output to change frequently.

Revisions

• April 29, 2022, by Jianjun Hu:
  Corrected the condition of swiching true back to false.
  This is for issue 2981.
• February 3, 2021, by Antoine Gautier:
  Corrected documentation.
  This is for issue 2246.
• August 5, 2020, by Michael Wetter:
  Added hysteresis.
  This is for issue 2076.
• January 3, 2017, by Michael Wetter:
  First implementation, based on the implementation of the Modelica Standard Library.