.Buildings.Controls.OBC.CDL.Logical.TrueFalseHold

Information

Block that holds a true or false signal for at least a defined time period.

Whenever the input u switches, the output y switches and remains at that value for at least duration seconds, where duration is a parameter. After duration elapsed, the output will be y = u. If this change required changing the value of y, then y will remain at that value for at least duration. Otherwise, y will change immediately whenever u changes.

This block could for example be used to disable an economizer, and not re-enable it for 10 minutes, and vice versa.

The image below shows the implementation with a state graph in which each transition is only triggered when the input has the corresponding value, and the current state has been active for at least duration seconds.

Simulation results of a typical example with duration = 1000 seconds.

Revisions

• November 12, 2020, by Michael Wetter:
  Reformulated to remove dependency to Modelica.Units.SI.
  This is for issue 2243.
• September 18, 2017, by Michael Wetter:
  Improved event handling.
• July 14, 2017, by Michael Wetter:
  Corrected model to set output equal to input during initialization.
• June 13, 2017, by Michael Wetter:
  Reimplemented model using a state graph to avoid having to test for equality within tolerance, and to correct a bug. This implementation is also easier to understand.
  This is for issue 789.
• May 24, 2017, by Milica Grahovac:
  First implementation.