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problem with Modelica.Blocks.MathBoolean.RisingEdge block

#5075  Permalink Top

problem with Modelica.Blocks.MathBoolean.RisingEdge block

Oct-07-14 17:46:25

Hello,

i have written a  program which detects crossing zeros from positive to negative. to do this, i have connected my source, a sine wave for instance to "Modelica.Blocks.Logical.LessEqualThreshold" block with threshold=0, and the output of this block is connected to "Modelica.Blocks.MathBoolean.RisingEdge" block. by this mean anytime value of the sine wave bocomes smaller or equal to zero the output of the comparator becomes one and which trigers the rising edge detection block and the output should generate a pulse consequently.

however when i look at the output of risingedge block it always remains zero.

please help me with this issue.

Thanks,
Arvin

PS: code is attached.

Code:


model tmp1

  Modelica.Blocks.Sources.Sine sine1(amplitude = 2, freqHz = 1, offset = 0) annotation(Placement(visible = true, transformation(origin = {-60, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Blocks.Logical.LessEqualThreshold lessequalthreshold1 annotation(Placement(visible = true, transformation(origin = {-20, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Blocks.MathBoolean.RisingEdge rising1 annotation(Placement(visible = true, transformation(origin = {20, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

equation

  connect(rising1.u, lessequalthreshold1.y) annotation(Line(points = {{6, 60}, {-8.4724, 60}, {-8.4724, 60}, {-9, 60}}, color = {255, 0, 255}));

  connect(lessequalthreshold1.u, sine1.y) annotation(Line(points = {{-32, 60}, {-49.5507, 60}, {-49.5507, 60.077}, {-49.5507, 60.077}}, color = {0, 0, 127}));

  annotation(Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2})), Diagram(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2})), experiment(StartTime = 0, StopTime = 5, Tolerance = 1e-06, Interval = 0.01));

end tmp1;

#5076  Permalink Top

Re: problem with Modelica.Blocks.MathBoolean.RisingEdge block

Oct-07-14 18:07:01

Well. rising1.y is an instantaneous change (dirac impulse). It is never true in the continuous sense. Maybe it would make sense to keep it as such in the result-file; I am unsure why we don't do so.

You can still use it as a condition in a when-equation, which is the primary use of the edge function:

Code:

model tmp1

  Modelica.Blocks.Sources.Sine sine1(amplitude = 2, freqHz = 1, offset = 0) annotation(Placement(visible = true, transformation(origin = {-60, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Blocks.Logical.LessEqualThreshold lessequalthreshold1 annotation(Placement(visible = true, transformation(origin = {-20, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Blocks.MathBoolean.RisingEdge rising1 annotation(Placement(visible = true, transformation(origin = {20, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Real r(fixed=true);

equation

  when rising1.y then

    r = pre(r) + 1;

  end when;

  connect(rising1.u, lessequalthreshold1.y) annotation(Line(points = {{6, 60}, {-8.4724, 60}, {-8.4724, 60}, {-9, 60}}, color = {255, 0, 255}));

  connect(lessequalthreshold1.u, sine1.y) annotation(Line(points = {{-32, 60}, {-49.5507, 60}, {-49.5507, 60.077}, {-49.5507, 60.077}}, color = {0, 0, 127}));

  annotation(Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2})), Diagram(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2})), experiment(StartTime = 0, StopTime = 5, Tolerance = 1e-06, Interval = 0.01));

end tmp1;

So it works fine. You just can't tell if it does or not from plotting it.

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