RelAccSensor

model RelAccSensor "Ideal sensor to measure the relative acceleration"
    extends Translational.Interfaces.PartialRelativeSensor;

    SI.Position s_rel "Distance between the two flanges (flange_b.s - flange_a.s)";
    SI.Velocity v_rel "Relative velocity between the two flanges (der(flange_b.s) - der(flange_a.s))";
    Modelica.Blocks.Interfaces.RealOutput a_rel(unit = "m/s2") "Relative acceleration between two flanges (= der(v_rel)) as output signal"
        annotation (Placement(transformation(
            extent = {
                {-10, -10}, 
                {10, 10}},
            rotation = 270,
            origin = {0, -110})));
equation
    0 = flange_a.f;
    a_rel = der(v_rel);
    s_rel = flange_b.s - flange_a.s;
    v_rel = der(s_rel);

    annotation (
        Documentation(info = "<html>\n<p>\nMeasures the <em>relative acceleration a</em> of a flange in an ideal way and provides the result as\noutput signals (to be further processed with blocks of the\nModelica.Blocks library).\n</p>\n\n</html>"),
        Icon(
            coordinateSystem(
                preserveAspectRatio = true,
                extent = {
                    {-100, -100}, 
                    {100, 100}}),
            graphics = {
                Text(
                    extent = {
                        {7, -68}, 
                        {41, -102}},
                    textString = "a"), 
                Line(
                    points = {
                        {0, -99}, 
                        {0, -60}},
                    color = {0, 0, 127})}));
end RelAccSensor;