This model outputs the density of the fluid flowing from
port_a to port_b.
The sensor is ideal, i.e., it does not influence the fluid.
If the parameter tau is non-zero, then its output
is computed using a first order differential equation.
Setting tau=0 is not recommend. See
Annex60.Fluid.Sensors.UsersGuide for an explanation.
tauInv
since this now exists in
Annex60.Fluid.Sensors.BaseClasses.PartialDynamicFlowSensor.
This is for
#372.
Modelica.Fluid.