Hi everyone,

i want to program a "crankshaftangle-generator" therfore i wanted to use an "Saw-Tooth-Block" (from the Modelica Standard Library) and change it like this:

- the parameter "period" isn't anymore an fix parameter it is given from an extra "Real-Input"-Block. This real Input is the engine speed. After all i can produce an engine speed dependend crankangle.

But there is some problem. When i declare the variable "period" as an "parameter" Dymola everytime says the variability of "period" is higher than the declared variable. When i try to declare "period" without the "parameter"-Index Dymola says that the "when"-condition must be discrete.

I would be glad if someone could help me with this problem, or if someone have some idea to program an "crankshaftangle-genarator"...



model frequencySaw
Modelica.Blocks.Interfaces.RealInput n annotation;
Modelica.Blocks.Interfaces.RealOutput y annotation;

parameter Real amplitude=1 "Amplitude of saw tooth";
parameter Real offset=0 "Offset of output signals";
parameter Modelica.SIunits.Time startTime=0
"Output = offset for time < startTime";

protected
Modelica.SIunits.Time T0(final start=startTime)
"Start time of current period";
Modelica.SIunits.Time period(final min=Modelica.Constants.small) = 1/(n*60/amplitude)
"Time for one period";

equation
when sample(startTime, period) then
T0 = time;
end when;
y = offset + (if time < startTime then 0 else (amplitude/period)*(time
- T0));
end frequencySaw;

Hello Meppel,

a parameter variable is like a constant value that can be assigned only before running the simulation. That's why your model doesn't work with period as parameter.

The problem with the "when-condition must be discrete value" is the sample command. The sample command can only take a constant value as its argument. You have to replace the sample command and implement your own functionality.

I've done it in this sample model.



I hope it does what you wanted to. You just have to be careful that you don't attach a period of zero because then you get a division by zero error.

Regards

Florian

Hello wagner,

many thanks, your version works well... I also found solution during weekend...

Regards Meppel