Resolve Global Parameter issue


I would like to model a PT1TT-system. Thus I have set up the following circuit:

The system is a hydraulic cylinder controlled by a servo-valve. The hydraulic cylinder actuates a force, which is the system-output. The system-input is the current of the valves spool.

The system shows a behavior as the system-gain V depends on the system-input y. The calulation is shown in the expression V.

I really find CircuitLab cool and easy to use - so: Is there a way I can model this and play with it in CircuitLab?

Best regards, LeFish

by LeFish
August 20, 2015

The short answer is, yes you can probably model a system like this in CL.

The longer answer is that for help with something like this you need to provide more information about how the physical system can be represented mathematically.

What is a PT1TT-system?

What does PT1TT actually mean?

Please point people to some links that help explain the background.

For example:

What is the dead time created by? Is it a real time delay such as the time it takes for a signal to propagate down a transmission line or is it due to a dead band or maybe hysteresis?

Sorry but you haven't given enough information to be able to give a useful answer your question.


by signality
August 20, 2015


Thank your for your reply! I used the last days to gain more knowledge on the sytem I would like to model.

This shows a scheme of the system:

Translations: Kraftmessdose := load cell PI-Regler := PI-controller Sollwert := Reference signal

I came to the point, that I cannot model the system as a whole, but I have to model the valve and the cylinder separately and then combine the models.

Thus I started to model the servo-valve, with pretty good results (critics welcome! =) ):

The valve is a MOOG D633 with Qn=5l/min. You can see steps I recorded at the real system - this is the reference. With circuitlab I try to simulate these results.

Now I am trying to take the cylinder into the model. Thus I created a first extension of the valve's model to get the flow Q through the valve:

The polynomial function is calculated from the pressure inside the cylinders chambers. These I can measure. There is a leakage because of the pressure inside the chamber. This leakage has to be compensated by the valve, but I cannot measure the flow itself. This is how I correlated the valves actual position y with the flow Qth.

So here is my question:

Is there a way to have y multiplied with a funcion Qv(y)? If this would be possible then I could probably simulate the whole model! This would be very cool!

The reason why I would like to do it with circuitlab is its ease of usage! Simulink would be an overkill for my needs. Plus, I have never worked with MatLab.

Would you be so kind and help me?

Thank you for all your efforts!

Best regards, LeFish

by LeFish
August 23, 2015

You can have a function of a variable multiplied by the variable itself.

What function of y do you need?


Documentation > Expressions

for more.


by signality
August 23, 2015


I did read Documentation > Expressions - in fact I have it open all the time.

I would need the function

Qy(y)=-7.22094e-13*y^2 + 2.65893e-08*y - 2.43936e-04

multiplied with y.

The background is, that Qy translates the position of the valve's piston y to a flow. As this shows a non-linear behavior for small y I need the above function.

Thank you!


by LeFish
August 23, 2015

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