transfer function with exponential factor?

[dimdim]

Dear all.

i want to implement a process model transfer function in labview with delay time Td.

G(s) =       K. exp(-s.Td)

            ------------------------

                      T.s+1

i've try Transfer function H(s)  block from PID toolskit. but there's no option for exponential factor.

Anyone can help me?

Thanks a lot.

[Barp · Accepted solution]

Do you have the LabVIEW Control Design and Simulation Module? Using this module, it will become EXTREMELY easy to create this transfer function.

What is the objective of your simulation? Research, class assignment, work related?

Which version of LabVIEW do you have?

Thanks

[dimdim]

I've solve my problem with this toolkit 🙂

I try to built network control system (NCS) to control DC motor over LAN with UDP protocol.

It's important to include delay time in my transfer function.

I'm using LabVIEW 7.1

Thanks Mr Barp.

[Barp]

Very good. Just want to let you know that the latest version of LabVIEW Control Design and Simulation is in 8.6 and they have several improvements compared to the 7.1 version and it is highly recommended that you have the most up to date version.

The Control Design and Simulation has much more capabilities and could help to design the controller.

All the best!

[ajita24patil@gmail.com]

Hi i am also trying to develope PID controller's transfer function with parameters Kp,Ki and T. An it also has e^-(ts)= [(2-st)/(2+st)]. I am not able to insert this time delay interms of exponential.

I am using evaluation copy of Labview 2011 and i am a student. 

Guide me for this.

thank you.

[Aldo_A]

Hi,

We have a great online tutorial which walks through the process of building a transfer function with the Control Design and Simulation Module here: http://www.ni.com/white-paper/5855/en 

If you have any specific questions afterwards, feel free to post back, thanks!

[mariuszl2]

Hi, I`m also trying to use sxpotential function in my model. How did You guys exactly solve this problem?

I have a MathScript Node with two inputs R and C.

Inside the node I wrote 

s=tf('s');

out=exp(-s*R*C)

I choose out as output with data type TF object. Then i would like to create this model and connect it to  CD Linear Simulation VI.

However I get an error in the MathScript Node saying that the function exp is not defined for non-numeric data types.

Do ou guys know any way I can work around that?

[Barp]

You are mixing Laplace Transform with Time Domain Response. When you write sys= exp (-s*R*C), this means a time delay in Laplace, but I think that is not what you want to do. In Laplace, the RC circuit is (the input of the voltage on the capacitor):

s=tf('s');

sys= 1 / (1+s*R*C); 

Then, you use the CD Impulse Response.vi to convert the model express in Laplace to time domain, which evaluates this equation internally:

y(t) = 1/RC * exp (-t/RC)

Or you can use the CD Step Response to obtain this equation:

y(t) = [1 - exp ( - t /R*C) ] * u(t)

Notice that you don't need to actually write those equations. They are evaluated internally inside the VI. If you want to do thsoe operation manually, then you just have to use the time domain equations directly and you don't need to use 'Laplace'. 

Check here for more information: https://en.wikipedia.org/wiki/RC_circuit

Hope this helps....

[mariuszl2]

Thaks for the information Bart, but this isn`t exactly what I`m looking for. The example I posted was just a simplification of what I`m trying to do. I would like to use this formula:

U(s)= (u1*exp(-y*s) + Z*exp(-y*(2*l-s) ) / (1+ Z*exp(-2*y*l))

and use it as an input for CD Linear Simulation VI.

I`ve done this with formulas that don`t have exponent in nominator or denominator using CD Construct Transfer Function Model VI. I would like to know if this is possible for functions that have exponent with "s" in nominator or denominator.

Simply, can i use a model like exp(s*2) / (s+s^2+exp(s*3)). Is this possible? 

[Barp]

The only support we have on CD Linear Simulation is the format:

Y(s) = exp (-Ts) *N(s)  / D(s)

which is a transfer function with transport delay. We also have the concept of input delay and output delay, but to use the function, you should be able to compute the total transport delay for each input/output. Any other type of algebraic equation with delay is not supported (like a lot of other tools out there). So, if you can't factor out your equation into the equation above, then the linear simulation will not work.

Then, another option is to use LabVIEW Control and Simulation Loop. There you can create any kind of model with delay where ever you would like to have and, then you can simulate that. Does it make sense?