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Thread Subject:
z-transformation with matlab

Subject: z-transformation with matlab

From: Leif Wiebking

Date: 5 Feb, 2001 17:49:40

Message: 1 of 5

To control technique-engineers using matlab!

Hi,
I've a question about the 'c2d'-command used to transform a continuous
function into a discrete z-function.
Therfore you can select the discretization method ('zoh', 'foh',...). By
default a 'zoh' (zero-order-hold-term) is used if 'method' is omitted.
My question: Is there a possibility to do the z-transformation without a
'zoh'-term included?
I want to obtain the results of the correspondence-tables for
z-Transformation, which don't include a zero-order-hold-term. That seems
to be impossible with the 'c2d'-command.
I'm using Matlab-version 5.3.

Thanks for your help !
Leif

Subject: z-transformation with matlab

From: Zdenek Hurak

Date: 6 Feb, 2001 10:13:24

Message: 2 of 5

Hi Leif,

the kind of transformation that is implemented in C2D command is NOT the
well-known z-transform. Instead, it is simply called DISCRETIZATION. The
result of this discretication is then a discrete-time SYSTEM.

On the other hand, the result of the z-transform is always a SEQUENCE. You
can think of the z-transform as a purely mathematical tool. One possible use
is for the above mentioned discretization of continuous-time systems.

In such cases however, you got to include the term accounting for some
physical aspects of the system. That is exactly what you call DISCRETIZATION
METHOD. I recommend to have a very brief look at how digital control or
signal processing works. You will find a block called HOLD somewhere in the
loop.

To conclude, C2D is NOT a tool performing z-transform. It is just for
engineers for one particular application. If you need to perform z-transform
with Matlab, you need SYMBOLIC MATH TOOLBOX. There is a function called
ZTRANS.

Best,
Zdenek


Leif Wiebking <leif@iei.tu-clausthal.de> wrote in message
news:3A7ED9A4.ADC50CBC@iei.tu-clausthal.de...
> To control technique-engineers using matlab!
>
> Hi,
> I've a question about the 'c2d'-command used to transform a continuous
> function into a discrete z-function.
> Therfore you can select the discretization method ('zoh', 'foh',...). By
> default a 'zoh' (zero-order-hold-term) is used if 'method' is omitted.
> My question: Is there a possibility to do the z-transformation without a
> 'zoh'-term included?
> I want to obtain the results of the correspondence-tables for
> z-Transformation, which don't include a zero-order-hold-term. That seems
> to be impossible with the 'c2d'-command.
> I'm using Matlab-version 5.3.
>
> Thanks for your help !
> Leif
>

Subject: z-transformation with matlab

From: Arthur Jutan

Date: 6 Feb, 2001 11:39:09

Message: 3 of 5

What you want is the 'impinvar' function in the Signals TB
-arthur jutan

Leif Wiebking wrote:

> To control technique-engineers using matlab!
>
> Hi,
> I've a question about the 'c2d'-command used to transform a continuous
> function into a discrete z-function.
> Therfore you can select the discretization method ('zoh', 'foh',...). By
> default a 'zoh' (zero-order-hold-term) is used if 'method' is omitted.
> My question: Is there a possibility to do the z-transformation without a
> 'zoh'-term included?
> I want to obtain the results of the correspondence-tables for
> z-Transformation, which don't include a zero-order-hold-term. That seems
> to be impossible with the 'c2d'-command.
> I'm using Matlab-version 5.3.
>
> Thanks for your help !
> Leif

--
<html>
<br>
===================================================<br>
<font color="#0000FF">Prof. Arthur Jutan, Ph.D., P.Eng.   
Dept. of Chemical Engineering,<br>
University of Western Ontario, London, ONT, Canada,N6A 5B9.<br>
Tel: (519)661-2111, Ext 88322, FAX:(519) 661-3498<br>
ajutan@uwo.ca | <a href="http://www.engga.uwo.ca/chemical/staff/Jutan/"
eudora="autourl">http://www.engga.uwo.ca/chemical/staff/Jutan/<;/a> <br>
</font></html>

Subject: Check the other methods

From: irodrigu@vt.edu (Isabel)

Date: 6 Feb, 2001 20:47:03

Message: 4 of 5

I don't understand what method is want you want to use if not the zero
order hold.

Subject: z-transformation with matlab

From: kamuran turksoy

Date: 8 Mar, 2012 21:09:17

Message: 5 of 5

"Zdenek Hurak" <z.hurak@c-a-k.cz> wrote in message <95ofgs$22dc$1@ns.felk.cvut.cz>...
> Hi Leif,
>
> the kind of transformation that is implemented in C2D command is NOT the
> well-known z-transform. Instead, it is simply called DISCRETIZATION. The
> result of this discretication is then a discrete-time SYSTEM.
>
> On the other hand, the result of the z-transform is always a SEQUENCE. You
> can think of the z-transform as a purely mathematical tool. One possible use
> is for the above mentioned discretization of continuous-time systems.
>
> In such cases however, you got to include the term accounting for some
> physical aspects of the system. That is exactly what you call DISCRETIZATION
> METHOD. I recommend to have a very brief look at how digital control or
> signal processing works. You will find a block called HOLD somewhere in the
> loop.
>
> To conclude, C2D is NOT a tool performing z-transform. It is just for
> engineers for one particular application. If you need to perform z-transform
> with Matlab, you need SYMBOLIC MATH TOOLBOX. There is a function called
> ZTRANS.
>
> Best,
> Zdenek
>
>
> Leif Wiebking <leif@iei.tu-clausthal.de> wrote in message
> news:3A7ED9A4.ADC50CBC@iei.tu-clausthal.de...
> > To control technique-engineers using matlab!
> >
> > Hi,
> > I've a question about the 'c2d'-command used to transform a continuous
> > function into a discrete z-function.
> > Therfore you can select the discretization method ('zoh', 'foh',...). By
> > default a 'zoh' (zero-order-hold-term) is used if 'method' is omitted.
> > My question: Is there a possibility to do the z-transformation without a
> > 'zoh'-term included?
> > I want to obtain the results of the correspondence-tables for
> > z-Transformation, which don't include a zero-order-hold-term. That seems
> > to be impossible with the 'c2d'-command.
> > I'm using Matlab-version 5.3.
> >
> > Thanks for your help !
> > Leif
> >
>
>

Actually, these days i have same problem, i want to find a way to use ztrans function as zero order hold sampling time. Because as i found it uses impulse invariant discritezation method. or a way to c2d with symbolic transfer function? I mean i have some symbolic variables in my transfer function and c2d can not handle with this, thus i had to take ztrans (but first i take inverse laplace of transfer function then z trans). But it takes z transform based on 'imp' way.

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