hello!! I hope you can help me out. I need to find the Z tansform from a Laplace expresi�n: 5(1-e^-sT)/s(s+1)(s+2) Now, I know that there is a table to calculate this but I can't find anything on the web, maybe you have one, or you'd know someway to solve this, I really need it, I hope you can help me, thanks!

# z transform of a digital filter

Started by ●March 24, 2007

Posted by ●March 24, 2007

On Mar 25, 7:39 am, "su" <macaroli...@yahoo.com.mx> wrote:> hello!! I hope you can help me out. > I need to find the Z tansform from a Laplace expresi=F3n: > > 5(1-e^-sT)/s(s+1)(s+2) > > Now, I know that there is a table to calculate this but I can't find > anything on the web, maybe you have one, or you'd know someway to solve > this, I really need it, I hope you can help me, thanks!This 5(1-z^-1)Z(1/s(s+1)(s+2)) Where Z is the z transform operation.

Posted by ●March 24, 2007

Hardy.Spicer@yahoo.co.uk wrote:> On Mar 25, 7:39 am, "su" <macaroli...@yahoo.com.mx> wrote: >> hello!! I hope you can help me out. >> I need to find the Z tansform from a Laplace expresi�n: >> >> 5(1-e^-sT)/s(s+1)(s+2) >> >> Now, I know that there is a table to calculate this but I can't find >> anything on the web, maybe you have one, or you'd know someway to solve >> this, I really need it, I hope you can help me, thanks! > > This 5(1-z^-1)Z(1/s(s+1)(s+2)) > Where Z is the z transform operation.Huh? What are those s's doing there? Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Posted by ●March 25, 2007

On Mar 25, 9:43 am, Jerry Avins <j...@ieee.org> wrote:> Hardy.Spi...@yahoo.co.uk wrote: > > On Mar 25, 7:39 am, "su" <macaroli...@yahoo.com.mx> wrote: > >> hello!! I hope you can help me out. > >> I need to find the Z tansform from a Laplace expresi?n: > > >> 5(1-e^-sT)/s(s+1)(s+2) > > >> Now, I know that there is a table to calculate this but I can't find > >> anything on the web, maybe you have one, or you'd know someway to solve > >> this, I really need it, I hope you can help me, thanks! > > > This 5(1-z^-1)Z(1/s(s+1)(s+2)) > > Where Z is the z transform operation. > > Huh? What are those s's doing there? > > Jerry > -- > Engineering is the art of making what you want from things you can get. > =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF==AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF It's for him to work out ie Z(1/s(s+1)(s+2)) is the z-transform of the Laplace part leaving out 1-exp(-sT) which is the bit I am assuming he had trouble with. I am not doing the whole calculation! H=2ES

Posted by ●March 25, 2007

su wrote:> hello!! I hope you can help me out. > I need to find the Z tansform from a Laplace expresi�n: > > 5(1-e^-sT)/s(s+1)(s+2) > > Now, I know that there is a table to calculate this but I can't find > anything on the web, maybe you have one, or you'd know someway to solve > this, I really need it, I hope you can help me, thanks! > >You're getting vague, unsatisfactory answers because you've asked a vague, unsatisfactory question. Unless you're willing to allow expressions with ln(z)/T, or unless you specify your system more thoroughly, you can't get an exact transformation between a Laplace model and a z-domain model. If you want an approximation you need to share information about how your sampling rate relates to your delay time and your pole positions. You can get an exact z-domain representation of a system that has a plant as described above plus a sampling stage (such as an ADC) and a hold stage (such as a DAC), but you have to specify what those stages are, as well as your sampling rate. So please, ask your question in a sensible way and maybe someone will give you a sensible answer. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html

Posted by ●March 25, 2007

On Mar 26, 5:27 am, Tim Wescott <t...@seemywebsite.com> wrote:> su wrote: > > hello!! I hope you can help me out. > > I need to find the Z tansform from a Laplace expresi=F3n: > > > 5(1-e^-sT)/s(s+1)(s+2) > > > Now, I know that there is a table to calculate this but I can't find > > anything on the web, maybe you have one, or you'd know someway to solve > > this, I really need it, I hope you can help me, thanks! > > You're getting vague, unsatisfactory answers because you've asked a > vague, unsatisfactory question. > > Unless you're willing to allow expressions with ln(z)/T, or unless you > specify your system more thoroughly, you can't get an exact > transformation between a Laplace model and a z-domain model. > > If you want an approximation you need to share information about how > your sampling rate relates to your delay time and your pole positions. > > You can get an exact z-domain representation of a system that has a > plant as described above plus a sampling stage (such as an ADC) and a > hold stage (such as a DAC), but you have to specify what those stages > are, as well as your sampling rate. > > So please, ask your question in a sensible way and maybe someone will > give you a sensible answer. > > -- > > Tim Wescott > Wescott Design Serviceshttp://www.wescottdesign.com > > Posting from Google? Seehttp://cfaj.freeshell.org/google/ > > Do you need to implement control loops in software? > "Applied Control Theory for Embedded Systems" gives you just what it says. > See details athttp://www.wescottdesign.com/actfes/actfes.htmlI assume he means that the (1-exp(-ST)/S is a zero order hold. In control text books they include this a lot. It's historical and goes back to the days when they couldn't sample high enough and had to include it. Of course I suppose you need always include it but it gets negligible the higher you sample. H=2ES