Re: Sampling time

Ali Khalaf (hkila@batelco.com.bh)
Sat, 22 Feb 1997 14:02:18 +0100


Jan Jantzen wrote:
>
> It should be chosen somewhat smaller than the dominating time constant in
> the process, for instance between 1/10 and 1/5 of the time constant.
> If the sample period is too short, the computation of CE will become
> too sensitive to noise. This normally shows up as a restless control
> signal. If CE happens to be implemented as a difference, several
> gains depend on the sample period; a change in sample period must then be
> followed by a compensation in a gain factor to keep the proportional,
> integral and derivative gains intact.
>
> The sample period can also be related to the derivative gain Td. Astrom
> and Wittenmark (1984) suggest that the sample period should be between
> 1/10 and 1/2 of Td. In connection with the Ziegler-Nichols rules,
> this implies that Ts should approximately equal 1-5 percent of the
> ultimate period Tu.
>
> Regards, Jan Jantzen
>
> Technical University of Denmark | Tel +45 4525 3561 (direct)
> Att: Jan Jantzen | Fax +45 4588 1295
> Dept. of Automation, Bldg. 326 | Jantzen@iau.dtu.dk
> DK-2800 Lyngby, DENMARK | http://www.iau.dtu.dk/~jj
>
> On Thu, 20 Feb 1997, Ali Khalaf wrote:
>
> > What is the required sampling rate required for a fuzzy logic
> > controller. I am mainly concerned with the application of fuzzy
> > controller in power system stabilizers. Also what effect does varying
> > sampling rate have ?
But if we take the sampling time as 1/10 to 1/5 of the dominant time
constant ,wouldn't that lead to ignoring the transients ?