Re: Definition of the error variable e

Dear John

Thanks for your enquiry. Although y is not available for the
controller to use it is the variable of interest. It therefore makes
sense to use it in the problem formulation. e=y-r is what we really
want to minimse so why not do just that.

Regards

Ian

> From: "Evans, John (BeWT)" <jxevans1@bechtel.com>
> To: "'ixp@le.ac.uk'" <ixp@leicester.ac.uk>
> Date: Thu, 01 Jul 1999 16:58:24 +0100
> Subject: Multivariable Feedback Control Book

> Dr Postlethwaite
>
> I have a question concerning a remark made in Chapter 2 of your excellent
> book.
>
> At the top of page 22 you make a remark concerning the error calculation.
> You use
> e = y - r
>
> and say '...Second, the error should involve the actual value (y) and not
> the measured value (ym)'.
>
> However, in practice it would be the measured value from the sensor (ym)
> that is used in the controller to calculate
> the error
>
> ie. e = ym - r
>
> and the noise would be part of the measured signal ym.
>
> Why do you assume that you can use (y) to calculate the error ?
>
> I look forward to your reply.
>
> Regards
> John Evans
> Bechtel
>
-------------------------------------------
Professor Ian Postlethwaite
Head of Department
Department of Engineering
University of Leicester
Leicester LE1 7RH
UK

Tel: +44 (0)116 252 2547
Fax: +44 (0)116 223 1369
Email: ixp@le.ac.uk
Received on Thu Jul 01 16:22:30 1999