>         (Derived from a speed sensor of immaterial description)  Subtract
the
> 'actual' from the 'setting', and, if a negative result, add to the
> result to the PWM register, or if a positive result, subtract it from
> the PWM register.  (In either case, leave the 'setting' unchanged, and
> just add to the PWM register, so the next comparison will be made with
> the 'setting' figure, not the actual PWM register)
>
>         So, in example, 1000 - 900 = 100. Add to PWM register, which
becomes
> 1100.  The motor speeds up, perhaps miraculously to 1000.  Then, at next
> comparison, 1000 minus 1000 = 0.  Add 0 to the PWM register and nothing
> changes, motor continues to run at 1000! Change the setting, or the
> motor changes, and it will compensate.
>
>         Won't it??????  It might oscillate a bit, but maybe not much.
>
As long as the load is constant, the above (proportional) method works quite
well. Don't expect too much in  terms of stability when applying random
changes in loading,though. Been there, done that  ;-)

Ian Rozowsky
Engineering Manager
Centurion Systems
P.O. Box 506
Cramerview 2060
South Africa
Tel   : +27-11-462-4499
Fax   : +27-11-704-3412
e-mail: roz@centsys.co.za
web: http://www.centsys.co.za

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