Fixed point PI control

glen herrmannsfeldt wrote:
> Tim Wescott wrote:
>> sorenbirk wrote:
> (snip)
> 
>> You have two problems:  What mathematical scheme to use, and how to 
>> translate your parameters so they make sense in your scheme.  You've 
>> further complicated your problem by expressing a time quantity (Ti) as 
>> a dimensionless number, when it has to have some time units behind it 
>> -- seconds?  Sample intervals?  Hours?  If your Ti is in anything 
>> other than control sample intervals, then you need to know your 
>> sampling rate, too (and you should be questioning how you're going to 
>> convert your controller design in the Laplace domain into a z domain 
>> model that you can use to design your difference equations for your 
>> software).
> 
> I thought the question was how to do scaled fixed point arithmetic.
> That is at least one question before getting much farther along
> in the design.
> 
> -- glen
> 
As I read it the question was "How do I translate Kp and Ti using fixed 
point arithmetic".  Since you can't translate Ti without knowing it's 
dimensions or your sampling rate, with or without fixed point 
arithmetic, I felt the OP needed more than a treatise on fixed point 
arithmetic.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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