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From: email@example.com (john jardine)
Subject: Re: Heated seat controller, open or closed loop temp.control
Date: 26 Oct 2002 12:06:16 -0700
NNTP-Posting-Date: 26 Oct 2002 19:06:16 GMT
Sylvan Butler wrote in message news:...
> On 25 Oct 2002 14:41:14 -0700, john jardine wrote:
> > "Jeroen" wrote in message news:...
> >> I'm making a controller for my heated seats in my car, and still havn't made
> >> a decision whether it should be a closed or open loop temp control. It will
> >> have 4 settings. In openloop that would simply be 25,50,75 and 100% output
> > For simplicity and sanity, keep it open loop.
> > If you go for closed loop then be prepared to implement (and tune) a 3
> > term PID control sytem.
> Why??? A simple thermostat is closed loop.
Agreed. A T/S is an excellent closed loop conrol system. I wish people
would use them more often in the simple applications that many times
I've seen implemented in horrendously complicated uP/DAC/ADC PID
Jeroen though is after 4 fixed settings. This would imply some kind of
4 position, presettable 'click stop' T/S (electrical or mechanical)
with a probe placed somewhere in/on the car seat. Hopefully, not where
Fred suggests. Dependant on the local thermal time constant the unit
would then temperature cycle between its own (unpredictable)
> > The heater has a significant time lag to setpoint and this creates all
> > the control problems.
> > Do you really need +/- .5degC control ;-).
> Trying for that level of control is what creates control problems.
> A simple closed loop which maintains temperature at a setpoint +/-
> several degrees is not complex.
That's right but ... Essentially, what I'm suggesting, is that
sticking a probe somewhere in the seat and allowing the setup to cycle
within an undefined temperature window without PID control is
actually still more complicated (even less comfortable!)than having a
completely open loop setup.
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