Re: Best Book on PID ??

From: John Popelish (jpopelish_at_rica.net)
Date: 11/25/04

  • Next message: Rhett Oracle: "Re: Best Book on PID ??" 
    Date: Wed, 24 Nov 2004 22:25:41 -0500

    Phil Hobbs wrote:
    >
    > John Popelish wrote:

    > > You could probably write a good one. A PID controller is just a
    > > follower amplifier (that forces a process measurement to follow a
    > > setpoint). The PID controller tuning is just a lead lag network that
    > > stabilizes that unity gain amplifier.
    > >
    >
    > I'd agree if we were talking about PI controllers, but PID are somewhat
    > different--the D term is there to compensate for slow transducers such as
    > motors and heaters.
    >
    > The slow transducers put a few wrinkles in practical control systems that are
    > different from ordinary amplifers: windup in motors and asymmetrical slewing
    > in heaters. The D term will turn the 2-pole response of a motor into 1-pole
    > so that it can be stabilized, but the settling behaviour won't be anything
    > pretty unless some sort of (nonlinear) windup control is in there somewhere.

    But follower amplifiers that drive big, slow, nonlinear devices have
    all those same problems. Slow is just not as slow. When I first got
    into process control, it seemed very strange, because I was unfamiliar
    with the jargon. Then I realized that I have been using oscilloscopes
    to study amplifiers doing all the things process control was doing,
    except that now, I could have a cup of coffee while the dynamics
    settled instead of it all happening in microseconds. but the
    principles are just the same. Gain bandwidth product, phase shift,
    slew rate limits, output nonlinearity, recovery from output overdrive,
    etc. all there.

    When I saw the Star Trek episode about the people who moved so fast
    that they were invisible, I realized that they was how I felt while
    tuning a control loop. 

    -- 
John Popelish
  • Next message: Rhett Oracle: "Re: Best Book on PID ??"

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