Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!uwvax!umn-d-ub!umn-cs!nis!pwcs!stag!trb
From: trb@stag.UUCP ( Todd Burkey )
Newsgroups: comp.realtime
Subject: Re: Data acquisition/control on i386
Message-ID: <1990Jan5.212040.5388@stag.UUCP>
Date: 5 Jan 90 21:20:40 GMT
References: <1989Dec10.094755.21999@me.toronto.edu> <1989Dec28.104004.5697@me.toronto.edu> <1990Jan4.074652.1026@stag.UUCP> <8461@rosevax.Rosemount.COM>
Reply-To: trb@stag.UUCP ( Todd Burkey )
Organization: Mindtools ST Access Group, Plymouth, MN
Lines: 36

In article <8461@rosevax.Rosemount.COM> bill@bert.Rosemount.COM (William M. Hawkins) writes:
>In article <1990Jan4.074652.1026@stag.UUCP> trb@stag.UUCP ( Todd Burkey ) writes:
>>In article <1989Dec28.104004.5697@me.toronto.edu> kokody2@me.utoronto.ca writes:
>>>Also of interest is
>>>how robust the data acquisition/control is under varying machine loads.
>>
>>Very robust, since our controllers use an extremely tunable analog PID
>>configuration.
>
>Todd, what do you mean by "extremely tunable"?  It has been my
>experience that PID's are not tuned to constants (P, I, and D)
>with more than a few significant digits, because the real world
>conspires to change the gains and time constants of electro-
>mechanical devices.

We use 8 bit D/A converters to control the PID of analog controllers.
The computer can adjust the PID, but the actual PID servo error
feedback loop mechanism is real-time (i.e. no delay between
sampling).

>The original question dealt with stability under varying machine
>loads.  This becomes a problem when the dead time between taking
>a measurement and manipulating the output is more than 10 percent
>of the dominant lag time.  If the external process has transport
>lag, add that to the processing time.

The analog PID adjustment inherently solves this problem.
Note that we build our controllers for materials testing using
hydraulic actuators. The only time we see the affects of transport lag
is if we are performing complex real-time curve-fitting of data in
order to dynamically adjust the control signals (i.e. as is required
in crack growth rate tests).

  -Todd Burkey
   Software Development Manager
   Interlaken Technology Corporation