[From Rick Marken (940718.1430)]
Paul George (940718 0930) --
The engineer is usually interested in 1) keeping some controlled variable
within a range (normal operation), 2) designing the system so that it has the
necessary sensors and instrumentality to keep the process under control, and
3) anticipating and detecting any circumstance that indicate the process is
getting out of control (i.e. a defect in 2).
I don't understand point 3). Are you trying to anicipate deviations of a
controlled variable from its reference state or are you trying to anticipate
disturbances to the controlled variable?
'Alerting' (ducking to avoid bricks from Rick Marken) is a big part of
industrial control systems
Satellite control systems, too. Of course, a signal is only "alerting" if the
operator has learned to treat the signal that way; "alertingness" is
determined by the the operator, not the signal.
Rick
[Paul George 940719 11:30]
[From Rick Marken (940718.1430)]
3) anticipating and detecting any circumstance that indicate the process is
getting out of control (i.e. a defect in 2).
I don't understand point 3). Are you trying to anicipate deviations of a
controlled variable from its reference state or are you trying to anticipate
disturbances to the controlled variable?
I didn't phrase it very clearly. The system normally perceives more than it can
affect. In design I must anticipate different kinds of disturbances that the
system must detect in order to control the process (sorry;-). Sometimes that
'controlled variable' can be controlled (i.e. affected by an action of a
control system) sometimes it can't. I must anticipate accident, ignorance, and
malice. Ideally I will design the control system so that the process _cannot_
run away and no hazardous situation can occurr. Otherwise I must detect the
condition and inform the operator, who (hopefully) can do something to correct
the situation, or prevent disaster, or at least mitigate the effects.
Kodan lieutenant : "We are trapped in the moon's gravitational pull, what do we
do!!"
Kodan commander: "We Die."
{From the movie 'The Last Starfighter'}
Paul
PS: I finally got ahold of B:CP, YEA!!
<[Bill Leach 940719.19:12 EST(EDT)]
[From Rick Marken (940718.1430)]
Paul George (940718 0930) --
3) anticipating and detecting any circumstance that indicate the
process is getting out of control (i.e. a defect in 2).
Rick:
I don't understand point 3). Are you trying to anicipate deviations of a
controlled variable from its reference state or are you trying to
anticipate disturbances to the controlled variable?
Among other things, in engineered control systems, there are often
environmental conditions whose status is quite important to the control
process but is not controlled by the engineered system hardware.
An example that I can think of right off the top of my head would be a
batch process tank that is manually made up by an operator. An
engineered control system would often be designed to at least estimate
when a new batch of chemicals might be needed.
A different sort of example is the situation where a sensor has a
lifetime and it is difficult to determine the sensor's status. The
control system then may attempt to create "lifetime statistics" for the
sensor and even attempt to derive failure clues from experience with the
actual operating process.
I would say that living control systems do the same sort of thing but 1)
we are often probably not aware of it even when we are doing it ourselves
and 2) we are so damned adaptive at times that even a careful observer
might not notice a change that we make to continue to control a
perception when something "goes wrong" with whatever method that we were
using.
-bill