# Distrurbing alerts

**URL:** <http://discourse.iapct.org/t/distrurbing-alerts/3553>\
**Category:** CSG1994\
**Created:** [July 18, 1994, 9:36pm UTC](http://discourse.iapct.org/t/distrurbing-alerts/3553 "1994-07-18T21:36:08Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Marken\_Richard\_S1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/977dab/32.png) [@Marken\_Richard\_S1](http://discourse.iapct.org/u/Marken_Richard_S1)\
**Post date:** [July 18, 1994, 9:36pm UTC](http://discourse.iapct.org/t/distrurbing-alerts/3553/1 "1994-07-18T21:36:08Z")

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[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

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**Author:** ![Paul\_George](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/p/e68b1a/32.png) [@Paul\_George](http://discourse.iapct.org/u/Paul_George)\
**Post date:** [July 19, 1994, 3:23pm UTC](http://discourse.iapct.org/t/distrurbing-alerts/3553/2 "1994-07-19T15:23:41Z")

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[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!!

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**Author:** ![Bill\_Leach1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/848f3c/32.png) [@Bill\_Leach1](http://discourse.iapct.org/u/Bill_Leach1)\
**Post date:** [July 20, 1994, 12:30am UTC](http://discourse.iapct.org/t/distrurbing-alerts/3553/3 "1994-07-20T00:30:53Z")

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\<[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