# Breaking the Loop

**URL:** <http://discourse.iapct.org/t/breaking-the-loop/1956>\
**Category:** CSG1998\
**Created:** [January 2, 1998, 3:05pm UTC](http://discourse.iapct.org/t/breaking-the-loop/1956 "1998-01-02T15:05:12Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Fred\_Nickols3](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/f/9de053/32.png) [@Fred\_Nickols3](http://discourse.iapct.org/u/Fred_Nickols3)\
**Post date:** [January 2, 1998, 3:05pm UTC](http://discourse.iapct.org/t/breaking-the-loop/1956/1 "1998-01-02T15:05:12Z")

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> Bill Powers (980101.0754 MST), responding to Martin Taylor 971231 17:45 --

Martin:

> > One way of studying any  
> > feedback structure is to break the loop somehwere and to look at the  
> > input-output relations among the components of the loop. That's what  
> > a psychophysical experiment (other than method of adjustment) does.

Bill:

> Breaking the loop works fine for an artificial nonadaptive control  
> organization. It is much harder to use with a living control system,  
> because breaking the loop means loss of control, and loss of control  
> usually leads to an immediate switch to a different mode of control. So  
> when you think you're measuring the same system open-loop, you're probably  
> looking at a different system.

Martin's original post almost enticed me into responding...

Alternatively, controlling for a perception of "knowledgeable," Martin's  
post offered me an opportunity to maintain that perception (at least in my  
own eyes, figuratively speaking)...

In any event, I agree with Martin and Bill (surprise, surprise).

What Martin's post reminded me of was my second generation of fire control  
computer, the MK 47. My first generation fire control computer was the old  
MK 1A, an electro-mechanical analog beast filled with cams and gears and  
resolvers, and miles of brightly colored spaghetti-like wiring. In the case  
of the old MK 1A, the emphasis was clearly on the mechanical portion of  
electro-mechanical. The MK47, like the MK 1A, was from the Ford Instrument  
Division of the Sperry-Rand Corporation, however, it placed the emphasis on  
the electro portion of electro-mechanical. Gone were the cams and most of  
the gears. The motor-driven time line remained but almost all computations  
were performed by a combination of resolvers and little solid-state plug-ins  
referred to as "Z" networks (quite literally, little black boxes). Many of  
these Z networks were embedded in what we called "rat race" loops, that is,  
closed loops consisting of still more closed loops (a hierarchy?) in which  
outputs were part of the inputs used to calculate the outputs.

When something went wrong, as it did from time to time, troubleshooting the  
MK47 was a bitch! Once you got into those rat-race loops, about the only  
way you could isolate the fault was to begin "breaking the loop," as Martin  
terms it. This entailed disconnecting the actual wiring. It proved far  
easier and quicker to keep on hand a ready stock of the various types of Z  
networks and simply "easter-egg" our way to the faulty component. That flew  
in the face of accepted troubleshooting practice and also contradicted stern  
Navy policy about not keeping "battle spares" in the working space. As a  
practical matter, we technicians ignored both restraints and, mindful of our  
mission to "keep the weapons systems in peak operating condition at all  
times and, if it goes down, bring it back up as quickly as possible," we (or  
at least I) kept a suitable supply of "battle spares" on hand. Further  
advances in technology led to a generation of digital computers and a  
generation of technicians whose troubleshooting skills were "raised a level"  
to where all they had to find was the faulty module, not the faulty  
component. The era of plug-in-a-new-module as the central process of fault  
isolation had arrived. Old timers, like me, were convinced that the new  
generation of technicians couldn't troubleshoot their way out of a wet paper  
bag -- but then "old timers" all feel that way, don't they?

But, as Bill observes, "breaking the loop" applies to artificial systems  
such as the MK47 computer, not to living control systems -- although, I  
wonder if sensory deprivation experiments might not qualify as "breaking the  
loop."

Anyway, a Happy New Year to one and all...

Regards,

Fred Nickols  
The Distance Consulting Company  
nickols@worldnet.att.net  
[http://home.att.net/~nickols/distance.html](http://home.att.net/~nickols/distance.html)