May arise— that of getting T to go to some state of equilibrium
That has some desired property. When this is so, the solution given
There for the Markovian machine is, of course, still valid: one cou-
Ples on a vetoer.
Continuous variation. After these primitive forms, we
Arrive at the regulators whose variables can vary continuously. (It
Must be remembered that the continuous is a special case of the
Discrete, by S.2/1.) Of the great numbers that exist I can take only
One or two for mention, for we are interested here only in their
General principles.
Typical is the gas-heated incubator. It contains a capsule which
Swells as the temperature rises. The mechanism is arranged so that
The swelling of the capsule cuts down the size of the gas flame (or
Of the amount of hot air coming to the incubator); an undue rise of
Temperature is thus prevented.
236
Concentration
CO2 in blood
Rate of Ex-
Cretion of CO2
Again the system shows the features just mentioned.
Among the innumerable examples of such mechanisms
Should be included the economic. Tustin’s Mechanism of Eco-
237
A N I N T R O D UC T I O N T O C Y B E R NE T I C S
TH E ERR O R- CO N TR O LLED REG U LA TO R
Nomic Systems shows how closely their properties are cussed
Here.
Ex. 1: Draw the diagram of immediate effects of any regulator known to you.
Ex. 2: (Continued.) Think of some other parameters whose change would affect
The regulator’s working; add them to the diagram.
A variant of this class, worth mention for the sake of com-
Pleteness, is that in which the regulating mechanism becomes
Active only intermittently.
A reservoir tank, for instance, may have the level of fluid in it
Kept between two given levels by a siphon which has its inner
Opening at the lower level and its bend at the upper level. If the
Supply is usually greater than the demand, the siphon, by coming
Into action when the fluid reaches the upper level and by stopping
Its action when it reaches the lower, will keep the level within the
Desired range.
Many physiological regulators act intermittently. The reaction
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To cold by shivering is such a case. This particular reaction is of
Special interest to us (compare S.12/4) in that activity in the regu-
Lator can be evoked either by an actual fall in the bodily tempera-
Ture (error-control, from E) or, before the body has had time to
Cool, by the sight of things that will bring cold (control from D).
TH E PO WE R AM PL IFIE R
The fact that the discussion in this chapter has usually
Referred to the output E as being constant must not be allowed to
Obscure the fact that this form can cover a very great number of
Cases that, at first sight, have no element of constancy in them. The
Subject was referred to in S.11/15. Here we shall consider an appli-
Cation that is important in many ways already, and that will be
Needed for reference when we come to Chapter 14. I refer to those
Regulators and controllers that amplify power.
Power amplifiers exist in many forms. Here I shall describe
Only one, selecting a form that is simple and clear (Fig. 12/21/1).
Compressed air is supplied freely at A and makes its way past
The constriction C before either going into the bellows B or escap-
Ing at the valve V. The pressure at A is much higher than the usual
Working pressure in B, and the aperture at C is small, so air flows
Past C at a fairly constant rate. It must then either escape at V or
Accumulate in B, driving up the pressure z. How fast the air escapes
At V, where a hole is obstructed to some degree by a cone, depends
On the movement up or down (x) of the cone, which is attached to
238
One end of a light stiff rod J, which can turn on a pivot K. Thus if
K is unmoving, a movement down at the other end L will lift the
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