Engineering - Molecular Theory of the Living Cell - page 150

Table 5.10 A comparison between thermodynamic and control systems

Thermodynamic
system (TS) Control system (CS)

Scientific discipline Thermodynamics Cybernetics

Key characteristics a

(1) Energy, (2) Entropy,
(3) T, (4) P, and
(5) V

(1) Energy, (2) Entropy, (3) Controller, (4)
Controlled, (5) Representation, (6) Agent,
(7) Information, (8) Goal/Aim/ Teleonomy,
(9) Action, (10) Perception, (11) Affected
variable, (12) Observed variable,
(13) Dynamics, and (14) Disturbances

Principles obeyed b (1) First Law, and

(2) Second Law

(1) First Law, (2) Second Law, (3) Principle
of feedback control (Sect. 5.3.1 ), (4) Principle
of the minimum energy requirement for
information flow (Sect. 4.8 ) , (5) Law
of requisite variety (Sect. 5.3.2 ), and
(6) Principle of Information and Energy
Requirement for Organization (PIERO)
(Sect. 3.1 ) , which may be referred to as
the Law of Requisite Information (LRI)

Relation c

CS
(depending on whether sets are defined extensionally or intensionally,
respectively)
a Some of the same concepts, factors and parameters essential for describing TS are also required
to describe CS in addition to those unique to CS
b Thermodynamic laws are universal and hence obeyed by all material systems including CS. But
there are the laws, rules or regularities found uniquely in control systems. These may be named as
follows: (3)

TS > CS or TS <

¼ the First Law of Cybernetics, (4) ¼ the Second Law of Cybernetics, (5) ¼ the Third

Law of Cybernetics, and (6) the Fourth Law of Cybernetics (see the second row and third column)

c All control systems are thermodynamic systems but not all thermodynamic systems are control
systems

¼

But S has only a small effect on C through the formation of perception. The
controller consists of two components - representation of the controlled system
and the agent responsible for the action of the controller. The relation between
representation and agent is the flow of information which determines the actions of
the agent. The controlled system can be described in terms of two variables - the
affected variable that is altered by the action of the agent and the observed variable
that is observed by the controller through perception. The observed variable also
includes uncontrollable disturbances on the controlled system.
Just as thermodynamics is defined as the scientific study of the thermodynamic
system (TS), control theory or cybernetics can be viewed as the scientific study of
the control system (CS). In Table 5.10 , TS and CS are compared in detail, treating
them as sets of elements. The second and third rows of the table list two different
classes of the elements of TS and CS. The second row lists system characteristics
and the third row lists the laws and the principles being obeyed. Of the 5 elements of
the TS set in the second row, only 2 are found in the CS set, while none of the 12
unique elements of the CS set is found in the TS set. All of the elements of TS in the
third row are included as the elements of CS but none of the four unique elements of