Industrial Communication Systems

20-6 Industrial Communication Systems

the sampling period T, while the time spent between the sampling and the actuation instants is negli-

gible

or

constant

and

known;

but

the

sampling

and

actuation

messages

take

some

time,

which

depends

on

the

access

scheme

and

the

relationship

used,

and

the

control

law

requires

some

computation

time,

so

the

above

assumption

does

not

hold.

is

eect

becomes

more

important

as

the

network

trac

load

increases.

Considering

an

NBC

scheme

(Figure

20.2),

in

which

the

control

loops

consist

of

plants

G,

and

con-

trollers

C,

which

exchange

through

messages

the

sampled

variables

y(kT)

and

the

control

variables

c(kT),