Page 88 - Sensors and Control Systems in Manufacturing

Classification and Types of Sensors
In an automatic process, the machine, the controller, and the sen- 49
sors interact with one another to exchange information. Mainly, there
are two types of interaction between the controller and the rest of the
system: through either an open-loop control system or a closed-loop
control system.
An open-loop control system (Fig. 2.4) can be defined as a system in
which there is no feedback. Motor motion is expected to faithfully
follow the input command. Stepping motors are an example of open-
loop control.
A closed-loop control system (Fig. 2.5) can be defined as a system in
which the output is compared to the command, with the result being
used to force the output to follow the command. Servo systems are an
example of closed-loop control.

Disturbance variables

Correcting Control path
device
Mass flow

Controller Open sequence
output of actions

Controller Input variable

Auxiliary energy
FIGURE 2.4 An open-loop control system.

Disturbance variables

Actuator Regulated Measuring device
control path
Mass flow

Correcting Closed sequence
variable of action
Regulated Actual value (controlled variable)
controller Reference value (command variable)

Auxiliary energy

FIGURE 2.5 A closed-loop control system.