wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Network-Based Control 20-3
Thus, the basic capabilities of any NBC are information acquisition (sensors/users), command
(controllers/users), communication, and network and control (actuators). In broader terms, NCS
research and application is categorized into two parts.
1. Control of network: Study and research on communications and networks to make them suitable
for real-time NCS, e.g., routing control, congestion reduction, efficient data communication, and
networking protocol.
2. Control over network: This deals more with control strategies and control systems design over
the network to minimize the effect of adverse network parameters on NCS performance such as
network delay.
This chapter is mainly focused on “control over network.”
20.3.1 Connection Types
There are two major types of control systems that utilize communication networks. They are (1) sharednetwork
control systems and (2) remote control systems.
20.3.1.1 Shared-Network Control Systems
Using shared-network resources to transfer measurements, from sensors to controllers and control signals
from controllers to actuators can greatly reduce the complexity of connections. This method, as shown in
Figure 20.2, is systematic and structured, provides more flexibility in installation, and eases maintenance
and troubleshooting. Furthermore, networks enable communication among control loops. This feature is
extremely useful when a control loop exchanges information with other control loops to perform more
sophisticated controls, such as fault accommodation and control. Similar structures for NBC have been
applied to automobiles and industrial plants.
20.3.1.2 remote Control Systems
On the other hand, a remote control system can be thought of as a system controlled by a controller
located far away from it. This is sometimes referred to as teleoperation control. Remote data acquisition
systems and remote monitoring systems can also be included in this class of systems.
There are two general approaches to design an NBC system. The first approach is to have several subsystems
form a hierarchical structure, in which each of the subsystems contains a sensor, an actuator,
and a controller by itself, as depicted in Figure 20.3. These system components are attached to the same
control plant. In this case, a subsystem controller receives a set point from the central controller C M . The
subsystem then tries to satisfy this set point by itself. The sensor data or status signal is transmitted back
via a network to the central controller.
A 1
A 2 S 3 A 3
S2
Network
S 1
C 1 C 2 C 3
: Sensor, : Actuator,
: Controller
FIGURE 20.2
Shared-network connections.
© 2011 by Taylor and Francis Group, LLC