Page 688 - Mechanical Engineers' Handbook (Volume 2)
P. 688
1 Characteristics of General-Purpose Control Devices 679
Figure 1 Plant control hierarchy using GPCDs, general-purpose computers (GPCs), and closed-loop
controllers (CLCs).
• Issuing commands to and receiving status information from a set of closed-loop con-
trollers that control individual machine and process variables such as velocity, position,
and temperature. These closed-loop controllers may be separate devices or integral
parts of the GPCD hardware and/or software architecture.
• Issuing commands to and receiving status information from a set of actuators and
sensors directly connected to the controlled operation. These actuators and sensors
may include signal-processing and transmission elements, as described in Chapter 6.
Figure 2 Communication and control paths of a GPCD.
