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1-2 The Role of the PC
The PC is the part of the Control System that directly controls the manufacturing
process. According to the program stored in its memory, the PC accepts data
from the input devices connected to it, and uses this data to monitor the con-
trolled system. When the program calls for some action to take place, the PC
sends data to the output devices connected to it, to cause that action to take
place. The PC may be used to control a simple, repetitive task, or it may be con-
nected to other PCs, or to a host computer in order to integrate the control of a
complex process.
1-2-1 Input Devices
PCs can receive input from either automated or manual devices. The PC could
receive data from the user via a pushbutton switch, keyboard, or similar device.
Automated input could come from a variety of devices: microswitches, timers,
encoders, photosensors, and so on. Some devices, like the Limit Switch shown
below, turn ON or OFF when the equipment actually makes contact with it. Other
devices, like the Photoelectric Switch and Proximity Switch shown below, use
other means, such as light or inductance, in order to get information about the
equipment being monitored.
Photoelectric switch Limit switch
Proximity switch
The Role of the PC Section 1-2
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