Hardware Reference
In-Depth Information
12 Applications
The PC is a potential prime mover in a huge variety of process control and
instrumentation applications ranging from simple stand-alone machine con-
trollers to fully integrated production control systems. This chapter aims to
provide readers with an introduction to the procedure for selecting and speci-
fying hardware and software for a PC-based instrumentation or process control
system. In addition, several representative applications of PC-based systems
are discussed.
Expansion cards
The range of PC expansion boards currently available from a large number of
manufacturers includes:
•
Analogue I/O cards with up to 16 analogue inputs and up to four buffered
analogue outputs.
•
Digital I/O cards with direct TTL-compatible inputs and outputs.
•
Digital I/O cards with opto-isolated inputs and outputs.
•
Digital I/O cards with buffered I/O lines.
•
Digital output cards fitted with relays or solid-state devices for AC or DC
power control.
•
EPROM programmers.
•
IEEE-488/GPIB interface cards.
•
Network adapter cards.
•
Modem cards.
•
Prototyping cards (these may include the necessary PC ISA/PCI bus interface
logic and provide the user with an area for soldering components fitted into
a 0.1
′′
matrix of plated through holes).
•
Serial communications cards for RS-232, RS-422, RS423, or RS-485 serial
ports.
•
Stepper motor controllers.
•
Multi-function I/O cards (offering mixed analogue and digital I/O facilities).
•
Thermocouple interface cards.
•
High-speed data acquisition cards.
•
Bus
expansion
cards
(which
interface
with
external
card
frames
or
motherboards).
•
PC instrument cards (e.g. function generators, counters/digital frequency
meters, spectrum analysers, etc.).
In addition, the system builder is able to select from a large range of signal
conditioning cards which provide the necessary interfacing circuitry for a wide
range of popular sensors and output devices. It is thus eminently possible to
construct a PC-based process control system simply by selecting 'off-the-shelf '
modules. Only when dealing with very specialized applications it is necessary to
manufacture ones own dedicated I/O cards and/or external signal conditioning
