Page 304 - Sensors and Control Systems in Manufacturing

The Role of Sensors and Contr ol Technology in CIM
5.7.4.4 Counter/Timer 261
A counter/timer can be used to perform event counting, flow meter
monitoring, frequency counting, pulse width and time period mea-
surement, and so on.
Most data acquisition and control hardware is designed with the
multiplicity of functions described earlier on a single card for maximum
performance and flexibility. Multifunction data acquisition for high-
performance hardware can be obtained through PC boards specially
designed by various manufacturers for data acquisition systems.

5.7.5 Computer System
Today’s rapidly growing PC market offers a great selection of PC
hardware and software in a wide price range. Thus, a CIM strategy
can be economically implemented.

5.7.5.1 Hardware Considerations
Different applications require different system performance levels.
Currently, 286, 386, and 486 CPUs will allow a PC to run at bench-
mark speeds from 20 up to 150 MHz. Measurements and process con-
trol applications usually require 80286 systems. However, for appli-
cations that require high-speed real-time data analysis, an 80386 or
80486 system is much more suitable.
5.7.5.2 Industrial PCs
An industrial PC (IPC) is designed specifically to protect the system
hardware in harsh operating environments. IPCs have rugged chas-
sis that protect system hardware against excessive heat, dust, mois-
ture, shock, and vibration. Some IPCs are even equipped with power
supplies that can withstand temperatures from –20 to +85°C for
added reliability in harsh environments.

5.7.5.3 Passive Backplane and CPU Card
More and more industrial data acquisition for sensors and control
systems are using passive backplane and CPU card configurations.
The advantages of these configurations are reduced mean time to
repair (MTTR), ease of upgrading the system, and increased PC-bus
expansion slot capacity.
A passive backplane allows the user to plug in and unplug a CPU
card without the effort of removing an entire motherboard in case of
damage or repair.

5.7.6 Communication Interfaces
The most common types of communication interfaces used in PC-
based data acquisition for sensor and control system applications are
RS-232, RS-422/485, and the IEEE-488 general-purpose interface bus
(GPIB).