Page 299 - Sensors and Control Systems in Manufacturing

The Role of Sensors and Contr ol Technology in CIM
5.7 Data Acquisition for Sensors and Control 257
Systems in CIM Environments
The input signals generated by sensors can be fed into an interface
board, called an I/O board. This board can be placed inside a PC-
based system. As personal computers for CIM have become more
affordable, and I/O boards have become increasingly reliable and
readily available, PC-based CIM data acquisition has been widely
implemented in laboratory automation, industrial monitoring and
control, and automatic test and measurement.
To create a data acquisition system for sensors and control sys-
tems that really meets the engineering requirements, some knowl-
edge of electrical and computer engineering is required. The follow-
ing key areas are fundamental in understanding the concept of data
acquisition for sensors and control systems:

• Real-world phenomena
• Sensors and actuators
• Signal conditioning
• Data acquisition for sensors and control hardware
• Computer systems
• Communication interfaces
• Software

5.7.1 Real-World Phenomena
Data acquisition and process control systems measure real-world
phenomena, such as temperature, pressure, and flow rate. These phe-
nomena are sensed by sensors, and are then converted into analog
signals that are eventually sent to the computer as digital signals.
Some real-world events, such as contact monitoring and event
counting, can be detected and transmitted as digital signals directly.
The computer then records and analyzes this digital data to interpret
real-world phenomena as useful information.
The real world can also be controlled by devices or equipment oper-
ated by analog or digital signals generated by the computer (Fig. 5.10).

5.7.2 Sensors and Actuators
A sensor converts a physical phenomenon—such as temperature,
pressure, level, length, position, or presence or absence—into a volt-
age, current, frequency, pulses, and so on.
For temperature measurements, some of the most common sen-
sors include thermocouples, thermistors, and resistance temperature
detectors (RTDs). Other types of sensors include flow sensors, pres-
sure sensors, strain gauges, load cells, and optical sensors.