Page 302 - Sensors and Control Systems in Manufacturing

The Role of Sensors and Contr ol Technology in CIM
An actuator is a device that activates process control equipment 259
by using pneumatic, hydraulic, electromechanical, or electronic sig-
nals. For example, a valve actuator is used to control fluid rate for
opening and closing a valve.

5.7.3 Signal Conditioning
A signal conditioner is a circuit module specifically intended to pro-
vide signal scaling, amplification, linearization, cold junction com-
pensation, filtering, attenuation, excitation, common mode rejection,
and so on. Signal conditioning improves the quality of the sensor sig-
nals that will be converted into digital signals by the PC’s data acqui-
sition hardware.
One of the most common functions of signal conditioning is
amplification. Amplifying a sensor signal provides an analog-to-
digital (A/D) converter with a much stronger signal and thereby
increases resolution. To acquire the highest resolution during A/D
conversion, the amplified signal should be equal to approximately
the maximum input range of the A/D converter.

5.7.4 Data Acquisition for Sensors and Control Hardware
In general, data acquisition for sensors and control hardware per-
forms one or more of the following functions:

• Analog input
• Analog output
• Digital input
• Digital output
• Counter/timer

5.7.4.1 Analog Input
An analog-to-digital (D/A) converter produces digital output directly
proportional to an analog signal input so it can be digitally read by
the computer. This conversion is imperative for CIM (Fig. 5.11).

Digital Code
D0
Analog Signal
D1
D/A
Driver
Converter
D15

FIGURE 5.11 Analog-to-digital converter.