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Plug-in I/O Cards

10-2

Data Acquisition and Control

Tutorial & Software

The layout of a typical PC-based data acquisition system

PC-based Data Acquisition System

Overview

In the last few years, industrial PC I/O interface products have become increasingly reliable,

accurate and affordable. Because of this, PC-based data acquisition and control systems

are now widely used in industrial and laboratory applications such as: monitoring, control,

data acquisition and automated testing.

Selecting and building a DA&C (Data Acquisition and Control) system that actually does

what you want it to do requires some knowledge of electrical and computer engineering.

This tutorial gives a brief introduction to what DA&C systems do and how to conﬁgure

them. It covers:

Transducers and Actuators

Signal Conditioning

Data Acquisition and Control Hardware

Getting Started

Computer System Software

Transducers and Actuators

A transducer converts temperature, pressure, level, length, position, etc. into voltage,

current, frequency, pulses or other signals.

Thermocouples, thermistors and resistance temperature detectors (RTDs) are common

transducers for temperature measurements. Other types of transducers include ﬂow

sensors, pressure sensors, strain gauges, load cells and LVDTs, which measure ﬂow

rate, pressure variances, force or displacement.

An actuator is a device that activates process control equipment by using pneumatic,

hydraulic or electrical power. For example, a valve actuator can open and close a valve

to control ﬂuid rates.



Signal Conditioning

Signal conditioning circuits improve the quality of signals generated by transducers before

they are converted into digital signals by the PC's data-acquisition hardware. Examples

of signal conditioning are signal scaling, ampliﬁcation, linearization, cold-junction

compensation, ﬁltering, attenuation, excitation, common-mode rejection, and so on.

One of the most common signal conditioning functions is ampliﬁcation. For maximum

resolution, the voltage range of the input signals should be approximately equal to the

maximum input range of the A/D converter. Ampliﬁcation expands the range of the

transducer signals so that they match the input range of the A/D converter. For example,

a x10 ampliﬁer maps transducer signals that range from 0 to 1 V into the range 0 to 10

V before they go into the A/D converter.

Using digital I/O and SSRs to open and close a valve

Courtesy of Steven Engineering, Inc.-230 Ryan Way, South San Francisco, CA 94080-6370-Main Office: (650) 588-9200-Outside Local Area: (800) 258-9200-www.stevenengineering.com

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