In less than two decades, the PC has become the most widely used platform for data acquisition and control. The main reasons for the popularity of PC-based technology are low costs, flexibility and ease of use, and, last but not the least, performance. This solid and dependable trait is all thanks to the use of ‘off-the-shelf’ components. Data acquisition with a PC enables one to display, log and control a wide variety of real world signals such as pressure, flow, and temperature. This ability coupled with that of easy interface with various stand-alone instruments makes the systems ever more desirable. Until the advent of the PC, data acquisition and process monitoring were carried out by using dedicated data loggers, programmable logic controllers and or expensive proprietary computers. Today’s superb software-based operator interfaces make the PC an increasingly attractive option in these typical applications:

• Laboratory data acquisition and control
• Automatic test equipment (ATE) for inspection of components
• Medical instrumentation and monitoring
• Process control of plants and factories
• Environmental monitoring and control
• Machine vision and inspection

The key to the effective application of PC-based data acquisition is the careful matching of real world requirements with appropriate hardware and software. Depending on your needs, monitoring data can be as simple as connecting a few cables to a plug-in board and running a menu-driven software package. At the other end of the spectrum, you could design customized sensing and conversion hardware, or perhaps develop application software to optimize a system. This guide gives both the novice and the experienced user a solid grasp of the principles and practical implementation of interfacing the PC and stand-alone instruments with real world signals. The main objective of this guide is to give you a thorough understanding of PC-based data acquisition systems and to enable you to design, specify, install, configure, and program data acquisition systems quickly and effectively. After reading this guide, we believe you will be able to:

• Demonstrate a sound knowledge of the fundamentals of data acquisition (with a focus on PC-based work)
• Competently install and configure a simple data acquisition system
• Choose and configure the correct software
• Avoid the common pitfalls in designing a data acquisition system

This guide is intended for engineers and technicians who are:

• Electronic engineers
• Instrumentation and control engineers
• Electrical engineers
• Electrical technicians
• Systems engineers
• Scientists working in the data acquisition area
• Process control engineers
• System integrators
• Design engineers

A basic knowledge of electrical principles is useful in understanding the outlined concepts, but this guide also focuses on the fundamentals; hence, understanding key concepts should not be too onerous.

Table of Contents

(D-E to be added soon)

Plug-in data acquisition boards

• 1 Introduction
• 2 A/D Boards
  • 2.1 Multiplexers
  • 2.2 Input signal amplifier
  • 2.3 Channel-gain arrays
  • 2.4 Sample and hold circuits
  • 2.5 A/D converters
  • 2.6 Memory (FIFO) buffer
  • 2.7 Timing circuitry
  • 2.8 Expansion bus interface
• 3 Single ended vs differential signals
  • 3.1 Single ended inputs
  • 3.2 Pseudo-differential configuration
  • 3.3 Differential inputs
• 4 Resolution, dynamic range and accuracy of A/D boards
  • 4.1 Dynamic range
  • 4.2 Resolution
  • 4.3 System accuracy
• 5 Sampling rate and the Nyquist theorem
  • 5.1 Nyquist's theorem
  • 5.2 Aliasing
  • 5.3 Preventing aliasing
  • 5.4 Practical examples
• 6 Sampling techniques
  • 6.1 Continuous channel scanning
  • 6.2 Simultaneous sampling
  • 6.3 Block mode operations
• 7 Speed vs throughput
• 8 D/A boards
  • 8.1 Digital to analog converters
  • 8.2 Parameters of D/A converters
  • 8.3 Functional characteristics of D/A boards
  • 8.4 Memory (FIFO) buffer
  • 8.5 Timing circuitry
  • 8.6 Output amplifier buffer
  • 8.7 Expansion bus interface
• 9 Digital I/O boards
• 10 Interfacing digital inputs/outputs
  • 10.1 Switch sensing
  • 10.2 AC/DC voltage sensing
  • 10.3 Driving an LED indicator
  • 10.4 Driving relays
• 11 Counter/timer I/O boards

Distributed and stand-alone loggers/controllers

• 1 Introduction
• 2 Methods of operation
• 2.1 Programming and logging data using PCMCIA cards
• 2.2 Stand-alone operation
• 2.3 Direct connection to the host PC
• 2.4 Remote connection to the host PC
• 3 Stand-alone logger/controller hardware
• 3.1 Microprocessors
• 3.2 Memory
• 3.3 Real time clock
• 3.4 Universal asynchronous receiver/transmitter (UART)
• 3.5 Power supply
• 3.6 Power management circuitry
• 3.7 Analog inputs and digital I/O
• 3.8 Expansion modules
• 4 Communications hardware interface
• 4.1 RS-232 interface
• 4.2 RS-485 standard
• 4.3 Communication bottlenecks and system performance
• 4.4 Using Ethernet to connect data loggers
• 5 Stand-alone logger/controller firmware
• 6 Stand-alone logger/controller software design
• 6.1 ASCII based command formats
• 6.2 ASCII based data formats
• 6.3 Error reporting
• 6.4 System commands
• 6.5 Channel commands
• 6.6 Schedules
• 6.7 Alarms
• 6.8 Data logging and retrieval
• 7 Host software
• 8 Considerations in using standalone logger/controllers
• 9 Stand-alone logger/controllers vs internal systems
• 9.1 Advantages
• 9.2 Disadvantages

Specific techniques

• 1 Open and closed loop control
• 1.1 Definitions
• 1.2 Fluid level closed loop control system
• 1.3 PID control algorithms
• 1.4 Transient performance – step response
• 1.5 Deadband
• 1.6 Output limiting
• 1.7 Manual control – bumpless transfer
• 2 Capturing high speed transient data
• 2.1 A/D board operation and memory requirements
• 2.2 Trigger modes (pre- and post-triggering)
• 2.3 Trigger source and level

NEXT: Introduction

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