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Chapter 9Data Acquisition

Introduction

MSP430 Teaching Materials

Texas Instruments IncorporatedUniversity of Beira Interior (PT)

Pedro Dinis Gaspar, António Espírito Santo, Bruno Ribeiro, Humberto Santos

University of Beira Interior, Electromechanical Engineering Departmentwww.msp430.ubi.pt

Copyright 2009 Texas Instruments All Rights Reserved

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Contents

Introduction

Operational Amplifiers Analogue-to-Digital Converter (ADC):

Successive Approximation Register (SAR) converter; Sigma-Delta (SD) converter; Slope converter.

Comparator_A

Laboratory 5: Signal Acquisition

Quiz

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Introduction (1/4)

Most engineering applications require some form of data processing: measurement, control, calculation, communication or data recording;

These operations, either grouped or isolated, are built into the measuring instruments;

The measuring equipment must maintain:• Compatibility and communication between measuring

devices;• Acceptable error margin;• Noise and interference immunity;• Predictable measurement uncertainty;• Suitable type of control (analogue/digital);• Mathematical processing capacity;• …

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Introduction (2/4)

Data acquisition system components:

Sensors:• Convert analogue measurements of physical quantities

(e.g. temperature, pressure, humidity, velocity, flow-rate, linear motion, position) into electrical signals (voltage or current).

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Introduction (3/4)


Signal conditioning (filtering and amplification):• The operations required to convert the measured analogue

signal measured to the electrical signal range of the analogue-to-digital converter (ADC) may involve filtering, amplification, attenuation or impedance transformation.

Analogue-to-Digital Converter (ADC):• Input: Signal to be measured; • Output: A digital code compatible with the digital

processing system;• Requires:

– Sample-and-hold: Used to take a snapshot of the continuously changing input signal and maintain the value over the sample interval set by a clock system;

– A sampling frequency based on the Nyquist theorem.

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Introduction (4/4)


Analogue-to-Digital Converter (ADC) (continued):

– Sample-and-Hold: (Note) Not necessary for Sigma-Delta (SD) converters, nor for slope converters, nor for all flash converters and is automatically implemented as part of the structure of capacitive successive approximation Register (SAR) converters on the MSP430.

– The specifications of these converters will be described in the following sections.

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Quiz (1/3)

1. Sensing:(a) Computes analogue quantities in nature;(b) Separates out analogue measurements into different

categories;(c) Converts quantities in nature to electrical signals;(d) Detects analogue quantities according to their magnitude.

2. Signal conditioning means:(a) The signals are being overlapped;(b) Some characteristics of the input signal is being changed;(c) Filtering, amplitude adjustment or impedance change;(d) None of above.

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Quiz (2/3)

3. The basic functions of analogue-to-digital conversions are:(a) Sense, compute digitally, convert to analogue;(b) Compute as analogue, sense, convert to digital;(c) Convert to digital, sense, condition to analogue;(d) Sense, condition, convert to digital.

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Quiz (3/3)

Answers:

1. (c) Changes quantities in nature to electrical signals.

2. (c) Amplitude adjustment, filtering or its impedance changed.

3. (d) Sense, condition, convert to digital.

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