me825 vi sensors lesson 01

7/27/2019 ME825 VI Sensors Lesson 01

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ME825 Virtual Instrumentation


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What has been seen in VI ?

Introduction What is Virtual Instrumentation ?

Why Virtual Instrumentation ?

To Whom? Components of a VI

Sensor

Signal Conditioning & Data Acquisition (DAQ)

Software to acquire, Analyze and present LabVIEW Basics & Practice

DAQ basics


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End to End Data Acquisition (DAQ)

Graphics from www.ni.com DAQ Fundamentals

Software
http://www.ni.com/http://www.ni.com/


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End to End Data Acquisition (DAQ)

Graphics from www.ni.com DAQ Fundamentals

Software


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Data Acquisition System


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What is DSP?

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25

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7

A/D Converter: Sampling Rate Determines how often conversions take

place.

The higher the sampling rate, the better

Analog Input 4 Samples/cycle

8 Samples/cycle 16 Samples /cycle


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8

A/D Converter: Sampling Rate Aliasing

Acquired signal gets distorted if sampling

rate is too small.(9Hz signal sampled at 11 S/s)


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Sensors

Temperature

Pressure

Flow

Torque

Force/Load

RPM


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Sensors

Light

Force

Displacement Acceleration

Strain

RPM


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Sensors


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Sensors and Transducers

Transducer

Voltage or current signal

Position sensor

Strain gauge, Load cell Pressure sensor


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Sensors

Thermistors


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What next ?

Assumption

Have fairly good basic information on

LabVIEW

Basics of DSP clear

Time to move to next component in VI

Sensors & measurement

Measurement terminology

Terms and definitions


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Credits and Courtesy acknowledgement

Some of the Slides were prepared by Prof.

Syakirin for his course at UMP, BE1313

Few slides prepared by John F. Muratore

for RICE University Mech 299 course

Graphics were taken from different

sources and acknowledged at each slide

All slides modified to suit our course on VI

Credits and Courtesy acknowledged


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Objectives

At the end of this Class, you should be able to:

explain units and quantities in

measurement

calculate various types of error in

measurement

Explain the meaning of some terms in

instrumentation field


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Introduction

Instrumentations serve three (3) basic

functions: -

indicating

recording

controlling


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3 basic functions

Indicating Recording Controlling

General-purpose electrical &

electronics test instrumentsIndustrial-process

Control / automated

system

Function & Characteristics of

Instruments


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Fundamental Quantity

Quantity Symbol Unit Unit Abbre.

Length l meter m

Mass m kilogram kg

Time t second s

Temperature T Kelvin K

Electric current I Ampere A

Units


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Derived Quantity


emf/ voltage V volt V

charge Q coulomb C

resistance R Ohm

capacitance C farad F

inductance L hendry H

Units cont..


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Measurement Standards

Standards are defined in 4

categories:

international standards. primary standards.

secondary standards.

working standards.


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Measurement

The process of comparing an

unknown quantity

with an accepted

standard quantity


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Think Pair Share

First 60 seconds

Think alone (reflect) on

What is the meaning of error? List thetype of error in measurement

Next 60 Seconds

Interact with your pair compare the list


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Define

Accuracy

Precision

Resolution

Take 60 seconds , write it down, compare

with your neighbour


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Accuracyand Precision

From www.ni.com Measurement Fundamentals, Sampling Quality


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Accuracy and Precision

Accuracy: The maximum expected

difference in magnitude between measured

and true values (often expressed as a

percentage of the full-scale value).

Precision: The ability of the instrument to

repeat the measurement of a constant

measurand. More precise measurements

have less random error.


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Standard Deviations In A Normal

Distribution

Source: Wikipedia

The probability of a value being between mean plus 3 sigma and

mean minus 3 sigma in a normal distribution is 99.6%

NoteThis is two sided can vary the same on either side of the mean not all

populations of data are two sided


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Resolution

Resolution: The smallest possible

increment discernible between measured

values. As the term is used, higher

resolution means smaller increments


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Error in Measurement

Error - The deviation of a

reading or set of readings

from the expected value of

the measured variable.


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There are various types of error in

measurement:

absolute error

gross error

systematic error

random error limiting error


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Absolute error.Absolute errormaybe defined as the difference

between the expected value of the variable

and the measured value of the variable, or

e = Yn Xn

where:

e = absolute error.Yn = expected value.

Xn = measured value


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to express as % error =

relative accuracy

where: e = absolute error.

Yn = expected value

Xn = measured value

)100(n

Y

e

n

nn

Y

XYA

1


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Errors are generally categorized

under the following three (3) major

headings: Gross Errors

Systematic Errors

Random Errors


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Gross Error

generally the fault of the person using

the instruments such as incorrect reading, incorrect

recording, incorrect use etc.


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Systematic Error

due to problems with instruments/

environmental effects/

or observational errors.

Example???

parallax error wrong estimation reading scale

Instrument errors

Environmental errors

Observational errors


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Ins trument errors

due to friction in the bearings of the metermovement,

incorrect spring tension, improper calibration

faulty instruments.

Ins trument error can be reduced by

proper maintenance, use, and handling ofinstruments


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Environmental errors

Environmental conditions

harsh environments such as

high temperature, pressure, or humidity,

strong electrostatic or electromagnetic fields


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Observational errors Observational errors are those errors

introduced by the observer.

The parallax error introduced in reading ameter scale

the error of estimation when obtaining a

reading from a meter scale.


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Random Errors

generally the accumulation of a large

number of small effects

maybe of real concern only in

measurements requiring a high degree of

accuracy.

such errors can only be analyzed

statistically.


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Limiting Errors

manufacturers of instruments state that an

instrument is accurate within a certain

percentage of a full-scale reading.

example is; a voltmeter is accurate within

2% at full-scale deflection.

this specification is called the limiting

errors.


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Measurement terminology

Measurement Error

Accuracy

Precision and Mean

Resolution Mean

Variance andStandard deviation

Finesse

Sensitivity

Range

Offset (bias) andscale factor shift

Linearity andLinear Regression

Hysteresis

Response Time

Real Time

Gain


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Summary

Some terms +definitions are as below:

Accuracy The degree of exactness of a

measurement compared to the expected

value Precision A measure of consistency, or

repeatability of measurements.

Error ---???


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Summary

Instrumenta device or mechanism used to

determine the present value of a quantity

Measurement

a process of comparing anunknown quantity with an accepted standard

quantity.

Standard an instrument or device having arecognized permanent (stable) value that is

used as a reference.


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Summary

expected value the most probable value we

should expect to obtain.

deviation the difference between any pieceof data in a set of numbers and the arithmetic

mean of the set of numbers.

transducer a device that converts one formof energy into another form


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Test


l meter

Capacitance F

Time second

T Kelvino

K

Charge

Evaluation


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Test - Answer


Length l meter

Capacitance C farad F

Time t second s

Temperature T Kelvino

K

Charge Q coulomb C

Evaluation


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Fundamental Quantity


Length l meter m

Mass m kilogram kg

Time t second s

Temperature T Kelvin K

Electric current I Ampere A

Units


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Derived Quantity


emf/ voltage V volt V

charge Q coulomb C

resistance R Ohm

capacitance C farad F

inductance L hendry H

Units cont..


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What to Read?

Sensors and Transducers, D Patranabis, 2ndEdition PHI Chapter 1. (page 1-13)

Experimental Methods for Engineers, J P Holman, VIth Edition, McGRAW Hill, Chapter 1&2 (Page 1-44)

Digital Signal processing Demystified , James DBroesch (621.38194 B865), Chapter1 to 5. (Page 3-74)

Virtual Instrumentation using LabVIEW, SanjayGupta and Joseph John Chapter 1 to 10 (Page 1-98)

Files & Slides in your Virtual Class Room

me825 vi sensors lesson 01

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