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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/7/27/2019 ME825 VI Sensors Lesson 01
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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/7/27/2019 ME825 VI Sensors Lesson 01
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Data Acquisition System
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What is DSP?
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1 3 5 7 911
13
15
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25
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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
Quantity Symbol Unit Unit Abbre.
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
http://www.ni.com/http://www.ni.com/7/27/2019 ME825 VI Sensors Lesson 01
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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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Error in Measurement
There are various types of error in
measurement:
absolute error
gross error
systematic error
random error limiting error
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Error in Measurement
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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Error in Measurement
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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Error in Measurement
Errors are generally categorized
under the following three (3) major
headings: Gross Errors
Systematic Errors
Random Errors
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Error in Measurement
Gross Error
generally the fault of the person using
the instruments such as incorrect reading, incorrect
recording, incorrect use etc.
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Error in Measurement
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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Error in Measurement
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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Error in Measurement
Environmental errors
Environmental conditions
harsh environments such as
high temperature, pressure, or humidity,
strong electrostatic or electromagnetic fields
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Error in Measurement
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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Error in Measurement
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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Error in Measurement
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
Quantity Symbol Unit Unit Abbre.
l meter
Capacitance F
Time second
T Kelvino
K
Charge
Evaluation
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Test - Answer
Quantity Symbol Unit Unit Abbre.
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
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
Quantity Symbol Unit Unit Abbre.
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