lecture 1- electronic measurement systems
DESCRIPTION
Electrical EngineeringTRANSCRIPT
04/19/2023 EAB 3602 2009/2010 2
INTRODUCTION
• Class schedule: Teusday, 8 am - 10 pm, BK10• Lab: Wednesday 2-5 pm (starts next week)– Instrumentation Lab, KEE (Tower, Level 6) :Lab 1-7– Makmal Pemprosesan BahanBio, KBP: Lab 8-10
• Grading:– Quiz & Assignment: 10 %– Lab : 20 %– Test 1 & 2 : 30 %– Final Exam : 40 %
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• References:– Fundamentals of Electricity for Agriculture- Robert
J Gustafon and Mark T Morgan 2004. 3rd Edition.– Electronic Instrumentation – H S Kalsi, 2004
(McGraw-Hill , 2nd Edition)– Introduction to Instrumentation and
Measurements – Robert B. Northrop, 2005 (CRC Press , 2nd Edition)
– Notes and Handouts
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Introduction
• To introduce electronic instrumentation systems so the students will acquire an ability to make accurate and meaningful measurements of mechanical and thermal quantity.
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Introduction
• Instrumentation is a technology of measurement
• Measuring is basically used to monitor a process or operation, or as well as the controlling process.
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Quantity
• Mechanical quantity:– Strain, force, pressure, moment, torque,
displacement, velocity, acceleration, flow velocity, mass flow rate, volume flow rate, frequency, and time
• Thermal quantity:– Temperature, heat flux, specific heat, and thermal
conductivity
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
Power supply provides the energy to drive the transducer
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
The transducer is an analog device that converts a change in the mechanical or thermal quantity being measured into a change of electrical quantity.
E.g. ∆Strain --- ∆Resistance
Strain gage type transducers
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
Signal conditioners are electronic circuit that convert, compensate, or manipulate the output from the transducer into a more usable electrical quantity.
E.g. ∆resistance --- ∆voltage using a Wheatstone Bridge
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
Amplifiers are required in the system when the voltage output from the transducer-signal conditioner combinations is small.
E.g. Amplifier with gains of 10 to 1000 are used to increase the signals to level (1-10V) that are compatible with the voltage-measuring devices used in the system.
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
Recorders are voltage-measuring devices used to display the measurement in a form that can be read and interpreted. Recorders may be analog (oscilloscopes and magnetic ape recorder) or digital (numerical array).
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
Data processors are used with instrument systems that incorporate analog- to-digital converters (A.D) and provide the output signal presenting the measurement in a digital code. The output from the processor is displayed in graphs or tables. Example: Computer
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Electronic Instrumentation System
Power Supply Transducer
Conditioning Circuit
Amplifier
Recorder Data processor Engineering Analysis
An Engineering analysis is conducted to evaluate new or modified designs of a machine component, structure, electronic system, or vehicle to ensure efficient and reliable performance when the prototype is placed in operation.
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QUALITIES OF MEASUREMENTS
• PERFORMANCE CHARACTERISTICS– Static– Dynamic
• HOW TO QUANTIFY?– Error Measurements– Statistical Analysis
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CHARACTERISTICS OF MEASUREMENT SYSTEMS
• Static Characteristic:– used to define the performance criteria for the
measurement of quantities that remain constant(Considered for instrument to measure unvarying
process condition)
Measurement Errors
• Deviation of a reading from the expected value of the measured variable
• Extent of measurement error must be stated with the measurement
• Error in measurement is expressed as absolute error or percentage of error
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Error Calculation
Absolute error (e)
The difference between the expected (Yn) and the measured (Xn) value of a variable
Percentage of error
e = Yn - Xn
Percent error = (100)Yn
Yn - Xn
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Types of Static Errors
• Divided into four categories:–Gross Errors–Systematic Errors–Random Errors–Limiting Errors
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Gross Errors
• Generally the fault of the person using the measuring instrument such as incorrect reading, incorrect recording, incorrect use etc
• Avoidable and must be identified and minimized if not eliminated
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Systematic Errors
• Probable causes:– Instrument error– Environmental effect– Observational errors
• Causes shall be identified and corrected
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Random Errors
o Generally an accumulation of large numbers of small inherent causes
o Shall be statistically analyzed and reduced
o Prompt for better accuracy and precise instrument
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Limiting Errors
o Manufacturing limitation to the accuracy of an instrument
o Stated as percentage of full-scale deflection
o Increases as measured value less than full-scale deflection
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Limiting Errors (cont’d)
• Example:
A 300-V voltmeter is specified to be accurate within ±2% at full scale. Calculate the limiting error when the instrument is used to measure a 120-V source.
The magnitude of the limiting error is
2/100 x 300 = 6V
Therefore, the limiting error at 120 V is
6/120 x 100 = 5%
(reading < full scale, limiting error increased)
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• Accuracy – The degree of exactness
of a measurement compared to the expected value
A = 1 - Yn
Yn - Xn
Accuracy vs. Precision
• Precision– A measure of consistency,
or repeatability of measurements
Xn - XnPrecision = 1 -Xn
Xn = the value of the nth measurement
nX = the average of the set of n measurements
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Example
The expected value of the voltage across a resistoris 5.0V. However, measurement yields a value of4.9V. Calculate:
a) absolute error (0.1)b)% error (2%)c) relative accuracy (0.98)d) % accuracy (98%)
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CHARACTERISTICS OF MEASUREMENT SYSTEMS
• Dynamic Characteristic– Concerned with the relationship between the
system input and output when the measured quantity is varying rapidly
Measurement Uncertainty
• Probability that a reading falls within the interval that contain true value
• Confidence level for margin of errors• Statistically determined• Reflect instrument imprecision
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Statistical Analysis of Error in Measurement
oMean value/ Arithmetic Mean oDeviationoAverage deviation (D)oStandard deviation (S)
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n
1i
n321 x x x x
n
x
nx i
Arithmetic mean/average
n = total number of piece of data
xn = the value of the nth measurement
xi = set of number
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Deviation
• The difference between each piece of data and arithmetic mean
xxd nn * Note
0 21 ntot dddd
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Average deviation (D)
• precision of a measuring instrument
- high D low precision
- low D high precision
n
dddD n
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Standard deviation (S)
• The degree to which the value vary about the average value
30nfor
1
1 1
2
1
2
n
d
n
xxS
n
ii
n
ii
30 n for 1
2
n
dS
n
ii
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ExampleFor the following data compute
(a) The arithmetic mean (49.9)
(b) The deviation of each value (0.2,-0.2,-0.3,0.3)
(c) The algebraic sum of the deviation (0)
(d) The average deviation (0.25)
(e) The standard deviation (0.294)
x1= 50.1
x2= 49.7
x3= 49.6
x4= 50.2
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Calibration
• Process of establishing the relation between the indication of a measuring instrument and the value of a measurement standard
• Traceability to International Standard• Calibration improve accuracy
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