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8/18/2019 Instrumentation and Measurement Introduction
1/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
ENEE4304Instrumentation and
MeasurementsL1
Introduction
Introduction to Measurements
Measurement techniques have beenof immense importance ever sincethe start of human civilization,
When measurements were firstneeded to regulate the transfer ofgoods in barter trade to ensure that
exchanges were fair.
The industrial revolution during thenineteenth century brought about arapid development of newinstruments and measurementtechniques to satisfy the needs ofindustrialized production techniques.
http://www.google.jo/imgres?imgurl=http://4.bp.blogspot.com/-VH8jKYdsQY0/TctHg0iaspI/AAAAAAAAARw/Ws0ap_GWGnk/s1600/Online-Measurement-Tools.jpg&imgrefurl=http://iwasafatbride.blogspot.com/2011/05/measurements.html&usg=__yj3GxiPM0yWN4k1GP4lXgy3MIcE=&h=600&w=900&sz=364&hl=ar&start=9&zoom=1&tbnid=1FpOv4yIVD5DUM:&tbnh=97&tbnw=146&ei=hGyJTs_PDujd4QSf6LyKDw&prev=/search?q=measurements&um=1&hl=ar&sa=N&tbm=isch&um=1&itbs=1http://www.google.jo/imgres?imgurl=http://4.bp.blogspot.com/-VH8jKYdsQY0/TctHg0iaspI/AAAAAAAAARw/Ws0ap_GWGnk/s1600/Online-Measurement-Tools.jpg&imgrefurl=http://iwasafatbride.blogspot.com/2011/05/measurements.html&usg=__yj3GxiPM0yWN4k1GP4lXgy3MIcE=&h=600&w=900&sz=364&hl=ar&start=9&zoom=1&tbnid=1FpOv4yIVD5DUM:&tbnh=97&tbnw=146&ei=hGyJTs_PDujd4QSf6LyKDw&prev=/search?q=measurements&um=1&hl=ar&sa=N&tbm=isch&um=1&itbs=1
8/18/2019 Instrumentation and Measurement Introduction
2/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Applications of Measurement Systems1. Regulating trade
2. Monitoring to allow human beings to take someaction accordingly
3. Use as part of automatic feedback controlsystems
Remember The Five Senses
See
Hear
Touch
Taste
Smell
8/18/2019 Instrumentation and Measurement Introduction
3/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Standardization of Units
Establishment of standards for themeasurement of physical quantitiesproceeded in several countries atbroadly parallel times, and inconsequence, several sets of unitsemerged for measuring the samephysical variable.
An internationally agreed set ofstandard units (SI units or Syst`emesInternationales d ’Unit ´es) has been
defined, and strong efforts are beingmade to encourage the adoption ofthis system throughout the world.
Standard Units
http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1
8/18/2019 Instrumentation and Measurement Introduction
4/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Fundamental Units andSupplementary Fundamental Units
Derived Units
8/18/2019 Instrumentation and Measurement Introduction
5/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Purpose and performance ofmeasurement systems
• We begin by defining a process as a system which generates information .• Examples are a chemical reactor, a jet fighter, a gas platform, a submarine,
a car, a human heart, and a weather system.• Table lists information variables which are commonly generated by
processes:• For example: a car generates displacement, velocity and acceleration
variables, and a chemical
• We then define the observer as a person who needs thisinformation from the process.
• This could be the car driver, the plant operator or the nurse.• The purpose of the measurement system is to link the observer to
the process,• Here the observer is presented with a number which is the current
value of the information variable.• We can now refer to the information variable as a measured
variable .• The input to the measurement system is the true value of the
variable; the system output is the measured value of the variable.• In an ideal measurement system, the measured value would be
equal to the true value.
8/18/2019 Instrumentation and Measurement Introduction
6/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Elements of a Measurement Systems
In simple cases, the system can consistof only a single unit that gives anoutput reading or signal according tothe magnitude of the unknown.
However, in more complexmeasurement situations, a measuringsystem consists of several separateelements.
These components might be containedwithin one or more boxes, and theboxes holding individual measurement
elements might be either closetogether or physically separate.
Elements of a Measurement Systems
In simple cases, the system canconsist of only a single unit thatgives an output reading or signalaccording to the magnitude ofthe unknown.
However, in more complexmeasurement situations, a
measuring system consists ofseveral separate elements.
These components might becontained within one or moreboxes, and the boxes holdingindividual measurementelements might be either closetogether or physically separate.
http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1
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7/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Elements of a Measurement Systemscomparison from different references
MeasuredVariable
“ Measurand ”
Sensor Variable
ConversionElement
SignalProcessing
Or Conditioning
Use of Measurement atRemote Location
SignalTransmission
Presentation /Recording Unit
Output
Elements of a Measurement Systems
[Figliola, Theory and Design of Mechanical Measurements]
8/18/2019 Instrumentation and Measurement Introduction
8/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Single Channel Measuring System
Structure of Measuring System
Sensing Element (Sensor):This is in contact with the process and gives an output whichdepends in some way on the variable to be measured (measurand)If there is more than one sensing element in a system, the elementin contact with the process is termed the primary sensing element ,the others secondary sensing elements .For most but not all sensors, this function is at least approximatelylinear.
8/18/2019 Instrumentation and Measurement Introduction
9/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Instrumentation 17
Different measurement systems
Sensing PrinciplesThe interaction of physical parameters with each other —most notably electricity withstress, temperature and thermal gradients, magnetic fields, and incident light —yieldsa multitude of sensing techniques which may be applied in measurements
Transductive ( ي ل و (ح
Piezoelectric
Thermoelectric
Photoelectric
etc.
Constitutive ( س) س
Resistive
Capacitive
Inductive
Etc.
Pressure
Temperature
Light
Current
Voltage
Other.
Transducer
Pressure
Temperature
Light
R, C. L, etc
Sensor
8/18/2019 Instrumentation and Measurement Introduction
10/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Examples Sensors
Liquid Mercury
Input: Temperature
Output: Mercury volume
Are these linear sensors?
Thermocouple
Input: Temperature
Output: Voltage
Strain gauge
Input: Strain
Output: Electric resistance
Examples Sensors
Liquid Mercury Thermometer
Measured Variable: Temperature
Sensor: Liquid Mercury
Variable Conversion Element: Stem
Signal Presentation Element: Display Scale
8/18/2019 Instrumentation and Measurement Introduction
11/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Signal conditioning elementThis takes the output of the sensing element and converts it into aform more suitable for further processing, usually a d.c. voltage, d.c.current or frequency signal.
Improve the quality of the output of a measurement system.Examples are:
Deflection bridge which converts an impedance change into a voltage change Amplifier which amplifies millivolts to voltsOscillator which converts an impedance change into a variable frequencyvoltage.
Other signal processing element are those that filter out inducednoise and remove mean levels etc. In some devices, signalprocessing is incorporated into a transducer, which is then known as
a transmitter.
Signal processing elementThis takes the output of the conditioning element and converts it intoa form more suitable for presentation.Examples are:
Analogue-to-digital converter (ADC) which converts a voltageinto a digital form for input to a computer Computer (digital signal processor “DSP ” , Microcontroller , FieldProgrammable Gate Array “FPGA ” )which calculates themeasured value of the variable from the incoming digital data.
Typical calculations are:Computation of total mass of product gas from flow rate anddensity data Integration of chromatograph peaks to give thecomposition of a gas streamCorrection for sensing element non-linearity.
8/18/2019 Instrumentation and Measurement Introduction
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U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Data presentation elementThis presents the measured value in a form which can
be easily recognized by the observer.It may be omitted altogether when the measurement isused as part of an automatic control system.
It takes the form either of a signal presentation unit or ofa signal-recording unit.
Examples are:Simple pointer – scale indicator Chart recorder
Alphanumeric displayVisual display unit (VDU) suchas an LCD display
Elements of a Measurement Systems :Variable Coversion Element
Needed where the output variable of aprimary sensor is in an inconvenient formand has to be converted to a moreconvenient form.
The displacement-measuring strain gaugehas an output in the form of a varying
resistance. The resistance change cannotbe easily measured and so it is convertedto a change in voltage by a bridge circuit,which is a typical example of a variableconversion element.
In some cases, the primary sensor andvariable conversion element arecombined, and the combination is knownas a transducer.
8/18/2019 Instrumentation and Measurement Introduction
13/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Elements of a Measurement Systems :Signal Transmission
Needed when the observation orapplication point of the output of ameasurement system is somedistance away from the site of theprimary transducer.
It has traditionally consisted ofsingle or multi-cored cable, which isoften screened to minimize signalcorruption by induced electricalnoise.
Fibre-optic cables are being used inever increasing numbers in moderninstallations because of their lowtransmission loss andimperviousness to the effects ofelectrical and magnetic fields.
Elements of a Measurement System
MeasuredVariable
Sensor Variable
ConversionElement
SignalProcessor
Presentation /Recording Unit
8/18/2019 Instrumentation and Measurement Introduction
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U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Elements of a Measurement Systems
Sensor Variable
ConversionElement
SignalProcessor
SignalTransmission
Presentation /Recording Unit
Transducer
MeasuredVariable
Elements of a Measurement Systems
Sensor Variable
ConversionElement
SignalProcessor
SignalTransmission
Presentation /Recording Unit
Transducer
MeasuredVariable
Transmitter
8/18/2019 Instrumentation and Measurement Introduction
15/18
U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Choosing appropriate measuring instruments Accuracy, resolution, sensitivity and dynamicperformance.
Environmental conditions that the instrument will besubjected to.
Measurement systems and instruments should bechosen that are as insensitive as possible to theoperating environment.
The extent to which the measured system will bedisturbed during the measuring process is anotherimportant factor in instrument choice.
For example, significant pressure loss can becaused to the measured system in some techniquesof flow measurement.
Instrumentation 30
Data Acquisition and Control• Data acquisition is the process by which physical
phenomena from the real world are transformed intoelectrical signals that are measured and converted into adigital format for processing, analysis, and storage by acomputer .
• In a large majority of applications, the data acquisition(DAQ) system is designed not only to acquire data, but toact on it as well. In defining DAQ systems, it is thereforeuseful to extend this definition to include the controlaspects of the total system .
• Control is the process by which digital control signals from thesystem hardware are convened to a signal format for use bycontrol devices such as actuators and relays. These devicesthen control a system or process. Where a system is referred toas a data acquisition system or DAQ system, it is possible that itincludes control functions as well.
8/18/2019 Instrumentation and Measurement Introduction
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U-ECE
NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
Instrumentation 31
Physicalworld Sensing S/C ADC
Activation S/C DAC
Display andDecisionMaking
(PC, mP or PIC)
Hardware &Software
I n t e r
f a c e
PC Based Data AcquisitionSystem
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NEE4304 Instrumentation & Measurement
2/11/201
ond 2015-2016tructor: Nasser Ismail
33
Fundamentals of Data Acquisition A data acquisition and control system, built around the power
and flexibility of the PC, may consist of a wide variety of diversehardware building blocks from different equipmentmanufacturers.It is the task of the system integrator to bring together these
individual components into a complete working system.The basic elements of a data acquisition system, as shownin the functional diagram of Figure 1.1, are as follows:
Sensors and transducersField wiringSignal conditioningData acquisition hardware
PC (operating system)Data acquisition software
34
Field wiring and communications cabling/
• Field wir ing
represents the physic a l con nect ion f rom thet ransdu cer s and sensors to the s igna l cond i t ion inghardw are and/or da ta acquis i t ion hardware .
When the signal conditioning and/or data acquisitionhardware is remotely located from the PC, then the fieldwiring provides the physical link between these hardware
elements and the host computer.If this physical link is an RS-232 or RS-485
communications interface, then this component of thefield wiring is often referred to as communicationscabling.
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NEE4304 Instrumentation & Measurement
2/11/201
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Field wiring and communications cabling/FYI
• Field wir ing
Since field wiring and communications cabling oftenphysically represents the largest component of the totalsystem, it is most susceptible to the effects of externalnoise, especially in harsh industrial environments.The correct earthing and shielding of field wires andcommunications cabling is of paramount importance inreducing the effects of noiseThis passive component of the data acquisition and controlsystem is often overlooked as an important integralcomponent, resulting in an otherwise reliable systembecoming inaccurate or unreliable due to incorrect wiringtechniques.
36
Signal conditioning• Electrical signals generated by transducers often need to
be converted to a form acceptable to the data acquisitionhardware, particularly the A/D converter which convertsthe signal data to the required digital format.
• In addition, many transducers require some form ofexcitation or bridge completion for proper and accurateoperation.
• The principal tasks performed by signal conditioning are:• Filtering• Amplification• Linearization• Isolation• Excitation