42 – Vol. 93 Register online at www.ATIcourses.com or call ATI at 888.501.2100 or 410.956.8805

Applied Measurement EngineeringHow to Design Effective Computer-driven Measurement Systems

Instructor

Charles P. Wright (Chuck), founder of TRW Spaceand Technology Division's Measurements EngineeringDepartment, has three decades of direct experience in thedesign and operation of advanced multichannel, computer-driven measurement systems. He developed theknowledge-based measurement system concept as thehighest expression of systems design and operationalperformance. He has published 60+ technical papers onmeasurement system design, operation, and test processimprovement. As a contributing editor of PersonalEngineering and Instrumentation News, he has written

40+ bimonthly expert columns on DataAcquisition since 1991. His book AppliedMeasurements Engineering -- How toDesign Effective Mechanical MeasurementSystems was published in 1995 by PrenticeHall. Education: BSME/MS Measurements

Engineering, Arizona State University; MSManagement, University of Southern

California.

Summary

How do you know your test measurements are valid?Since NIST traceability actually guarantees little aboutyour test data, how do you know? Could you provevalidity to your customer? What is the rightmeasurements solution for your testing requirements? Is itreally as simple as the vendors say? What is your real costof invalid, ambiguous data causing retest or, worst of all,hardware redesign?

This course is for engineers, scientists, and managerswho must use systems to understand experimental testmeasurements on a daily basis. Learn how to design, buyand operate effective automated measurement systemsproviding demonstrably valid test data, the first time.

Fundamental & underlying engineering principlesgoverning the design and operation of effectiveautomated systems are demonstrated experimentally.

The result? Skilled people running more effectivetesting programs generating unambiguous data, lowereddesign verification risk and cost, and delighted customers.Attendees receive a workbook and the instructor's book,Applied Measurements Engineering.

Course Outline

1. Basic Measurement Concepts. Fourteen real measurement horror stories andwhy they happened. Measurements or instrumentation? Data validity or dataaccuracy? Why you want less than 1/16th of the information from your system.

2. Measurement System Transfer Functions and Linearity. Frequency andphase responses -- more complicated than most think. First, second and higherorder systems. Single degree-of-freedom systems and damping. Output/inputlinearity.

3. Frequency Content or Wave Shape Reproduction? Rules for thereproduction of frequency content. Rules for the reproduction of wave shape.What price do you pay when you violate the rules? How can you recover?

4. Non-Self Generating Transducers. Load cells, strain gages, resistancetemperature transducers, piezoresistive and servo transducers, etc. The basictransducer model. Proper techniques for system set-up and operation.

5. Wheatstone Bridge. The bridge as a computer. Bridge equations. Valid shuntcalibration techniques and calculation. The three wire circuit. Up to ten wirecircuits!

6. Self Generating Transducers. Piezoelectric transducers. "Charge" amplifiersand why they work. Thermoelectricity and thermocouples. The gradientapproach to thermocouple temperature measurements.

7. The General Transducer Model and Noise. How all transducers andcomponents really work. Bulletproof noise level hunting and documentationprocedures. Differential systems and common mode performance.Noise/Identification/Reduction Methods.

8. Information Conversion. Carrier systems and why they work. Sinusoidalexcitation. Pulse train excitation--zero based and zero centered. Real examples.

9. Frequency Analysis. Fourier spectra. Power or auto spectral density. Octaveand one-third octave analyses. Shock response spectra--what do they really tellyou?

10. Sampled Measurement Systems. The twelve things you must know beforeyou sample. Nonsimultaneous or simultaneous sample and hold? Aliasing andundersampling errors and how to prevent them. What antialiasing filters shouldyou use and why?

11. Data Validation Methodologies. How do you know your data is valid? Howto use your software to answer the question.

12. Knowledge-Based System Design Principles. The highest level of systemdesign. Operating effective measurement systems. World-class examples fromthe spacecraft dynamics, thermal, and quasi-static structural test worlds.

13. The Subject of Software. Commercial software. Commercial vs. in-housedeveloped software. Where's the risk?

14. The Crucial Stuff They Didn't Teach You in College. The subjects of craft,skill, responsibility, and professionalism as they relate to test measurements.

November 17-19, 2008Laurel, Maryland

$1590 8:30am - 4:00pm

What You Will Learn• How to guarantee your data.• How to set the crucial system transfer functions to assure

valid data.• How to follow the rules for waveshape and spectral

reproduction of data.• The twelve things you have to control before you can

sample properly.• How to absolutely eliminate deadly aliasing.• How to identify and prevent 40% errors in 0.1%

systems!• Foolproof automated methods for noise level

identification and control.• How to operate successfully in the PC-based data

acquisition system market.

"Register 3 or More & Receive $10000 eachOff The Course Tuition."

EN

GIN

EE

RIN

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www.ATIcourses.com

Boost Your Skills with On-Site Courses Tailored to Your Needs The Applied Technology Institute specializes in training programs for technical professionals. Our courses keep you current in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highly competitive marketplace. Since 1984, ATI has earned the trust of training departments nationwide, and has presented on-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our training increases effectiveness and productivity. Learn from the proven best. For a Free On-Site Quote Visit Us At: http://www.ATIcourses.com/free_onsite_quote.asp For Our Current Public Course Schedule Go To: http://www.ATIcourses.com/schedule.htm

2

Applied Measurements Engineering

You get judged by English Common Law.You are innocent until proven guilty.

Your measurement systems must be judged by Napoleonic Law.

They are guilty until proven innocent.

Prof. Peter Stein

Can you provide the proof?

3

Applied Measurements Engineering

PROFESSIONAL CONTEXT FOR MEASUREMENTS ENGINEERING

Context, n: the interrelated conditions in which something exists or occurs

TEST ENVIRONMENT & NOISE LEVEL CONTROL/DOCUMENTATION

MECHANICALENGINEERINGKNOWLEDGE

BASE

ENERGY ANDINFORMATIONFLOW

TRANSDUCERS SIGNAL CONDI-TIONING

SIGNALSHAPING

ANALOG DATAACQUISITION

DIGITAL DATAACQUISITION

ANALOG SIGNAL HANDLING AND TRANSMISSION

DIGITAL SIGNAL HANDLING, ANALYSIS AND DISPLAY

SOFTWARE DEVELOPMENT AND CONTROL

TESTPHENOMENON

THECUSTOMER

VALIDITYCHECKINGMETHODS

4

Applied Measurements Engineering

A POPULAR VIEW OF THE MEASUREMENTS UNIVERSE

WARP DRIVE LASER PRINTER/PLOTTER

SUPERFASTSTELLAR CLASS

FUSION POWEREDCOMPUTER!!

A Billion Samples Per Second!On Beyond Windows!

Pentium XXV Class!Hyper this and hyper that! Modular!

Hoo Haa! Belchfire Gimmicks! 50 Mips!

A Really Fast Front End! 80 Mflops!Quadruple Precision! Expandable!

Optimized Compilers! Cute ICONS!We have buses for you!

Universal Signal Conditioning Pods! Hook Up Anything!

Cryogenically cooled!

WORLD’SMOST

INCREDIBLETERMINALS!

NET

WO

RK

S!G

IGA

BYTES/SEC

ON

D!

PLUG AND PLAY!!

5000 x 5000 pixels!10,000 colors in palette!Mice!!Trackballs!!Virtual Reality!!

GAZILLIONBYTE LASER

DISC

ANNOYINGTRANSDUCER,

CABLE &SIGNAL CONDITIONING

DOHICKEYS

VXI!

VME! PCI!

Sigma-Delta A/Ds

COMPLETE TESTENVIRONMENT

SUPERSPEEDYNETWORKS

5

Applied Measurements Engineering

A MORE EFFECTIVE VIEW OF THEMEASUREMENTS UNIVERSE

TESTPHENOMENON

TRANS-DUCERS &CABLINGSYSTEM

SIGNALCONDI-TIONING

SIGNALSHAPING

SIGNALCONVER-SION

SIGNALPROCES-SING

DIGITAL COMPONENTS& SOFTWARE

(maybe)

ENERGY

INFO

TESTENVIRONMENT

NOISE LEVELS

CUSTOMER’SNEEDS

CUSTOMER’SCUSTOMER’S

NEEDS

TESTDATA

AND

SOME INSTRUMENTATION ORGANIZATIONS

MOST INSTRUMENTATION ORGANIZATIONS

PROFESSIONAL MEASUREMENTS ORGANIZATIONS

SYSTEMS LEVEL MEASUREMENTS THINKING

6

Applied Measurements Engineering

WHAT MEASUREMENT SYSTEMS AREWE TALKING ABOUT?

Measurements forDESIGN

What would the input be if the measuring system

were not there?

Measurements forCALIBRATION

What are the characteristicsof this system under specific

boundary conditions?

Measurement forCONTROL

What is the output ofthe controlled phenomenon

or process?

MEASUREMENTSYSTEM

PhenomenonSourceInputStimulusExcitationForcing FunctionService Conditions

ObservationOutputResponseOvert, Observable

Behavior

INTERPRETATION:How much is too much?How much is too little?

DecisionsAdjustments

Feedback for Control

7

Applied Measurements Engineering

INSTRUMENTATION . . . OR . . . MEASUREMENTS?

• Instrumentation– The arrangement of preselected individual

links of a measuring chain into an operating unit

– Emphasis is on the individual links and their accuracy

– Boundary conditions are generally not emphasized nor controlled

– Asks the question “What did the meter read?”

8

Applied Measurements Engineering

INSTRUMENTATION . . . OR . . . MEASUREMENTS?

• Measurements– The application of scientific and engineering principles

to the design and use of measuring systems– Emphasis is on the entire system and on the validity of

the data– Validity implies the system output faithfully represents

the phenomenon under investigation as if the measuring system were not there

– Boundary conditions are both understood and controlled

– Asks the question “What would the system have read if it had not been there exchanging energy with the process?”

9

Applied Measurements Engineering

DATA ACCURACY . . . OR. . .DATA VALIDITY?

• Accuracy– System output reflects the achieved value within the

transducer -- accurately answers the question “What did the meter read?”

– Changes in process caused by the measurement system are neither controlled nor accounted for, and may be appreciable (uncorrected error).

– Boundary conditions at the transducer/process boundary interface are not necessarily accounted for or controlled.

– Requires little knowledge of the process under investigation.

– 10 engineers will give you 15 definitions -- all different.

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Applied Measurements Engineering

ACCURACY - CENTRIC VIEW CAN LEAD TO ASSUMED UNCERTAINTIES LIKE THESE

Do you believe these numbers?What’s missing with this view?

Do you believe these numbers?What’s missing with this view?

Courtesy of a certain periodical’s website tutorial on error analysis

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Applied Measurements Engineering

ACCURACY - CENTRIC VIEW CAN LEAD TOPROBLEMS LIKE THESE

5.6% low

1% low

Accurate but Invalid….The Valid Reality….

The addition of a single 8 gmaccelerometer on the front sidesplits the mode into two new modes@ 5562 and 5830 Hz and changes themode shape. These are accuratelymeasured and totally invalid modes.

The addition of a single 8 gmaccelerometer on the front sidesplits the mode into two new modes@ 5562 and 5830 Hz and changes themode shape. These are accuratelymeasured and totally invalid modes.

Hologram of the backside ofa 7” dia, 800 gm symmetrical

turbine disk

Courtesy of Sandia National Laboratories,Albuquerque, New Mexico

12

Applied Measurements Engineering

ACCURACY - CENTRIC VIEW CAN LEAD TOPROBLEMS IN A FREQUENCY RICH ENVIRONMENT

- 2%

+2%

Phase implications?Magnitude & phase corrections made? Reflected in uncertaintyanalysis?

Phase implications?Magnitude & phase corrections made? Reflected in uncertaintyanalysis?

Accelerometer calibrationfrom an aerospace contractor,25 to 5000Hz shows amplitudevariations of over 4%.

13

Applied Measurements Engineering

A SYSTEMS VIEW OF MEASUREMENTS UNCERTAINTY

1. Undisturbed value: Value of the measureand if the system were not there to measure it.

2. Available value: Value with the system in place.

3. Achieved value: Value of the measureand achieved withinthe transducer.

4. Observed value: Value returned from the transducer using calibration relationships.

5. Corrected value: Value after all recognized errors have beenapplied.

Courtesy of Dr.Robert Moffatt,Moffatt Thermosciences, Menlo Park, CA

Almost all uncertainty analyses existonly in this box.

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Applied Measurements Engineering

TYPICAL EXAMPLE FROMTHE LITERATURE

1. Undisturbed Value

2. Available Value

3. Achieved Value

4. Observed Value

5. Corrected Value

ERRORS NOTED IN A REPUTABLE THERMOCOUPLE SIGNAL CONDITIONING

MANUFACTURER’S WEB SITEThermocouple wire-based error

Cold junction compensation errorA/D resolution and accuracy error

Linearization error

15

Applied Measurements EngineeringTRANSIENT SURFACE TEMPERATURES IN A SOLID ROCKET NOZZLE WITH ASBESTOS PHENOLIC

THROAT -- MEASURED BY VARIOUS FLUSH MOUNTED PT-PT 10% RHO THERMOCOUPLES

0

500

1000

1500

2000

2500

3000

3500

0 2 4 6 8 10 12 14 16 18 20

TIME AFTER IGNITION IN SECONDS

THE

RM

OC

OU

PLE

JU

NC

TIO

N T

EM

PE

RA

TUR

E (o F)

ASBESTOS PHENOLIC THERMOWELL

STAINLESS STEELTHERMOWELL

MOLYDENUMTHERMOWELL

MOLYBDENUM THERMOWELLWITH RDP150 INSERTS

DATA FROM "THERMAL PROPERTIES OF THERMOCOUPLES,' BY J. NANIGIAN, NANMAC CORP.

throat

ASBESTOSPHENOLICNOZZLE

VARIABLETHERMOWELLMATERIALS

2500F Error!

16

Applied Measurements Engineering

DATA ACCURACY . . . OR . . . DATA VALIDITY?• Validity

– System output faithfully represents the measured parameter as if the system were not there.

– Validity includes accuracy and is, therefore, a higher level quality.

– Measurement caused process changes controlled by design and negligible in an engineering sense.

– Boundary conditions at all interfaces are controlled by design.

– Requires knowledge of the process under investigation (solid mechanics, kinematics, dynamics, heat transfer, fluid mechanics, thermodynamics, materials, manufacturing, etc..).• How can you know whether than answer makes

sense without understanding the phenomenon?

17

Applied Measurements Engineering

ENERGY AND INFORMATION FLOW IN MEASUREMENT SYSTEMS

MEASUREMENT = TRANSFER OF

INFORMATION ABOUT A STATE OR PROCESS

(The Data)

THE ANSWER!

TRANSFER OFENERGY WITH A

STATE OR PROCESS+

(Applied Physics)

THE PROBLEM!

18

Applied Measurements Engineering

THE ENERGY RELATED CHALLENGE OF MEASUREMENTS ENGINEERING

• It is inevitable that you are going to transfer energy with the process any time you make a measurement -- you will change the process.

• Your job is to (1) allow the valid transfer of information from the process, while (2) minimizing the energy transfer with the process so it is insignificant in an engineering sense. You do this (or not!) with your design.

• This crucial point is not well understood in the test community and major and bizarre uncorrected errors occur because of it every day.

• Be aware.

19

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROMES -- AN EXAMPLE

Syndrome, n.: a set of concurrent things that usually form an identifiable pattern

• Strain: A turbine case is deflecting too much in operation. You want to measure this strain (desired environment).

• Temperature: You are working on a hot turbine case.• Pressure: Strain gages and lead wires are inside the case

subject to high dynamic pressure variations.• Motion: Turbine is vibrating like mad -- That’s why we’re

running the test!• Radiation: The turbine sits next to a reactor.• Corrosion: The gas is corrosive.

20

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROMES -- AN EXAMPLE

• Moisture: The gas is high pressure wet steam.• Electromagnetic fields: There’s a generator 3 feet away,

and a superconducting magnet 18 inches away.• Time: By definition, time always passes during a test.• Etc.: You don’t even want to know about these!

21

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROMESMeasurement system component responses to their environments are characterized by four levels of evidence….

• #1: Respond to both the desired and undesired portions of the environment simultaneously. What’s worse. . . .

• #2: Respond with self generating and nonself generating mechanisms simultaneously. What’s worse. . . . .

• #3: Evidence of these responses can be both temporary and permanent. What’s worse. . . .

• #4: Any response can affect both amplitude (zero) and gain.

22

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROME MODEL

1. Environment

2. Response Type

3. Response Evidence

4. Response Effect

NSG = nonself generatingT = temporaryA = additive (affects level, zero)

SG = self generatingP = permanentM = multiplicative (affects gain)

A M A M A M A M A M A M A M A M

T P T P T P T P

NSG SG NSG SG

DESIRED(STRAIN)

UNDESIRED #1(TEMPERATURE)

23

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROME -- VALID STRAIN DATA

1. Environment

2. Response Type

3. Response Evidence

4. Response Effect

NSG = nonself generatingT = temporaryA = additive (affects level, zero)

SG = self generatingP = permanentM = multiplicative (affects gain)

A M A M A M A M A M A M A M A M

T P T P T P T P

NSG SG NSG SG

DESIRED(STRAIN)

UNDESIRED #1(TEMPERATURE)

VALID STRAIN DATA

24

Applied Measurements Engineering

CONSTANTAN STRAIN GAGE MOUNTED ON KEVLAR COMPOSITE CANTILEVER BEAM

..

Nonself generatingConstantan gage

16 awg copper leads

5oF thermal gradient

If you were reading strain…2Vdc excitation for composite,GF = 2 for the gage, you wouldread an equivalent 100µε withzero mechanical strain!

0.100 mVdc

Digital Multimeter reading dc voltage

Self generated noise level

5” long1” wide1/16th” thick

25

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROMES - THERMAL ZERO SHIFT DUE TO THERMOCOUPLE EMFS

1. Environment

2. Response Type

3. Response Evidence

4. Response Effect

NSG = nonself generatingT = temporaryA = additive (affects level, zero)

SG = self generatingP = permanentM = multiplicative (affects gain)

A M A M A M A M A M A M A M A M

T P T P T P T P

NSG SG NSG SG

DESIRED(STRAIN)

UNDESIRED #1(TEMPERATURE)

26

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROME -- TEMPERATURE INDUCED GAGE FACTOR

CHANGE

1. Environment

2. Response Type

3. Response Evidence

4. Response Effect

NSG = nonself generatingT = temporaryA = additive (affects level)

SG = self generatingP = permanentM = multiplicative (affects gain)

A M A M A M A M A M A M A M A M

T P T P T P T P

NSG SG NSG SG

DESIRED(STRAIN)

UNDESIRED #1(TEMPERATURE)

NOISE LEVEL - TEMPERATURE INDUCEDGAGE FACTOR CHANGE

27

Applied Measurements Engineering

CONSTANTAN GAGE INSTALLED ON ALUMINUM CANTILEVER BEAM SUBJECT TO SHOCK

WHACK WITHHAMMER

+

-

Vertical oscilloscopeamplifier, differentialinput, 50 µV/cm,1MHz BW

Self generated noise level

.5”x.5”X 6” LONGALUMINUM BEAM

Nonself generatingConstantan strain gage

16 awg copper wire

28

Applied Measurements Engineering

MEASUREMENT SYSTEM RESPONSE SYNDROME -- “PIEZOELECTRIC” STRAIN GAGE

1. Environment

2. Response Type

3. Response Evidence

4. Response Effect

NSG = nonself generatingT = temporaryA = additive (affects level, zero)

SG = self generatingP = permanentM = multiplicative (affects gain)

A M A M A M A M A M A M A M A M

T P T P T P T P

NSG SG NSG SG

DESIRED(DYNAMIC STRAIN)

UNDESIRED #1(MOTION)

NOISE LEVEL - THE “PIEZOELECTRIC” STRAIN GAGE

29

Applied Measurements Engineering

SHOCK OUTPUT FROM "PIEZOELECTRIC" STRAIN GAGE (SELF GENERATING RESPONSE FOR ZERO EXCITATION)

-200

-150

-100

-50

0

50

100

150

200

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

TIME (SECONDS)

APPA

RENT

MICR

OSTR

AIN

(NO

ISE

LEVE

L)

30

Applied Measurements Engineering

FOUR BASIC DESIGN APPROACHES

• Use any old components, hook them up to something and take readings.

• Use a system calibrated over the entire environmental range– Measure the parameter of interest AND the entire

environment – Compute corrections based on physics

• Use a calibrated system, but modify the test environment so it duplicates the calibration environment

31

Applied Measurements Engineering

FOUR BASIC DESIGN APPROACHES

• Design a measurement system to operate in the entire test environment and give acceptable experimental errors without correction

Only this last approach falls into the design category:VALID DATA, ON PURPOSE, THE FIRST TIME.This is based on the Unified Approach to the

Engineering of Measurement Systems