Applied Measurement Engineering Course

Professional Development Short Course On:

Applied Measurements Engineering

Instructor:

Charles P. Wright

ATI Course Schedule: http://www.ATIcourses.com/schedule.htm

ATI's Applied Measurements Engineering: http://www.aticourses.com/applied_measurement_engineering.htm

Applied Measurement Engineering
How to Design Effective Computer-driven Measurement Systems
Summary
How do you know your test measurements are valid?
November 17-19, 2008
Since NIST traceability actually guarantees little about
your test data, how do you know? Could you prove
Laurel, Maryland
validity to your customer? What is the right
measurements solution for your testing requirements? Is it $1590 8:30am - 4:00pm
really as simple as the vendors say? What is your real cost
"Register 3 or More & Receive $10000 each
of invalid, ambiguous data causing retest or, worst of all, Off The Course Tuition."
hardware redesign?
This course is for engineers, scientists, and managers
who must use systems to understand experimental test
measurements on a daily basis. Learn how to design, buy
and operate effective automated measurement systems Course Outline
providing demonstrably valid test data, the first time. 1. Basic Measurement Concepts. Fourteen real measurement horror stories and
Fundamental & underlying engineering principles why they happened. Measurements or instrumentation? Data validity or data
governing the design and operation of effective accuracy? Why you want less than 1/16th of the information from your system.
automated systems are demonstrated experimentally.
2. Measurement System Transfer Functions and Linearity. Frequency and
The result? Skilled people running more effective
testing programs generating unambiguous data, lowered phase responses -- more complicated than most think. First, second and higher
design verification risk and cost, and delighted customers. order systems. Single degree-of-freedom systems and damping. Output/input
Attendees receive a workbook and the instructor's book, linearity.
Applied Measurements Engineering. 3. Frequency Content or Wave Shape Reproduction? Rules for the
reproduction of frequency content. Rules for the reproduction of wave shape.
What You Will Learn What price do you pay when you violate the rules? How can you recover?
• How to guarantee your data. 4. Non-Self Generating Transducers. Load cells, strain gages, resistance
• How to set the crucial system transfer functions to assure temperature transducers, piezoresistive and servo transducers, etc. The basic
valid data. transducer model. Proper techniques for system set-up and operation.
• How to follow the rules for waveshape and spectral 5. Wheatstone Bridge. The bridge as a computer. Bridge equations. Valid shunt
reproduction of data. calibration techniques and calculation. The three wire circuit. Up to ten wire
• The twelve things you have to control before you can circuits!
sample properly.
6. Self Generating Transducers. Piezoelectric transducers. "Charge" amplifiers
• How to absolutely eliminate deadly aliasing.
and why they work. Thermoelectricity and thermocouples. The gradient
• How to identify and prevent 40% errors in 0.1%
ENGINEERING

systems! approach to thermocouple temperature measurements.
• Foolproof automated methods for noise level 7. The General Transducer Model and Noise. How all transducers and
identification and control. components really work. Bulletproof noise level hunting and documentation
• How to operate successfully in the PC-based data procedures. Differential systems and common mode performance.
acquisition system market. Noise/Identification/Reduction Methods.
8. Information Conversion. Carrier systems and why they work. Sinusoidal
Instructor excitation. Pulse train excitation--zero based and zero centered. Real examples.
Charles P. Wright (Chuck), founder of TRW Space 9. Frequency Analysis. Fourier spectra. Power or auto spectral density. Octave
and Technology Division's Measurements Engineering and one-third octave analyses. Shock response spectra--what do they really tell
Department, has three decades of direct experience in the you?
design and operation of advanced multichannel, computer-
driven measurement systems. He developed the
10. Sampled Measurement Systems. The twelve things you must know before
knowledge-based measurement system concept as the you sample. Nonsimultaneous or simultaneous sample and hold? Aliasing and
highest expression of systems design and operational undersampling errors and how to prevent them. What antialiasing filters should
performance. He has published 60+ technical papers on you use and why?
measurement system design, operation, and test process 11. Data Validation Methodologies. How do you know your data is valid? How
improvement. As a contributing editor of Personal
Engineering and Instrumentation News, he has written to use your software to answer the question.
40+ bimonthly expert columns on Data 12. Knowledge-Based System Design Principles. The highest level of system
Acquisition since 1991. His book Applied design. Operating effective measurement systems. World-class examples from
Measurements Engineering -- How to the spacecraft dynamics, thermal, and quasi-static structural test worlds.
Design Effective Mechanical Measurement
Systems was published in 1995 by Prentice 13. The Subject of Software. Commercial software. Commercial vs. in-house
Hall. Education: BSME/MS Measurements developed software. Where's the risk?
Engineering, Arizona State University; MS 14. The Crucial Stuff They Didn't Teach You in College. The subjects of craft,
Management, University of Southern skill, responsibility, and professionalism as they relate to test measurements.
California.

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

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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? 2


PROFESSIONAL CONTEXT FOR
MEASUREMENTS ENGINEERING
Context, n: the interrelated conditions in which something exists or occurs

TEST ENVIRONMENT & NOISE LEVEL CONTROL/DOCUMENTATION

MECHANICAL ENERGY AND TRANSDUCERS SIGNAL SIGNAL ANALOG DATA
ENGINEERING INFORMATION CONDI- SHAPING ACQUISITION
KNOWLEDGE FLOW TIONING
BASE
TEST
PHENOMENON DIGITAL DATA
ACQUISITION
ANALOG SIGNAL HANDLING AND TRANSMISSION
THE
CUSTOMER

DIGITAL SIGNAL HANDLING, ANALYSIS AND DISPLAY
VALIDITY
CHECKING
METHODS
SOFTWARE DEVELOPMENT AND CONTROL

3


A POPULAR VIEW OF THE
MEASUREMENTS UNIVERSE

A Billion Samples Per Second!
On Beyond Windows! Cryogenically cooled!
VME! Pentium XXV Class! PCI!
Hyper this and hyper that! Modular!
Belchfire Gimmicks! GAZILLION
Hoo Haa! 50 Mips!
PLUG AND PLAY!! BYTE LASER

GIGABYTES/SECOND!
DISC
SUPERFAST
NETWORKS!

STELLAR CLASS
ANNOYING
SUPERSPEEDY
FUSION POWERED
COMPLETE TEST TRANSDUCER,
ENVIRONMENT CABLE &
SIGNAL CONDITIONING NETWORKS
DOHICKEYS

COMPUTER!!
WORLD’S
A Really Fast Front End! 80 Mflops! MOST
Quadruple Precision! VXI! Expandable! INCREDIBLE
Optimized Compilers! Cute ICONS!
Sigma-Delta A/Ds We have buses for you!
TERMINALS!
Universal Signal Conditioning Pods! Hook Up Anything!

WARP DRIVE LASER PRINTER/PLOTTER 5000 x 5000 pixels!
10,000 colors in palette!
Mice!!
Trackballs!!
Virtual Reality!!
4


A MORE EFFECTIVE VIEW OF THE
MEASUREMENTS UNIVERSE

TEST
ENVIRONMENT
NOISE LEVELS
DIGITAL COMPONENTS
& SOFTWARE
(maybe)
INFO
TEST
TEST TRANS- DATA CUSTOMER’S
SIGNAL SIGNAL SIGNAL CUSTOMER’S
AND DUCERS & SIGNAL
PHENOMENON CONDI- CONVER- PROCES- NEEDS CUSTOMER’S
CABLING SHAPING
TIONING SION SING NEEDS
SYSTEM
ENERGY

SOME INSTRUMENTATION
ORGANIZATIONS

MOST INSTRUMENTATION ORGANIZATIONS

PROFESSIONAL MEASUREMENTS ORGANIZATIONS

SYSTEMS LEVEL MEASUREMENTS THINKING

5


WHAT MEASUREMENT SYSTEMS ARE
WE TALKING ABOUT?
Measurements for Measurements for Measurement for
DESIGN CALIBRATION CONTROL
What would the input be What are the characteristics What is the output of
if the measuring system of this system under specific the controlled phenomenon
were not there? boundary conditions? or process?

Phenomenon
Source Observation
Input Output
MEASUREMENT
Stimulus Response
SYSTEM
Excitation Overt, Observable
Forcing Function Behavior
Service Conditions

INTERPRETATION:
How much is too much?
How much is too little?
Decisions
Adjustments
Feedback for Control
6


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?”

7


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?”

8


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.

9


ACCURACY - CENTRIC VIEW CAN LEAD TO
ASSUMED UNCERTAINTIES LIKE THESE

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

Courtesy of a certain periodical’s website tutorial on error analysis 10

PROBLEMS LIKE THESE
The Valid Reality…. Accurate but Invalid….
5.6% low

Hologram of the backside of 1% low
a 7” dia, 800 gm symmetrical
turbine disk
The addition of aasingle 88gm
The addition of single gm
accelerometer on the front side
accelerometer on the front side
splits the mode into two new modes
splits the mode into two new modes
@ 5562 and 5830 Hz and changes the
@ 5562 and 5830 Hz and changes the
mode shape. These are accurately
mode shape. These are accurately
measured and totally invalid modes.
measured and totally invalid modes.
11
Courtesy of Sandia National Laboratories,
Albuquerque, New Mexico


PROBLEMS IN A FREQUENCY RICH ENVIRONMENT

Accelerometer calibration
from an aerospace contractor,
25 to 5000Hz shows amplitude
variations of over 4%.

+2%

Phase implications?
Phase implications? - 2%
Magnitude & phase
Magnitude & phase
corrections made?
corrections made?
Reflected in uncertainty
Reflected in uncertainty
analysis?
analysis?

12


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 within
the transducer.

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

5. Corrected value: Value after all recognized errors have been
applied.

Courtesy of Dr.Robert Moffatt, Almost all uncertainty analyses exist
Moffatt Thermosciences, Menlo Park, CA only in this box. 13


TYPICAL EXAMPLE FROM
THE LITERATURE

1. Undisturbed Value

2. Available Value

3. Achieved Value

4. Observed Value ERRORS NOTED IN A REPUTABLE
THERMOCOUPLE SIGNAL CONDITIONING
5. Corrected Value MANUFACTURER’S WEB SITE
Thermocouple wire-based error
Cold junction compensation error
A/D resolution and accuracy error
Linearization error

14

TRANSIENT SURFACE TEMPERATURES IN A SOLID ROCKET NOZZLE WITH ASBESTOS PHENOLIC
THROAT -- MEASURED BY VARIOUS FLUSH MOUNTED PT-PT 10% RHO THERMOCOUPLES

3500
DATA FROM "THERMAL PROPERTIES OF THERMOCOUPLES,'
THERMOCOUPLE JUNCTION TEMPERATURE ( F)

BY J. NANIGIAN, NANMAC CORP.
o

3000
ASBESTOS PHENOLIC
THERMOWELL

2500
STAINLESS STEEL
MOLYBDENUM THERMOWELL
THERMOWELL
WITH RDP150 INSERTS

2000

1500
MOLYDENUM VARIABLE
2500F Error! THERMOWELL THERMOWELL
MATERIALS
1000
throat

500
ASBESTOS
PHENOLIC
NOZZLE
0
0 2 4 6 8 10 12 14 16 18 20
TIME AFTER IGNITION IN SECONDS
15


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?
16


ENERGY AND INFORMATION FLOW IN
MEASUREMENT SYSTEMS

TRANSFER OF TRANSFER OF
MEASUREMENT = INFORMATION ABOUT + ENERGY WITH A
A STATE OR PROCESS STATE OR PROCESS

(The Data) (Applied Physics)

THE ANSWER! THE PROBLEM!

17


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.
18


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.

19


-- 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!

20


Measurement 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. 21


MEASUREMENT SYSTEM RESPONSE
SYNDROME MODEL
DESIRED UNDESIRED #1
1. Environment (STRAIN) (TEMPERATURE)

2. Response Type
NSG SG NSG SG

3. Response Evidence
T P T P T P T P

4. Response Effect
A M A M A M A M A M A M A M A M

NSG = nonself generating SG = self generating
T = temporary P = permanent
A = additive (affects level, zero) M = multiplicative (affects gain)

22


MEASUREMENT SYSTEM RESPONSE SYNDROME
-- VALID STRAIN DATA
VALID STRAIN DATA


2. Response Type NSG SG NSG SG

3. Response Evidence T P T P T P T P

4. Response Effect A M A M A M A M A M A M A M A M


23


CONSTANTAN STRAIN GAGE MOUNTED
ON KEVLAR COMPOSITE CANTILEVER BEAM

If you were reading strain…
5” long 2Vdc excitation for composite,
1” wide GF = 2 for the gage, you would
1/16th” thick
read an equivalent 100µε with
zero mechanical strain!

Nonself generating
Constantan gage
Self generated noise level

.. 16 awg copper leads 0.100 mVdc
5oF thermal gradient Digital Multimeter
reading dc voltage

24


- THERMAL ZERO SHIFT DUE TO THERMOCOUPLE EMFS


2. Response Type
NSG SG NSG SG

T P T P T P T P

4. Response Effect


25

MEASUREMENT SYSTEM RESPONSE SYNDROME -
- TEMPERATURE INDUCED GAGE FACTOR
CHANGE
NOISE LEVEL - TEMPERATURE INDUCED
GAGE FACTOR CHANGE


T P T P T P T P

4. Response Effect

A = additive (affects level) M = multiplicative (affects gain)

26


CONSTANTAN GAGE INSTALLED ON ALUMINUM
CANTILEVER BEAM SUBJECT TO SHOCK

WHACK WITH
HAMMER

Self generated
noise level

.5”x.5”X 6” LONG Nonself generating
ALUMINUM BEAM Constantan strain gage

16 awg copper wire + Vertical oscilloscope
amplifier, differential
- input, 50 µV/cm,
1MHz BW

27


MEASUREMENT SYSTEM RESPONSE SYNDROME -
- “PIEZOELECTRIC” STRAIN GAGE
NOISE LEVEL - THE “PIEZOELECTRIC” STRAIN GAGE

1. Environment (DYNAMIC STRAIN) (MOTION)


3. Response Evidence T P T P T P T P

4. Response Effect A M A M A M A M A M A M A M A M


28


SHOCK OUT PUT FROM "PIEZOELECT RIC" ST RAIN GAGE
(SELF GENERAT ING RESPONSE FOR ZERO EXCIT AT ION)
200
(NOISE

150

100

50
APPARENT MICROSTRAIN
LEVEL)

0

-50

-100

-150

-200
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

T IME (SECONDS)

29


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

30


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

31

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Applied Measurement Engineering Course

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