Overview

OverviewOverview Measurement StandardsMeasurement Standards

What are they?What are they? How are basic units of measure How are basic units of measure

defined?defined? How are measurement standards used?How are measurement standards used?

CalibrationCalibration Conversion UnitsConversion Units

What is a “Standard”?What is a “Standard”?A standard is something established A standard is something established as a rule or basis of comparison in as a rule or basis of comparison in measuring or judging capacity. measuring or judging capacity. Webster’s New World DictionaryWebster’s New World Dictionary

Measurement Standards Measurement Standards Before we can measure we need Before we can measure we need

to define the unit of measure.to define the unit of measure. How long is 1 meter?How long is 1 meter? How much is 1 kg?How much is 1 kg? How long is 1 second?How long is 1 second? How hot is 50 degrees C?How hot is 50 degrees C?

Who defines standards?Who defines standards? International Standards Organization, International Standards Organization,

ISOISO Maintains SI (metric) standards.Maintains SI (metric) standards.

National Institute of Standards and National Institute of Standards and Technology, NISTTechnology, NIST Mandated by the US ConstitutionMandated by the US Constitution

International Bureau of Weights and International Bureau of Weights and Measures, BIPM (Bureau international Measures, BIPM (Bureau international des poids et mesures) in Sevres, France.des poids et mesures) in Sevres, France.

CharacteristicsCharacteristics What are characteristics of a What are characteristics of a

measurements standard?measurements standard? They must have global availabilityThey must have global availability

They must be accessible and “usable”They must be accessible and “usable” They must be stableThey must be stable

They must not change over time or locationThey must not change over time or location

What is the basic unit of What is the basic unit of time?time?

What is a year?What is a year? The time required for the earth to make The time required for the earth to make

one complete orbit about the sun.one complete orbit about the sun. What is a day?What is a day? The time required for the sun to go from The time required for the sun to go from

noon to noon.noon to noon. What is a second?What is a second? Could be defined as: 1/(24X60X60) of a dayCould be defined as: 1/(24X60X60) of a day

Just a second!Just a second! Measurement standards must be Measurement standards must be

stable.stable. But the length of a day is constantly But the length of a day is constantly

changingchanging Earth’s rotation is slowing Earth’s rotation is slowing Slowing is inconsistentSlowing is inconsistent

Defining a second as 1/(24X60X60) Defining a second as 1/(24X60X60) of a day is no longer adequate!of a day is no longer adequate!

Next option?Next option?

One MississippiTwo Mississippi

Three MississippiFour ….

A “new” second?A “new” second? Since 1967 the second has been Since 1967 the second has been

defined as:defined as: ““The duration of 9,192,631,770 The duration of 9,192,631,770

periods of the radiation periods of the radiation corresponding to the transition corresponding to the transition between the two hyperfine levels of between the two hyperfine levels of the fundamental state of the atom of the fundamental state of the atom of cesium-133”.cesium-133”. Beckwith, et al. Beckwith, et al.

““Atomic Clocks”Atomic Clocks” Microwaves strike the Microwaves strike the

cesiumcesium The frequency that The frequency that

maximizes the maximizes the fluorescence is the natural fluorescence is the natural resonance frequencyresonance frequency

The natural resonance The natural resonance frequency is frequency is 9,192,631,770Hz9,192,631,770Hz

This This defines defines the second.the second.

Is there a problem?Is there a problem? What happens when a day does not What happens when a day does not

contain 24X60X60 seconds? contain 24X60X60 seconds? Sundials don’t match the atomic clock.Sundials don’t match the atomic clock. Noon will shift, eventually occurring at Noon will shift, eventually occurring at

night.night. Leap seconds are added as requiredLeap seconds are added as required

Keeps noon in the middle of the dayKeeps noon in the middle of the day Just like leap days keep June at the Just like leap days keep June at the

beginning of summerbeginning of summer

How long is a meter?How long is a meter? In 1889 the meter was redefined as In 1889 the meter was redefined as

the length of the International the length of the International Prototype Meter (a physical artifact Prototype Meter (a physical artifact that defined a meter).that defined a meter).

Since 1983 the meter has been Since 1983 the meter has been defined as the length light travels in a defined as the length light travels in a vacuum in 1/299,792,458 seconds.vacuum in 1/299,792,458 seconds.

Inversely, the speed of light is now, Inversely, the speed of light is now, by by definitiondefinition, 299,792,458m/s., 299,792,458m/s.

What about US?What about US? Since 1959, the “international inch” is Since 1959, the “international inch” is

defined as 2.54 cm defined as 2.54 cm exactlyexactly!! However, the US Coast and Geodetic However, the US Coast and Geodetic

Survey, (established in 1893) was Survey, (established in 1893) was based on the metric system and defined based on the metric system and defined an inch as 1/39.37 meter (39.37inch = an inch as 1/39.37 meter (39.37inch = 1 meter, 1 meter, exactlyexactly). ). Beckwith, et al.Beckwith, et al.

The “survey inch” is 2.54000508 cm The “survey inch” is 2.54000508 cm (1/39.37)(1/39.37)

MassMass The kilogram was originally defined as the mass The kilogram was originally defined as the mass

of 1 liter of water at 4ºC and 76 cm mercury of 1 liter of water at 4ºC and 76 cm mercury atmospheric pressure (1 liter contains 1000 atmospheric pressure (1 liter contains 1000 cubic centimeter).cubic centimeter).

The kilogram was quickly replaced by a physical The kilogram was quickly replaced by a physical artifact.artifact.

The mass of this specific platinum iridium bar is The mass of this specific platinum iridium bar is by definition, 1kg.by definition, 1kg.

This is still the definition, and it is the only This is still the definition, and it is the only primary standard based on a physical artifact.primary standard based on a physical artifact.

It is maintained by the International Bureau of It is maintained by the International Bureau of Weights and Measures in Sèvres, France. Weights and Measures in Sèvres, France.

What about US?What about US?

Since 1959 the pound-mass has been Since 1959 the pound-mass has been defined as 0.4535937kgdefined as 0.4535937kg

NIST maintains the US’s physical NIST maintains the US’s physical artifact, which is secondary to the artifact, which is secondary to the International artifact in France.International artifact in France.

Getting warm? How Getting warm? How warm?warm?

Temperature is much more complex Temperature is much more complex to define. to define.

It requires definition at multiple It requires definition at multiple pointspoints

Fixed point Fixed point Temperature (K) Temperature (K)Triple point of hydrogenTriple point of hydrogen 13.803313.8033Triple point of neonTriple point of neon 24.556124.5561Triple point of oxygenTriple point of oxygen 54.358454.3584Triple point of argonTriple point of argon 83.805883.8058Triple point of mercuryTriple point of mercury 234.3156234.3156Triple point of waterTriple point of water 273.16273.16Melting point of galliumMelting point of gallium 302.9146302.9146Freezing point of lanthanumFreezing point of lanthanum 429.7485429.7485Freezing point of tinFreezing point of tin 505.078505.078Freezing point of zincFreezing point of zinc 692.677692.677Freezing point of aluminumFreezing point of aluminum 933.473933.473Freezing point of silverFreezing point of silver 1234.931234.93Freezing point of goldFreezing point of gold 1337.331337.33Freezing point of copperFreezing point of copper 1357.771357.77

Triple point: the temperature at which solid, liquid and gas phases coexist.Triple point: the temperature at which solid, liquid and gas phases coexist. Interpolation between temperatures is defined by means of a platinum Interpolation between temperatures is defined by means of a platinum

resistant thermometer, calibrated at the above temperatures. resistant thermometer, calibrated at the above temperatures. Wheeler and Wheeler and GanjiGanji

Triple Point video part I (in the video, watch at least from the 30 sec mark to (in the video, watch at least from the 30 sec mark to the 4:30 mark) the 4:30 mark) http://www.youtube.com/watch?v=qKDW1e3iNfsTriple Point video part II (watch through the 1:30 mark) (watch through the 1:30 mark) http://www.youtube.com/watch?v=GafCi-3Xqko

What about US?What about US? Conversion:Conversion: F = 1.8C + 32F = 1.8C + 32

What about other things?What about other things? The above units of measure are known The above units of measure are known

primary or fundamental standards.primary or fundamental standards. Time (second)Time (second) Length (meter)Length (meter) Mass (kg)Mass (kg) TemperatureTemperature Others (electrical, luminosity, angles, mole)Others (electrical, luminosity, angles, mole)

All other measures are based off of the All other measures are based off of the above basic units. These are known as above basic units. These are known as secondary or derived standards.secondary or derived standards. Velocity is distance per timeVelocity is distance per time Volume is length cubed, etc.Volume is length cubed, etc.

NISTNIST(National Institute of Standards and (National Institute of Standards and

Technology)Technology) Government agency mandated by the US Government agency mandated by the US

Constitution (Article I, Section 8).Constitution (Article I, Section 8). Responsible for defining and regulating Responsible for defining and regulating

weights and measures associated with US weights and measures associated with US commerce.commerce.

All measurements for engineering should All measurements for engineering should be conducted using calibrated and certified be conducted using calibrated and certified instruments and tools (traceable to NIST).instruments and tools (traceable to NIST).

How does it work?How does it work? NIST and other closely associated labs NIST and other closely associated labs

create physical artifacts and create physical artifacts and determine their characteristics (how determine their characteristics (how long are they, etc.)long are they, etc.)

Physical artifacts = calibration Physical artifacts = calibration standardsstandards

Calibration standards are used by labs Calibration standards are used by labs to calibrate measurement instruments to calibrate measurement instruments and tools.and tools.

Calibration and Calibration and CertificationCertification

Calibration determines the uncertainty (error) of Calibration determines the uncertainty (error) of a measurement device by comparing its a measurement device by comparing its measurement with the appropriate measurement measurement with the appropriate measurement standard. standard.

““Uncertainty” is a statistical description of the Uncertainty” is a statistical description of the difference between a measured value and the difference between a measured value and the true value (the true value is never known, it is true value (the true value is never known, it is only estimated). only estimated).

Uncertainty is sometimes referred to as error. Uncertainty is sometimes referred to as error. Certification is the documentation of the Certification is the documentation of the

calibration calibration

““Unusual” Conversion Unusual” Conversion Units…Units…

Ratio of an igloo’s circumference to its diameter: Ratio of an igloo’s circumference to its diameter: Eskimo PiEskimo Pi

2000 pounds of Chinese soup – Won ton2000 pounds of Chinese soup – Won ton 1 millionth of a mouthwash – 1 microscope1 millionth of a mouthwash – 1 microscope Time between slipping on a peel and smacking the Time between slipping on a peel and smacking the

pavement – 1 bananosecondpavement – 1 bananosecond Weight an evangelist carries with God: 1 billigramWeight an evangelist carries with God: 1 billigram Time it takes to sail 220 yards at 1 nautical mile per Time it takes to sail 220 yards at 1 nautical mile per

hour: Knot-furlonghour: Knot-furlong 365.25 days of drinking low-calorie beer because it’s 365.25 days of drinking low-calorie beer because it’s

less filling – 1 lite yearless filling – 1 lite year 16.5 feet in the Twilight Zone: 1 Rod Serling16.5 feet in the Twilight Zone: 1 Rod Serling Half of a large intestine: 1 semicolonHalf of a large intestine: 1 semicolon 1000 aches: 1 megahurtz1000 aches: 1 megahurtz Basic unit of laryngitis: 1 hoarsepowerBasic unit of laryngitis: 1 hoarsepower Shortest distance between two jokes: a straight lineShortest distance between two jokes: a straight line

454 graham crackers: 1 pound cake454 graham crackers: 1 pound cake 1 million-million microphones: 1 megaphone1 million-million microphones: 1 megaphone 1 million bicycles – 2 megacycles1 million bicycles – 2 megacycles 2000 mockingbirds: two kilomockingbirds2000 mockingbirds: two kilomockingbirds 120 cards: 1 decacards120 cards: 1 decacards 1 kilogram of falling figs: 1 Fig Newton1 kilogram of falling figs: 1 Fig Newton 1000 grams of wet socks: 1 literhosen1000 grams of wet socks: 1 literhosen 1 millionth of a fish – 1 microfiche1 millionth of a fish – 1 microfiche 1 trillion pins: 1 terrapin1 trillion pins: 1 terrapin 10 rations: 1 decoration10 rations: 1 decoration 100 rations: 1 C-ration100 rations: 1 C-ration 2 monograms: 1 diagram2 monograms: 1 diagram 8 nickels: 4 paradigms8 nickels: 4 paradigms 2.4 statue miles of intravenous surgical tubing at Yale 2.4 statue miles of intravenous surgical tubing at Yale

University Hospital: 1 I.V. LeagueUniversity Hospital: 1 I.V. League 100 Senators: Not 1 decision100 Senators: Not 1 decision

REFERENCESREFERENCES Beckwith, Marangoni, and Lienhard, Beckwith, Marangoni, and Lienhard,

Mechanical MeasurementsMechanical Measurements, 5th ed., , 5th ed., Addison-Wesley Publishing, 1993.Addison-Wesley Publishing, 1993.

Wheeler and Ganji, Wheeler and Ganji, Introduction to Introduction to Engineering ExperimentationEngineering Experimentation, , Prentice Hall, 1996)Prentice Hall, 1996)

DISCOVER, DISCOVER, Vol. 25 No. 03, March Vol. 25 No. 03, March 20042004

Questions?Questions?