2 Standards n Units

8/8/2019 2 Standards n Units

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STANDARDS, UNITS ANDDATA PRESENTATION

Mohd Zaki NuawiMohd Hanif Md Saad

Dept of Mechanical & Materials EngineeringUniversiti Kebangsaan Malaysia

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KJ2313 Sem 1 Session 0809 2

Introduction

w A vital part of the measurement-evaluation process isthe comparison of the result of your measurementagainst an appropriate reference or standard.

w This comparison process allows you to attach some judgment of quality or merit to your measurementresult.

w When a measurement system is calibrated, itsindicated value is compared directly with a referencevalue the standard .



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Standards of Length and Time

w In the past, standards of length included sepemeluk, sehastaetc. Standards for time included a standard burning candle,a sundial, sepuntung rokok...

w Nowadays, the standard may be based on the output from apiece of equipment, from an object having a well-definedphysical attribute to be used as comparison, or from a well-accepted technique known to produce a reliable value.



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Standards

w A dimension defines a physical variable that is used todescribe some aspect of a physical system.

w A unit defines a quantitative measure of a dimension.

w A primary standard defines the value of a unit.

Dimension Unit

Mass Kg

Length Meter

Time second



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Standards

w To avoid confusion, units are defined by internationalagreement through the use of primary standards.

w

Primary standard of time:n 1 s = duration of 9,192,631,770 periods of cesium 133

radiation... (essentially Atomic clock is the standard)w Primary standard of length:

n 1 m = path traveled by light in vacuum in 1/299,792,458 s

(i.e, speed of light is 299,792,458 m/s)



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Standards

w Primary standard of mass:n Originally, the unit of the kilogram was defined by the

mass of one liter of water at room temperature.n Today, more consistent definition the kilogram is the

mass of a particular platinum-iridium cylindrical bar thatis maintained under very specific conditions at theInternational Bureau of Weights and Measures located in

Sevres, France.n This bar forms the primary standard for the kilogram.



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Hierarchy of standards

w Actual primary standards are impractical as standards fornormal calibration use.

w But they serve as a reference for exactness.w For practical reasons, there exists a hierarchy of reference

and secondary standards used to duplicate the primarystandards.

w As one moves down through the standards lineage, the

degree of exactness by which a standard approximates theprimary standard deteriorates.



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Hierarchy of Standards



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... and on and on ...



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And just when you thought thats all


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SI Unit systems:Primary & Derived

Units

Only a fewderived unitsare shown asexamples;there aremany more.




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More on Primary Standardsampere [A]

The ampere is the basic unit of electric current. It is that currentwhich produces a specified force between two parallel wireswhich are 1 metre apart in a vacuum.It is named after the Frenchphysicist Andre Ampere (1775-1836).

kelvin [K]

The kelvin is the basic unit of temperature. It is 1/273.16th of thethermodynamic temperature of the triple point of water. It is

named after the Scottish mathematician and physicist WilliamThomson 1st Lord Kelvin (1824-1907).




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More on Primary Standards

mole [mol]

The mole is the basic unit of substance. It is the amount of

substance that contains as many elementary units as thereare atoms in 0.012 kg of carbon-12.

candela [cd]

The candela is the basic unit of luminous intensity. It is the

intensity of a source of light of a specified frequency, whichgives a specified amount of power in a given direction.



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The full range of prefixes with their [symbols or abbreviations] and theirmultiplying factors

yotta [Y] 1 000 000 000 000 000 000 000 000 = 10^24

zetta [Z] 1 000 000 000 000 000 000 000 = 10^21exa [E] 1 000 000 000 000 000 000 = 10^18peta [P] 1 000 000 000 000 000 = 10^15tera [T] 1 000 000 000 000 = 10^12giga [G] 1 000 000 000 ( a t h o us a n d mi l l i o ns = a b i l l i o n ) mega [M] 1 000 000 ( a mi l l i o n ) kilo [k] 1 000 ( a t h o u s a n d )

hecto [h] 100 ( a h un d r e d ) deca [da]10 ( t e n ) 1

deci [d] 0.1 ( a t e n t h ) centi [c] 0.01 ( a h u nd r e d t h ) milli [m] 0.001 ( a t h ou s an d t h ) micro [] 0.000 001 ( a mi l l i o n t h ) nano [n] 0.000 000 001 ( a t h o u s a n d mi l l i o n t h )

pico [p] 0.000 000 000 001 = 10^-12femto [f] 0.000 000 000 000 001 = 10^-15atto [a] 0.000 000 000 000 000 001 = 10^-18zepto [z] 0.000 000 000 000 000 000 001 = 10^-21yocto [y] 0.000 000 000 000 000 000 000 001 = 10^-24

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Data Presentation

w There is a difference between data andinformation. Raw numbers need to be

processed in order to give useful information.w Eg: The numbers 78, 64, 36, 70 52, can be

processed in different ways

78 64 36 70 52

http://www.crowsworld.co.uk/rcat/datapresentation.htm




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Data Presentation

w If they were student marks, they could be averaged to givethe result of 60%. The minimum mark, however, is less thanthe pass mark, and the maximum would be a Distinction.

This kind of processing gives more useful information to atutor or course manager than the raw data.w You can show the characteristics of a set of data or highlight

important patterns.w People tend to look at diagrams (hence the saying One

picture is worth a thousand words). People are good atrecognising patterns and can extract a lot of information in ashort time. However, a badly presented diagram will notinform at all, and so they need careful planning and thought.




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Data Reduction

w If raw data is given in report form, as lists of numbers,people would find it boring at best and indigestible at worst.They would skip to more interesting material. They wouldignore the figures, despite the fact that they may beimportant. They would not take the time to pick out anyoutstanding data or try to extract any meaning from thewhole.

w To try to make figures less daunting. In most cases we arenot interested in the small detail and merely want an overall

picture.w Data reduction can give a simplified and accurate view of

the data which shows the underlying patterns but does notoverwhelm with detail.

p y



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Data Reduction

w Data reduction has the advantages of enablingresults to be viewed:

n in a compact formn easy to understandn presented graphicallyn demonstrate overall patternsn make comparisons

w However, it has disadvantages in thatn details of the original data are lostn the process is irreversible.



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Data Presentation: Graphs

w A bar graph compares values across categories ortreatments. The x-axis gives the treatment values

(independent var iable ), while the y-axis depictsthe values of the dependent var iable .w The values of the bars can be raw data, totals or

means .

http://scene.asu.edu/habitat/data_present.html



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Sample graph: numbers of insects of three different species found in

plants growing at different densities. The independent variable on the x-axis is plant density and the dependent variable on the y-axis is the rawnumber of insects.



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Combining two sets of data on one graph can be done, andthe visual juxtaposition of the two different sets of information that results can be very illuminating



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A common statistical test calculated with means is the standarddeviation . Standard deviations can be presented visually on bar, line anddata point graphs. Here is a bar graph with the standard deviation valuefor each mean. They are called error bars when on a graph.



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Line graph: Line graphs are used to show data pointsover time. Each line is for a single treatment (independent

variable).



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The x-axis shows the time interval and the y-axis depicts thevalues of the dependent variable. The graph can have datapoints (shown in the preceding slide) or just the lines (below).



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Pie Char t: Pie charts are used to show the contribution of each item to the whole. The values are commonly given as

a percent or a proportion.



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ATOMIC CLOCK

Atomic clocks are so accurate that minute adjustments must be madeperiodically to the length of the year to keep the calendar exactly synchronizedwith the Earth's rotation, which has a tendency to slow down. 3 types of atomic clock

1. ammonia clock , invented at the US National Bureau of Standards in 1948. It was regulatedby measuring the speed at which the nitrogen atom in an ammonia molecule vibrated back andforth. The rate of molecular vibration is not affected by temperature, pressure, or other externalinfluences, and can be used to regulate an electronic clock.2. A more accurate atomic clock is the caesium clock . Because of its internal structure, acaesium atom produces or absorbs radiation of a very precise frequency (9,192,631,770 Hz) thatvaries by less than one part in 10 billion. This frequency has been used to define the second, and

is the basis of atomic clocks used in international timekeeping.3. Hydrogen maser clocks , based on the radiation from hydrogen atoms, are the most accurate.The hydrogen maser clock at the US Naval Research Laboratory, Washington, DC, is estimatedto lose one second in 1,700,000 years. Cooled hydrogen maser clocks could theoretically beaccurate to within one second in 300 million years.

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