Industrial Engineering

Measurement Standards

JAHANZEB IKRAM (ME -011)

Shahid Mahmood (ME-005)

Mubashir Ahmad (ME-001

16th April, 2010

Precision is religion and measurement standards make it happen

Measurement

Measurement is key to research and development.

Standard

The meaning of "standard" is something that is set up and established by authorities as a rule for the measurement of quantity, weight, value quality, etc.

Measurement Standards

A measurement standard (Etalon) is a material measure, measuring instrument, reference material or measuring system intend to define, realize, conserve or reproduce a unit or one or more value of a quantity to serve as a reference.

Line and End standard are referred as Measurement standard in industries, which are used as references for calibration purpose. In the modern metrological era, digital instruments such as a periodically calibrated digital height gauge are commonly used. Light wave standards are used for laboratory purposes only.

Introduction

1) in 3000BC Royal cubit was defined as the length of the forearm of the ruling Pharaoh, plus the breadth of his hand

2) in 16th century feet was created3) in 18th century yard was declared by King Henry4) in 19th century Meter was upgraded and wave lengths of light proved a remarkable stable

standard

Types of Standards

After realizing the importance and advantage of metric system, most of the countries in the world have adopted the meter as the fundamental unit of linear measurement. Recently wave length of monochromatic light is used as fundamental unit of measurement. A meter is defined as 1650763.73 wavelengths of the orange radiation in vacuum of krypton-86.

The yard is defined as 0.9144 meter.

Hence three types of measurement standards are discussed below

a) Line standardb) End standardc) Wave length standard

Line standard

According to line standard the yard or meter is defined as the distance between inscribed line on a bar of metal under certain conditions of temperature and support.

a. The imperial standard Yard: This standard served its purpose from 1855 to 1960. it is made of a one-inch square cross section bronze bar(82% copper, 13% tin, 5% zinc) and is 38 inches long. The bar has a 1/2 inch deep hole, which are fitted with a 1/10 th

inch diameter gold plug. The highly polished top surfaces of these plug contain three transversely and two longitudinally engraved lines lying on the natural axis of the bronze bar. The yard is defined as the distance between two central transverse lines on the plugs when the temperature of the bar is constant at 62F.

b. International standard Prototype meter: The International bureau of Weights and Measures established the meter as the linear measuring standard in the year 1875. the meter is the distance between the centre portions of two lines engraved on the polished surface of a bar made of platinum (90%) iridium (10%) alloy having a unique cross section . this bar is kept at 0C and under normal ATM pressure

End standard

The need of end standard arises as the use of line standards and their copies was difficult at various places in the workshop. End standards are used in workshops and general use in precision engineering in standard laboratories. These are in the form of end bars and slip gauges.

a. End bar:End bars made of steel having cylindrical cross section of 22.2 mm dia with face lapped and hardened at the ends are available in sets of various lengths. End bars made from high carbon chromium steel, ensuring that faces are hardened to 64 RC and the bars have round section of 30mm for greater stability. Both ends are threaded, recessed and precion lapped to meet requirements of finish,flatness,parallelism and guage length. End bars are usually provided in sets of 9 to 12 pieces in step size of25 mm upto a length of 1m

b. Slip Guages:They are used in linear measurement in many ways. Slip gauges are rectangular block of hardened and stabilized high grade cast steel or the ceramic compound zirconium oxide. They are available 9mm wide, 30-35mm long cross section. There are different accuracy grades of slip gauges.

Wave length standard

The CGPM (Conference Generale das Poids et Mesurs) adopted a definition of the metre in terms of the wavelength.

These standards are used for high sensitivity length measurements have to be taken. The primary wavelength standard can be a laser standard which has its frequency compared with Cs time, and

frequency standard. High frequency accuracy, high-frequency stability and high re-producability help in high-accuracy interferometry length measurements.

METER:

The meter is defined as the wavelength of a krypton-86 lamp as the length equal to 1,650,763.73 wavelengths in vacuum corresponding to the transition between two energy levels of the atom Krypton-86.

YARD:

1 YARD=0.914 METERS

Sub Divisions of Standards:

There are four level of standards used as references all over the world

1) Primary standard is the one that is kept in Paris.2) Secondary standards are kept in the custody of every country in laboratory.3) Tertiary standard used in the industry.4) Working standards is used on the shop floor.

Calibration

Calibration is a comparison of instrument performance to standards of known accuracy. Calibrations directly link customers' measurement equipment to national and international standards. The advantages of calibration are accuracy in performing manufacturing operations, reduced inspection, and ensured quality products by reducing errors in measurement.