Metrology

 Metrology

Metrology is the science of measurement. The word metrology derives from two Greek words: matron (meaning measure) and logos (meaning logic). With today’s sophisticated industrial climate, the measurement and control of products and processes are critical to the total quality effort. Metrology encompasses the following key elements:

The establishment of measurement standards that are both internationally accepted and definable

The use of measuring equipment to correlate the extent that product and process data conform to specifications (expressed in recognizable measurement standard terms)

The regular calibration of measuring equipment, traceable to established international standards

Units of Measurement

There are three major international systems of measurement: English, Metric, and the System International D‘unites (or Sl). The metric and SI systems are decimal-based, the units and their multiples are a related to each other by factors of 10. The English system, although logical to us, has numerous relic defined measurement units that make conversions difficult. Most of the world is now committed to the adoption of the SI system. The SI system was established in 1968 and the transition is occurring very slowly. The final authority for standards rests with the internationally based system of units. This system classifies measurements into seven distinct categories:

Length (meter). The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The speed of light is fixed at 186,282.3976 statute miles per second, with exactly 2.540 centimeters in one inch.

 Time (second). The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium – 133 atom.

Mass (kilogram). The standard unit of mass, the kilogram is equal to the mass of the international prototype which is a cylinder of platinum iridium alloy kept by the International Bureau of Weights and Measures at Sevres (near Paris, France). A duplicate, in the custody of the National Institute of Standards and Technology, serves as the standard for the United States. This is the only base unit still defined by an artifact.

 Electric current (ampere). The ampere is a constant current that, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 x 10” Newtons per meter of length

Light (candela). The candela is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and has a radiant intensity in that direction of 1/683 of a watt per steradian.

 Amount of substance (mole). The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. The elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles or specified groups of such particles.

 Temperature (Kelvin). The Kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. It follows from this definition that the temperature of the triple point of water is 273.16 K (0.01 C). The freezing point of water at standard atmospheric pressure is approximately 0.01 K below the triple point of water. The relationship of Kelvin, Celsius, and Fahrenheit is shown below.

Temparture scaleSI stystem

Enterprise Measurement Systems

Enterprise Measurement systems relates to items that can be directly or indirectly measured or counted. Often overlooked are those key enterprises measures that can be service-oriented and/or transactional in nature. These measures are often expressed in percentages or presented to management in time line or graphical formats.

Enterprise performance can be measured and presented by using:

Automatic counters

Computer generated reports

Internal and external audits

Supplier assessments

Management reports

Internal and external surveys

A variety of feedback reports

The following is a non-exclusive list of items that can be measured:

Suppliers

Number of product deviations

Percentage of on-time deliveries

Percentage of early deliveries

Shipment costs per unit

Shipment costs per time interval

Percentage of compliance to specifications

Current unit cost compared to historical unit cost

Dollars rejected versus dollars purchased

Timeliness of supplier technical assistance

Marketing/Sales

Sales growth per time period

Percentage of market compared to the competition

Dollar amount of sales/month

Amount of an average transaction

Time spent by an average customer on website

Effectiveness of sales events

Sales dollars per marketing dollar

External Customer Satisfaction

A weighted comparison with competitors

Perceived value as measured by the customer

 Ranking of product/service satisfaction

Evaluation of technical competency

Percentage of retained customers

Internal Customer Satisfaction .

 Employee rating of company satisfaction

Rating of job satisfaction

An indication of training effectiveness

An evaluation of advancement fairness

Feedback reaction to major policies and procedures

Knowledge of company goals and progress to reach them

Research and Development

Number of development projects in progress

Percentage of projects meeting budget

Number of projects behind schedule

Development expenses versus sales income

Reliability of design change requests

Engineering

Evaluation of product performance

Number of corrective action requests

Percentage of closed corrective action requests

An assessment of measurement control

Availability of internal technical assistance

Manufacturing

Key machine and process capabilities

Machine downtime percentages

Average cycle times (key product lines)

Measurement of housekeeping control

Adequacy of operator training

Measurement Error

The total variability in a product includes the variability of the measurement process:

σ2Total = σ2Process + σ2Measurement

The error of a measuring instr

ument is the indication of a measuring instrument minus the true value.