We shall try to define and understand some of the terms used in quality management system. The standard ISO 9000:2005 is the basis on which the terms are defined.
10) Terms related to Quality Management for Measurement Processes
10.1) Measurement Management System
ISO 9000 definition:
“Set of interrelated and interacting elements necessary to achieve metrological confirmation and continual control of measurement processes “
The measurement management system is the set of business processes that control all of the measurement processes, and ensures that the measuring systems conform to defined requirements. A good measurement management system will be able to identify the required measurements for every important parameter or feature, identify the equipment used to make the measurement, demonstrate that the equipment is capable and the measurement process is validated, and document traceability to appropriate SI units.
Metrological confirmation is the process of ensuring that the measuring instruments (and the whole measurement system) are capable of making valid measurements of the required parameters or features of the product. Some of the things to do or consider are in this list. Metrological (measurement) requirements are obtained from the product. The measurement management system ensures that the requirements are known and documented the correct measurements are being made the risks and consequences of not managing the measurement process are accounted for measurement processes are controlled measurement equipment is available and adequate for making the measurements. People performing measurements are properly trained software used to make measurements is validated. Measuring equipment and work procedures are identified and controlled the environment of the measurement area is considered, and controlled as necessary.
Metrological confirmation ensures that the measuring instruments are suitable and capable of making the required measurements the current status is available to the user. Records are maintained. Measuring instruments are calibrated.
Measurement processes must be planned, validated, controlled, documented and implemented. A measurement process specification includes the measurement to be made, the equipment to be used, the skills and training required, and any other relevant factor. Measurement requirements come from the customer, the product, the organization, and statutory or regulatory requirements. Every measurement process must have an estimate of the measurement uncertainty, and the uncertainty should be small enough that it does not have a significant effect on the measurement result. Measurements must be traceable to appropriate International or National units of measurement (meter, kilogram, second, ampere, kelvin, candela, mole, radian and the supplemental units based on these). Nonconforming measuring equipment shall not be used.
10.2) Measurement process
ISO 9000 definition:
“Set of operations to determine the value of a quantity”
Measurement is the process by which the fundamental quantities and qualities of members of a system, together with their relationships are derived and documented. The clearest example of this process is measurement of physical properties such as counts – how many, mass, weights, distance.The process of measurement consists of obtaining a quantitative comparison between a predefined standard and a measurand.
Measurand = Physical parameter being measured: length, temperature, fluid flow, acoustics, motion etc
Standard of comparison: must be of the same characters as the measurand, and is prescribed and defined by a legal of recognized agency, e.g.:
NIST = The National Institute of Standards and Technology.
ISO = The International Organization for Standardization.
ANSI = The American National Standards Institute.
Measurement is fundamental basis for all research, design, and development and its role is :
- fault diagnosis and trouble shooting (process monitoring).
- Quality control.
- Fits and tolerances.
- CL (Feedback) system.
- Feed-forward control systems.
- New understanding of physical world.
- Test for any theory, design or development.
Fundamental Methods of Measurement:
- Direct Comparison with either a primary or secondary standard.
- Indirect Comparison through the use of a calibration.
The generalized Measuring System
Most measuring systems fall within the framework of a general arrangement consisting of three phases (stages):
Stage 1 : Detection- transduction, or sensor- transducer, stage.
Stage 2 : Signal conditioning stage.
Stage 3 : Readout- recording stage.
10.3) Metrological Confirmation
ISO 9000 definition :
“Set of operations required to ensure that measuring equipment conforms to the requirements for its intended use.”
NOTE 1 Metrological confirmation generally includes calibration or verification, any necessary adjustment or repair and subsequent recalibration, comparison with the metrological requirements for the intended use of the equipment, as well as well as any required sealing and labelling.
NOTE 2 Metrological Confirmation is not achieved until and unless the fitness of the measuring equipment for the intended use has been demonstrated and documented.
NOTE 3 The requirements for intended use include such considerations as range, resolution and maximum permissible errors.
NOTE 4 Metrological requirements are usually distinct from, and are not specified in, product requirements.
Metrological Confirmation is a set of operation required to ensure the measuring equipment is in a state of compliance with the requirement of its intended use. Metrological confirmation generally includes calibration and verification, any necessary adjustment or repair, and subsequent recalibration, comparison with the metrological requirements for the intended use of the equipment, as well as any required sealing and labeling. Metrological confirmation is not achieved until and unless the fitness of the measuring equipment for the intended use has been demonstrated and documented. The requirements for intended use include such considerations as range, resolution and maximum permissible errors. Metrological requirements are usually distinct from, and are not specified in, product requirements.
ISO 9000 definition:
“Measuring instrument, software, measurement standard, reference material or auxiliary apparatus or combination thereof necessary to realize a measurement process .”
In the context of this standard, measuring equipment includes all the things that are needed to carry out a measurement process for carrying out a specified and defined measurement. Accordingly, measuring equipment includes measuring instruments and apparatuses as well as all the associated software, standards, and reference materials.
A measuring instrument is a device for measuring a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement. Measuring instruments, and formal test methods which define the instrument’s use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty.
Scientists, engineers and other humans use a vast range of instruments to perform their measurements. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes and particle accelerators. Virtual instrumentation is widely used in the development of modern measuring instruments.
10.5) Metrological characteristic
ISO 9000 definition:
“Distinguishing feature which can influence the results of measurement.”
NOTE 1 Measuring equipment usually has several metrological characteristics.
NOTE 2 Metrological characteristics can be the subject of calibration.
Metrological characteristics are distinguishing feature of the Measuring Instrument which can influence the measurement.
Some of the metrological characteristics are:
1. Range of Measurement: It indicates the size values between which measurements may be made on the given instrument.
2. Scale range: It is the difference between the values of the measured quantities corresponding to the terminal scale marks.
3. Instrument range: It is the capacity or total range of values which an instrument is capable of measuring.
4. Scale Spacing: It is the distance between the axes of two adjacent graduations on the scale. Most instruments have a constant value of scale spacing throughout the scale. Such scales are said to be linear. In case of non-linear scales, the scale spacing value is variable within the limits of the scale.
5. Scale Division Value: It is the measured value of the measured quantity corresponding to one division of the instrument, e.g., for ordinary scale, the scale division value is 1 mm. As a rule, the scale division should not be smaller in value than the permissible indication error of an instrument.
6. Sensitivity (Implication or gearing ratio): It is the ratio of the scale spacing to the division value. It could also be expressed as the ratio of the product of all the larger lever arms and the product of all the smaller lever arms. It is the property of a measuring instrument to respond to changes in the measured quantity.
7. Sensitivity Threshold: It is defined as the minimum measured value which may cause any movement whatsoever of the indicating hand. It is also called the discrimination or resolving power of an instrument and is the minimum change in the quantity being measured which produces a perceptible movement of the index.
8. Reading Accuracy: It is the accuracy that may be attained in using a measuring instrument.
9. Reading Error: It is defined as the difference between the reading of the instrument and the actual value of the dimension being measured.
10. Accuracy of observation: It is the accuracy attainable in reading the scale of an instrument. It depends on the quality of the scale marks, the width or the pointer/index, the space between the minter and the scale, the illumination of the scale, and the skill of the inspector. The width of scale :ark is usually kept one-tenth of the scale spacing for accurate reading of indications.
11. Parallax: It is apparent change in the position of the index relative to the scale marks, when scale is observed in a direction other than perpendicular to its plane.
12. Repeatability : It is the variation of indications in repeated measurements of the same dimension. The variations may be due to clearances, friction and distortions in the instrument’s mechanism. Repeatability represents the reproducibility of the readings of an instrument when a series of measurements are carried out under fixed conditions of use.
13. Measuring force: It is the force produced by an instrument and acting upon the measured surface in the direction of measurement. It is usually developed by springs whose deformation and pressure change with the displacement of the instrument’s measuring spindle.
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