DESIGN FEATURES OF AN UNDERGROUND METROLOGY LABORATORY

The basic requirements for an ideal Metrological Laboratory are:

The Room:

1. Should be below the ground level to certain meters (say 6m), to take advantage of constancy of underground temperature and to isolate it from the vibrations, acoustics and other external influences, which affect the lab environment.
2. Should be insulated with expanded polystyrene insulation on all six sides.
3. Should have double walls with air gap on all the four sides to be made.
4. Should have special RCC floor blocks, cooled with circulation of chilled water is required.
5. Should have swirl type air diffusers to be fixed for thorough air mixing.
6. Should have an system so return air flows all along the wall surface.
7. Should have a high 30 air changes per hour.
8. Should have an air shower and air lock at entry, to keep the environment controlled under standard requirements.
9. Should have a vibration damping foundation with massive 1.5m monolithic RCC blocks. 
10. Should have Anti-static PVC flooring.

Environment

1. For effective handling of instruments and stainless checking of the readings, high efficient fluorescent lamps to be used as per NABL recommendation.
2. Importance to be given in temperature and humidity control all over the lab premises by strategically locating sensors and direct digital control.
3. Stainless steel pipes and fittings should be provided for compressed air supply system.
4. Separate pre-cleaning room with ultrasonic cleaning machine to be maintained.
5. Separate material stock room for storage of the calibrated instruments and gauges is a must.
6. Built-in emergency lighting and fire alarm system to be installed as a preventive maintenance inside the calibration laboratory.

Parameters to be considered before designing for the underground metrological laboratory.

PARAMETER	METROLOGY LABORATORY
Temperature	20 ± 0.2° C
Humidity	50 ± 5% RH
Clean room Class	10,000 (5VDI 2083)
Air velocity	< 0.2 m/sec
Differential Air Pressure	> 10 pa (1mm Wg)
Ground vibration (@<10 Hz)	< 0.2 µm
Illumination	400 lux
Noise level	< 45 dB (A)
Floor covering	Anti static PVC
Area	200 – 250 Sq.m.

Why use a 17025 Calibration?

ISO 17025
17025 calibration is our guarantee of confidence in our calibration results through internationally recognized technical auditing of a laboratory's competence. ISO17025 is virtually now the only Internationally Recognized Calibration System. Traceable Calibrations from Non ISO17025 Accredited Calibration Sources are now generally technically questioned. To quote from the ISO Standard, Certification against ISO9001 and ISO9002 does not of itself demonstrate the competence of the laboratory to produce technical valid data and results."

In the United Kingdom , UKAS Calibration is the only Accreditation Body who assesses Test & Calibration Laboratories to ISO 17025. National & International Technical Trade Barriers for your company's products and services become transparent when all your calibrations to the ISO17025 standard.

A Background to ISO 17025
ISO 17025 addresses every element of laboratory management. It is not exclusive to the laboratory manager, assistant laboratory manager, or quality manager. The standard involves all laboratory staff whose functions relate to the quality of laboratory data generated. It replaces NAMAS M10 and laboratories, which are currently accredited to M10, have until 30th June 2002 to meet the requirements of ISO 17025 if they are to retain their certification.
The ISO management system will provide a defined, ordered process for operating all facets of a laboratory. The laboratory community throughout the world has expressed, through the International Organization for Standardization, the essential elements for a laboratory management system in the text of ISO 17025. That document provides the nucleus for most laboratory accreditation programs today. ISO 17025 provides the framework for a Quality Management System for a testing or calibration laboratory.
 
The Opportunities
The Transition Management Tool gives the following benefits:

1. Clear identification of the new requirements in ISO 17025
2. Simple workbook format 
3. Addresses every clause and sub-clause of the standard
4. Cuts through the jargon of the standard
5. Breaks the standard down into manageable chunks
6. Identifies the gaps in the existing system 
7. Fully costs the transition project 
8. Assigns responsibilities for all the key project tasks

What is driving accreditation?

1. The automotive standards QS 9000 and 16949 require testing and calibration laboratories to be accredited.
2. Laboratories may need a quality system that is recognized internationally.
3. The marketplace - laboratories must keep up with competitors who are becoming accredited.
4. Internal motives - laboratories can improve their internal systems. 

ISO 9001 certified organisations : Calibration of measuring instruments

ISO 9001

ISO 9001 certified organisations have to make decisions regarding where to send their measuring instruments for calibration. Nowadays, many calibration laboratories have ISO 17025 accreditation. But some are not accredited, but still doing calibration work for other organisations. Also, many accredited laboratories are not accredited for all the services they offer. The use of non-accredited calibration labs, or non accredited services of partially accredited labs, may reduce operating costs in the short term, but could turn out to be costly in the long term. Examination of ISO 9001 (2000) and ISO 17025 suggests that ISO 9001 certified organisations should select their calibration labs carefully and make sure that the labs they use are properly accredited for the services they provide. Organisations certified to ISO 9001 are required to calibrate all their measuring equipment used to verify or control quality, and all such calibrations are required to be traceable to national or international standards (ISO 9001 1994 section 4.11, ISO 9001 2000 section 7.6). All the records of calibrations are required to be maintained properly and corrective action to be taken when measurement equipment is found to be out of specification. Some of the implications of calibration and traceability requirements for ISO 9001 certified organisations and for calibration and test laboratories begins with the investigation, regarding the meaning and components of the term `traceable'. Many calibration laboratories claim accreditation to ISO 17025. Here we go for NABL for accreditation and in Australia NATA is the accrediting body. Accredited labs are entitled to use the NABL logo on their documents and web pages. ISO 17025 is an international standard that specifies quality and technical competence requirements for testing and calibration laboratories. ISO 17025 replaced ISO Guide 25 in 1999.  Hiring and keeping competent technical staffs, internal audits, maintenance of in-house quality checks and participation in proficiency testing programs will improves the likelihood of an error-free service but it alone can never guarantee complete absence of calibration or other errors. However, customers of reputable ISO 17025 accredited labs can expect to be informed promptly and fully of errors when they are discovered, and of the particular consequences related to the calibration of their equipment (as per sections 4.9, 4.10).  Calibration, uncertainty and traceability The ISO 9001 requirement for traceable calibration of test and measurement equipment raises questions concerning the term `traceable'. When we examine definitions and components of traceability extracted from ISO 9001, ISO 17025 and other documents, we get the answer for it in clear way and along with that discussion regarding the implications were also made in following lines.  Tractability is defined as, ‘the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties....' The unbroken chain of comparisons is called a `traceability chain'. An unbroken chain of comparisons is a logical and easily understood component of traceability. The manager of a non-accredited lab might claim that his calibrations are traceable because he is able to trace only the calibration pedigree of the references and standards, which he uses. This aspect can be analyzed by an example. Assume we keep a set of weights which we use to check balances in a chemical laboratory. The balance should have a resolution and repeatability within the uncertainty required in the final result, when compared with a set of calibrated weights. It must be properly serviced and maintained, mounted on an appropriately rigid and vibration-free bench in a temperature controlled environment. Air movement around the balance may need to be restricted. If the weights to be compared are of different density, compensation for buoyancy might be necessary. Buoyancy compensation might require measurements of air temperature, humidity and barometric pressure. If the lab provides other calibration services then the presence of other equipment nearby may alter the environment in the vicinity of the balance, e.g. a temperature calibration oven might alter the mean radiant temperature in the vicinity of the balance.

If we appreciate the potential complexity of the calibration process then we should require that the lab calibrating our weights employ a technician with sufficient competence and training to appreciate all the potential sources of error in the calibration. He should be capable of setting up the equipment properly and deciding which errors are significant and which can be ignored for a particular calibration. Competence as a component of traceability is addressed in ISO 17025 section 5.6. The Section 5.6.2.1.1 states that traceability of measurement shall be assured by the use of calibration services from laboratories that can demonstrate competence, measurement capability and traceability. The use of the word 'shall' in a standard usually means that there is no other way to achieve compliance. ISO 17025 further states that, any calibration laboratories fulfilling the requirements of this International Standard are considered to be competent . A calibration certificate from a calibration laboratory accredited to this International Standard for the calibration concerned is sufficient evidence of traceability.  Uncertainty as an essential component of traceability No measurement is ever true. There is always a difference between the true value of a measurand and the output of an instrument. Measurement uncertainty is a quantitative statistical estimate of the limits of that difference. The measurement uncertainty is ' a parameter associated with the results of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand'.  Uncertainty estimates document the rationality and consistency of the comparisons. A traceability chain is a documented set of comparisons between consecutive pairs of instruments or measurement systems: A-B, B-C, C-D, etc. Usually instrument A is compared with instrument or standard B for the purposes of calibrating A, and the uncertainty estimated is that associated with that calibration process. The contribution of instrument or standard B to the overall calibration uncertainty is typically 4-10 times smaller than the contribution of A. Similar process to be handled between C & D also. Properly calculated and documented uncertainty estimates in a calibration chain indicate the `direction' of traceability.  Everyone should view uncertainty estimates as confirmation that his instrument is calibrated against a reference of adequate performance and that all-potential sources of error are under control during the calibration process. The essential component for traceable calibration is stated as below, Traceable calibration involves comparisons with traceable standards or reference materials. Only laboratories, which demonstrate their competence can perform traceable calibrations, by accreditation to ISO 17025. A traceable calibration certificate must contain an estimate of the uncertainty associated with the calibration.  Organizations using non-accredited calibration labs do not conform to ISO 9001 and  should not claim conformance. At the same time, some calibration laboratories offer a wide range of calibration services but are accredited for only a subset of those services.  In some cases labs claim `ISO 17025 accreditation' but are vague about exactly which services are accredited and which are not. ISO 9001 organizations should be careful to select calibration labs that are explicitly accredited for the services they are using. NABL keeps an up-to-date ,publicly available list of accredited labs with details of the calibration services for which they are accredited and their least uncertainties of measurement. In a manufacturing environment it is often the case that more than one measurement system is used to monitor or control the quality of the product, and inevitably some measurements contribute more than others to uncertainty in product quality. ISO 9001 does not require all measurement systems to be rigorously calibrated - only those that contribute significantly to the control or verification of the quality of the product. One approach to this problem might be to perform uncertainty analyses on quality-related measurements using techniques similar to those outlined in the ISO to determine which measurement systems require calibration and the maximum associated uncertainties.  Thus, an ISO 9001 certified organization should analyze the measurement systems it uses to verify or control quality, make informed decisions on which instruments require calibration, and have these instruments calibrated by selected ISO 17025 accredited labs.

GMT METROLOGY DIVISION - SYSTEMS OF MEASUREMENT

SYSTEMS OF MEASUREMENT

Errors in Measurements There is a true fact that, no measurement is exact. All measurements are subject to some error. It is therefore necessary to state not only the measured dimension, but also the accuracy of determination to which the measurement is made. As for as possible the errors inherent in the method of measurement used should be kept to a minimum, and having minimized the error, its probable magnitude, or accuracy of determination should be stated. Along with the actual gauge block size details, there should be details regarding the measured error in the block and the accuracy of determination with it enclosed. The accuracy of determination can be improved by repeating the measurement a number of times and stating the mean value. Types of errors: There are two types of errors, •  Those which should not occur and can be eliminated by careful work and attention. •  Those which are inherent in the measuring process. Misreading an instrument, arithmetic errors, alignment errors, parallax error, errors due to temperature were some of the errors that we can eliminate on proper procedural handling of the system. When we can truly believe a measurement?   We can never have 100% confidence in a measurement. No measurement is ever correct. There is always an unknown, finite, non-zero difference between a measured value and the corresponding true value. Most instruments have specified or implied tolerance limits within which the true value of the measurement should lie if the instrument is functioning correctly. One can never be 100% sure that an instrument is operating within its specified tolerance limits. There are steps we can take to minimize the probability of a measurement falling outside specified tolerance or uncertainty bands. Regular traceable calibration is a method for gaining quantifiable confidence in a measurement system. For example, if we consider about the pressure transducer, there are a number of modes in which electronic circuitry and the digital display can fail or malfunction. Most of the faults and malfunctions would not be visible to an operator therefore it is impossible to verify the absence of faults and electronic drift by simple inspection. We cannot tell by inspection if the instrument has recently been dropped, subjected to an over-range pressure or otherwise mistreated. When we make a measurement in the field we are forced to trust the instrument. The only way we can gain confidence in the electronic manometer is by regularly comparing its response with another similar or preferably superior instrument in which we have a high level of confidence. A quantitative comparison or verification of the performance of an instrument is called a calibration.

GMT Granite Surface Plates-Application and Accuracy

Application
Surface plates are used as reference planes for dimensional inspection and calibration of mechanical artifacts. This plate acts as a datum line or surface. So, the flatness of the plate is very important. Dolerite is the perfect material for metrology, because of its inherent characteristics mentioned in an earlier blog. The definition of flatness is, ‘all points on the surface being contained within two parallel planes, the base plane and the roof plane’. This flatness measurement commonly carries a tolerance and may include a grade designation. Flatness tolerance of the surface plate is provided in the standards with different grades based on flatness.

GMT Metrology Granite Surface Plates meet the DIN and IS Standards specified in the table above. Granite Surface Plates are manufactured to precision standards using the highest quality granite.

Accuracy
Rigorous quality control inspection is carried out at all stages. Final inspection is carried out with a High Precision Computerised Electronic Level calibrated by an NABL accredited lab at regular intervals..

Accuracy under Load
Granite Surface Plates are capable of supporting a total normal load of 25 kgs. per 0.1 sq.mtr.

Certificate
A certificate of accuracy is supplied with each plate as per standards specified.

Technical Data
Granite Surface Plates are manufactured in five grades. The typical application of these five grades of plates is as under:

• GRADE 00 as per DIN : 876 : 84 is of laboratory grade. It is specified for precision measurement in gauge rooms and metrology laboratories for calibration masters.
• GRADE 0 is of inspection grade. It is specified for general work in quality control.
• GRADE 1 is of tool room grade. It is specified for work shop use.
• GRADE 2 & 3 are intended for use in shops for general inspection. The choice of Grade 2 & 3 will depend on the application needs of the customer.

Material
Granite Surface Plates are made from select granite with uniform distribution of light and dark constituents. In such granite the minerals are evenly distributed resulting in a homogenous appearance.
The following are the representative properties of our granites :
Texture                           Fine
Specific Gravity             3.08 g/cm3
Hardness                        Scleroscope over 90
Modules of Elasticity     9.0 to 12.0 x 105kg/cm2
Moisture absorption       Nil

Flatness Tolerance
The flatness deviation of a local area of 250 mm x 250 mm of the working surface shall not exceed :

1. 3.0 µm for plates of Grade 00
2. 3.5 µm for plates of Grade 0
3. 7.0 µm for plates of Grade 1
4. 15.0 µm for plates of Grade 2
5. 30.0 µm for plates of Grade 3

Granite Surface Plate Stands
These are fabricated of heavy angle iron and reinforced to ensure rigidity. The stands are designed to withstand the weight of the granite surface plates and are supplied with 3 leveling screws for leveling the granite surface plates.

Optional Accessories
Plate will be supplied with a suitable Rexine Cover to protect both the working surface and side faces of the plate at extra cost.