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.

REQUIREMENTS FOR METROLOGICAL LABORATORY

A product or service should be 'Fit for purpose', conforming to specified requirements with respect to National standard / International standard / User's specification. This requires the services of a calibration laboratory, which should be accredited. 'Accreditation is a process of formal recognition of technical competence in accordance with the prevailing international standard' by a recognized accreditation institution.

The National Accreditation Board for testing and calibration Laboratories (NABL) is a full member of Asia Pacific Laboratory Accreditation Co-operation (APLAC) and International Laboratory Accreditation Co-operation (ILAC). Because of a comprehensive requirement of combining inspection and testing in many areas, NABL  provides accreditation  for inspection bodies in accordance with ISO/IEC 17020 International standard, and ISO/IEC 17025:1999. 

A  Calibration laboratory shall be accredited according to their 'Best measurement capability'. It means the least uncertainity of measurement (±) at a confidence probability level of 95%. The calibration laboratory is not permitted to report a smaller uncertainity of measurement than the best measurement capability on its endorsed documents. Obviously, the actual uncertainty of measurement can never be smaller than the best measurement capability. 

The calibration laboratory shall be organized in such a way as to ensure the integrity and training of its staff and operations for ensuring unbiased calibration. There should be an authorized signatory for the calibration certificates/reports issued by the laboratory. It should have a quality manual, which should be maintained up-to-date and available for scrutiny, in compliance with ISO/IEC 17025 and NABL requirements. The quality manual should contain a quality policy statement, objectives, commitments by the top management, names, qualifications, experience of persons responsible for the managerial, scientific/technical activities, measurement capability, Traceability of calibration of all measuring instruments to standard, calibration procedures adopted, National/International standards referred/used. 

The laboratories should have authorized signatories for approving and issuing calibration certificates for each calibration parameter as mentioned in the scope of accreditation. The laboratory should have an adequate number of qualified and trained staff with at least a degree in Physics or Diploma in Engineering. The team should be headed by a P.G. in Physics or Graduate in Mechanical/Instrumentation Engineering. 

The calibration area shall be adequately free from vibrations generated by air-conditioning plant, vehicular traffic or any other such sources. Acoustic noise level shall be maintained for proper performance of calibration. A threshold noise level of 60 dBA is to be maintained as recommended. Adequate level of illumination has to be maintained, fluorescent lighting is preferred to avoid localized heating and temperature drift. The recommended level of illumination is 450-700 lux on the working table with glare index of 19 for the laboratory. 

The environmental conditions for the activity of the laboratory shall be such as not to adversely affect the required accuracy of measurements. As possible, only the staff engaged in calibration activity should be permitted entry inside the calibration area. Laboratory should have equipment of required accuracy in respect of each parameter covered. Stability of the standards, accuracy of the values realized through them and repeatability, should be regularly monitored.

Calibration certificates, performance history sheets, working standard details should be held safely by the laboratory. Each equipment should have a record of name, manufacturers name and address, type, range, identification and serial no., date of procurement and commissioning, details of calibration, details of maintenance, performance history with dates. The service manual has to be available at all times.

All the standard equipment of the laboratory should be calibrated periodically against calibration standards of a laboratory accreditated by NABL/ equivalent MRA partners having superior measurement capability or NPL/ other international NMIs. To give further assurance to the accuracy or uncertainty of measurements, a laboratory should be required to participate from time to time, in Proficiency Testing Programmes. There the abnormalities of equipment are detected in terms of En number, through inter-comparisons and the appropriate corrective actions should be taken. The standard equipment shall be replaced/ repaired and re-calibrated with a higher accuracy standard. Reports on such inter-comparisons should be documented with reference. This Proficiency Testing practice should be included in the Quality Manual.

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.