ACCREDITED CALIBRATION LABORATORY
A product or service should ‘Fit for purpose’, conforming to specified requirements with respect to National standard / International standard / User’s specification. This requires the services by a calibration laboratory, which should be accreditated. ‘Accreditation is a process of formal recognition of technical competence of the conformity assessment body in accordance with the prevailing international standard’.
National Accreditation Board for testing and calibration Laboratories (NABL) happens to be a full member of Asia Pacific Laboratory Accreditation Co-operation (APLAC) and International Laboratory Accreditation Co-operation (ILAC). B’coz of a comprehensive requirements of combining inspection and testing in many areas, NABL is providing accreditation activity for inspection bodies in accordance with ISO/IEC 17020 International standard, and ISO/IEC 17025:1999.
This 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%. This 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.
Organisation of calibration laboratory
The calibration laboratory shall be organized in such a way, so as to ensure the integrity and training of its staffs 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. That quality manual should hold 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 staffs with at least, a degree in Physics or Diploma in Engineering. Headed by a P.G. in Physics or Graduate in Mechanical/Instrumentation Engineering. 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 to be maintained, fluorescent lighting is preferred to avoid localized heating and temperature drift. The recommended level of illumination in 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 hold 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 and availability of service manual to be checked and preserved.
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, throu’ 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.
DESIGN FEATURES OF AN UNDERGROUND LABORATORY
The basic requirements for an ideal metrological laboratory are
- Metrology Laboratory should be below the ground level to certain meters (say 6m), to take advantage of constancy of underground temperature. And also to isolate it from the vibrations, acoustics and other external influences, which affect the lab environment.
- Expanded polystyrene insulation to be made on all six sides.
- Double walls with air gap on all the four sides to be made.
- Special RCC floor blocks, cooled with circulation of chilled water is required.
- Swirl type air diffusers to be fixed for thorough air mixing.
- Return air is made all along the wall surface.
- A high 30 air changes per hour.
- At entry into the calibration room, air shower and air lock are made effectively to keep the environment controlled under standard requirements.
- To avoid vibration through floor, massive 1.5m monolithic RCC floor blocks to be used.
For effective handling of instruments and stainless checking of the readings, high efficient fluorescent lamps to be used as per NABL recommendation.
- Importance to be given in temperature and humidity control all over the lab premises by strategically locating sensors and direct digital control. To monitor the changes in this regard now and then, and corrections to be made if required.
- Suitable stainless steel pipes and fittings to be provided for compressed air supply system.
- Anti-static PVC flooring to be provided.
- Separate pre-cleaning room with ultrasonic cleaning machine to be maintained.
- Separate material stock room for storage of the calibrated instruments and gauges is a must.
- Built-in emergency lighting and fire alarm system to be installed as a preventive maintenance inside the calibration laboratory.
- These were some of the things to be considered before designing for the underground metrological laboratory.
These were some of the things to be considered before designing for the underground metrological laboratory.
|Temperature||20 ± 0.20C|
|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|
|Noise Level||<45 dB (A)|
|Floor Covering||Anti static PVC|
|Area||200 – 250 Sq.m.|