Due to mechanical, chemical or thermal stress, the measuring instruments are subject to ageing and thus the value they measure changes over time. This cannot be averted, but can be redressed if detected in proper time by calibration. In this process, called calibration, the displayed result in a measuring instrument is compared with the measuring result of a different measuring device which is known to work with accuracy and has been made in accordance with national or international standards.
Importance of calibration
The report of survey of 100 management executives of international companies shows, manufacturing companies lose more than 1.7 million dollars per annum on average. This is never a good thing, if you keep in mind day by day the increasing deficit of resources. To maintain an inclined growth, overlooking the limitation of resources your company must require increasing the efficiency in the manufacturing process and efficiency cannot be increased without proper accuracy in measured data i.e. without time to time calibration.
Types of Calibration
When the calibration is carried out or supervised by an official body, it is called verification. The sole purpose of this is to determine the quality of the displayed results. In contrary to this, in-house calibrations are carried out by individual companies for regular assurance of quality standards. In-house calibrations are also necessary at various stages of the manufacturing process, but the equipments used in in-house calibrations must possess their own reference standards and must coincide directly or indirectly with a national reference instrument.
In-house calibration Services
There are laboratories providing in-house calibration services for their own measuring and test equipments. The calibration standards used by the In-house calibration service are to be calibrated by a calibration service provider that is accredited to ISO Standard 17025. Although, prior to selecting a non-accredited calibration supplier, you need to exhaust all potential accredited laboratories first, in some cases, non-accredited calibration labs (possessing unique skill or knowledge of a specialized calibration process) can be utilized.
Requirements of In-House Calibrations
- Calibration standards and reference material
The in-house calibration services must be equipped with standard reference materials for the in-house calibrations performed. The calibration standards supporting calibration systems are to be calibrated on a regular basis using traceable measurement standards to maintain the accuracy. Instead of measurement results, the certificate issued by in-house calibration services shall contain the measurement uncertainty statement of the calibration standards or a statement of compliance to an accepted meteorological specified.
- Physical environment of in-house calibration service provider
To assure the correct performance of calibration, the in-house calibration services or calibration service providers must maintain a favorable environmental condition (e.g. Humidity, temperature, vibration, etc.), in accordance with documented calibration procedures. You should control few other conditions (such as dust, electromagnetic disturbances, electrical supply radiation, and biological sterility) too, which may affect the calibrating instruments and the measured data.
- Calibration Test Methods and Procedures
Laboratories performing in-house calibration shall have methods and procedures the calibration. Personnel performing the calibration is to be availed with the documents regarding calibration methods. All the up-to-date details and information about in-house calibrations, including resulting estimation of measurement uncertainty and this procedure must be in compliance with the national, international and other recognized specific regulations, that contains concise information about how to perform the in-house calibration of certain instruments.
- Computer Software Validation Procedure
Where computer software is utilized to perform in-house calibrations in data recording, processing, retrieval, analysis and calculation, the laboratory must retain the proof that computer software is documented and verified for use. This is applicable for other automated equipments as well. There must be safeguards to protect the data recorded by these equipments as well.
- Control of Nonconforming Calibration Work
A calibration standard found to be out-of-tolerance, i.e. data recording errors that require corrective actions are known as non-conforming work. Nonconforming works affect calibration data, so each in-house calibration service must maintain records of every event where con-conforming work found to determine if there is any defect in the calibration processes.
- Reports and Certificates
Before choosing this, you must consider the reports and certifications. The reports provided, and certificates issued by the in-house calibration services and service providers must be fulfill the requirements of ISO 17025. The few following information if not included on certificated, the in-house calibration laboratories must retain for their own:
- Description of the method used
- Description of the environmental conditions of the lab and identification of the items calibrated
- The results of calibration with the mention of measurement units
- The name(s), function(s), signature(s) of personnel authorizing the calibration certificate
Except all the above-mentioned requirements to provide in-house calibration service, calibrations, the calibration labs must verify their equipments time to time and must retain supplier evaluation records as a proof of the quality of the equipments used in their labs.