T&M Equipment: Why Is Regular Calibration Important?

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Calibration: Challenges to overcome
1. Identifying calibration needs and devoting time for calibrations
2. Lack of knowledge related to calibration cycle, calibration process and accredited laboratories
3. Lack of appreciation for the role of calibration
4. Calibrating the master/reference equipment and maintaining ideal environment for it
5. Calibration of equipment that don’t have a set procedure and you have to test them with first principles
6. Lack of training for the calibration technician/engineer
7. Undetermined traceability

Training the technician
All the measurement processes are accompanied by errors and uncertainties that cannot be eliminated. Sulfikaruddin says, “Calibration quantifies and controls the errors or uncertainties of the measurement processes to an acceptable level.” This makes calibration a challenging job that must be handled by a trained technician or engineer.

According to Kela, the uncertainty of results is affected by 4 ‘M’s—man, machine, method and material. Therefore utmost importance is given to train the people who perform calibration of equipment. They are also trained to use standard calibration methods and standard accessories to get accurate results.

Adjustment is not calibration
Most users are always confused between calibration and adjustment. It is important for the user to understand the difference between the two. When you are experimenting in a lab, and you do not see a ‘zero’ reading when the equipment is not connected, you make ‘adjustments’ to remove the offset. This is not calibration.

“Calibration is process of parameters verification of any equipment against a well-known standard. Calibration report is a data that shows what parameters of the equipment are within the manufacturer specification or what are out of specification. It does not include adjustment of parameters that are out of specification,” explains Gaurav Tyagi, senior engineer-application and support at Aimil.

“Adjustment is a procedure in which parameters are adjusted within the specification range and usually done by the manufacturer or user,” Tyagi adds. Although most companies maintain high levels of standards, they need to calibrate the equipment regularly.

Agreeing to this, Kela says, “Drift in accuracies over a period is unavoidable but can be detected in time, corrected mathematically and adjusted by calibration, i.e., by using a reference or a standard equipment. All calibration labs do not have capabilities of adjustments and fine-tuning.”

Calibration cycle
For how long is your calibration certificate valid? Or how frequently you need to calibrate your equipment? This is a very subjective question. The answer depends on many factors like the type of the measuring equipment, usage of the equipment, man-handling and atmospheric changes that may influence the reading. In all the cases, these are variables.

“The calibration cycle of the equipment depends on the sensitivity of the equipment, environmental condition, usage, etc. Hence the calibration cycle varies from six months to 36 months depending upon the type of the equipment. Calibration cycles are generally recommended by OEMs,” explains Sulfikaruddin.

“A regular user can get his equipment calibrated by having it checked by the OEM or sending it to an NABL-accredited laboratory with the details of the specifications of the product. Usually, it is required to be calibrated after an interval of twelve months from the date of previous valid calibration,” shares Chandmal Goliya, managing director, Kusam Meco. He recommends recalibration at the earliest to avoid further errors if the readings in between are suspect.

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International Organisation for Standardisation (ISO) issued ICO/IEC 17025 as the primary standard used for testing and calibration laboratories. These standards specify the general requirements for the competence to carry out tests and calibrations using standard methods, non-standard methods, and laboratory-developed methods. There are many commonalities between ISO 17025 and ISO 9000 standards, but the latter does not include the competence to the equation.

All the accredited laboratories around the world follow these ISO 17025 standards to improve their ability to consistently produce valid results. ISO 17025 includes the technical requirements that determine the correctness and reliability of the tests and calibrations performed in a laboratory

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Citing the case of how low-end, low-cost equipment are handled, Goliya says, “The user tends to handle these equipment with very less care and precaution. As these are already low-budget equipment, such mishandling disturbs the accuracy and needs frequent recalibration. Mishandling results in erroneous results apart from damaging these equipment.”

Some equipment have a highly sensitive electronic circuit. For example, a digital multimeter may be calibrated once in six months, while an automated test equipment or a tester may need full calibration of all its boards and resources once in two weeks. In equipment that have time-base oscillators involving frequency counters and sensors, signal generators, spectrum analysers, precision digital multimeters, network analysers and LCR meters, drifts are caused very easily by usage and environmental conditions. Such equipment need calibration at least once a year to meet their specifications and accuracy.

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