The Process of Calibration


Introduction: The Process of Calibration

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Calibration of instrument is critical for reporting test results accurately, so that the outcome stays within the validated performance levels.

Step 1: Understanding the Concept of Instrument Calibration

Calibration involves configuration of an instrument to generate accurate results in the industry accepted range for test samples. The exercise seeks to eliminate or minimize the adverse factors affecting streamlined performance of an instrument of calibration.

Calibration procedure is instrument specific. That means there are separate procedures for temperature calibration, pressure, flow, pipette, dimension calibration etc. The calibration process seeks to make the instrument test against a number of calibrators, whose exact values are known. The outcomes are analyzed for gauging the sanctity of measurement techniques and the integrity of sample test results. The process fine tunes the instrument to make it immune to unfavorable conditions and produce unwavering results against unknown test products.

The emphasis is on establishing the correlation at critical points within the instrument’s functional scope. Using large number of calibrators may be desirable, however the feasibility of the same cannot be justified in terms of labor, time and capital involved. The product’s intended performance level and calibration related efforts have to be balanced. Optimum performance can be guaranteed when compliance to manufacturer’s performance specifications is accomplished by eliminating innate instrument errors at vulnerable intermediate points.

Step 2: Importance of Calibration

The results of calibration would indicate the points within the operating range of instrument. Where deviations are observed can significantly hamper the accuracy of outcome. Equipment calibration will bring about improvements in the situation. Testing equipment against calibrators with known values will serve to set right all errors between given points to attain ideal condition. Minor errors, if any would be reconciled to stay within the accuracy specification published by manufacturer.

Step 3: Factors Affecting Calibration

Knowledge of factors affecting calibration results have to be understood to minimize their impact. Major factors are:

Use of incorrect calibrator values: Any inadvertent disregard to instructions for use or choosing the incorrect calibrator values can program the instrument wrongly, generating substantial errors over the equipment’s functional range. Operator error should be detected and the process should be checked against diagnostic software.

Calibrator formulation tolerance: It is imperative that calibrators having undergone strict tolerance specifications’ formulation from renowned manufacturer be used. The tolerance (owing to usual instrumentation and quality control process induced variations) can alter the mean value achievable through calibrator use. Any deviation can make the calibrators ‘teach’ the instrument wrongly.

Sample preparation method: Correct technique is innately associated with calibration process’s optimal performance. Numerous contributing conditions like using varied sample quantities, permitting air bubbles to creep in the sample, early preparation of samples causing evaporation can result in degrading the results.

Ambient temperature impact: Calibrating the instrument at regular intervals at a temperature resembling the one under which it operates is a must. Ambient temperature can induce errors that are not apparent. Sensitive electronic components can be erroneously affected by alterations in operating temperature. The accuracy of outcome will be severely compromised if the instrument is made to function at a temperature way different from the temperature calibration.

Step 4: Frequency of Instrument Calibration

Calibration of instrument should occur when the instrument needs it, based on logical conclusion drawn from the patterns exhibited over a range of operational period. Daily or periodic test of control solutions of known values will yield quantitatively the performance efficiency. This history of control data can be analyzed to gauge the stability of performance. Any random variation within stipulated value range does not warrant instrument calibration. If the trend indicates notable shift towards or away from the accepted range limits, or occasional shift of substantial nature while operating under different environmental condition, then a recalibration is imperative. However, industry specific standard operating procedures or regulations may mandate calibration at some fixed intervals.



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