Calibration is needed due to

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Examoogle · Accepted Answer

All of above

Explanation: Calibration is the quantitative process of comparing the output of an instrument against a known standard or reference to determine its performance characteristics. This process helps identify deviation (error), verify the instrument's accuracy, and confirm its class (precision/accuracy grade) relative to international standards.

Working Principle: Calibration works by applying a known input $I_{std}$ from a primary or secondary standard to the instrument under test and measuring its output $O_{meas}$. The difference between the measured value and the true value determines the absolute error $e = O_{meas} - I_{std}$. By performing this over the entire measuring range, one can establish the correction curve, verify the class index, and define the instrument's reliability.

Key Formulas: $Absolute\ Error = A_m - A_t$; $Relative\ Error = \frac{A_m - A_t}{A_t} 	imes 100\%$; $Accuracy = 1 - |Relative\ Error|$

Key Points: Calibration ensures traceability to national or international standards.; Instrument class defines the maximum permissible error as a percentage of full-scale reading.; Regular calibration is necessary due to physical wear, aging of components, and environmental exposure.; Calibration provides a record of traceability for quality assurance audits.

Advantages: Ensures measurement reliability and safety.; Maintains regulatory and industry compliance.

Disadvantages: Can be time-consuming for high-precision equipment.; High cost associated with maintenance of standard references.

Applications: Electrical power meters (energy meters).; Pressure gauges and temperature sensors.; Industrial control systems in automation.

Additional Info: In electrical measurements, instruments are assigned a 'Class' (e.g., 0.5, 1.0) which specifies the error limit in terms of percentage of the full-scale deflection.. Option C refers to finding the 'Class', which is effectively determined during the calibration process to label the instrument's accuracy grade.

Answer: D is correct — Calibration encompasses the determination of absolute error, verification of accuracy, and assignment of the instrument class.

Exam Tip: Always remember that accuracy is inversely related to error; hence, determining the error of an instrument is synonymous with quantifying its accuracy and precision grade.

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