Automotive Research Association of India
Research Institute of the Automotive Industry with the Ministry of Heavy Industries & Public Enterprises, Govt. of India
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Testing & Calibration » Calibration

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Fundamentals
Definitions
Instrument : A Device for determining a value.

Measurement : A comparison against true value
Calibration : Calibration is the comparing of a Measurement Device (an unknown) against an equal or better standard. A standard in a measurement is considered the Reference; it is the one in the comparison taken to be the more correct of the two. One calibrate to find out how far the unknown is from the standard.

Really Calibration is required
  Whether Time Measurement used in Testing activity gives correct result.
  Whether Temperature Indicators in your factories gives correct Process Temperature
  Whether Pressure Displayed by Transducer gives correct Process Pressure etc.

Calibration will help you to have confidence on your measurement which will in turn improve your product, by having less defects in production.
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Definitions
Traceability: It is an unbroken chain of a comparison from the measurement being made to a recognize national legal standard.

A typical Pyramid of Traceability:

Precision: Closeness of agreement between independent observations under prescribed conditions.

Error : Deviation from the True Value of the measured variable.

Repeatability : Is a condition when the factors like Operator, Equipment, environment and short time between observations are considered constant.

Reproducibility : All the factors like Operator, Test Instrument, Environment and Time of Measurement are all Different except the Test Method.

Accuracy : Closeness of agreement between the Test Result and the accepted reference or the True Value.

Sensitivity : The ratio of output signal of the instrument to a change of input.

Resolution : The smallest change in measured value to which the instrument will respond.

Uncertainty : The uncertainty of measurement is the range about the measured value within which the True Value of the measured quantity is likely to lie at the stated level of confidence.

Type A Uncertainty: This is calculated by the normal procedure of estimating the variance of the mean of the observations.

Type B Uncertainty: This uncertainty is calculated by judgment using all information, which may include previous measurement data, manufacture specification, data provided in calibration and other certificates and uncertainties assigned to reference data.

Contribution of Various Factors to Precision of Measurement
  Environmental Conditions like Temp., Humidity, Pressure etc.   Operator
  Reference Instrument Used   Time of Measurement
  Calibration status of Reference Instrument   Method of Measurement
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