Qualities of measuring instrument

Following are the qualities of measuring instruments :


  • It is the closeness with which an instrument reading approaches the true value of the quantity under measurement or it is defined as the ability of a device a system to respond to a true value of a measured variable under reference conditions. Thus accuracy of a measurement means conformity to truth.


  • Sensitivity as the ratio of a change in output to the change in input which causes it at steady state conditions.It is also known as the maximum change in an input signal that will not initiate on the output.


  • Precision is a measure of consistency or repeatability of measurements. It is also known as the degree of exactness for which an instrument is designed to perform.


  • Repeatability of measuring device may be defied as the closeness among a number of consecutive measurement of the output for the same value of input, under the same direction and for full range traverses.


  • Reproducibility of measuring device may be defined as the closeness among a number of repeated measurements of  the output for the same value of input, under the same operating conditions over a long period of time such as a week a month or even a year, approaching for the directions.


  • Drift is a gradual variation in output over a period of time that is independent to change in output operating conditions etc.
  • This undesirable change is usually occurs because of the ageing of component parts.


  • Resolution is the least incremental value at input or output that can be detected by the measuring device.

Dead zone

  • Dead zone is the maximum values of a quantity under measurement to which the instrument does not respond.
  • Dead zone usually occurs due to friction among the components of the indicating instruments.

Back lash

  • It is also known as mechanical hysteresis and it is a loss of motion in mechanical elements such as gears, linkages etc which are used for transmission of motion.


  • It is defined as the deviation of the true value from the desired value.

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