Some important terminologies used in measurement

Things Should Known by Quality Engineer related measurement.

Some important terminologies used in measurement


It should be noted that sensitivity is a term associated with the measuring equipment whereas accuracy and precision are association with measuring process. Sensitivity means the ability of a measuring device to detect small differences in a quantity being measured. For instance if a very small change in voltage applied to 2 voltmeters results in a perceptible change in the indication of one instrument and not in the other. Then the former (A0 is send to be more sensitive. Numerically it can be determined in this way for example if on a dial indicator the scale spacing is 1.0 mm and the scale division value is 0.01 mm then sensitivity =100. it is also called amplification factor or gearing ratio.
Sensitivity Of Measuring instrument
Sensitivity Of Measuring instrument 
It is possible that the more sensitive instrument may be subjected to drifts due to thermal and other effects so that its indications may be less repeatable than these of the instrument of lower sensitivity.

Readability refers to the case with which the readings of a measuring instrument can be read. It is the susceptibility of a measuring device to have its indication converted into more meaningful number. Fine and widely spaced graduation lines ordinarily improve the readability. If the graduation lines are very finely spaced the scale will be more readable by using the microscope however with naked eye the readability will be poor.
In order to make micrometer more readable they are provided with vernier scale. It can also be improve by using magnifying devices.

It is the ability of the measuring instrument to repeat the same results when measurement are
carried out
  • By same observer
  • With the same instrument
  • Under the same conditions
  • Without any change in location
  • Without change in the method of measurement
  • And the measurement is carried out in short interval of time.
It may be expressed quantitatively in terms of dispersion of the results.

4. Reproducibility
Reproducibility is the consistency of pattern of variation in measurement i.e closeness of the
agreement between the results of measurement of the same quantity when individual measurement are carried out
  1. By different observer
  2. By different methods
  3. Using different instruments
  4. Under different condition, location and times.
It may also be expressed quantitatively in terms of dispersion of the results.

  • The calibration of any measuring instrument is necessary for the sake of accruing of measurement process. It is the process of framing the scale of the instrument by applying some standard (known) signals calibration is a pre-measurement process generally carried out by manufactures.
  • It is carried out by making adjustment such that the read out device produces zero output for zero measured input similarly it should display output equipment to the known measured input near the full scale input value.
  • If accuracy is to be maintained the instrument must be checked and recalibration if necessary.
  • As far as possible the calibration should be performed under similar environmental condition with the environment of actual measurement
Magnification means increasing the magnitude of output signal of measuring instrument many times to make it more readable. The degree of magnification should bear some relation to the accuracy of measurement desired and should not be larger than necessary. Generally the greater the magnification the smaller is the range of measurement.

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